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ChemPaths UW-Madison

Electron Configurations - 1 views

chemed.chem.wisc.edu/...index.php

shared by ChemPaths UW-Madison on 27 Jan 09 - Snapshot
  • ChemPaths UW-Madison
    ChemPaths UW-Madison on 27 Jan 09
     
    This site is very helpful for problem 43.
ChemPaths UW-Madison

Atomic Structure and Isotopes - 0 views

chemed.chem.wisc.edu/...index.php

shared by ChemPaths UW-Madison on 26 Jan 09 - Snapshot
Justin Shorb

Thermo-chemistry - 0 views

chemed.chem.wisc.edu/...index.php

shared by Justin Shorb on 26 Jan 09 - Snapshot
  • Justin Shorb
    Justin Shorb on 26 Jan 09
     
    Does anyone understand why melting ice is endothermic?
Becky Kriger

Chemistry - Condensation polymer - 0 views

www.chemistrydaily.com/...Condensation_polymer

shared by Becky Kriger on 08 Dec 08 - Snapshot
  • Condensation polymers are any class of polymer formed through a condensation reaction, as opposed to addition polymers which involve the reaction of unsaturated monomers. Types of condensation polymer include polyamides and polyesters.
  • The carboxylic acids and amines link to form peptide bonds, also known as amide groups. Proteins are condensation polymers made from amino acid monomers. Carbohydrates are also condensation polymers made from sugar monomers such as glucose and galactose.
  • Condensation Polymers, unlike Addition polymers are bio-degradable. The peptide or ester bonds between monomers can be hydrolysed by acid catalysts or bacterial enzymes breaking the polymer chain into smaller pieces.
Becky Kriger

Scientific Principles:Polymers - 0 views

matse1.mse.uiuc.edu/...prin.html

shared by Becky Kriger on 08 Dec 08 - Snapshot

  • The chemical reaction in which high molecular mass molecules are formed from
    monomers is known as polymerization. There are two
    basic types of polymerization, chain-reaction (or addition) and step-reaction (or condensation) polymerization.

  • One of the most common types of polymer reactions is chain-reaction
    (addition) polymerization. This type of polymerization is a three step process
    involving two chemical entities. The first, known simply as a monomer, can be regarded as one link in a polymer chain.
    It initially exists as simple units. In nearly all cases, the monomers have at
    least one carbon-carbon double bond. Ethylene is one example of a monomer used
    to make a common polymer.

  • The other chemical reactant is a catalyst. In chain-reaction polymerization, the
    catalyst can be a free-radical peroxide added in
    relatively low concentrations. A free-radical is a chemical component that
    contains a free electron that forms a covalent bond with an electron on another
    molecule. The formation of a free radical from an organic peroxide is shown
    below:
  • ...25 more annotations...
  • The first step in the chain-reaction polymerization process, initiation, occurs
    when the free-radical catalyst reacts with a double bonded carbon monomer,
    beginning the polymer chain. The double carbon bond breaks apart, the monomer
    bonds to the free radical, and the free electron is transferred to the outside
    carbon atom in this reaction.
  • The next step in the process, propagation, is a repetitive operation in which
    the physical chain of the polymer is formed. The double bond of successive
    monomers is opened up when the monomer is reacted to the reactive polymer chain.
    The free electron is successively passed down the line of the chain to the
    outside carbon atom.
  • Thermodynamically speaking, the sum of the energies of the polymer is less than
    the sum of the energies of the individual monomers. Simply put, the single
    bounds in the polymeric chain are more stable than the double bonds of the
    monomer.

  • Termination occurs when another free radical (R-O.), left over
    from the original splitting of the organic peroxide, meets the end of the
    growing chain. This free-radical terminates the chain by linking with the last
    CH2. component of the polymer chain. This reaction
    produces a complete polymer chain. Termination can also occur when two
    unfinished chains bond together. Both termination types are diagrammed below.
    Other types of termination are also possible.

  • This exothermic reaction occurs extremely fast, forming individual chains of polyethylene often in less than 0.1 second.
  • Step-reaction (condensation) polymerization is another common type of
    polymerization. This polymerization method typically produces polymers of lower
    molecular weight than chain reactions and requires higher temperatures to occur.
    Unlike addition polymerization, step-wise reactions involve two different types
    of di-functional monomers or end groups that react
    with one another, forming a chain. Condensation polymerization also produces a
    small molecular by-product (water, HCl, etc.).

  • As indicated above, both addition and condensation polymers can be linear,
    branched, or cross-linked. Linear polymers are made
    up of one long continuous chain, without any excess appendages or attachments.
    Branched polymers have a chain structure that
    consists of one main chain of molecules with smaller molecular chains branching
    from it. A branched chain-structure tends to lower the degree of crystallinity
    and density of a polymer. Cross-linking in polymers
    occurs when primary valence bonds are formed between separate polymer chain
    molecules.

    Chains with only one type of monomer are known as homopolymers. If two or more different type monomers are
    involved, the resulting copolymer can have several
    configurations or arrangements of the monomers
    along the chain. The four main configurations are depicted below:

  • They can be found in either crystalline or amorphous forms. Crystalline polymers are only possible
    if there is a regular chemical structure (e.g., homopolymers or alternating
    copolymers), and the chains possess a highly ordered arrangement of their
    segments. Crystallinity in polymers is favored in symmetrical polymer chains,
    however, it is never 100%. These semi-crystalline polymers possess a rather
    typical liquefaction pathway, retaining their solid state until they reach their
    melting point at Tm.
  • Amorphous polymers do not show order. The molecular segments in amorphous
    polymers or the amorphous domains of semi-crystalline
    polymers are randomly arranged and entangled. Amorphous polymers do not have a
    definable Tm due to their randomness
  • At low temperatures, below their glass transition temperature (Tg), the segments are immobile and the
    sample is often brittle. As temperatures increase close to Tg,
    the molecular segments can begin to move. Above Tg, the
    mobility is sufficient (if no crystals are present) that the polymer can flow as
    a highly viscous liquid.
  • Thermoplastics are generally carbon containing polymers synthesized by addition
    or condensation polymerization. This process forms strong covalent bonds within
    the chains and weaker secondary Van der Waals bonds
    between the chains. Usually, these secondary forces can be easily overcome by
    thermal energy, making thermoplastics moldable at high temperatures.
  • Thermosets have the same Van der Waals bonds that thermoplastics do. They also
    have a stronger linkage to other chains. Strong covalent bonds chemically hold
    different chains together in a thermoset material. The chains may be directly
    bonded to each other or be bonded through other molecules. This "cross-linking"
    between the chains allows the material to resist softening upon heating.

  • Compression Molding

    This type of molding was among the first to be used to form plastics. It
    involves four steps:


  • Pre-formed blanks, powders or pellets are placed in the bottom section of a
    heated mold or die.
  • The other half of the mold is lowered and is pressure applied.
  • The material softens under heat and pressure, flowing to fill the mold.
    Excess is squeezed from the mold. If a thermoset, cross-linking occurs in the
    mold.
  • The mold is opened and the part is removed.

    • For thermoplastics, the mold is cooled before removal so the part will not
    lose its shape. Thermosets may be ejected while they are hot and after curing is
    complete. This process is slow

  • Injection Molding

    This very common process for forming plastics involves four steps:


  • Powder or pelletized polymer is heated to the liquid state.
  • Under pressure, the liquid polymer is forced into a mold through an opening,
    called a sprue. Gates control the flow of material.
  • The pressurized material is held in the mold until it solidifies.
  • The mold is opened and the part removed by ejector pins.

    • Advantages of injection molding include rapid processing, little waste, and
    easy automation.

  • Transfer Molding

    This process is a modification of compression molding. It is used primarily
    to produce thermosetting plastics. Its steps are:


  • A partially polymerized material is placed in a heated chamber.
  • A plunger forces the flowing material into molds.
  • The material flows through sprues, runners and gates.
  • The temperature and pressure inside the mold are higher than in the heated
    chamber, which induces cross-linking.
  • The plastic cures, is hardened, the mold opened, and the part removed.

    • Mold costs are expensive and much scrap material collects in the sprues and
    runners, but complex parts of varying thickness can be accurately produced.

  • Blow Molding

    Blow molding produces bottles, globe light fixtures, tubs, automobile
    gasoline tanks, and drums. It involves:


  • A softened plastic tube is extruded
  • The tube is clamped at one end and inflated to fill a mold.
  • Solid shell plastics are removed from the mold.

    • This process is rapid and relatively inexpensive.

  • Extrusion

    This process makes parts of constant cross section like pipes and rods.
    Molten polymer goes through a die to produce a final shape. It involves four
    steps:


  • Pellets of the polymer are mixed with coloring and additives.
  • The material is heated to its proper plasticity.
  • The material is forced through a die.
  • The material is cooled.

  • In 1989, a billion pounds of virgin PET were used to make beverage bottles of
    which about 20% was recycled. Of the amount recycled, 50% was used for fiberfill
    and strapping. The reprocessors claim to make a high quality, 99% pure,
    granulated PET. It sells at 35 to 60% of virgin PET costs.

    The major reuses of PET include sheet, fiber, film, and extrusions.

  • Of the plastics that have a potential for recycling, the rigid HDPE container is
    the one most likely to be found in a landfill. Less than 5% of HDPE containers
    are treated or processed in a manner that makes recycling easy.
  • There is a great potential for the use of recycled HDPE in base cups, drainage
    pipes, flower pots, plastic lumber, trash cans, automotive mud flaps, kitchen
    drain boards, beverage bottle crates, and pallets.
  • LDPE is recycled by giant resin suppliers and merchant processors either by
    burning it as a fuel for energy or reusing it in trash bags. Recycling trash
    bags is a big business.
  • There is much controversy concerning the recycling and reuse of PVC due to
    health and safety issues. When PVC is burned, the effects on the incinerator and
    quality of the air are often questioned. The Federal Food and Drug
    Administration (FDA) has ordered its staff to prepare environmental impact
    statements covering PVC's role in landfills and incineration. The burning of PVC
    releases toxic dioxins, furans, and hydrogen chloride.
  • PVC is used in food and alcoholic beverage containers with FDA approval. The
    future of PVC rests in the hands of the plastics industry to resolve the issue
    of the toxic effects of the incineration of PVC. It is of interest to note that
    PVC accounts for less than 1% of land fill waste.
  • PS and its manufacturers have been the target of environmentalists for several
    years. The manufacturers and recyclers are working hard to make recycling of PS
    as common as that of paper and metals. One company, Rubbermaid, is testing
    reclaimed PS in service trays and other utility items.
  • Table 3: Major Plastic Resins and Their Uses












    Resin CodeResin NameCommon UsesExamples of Recycled Products
    Polyethylene Terephthalate (PET or PETE)
    		Soft drink bottles, peanut butter jars, salad dressing bottles, mouth wash jars
    		Liquid soap bottles, strapping, fiberfill for winter coats, surfboards, paint brushes, fuzz on tennis balls, soft drink bottles, film
    High density Polyethylene (HDPE)
    		Milk, water, and juice containers, grocery bags, toys, liquid detergent bottles
    		Soft drink based cups, flower pots, drain pipes, signs, stadium seats, trash cans, re-cycling bins, traffic barrier cones, golf bag liners, toys
    Polyvinyl Chloride or Vinyl (PVC-V)
    		Clear food packaging, shampoo bottles
    		Floor mats, pipes, hoses, mud flaps
    Low density Polyethylene (LDPE)
    		Bread bags, frozen food bags, grocery bags
    		Garbage can liners, grocery bags, multi purpose bags
    Polypropylene (PP)
    		Ketchup bottles, yogurt containers, margarine, tubs, medicine bottles
    		Manhole steps, paint buckets, videocassette storage cases, ice scrapers, fast food trays, lawn mower wheels, automobile battery parts.
    Polystyrene (PS)
    		Video cassette cases, compact disk jackets, coffee cups, cutlery, cafeteria trays, grocery store meat trays, fast-food sandwich container
    		License plate holders, golf course and septic tank drainage systems, desk top accessories, hanging files, food service trays, flower pots, trash cans
    • Becky Kriger

    Chemical of the Week -- Polymers - 0 views

    scifun.chem.wisc.edu/...Polymers.html

    shared by Becky Kriger on 08 Dec 08 - Snapshot
    •  Polymers
      are substances whose molecules have high molar masses and are composed of a
      large number of repeating units. There are both naturally occurring and synthetic
      polymers. Among naturally occurring polymers are proteins, starches, cellulose,
      and latex. Synthetic polymers are produced commercially on a very large scale
      and have a wide range of properties and uses. The materials commonly called
      plastics are all synthetic polymers.
    •    Polymers
      are formed by chemical reactions in which a large number of molecules called
      monomers are joined sequentially, forming a chain.
    • If all atoms in the monomers are incorporated into the polymer,
      the polymer is called an addition polymer. If some of the atoms of the
      monomers are released into small molecules, such as water, the polymer is called
      a condensation polymer.
    • ...27 more annotations...
    • Polyethylene
      terephthalate (PET), or polyethylene terephthalic ester (PETE), is a condensation
      polymer produced from the monomers ethylene glycol, HOCH2CH2OH,
      a dialcohol, and dimethyl terephthalate, CH3O2C–C6H4–CO2CH3,
      a diester. By the process of transesterification, these monomers form ester
      linkages between them, yielding a polyester
    • PETE fibers are manufactured under
      the trade names of Dacron and Fortrel.
    • Pleats and creases can be permanently
      heat set in fabrics containing polyester fibers, so-called permanent press fabrics.
      PETE can also be formed into transparent sheets and castings.
    • Transparent 2-liter carbonated beverage bottles are made
      from PETE.
    • ne
      form of PETE is the hardest known polymer and is used in eyeglass lenses.
    •      Polyethylene
      is perhaps the simplest polymer, composed of chains of repeating –CH2–
      units. It is produced by the addition polymerization of ethylene, CH2=CH2
      (ethene)
    • HDPE is hard, tough, and resilient. Recycling code for low density Polyethylene
      Most HDPE is used in the manufacture of containers, such as milk bottles and
      laundry detergent jugs.
    • LDPE is relatively soft, and most of
      it is used in the production of plastic films, such as those used in sandwich
      bags.
    • Polymerization
      of vinyl chloride, CH2=CHCl (chloroethene), produces a polymer similar
      to polyethylene, but having chlorine atoms at alternate carbon atoms on the
      chain.
    • About two-thirds
      of the PVC produced annually is used in the manufacture of pipe. It is also
      used in the production of “vinyl” siding for houses and clear plastic
      bottles.
    • is used to form flexible articles such as raincoats and
      shower curtains.
    • This
      polymer is produced by the addition polymerization of propylene, CH2=CHCH3
      (propene). Its molecular structure is similar to that of polyethylene, but has
      a methyl group (–CH3) on alternate carbon atoms of the chain.
    • olypropylene is used extensively in the automotive industry
      for interior trim, such as instrument panels, and in food packaging, such as
      yogurt containers. It is formed into fibers of very low absorbance and high
      stain resistance, used in clothing and home furnishings, especially carpeting.
    • Styrene,
      CH2=CH–C6H5, polymerizes readily to form
      polystyrene (PS), a hard, highly transparent polymer.
    • A large portion
      of production goes into packaging. The thin, rigid, transparent containers in
      which fresh foods, such as salads, are packaged are made from polystyrene. Polystyrene
      is readily foamed or formed into beads. These foams and beads are excellent
      thermal insulators and are used to produce home insulation and containers for
      hot foods. Styrofoam is a trade name for foamed polystyrene.
    • eflon
      is a trade name of polytetrafluoroethylene, PTFE. It is formed by the addition
      polymerization of tetrafluoroethylene, CF2=CF2 (tetrafluoroethene).
      PTFE is distinguished by its complete resistance to attack by virtually all
      chemicals and by its slippery surface. It maintains its physical properties
      over a large temperature range, -270° to 385°C. These properties make
      it especially useful for components that must operate under harsh chemical conditions
      and at temperature extremes. Its most familiar household use is as a coating
      on cooking utensils.
    • his
      important class of polymers is formed by the addition polymerization of an diisocyanate
      (whose molecules contain two –NCO groups) and a dialcohol (two –OH
      groups).
    • Polyurethane is spun
      into elastic fibers, called spandex, and sold under the trade name Lycra. Polyurethane
      can also be foamed. Soft polyurethane foams are used in upholstery, and hard
      foams are used structurally in light aircraft wings and sail boards.
    • Polyamides
      are a group of condensation polymers commonly known as nylon. Nylon is made
      from two monomers, one a dichloride and the other a diamine.
    • Nylon can be readily formed into fibers that are
      strong and long wearing, making them well suited for use in carpeting, upholstery
      fabric, tire cords, brushes, and turf for athletic fields. Nylon is also formed
      into rods, bars, and sheets that are easily formed and machined.
    • Polyacrylamide
      is a condensation polymer with an unusual and useful property.
    • This produces a network
      of polymer chains, rather like a tiny sponge. The free, unlinked amide groups,
      because they contain –NH2 groups, can form hydrogen bonds with
      water. This gives the tiny cross linked sponges a great affinity for water.
      Polyacrylamide can absorb many times its mass in water. T
    • his property is useful
      in a variety of applications, such as in diapers and in potting soil. The polyacrylamide
      will release the absorbed water if a substance that interferes with hydrogen
      bonding is added. Ionic substances, such as salt, cause polyacrylamide to release
      its absorbed water.
    • Over
      the past few decades, the use of polymers in disposable consumer goods has grown
      tremendously. This growth is proving to be taxing on the waste disposal system,
      consuming a large fraction of available landfill space.
    • To help sort wastes by type of polymer, most disposable polymeric goods
      are labeled with a recycling code: three arrows around a number above the polymer's
      acronym. These are intended to help consumers separate the waste polymers according
      to type before disposing of them. In the city of Madison, currently only type
      1 (PETE) and type 2 (HDPE) polymers are being recycled – see below. The
      recycling of polymers is not a closed loop, where a material is reformed into
      new products repeatedly, such as in the case with aluminum. Most polymeric materials
      are recycled only once, and the product made of recycled polymer is discarded
      after use

    • General Rules




      1. Remove and discard all lids or caps.
      2. Rinse all containers.
      3. Remove and discard sprayer tops.
      4. CRUSH all plastic bottles to save space.
      5. No 5 gallon pails.
      6. No containers with metal handles.

    • What can be Recycled?

      Plastic Code Number


      Recyclable Containers

      Soda Bottles
      Water Bottles
      Juice Bottles
      Cooking Oil Bottles
      Soap/Detergent Bottles
      Shampoo Bottles
      Clear Liquor Bottles
      Food Jars (Peanut Butter etc.)

      Plastic Code Number

      Recyclable Containers

      Milk Bottles

      Water Bottles

      Juice Bottles

      Cooking Oil Containers

      Windshield Washer Fluid Bottles

      Shampoo Bottles

      Butter/Margarine Tubs

      Cottage Cheese Containers

      Ice Cream Containers Without Metal Handles

      Baby Wipe Containers


      Do NOT Recycle This Plastic


      1. Automotive Product Containers Including:
      • Motor Oil Bottles
      • Anti-Freeze Containers
      • Gasoline and Oil Additive Bottles

      2. Brown Liquor Bottles


      3. All Containers Marked With The Following Codes:

           
           

    Becky Kriger

    Polymer - Condensation polymers - 0 views

    science.jrank.org/...Polymer.html

    shared by Becky Kriger on 08 Dec 08 - Snapshot
    • Polymers are made up of extremely large, chainlike molecules consisting of numerous, smaller, repeating units called monomers. Polymer chains, which could be compared to paper clips linked together to make a long strand, appear in varying lengths. They can have branches, become intertwined, and can have cross-links. In addition, polymers can be composed of one or more types of monomer units, they can be joined by various kinds of chemical bonds, and they can be oriented in different ways. Monomers can be joined together by addition, in which all the atoms in the monomer are present in the polymer, or by condensation, in which a small molecule byproduct is also formed.
    • The importance of polymers is evident as they occur widely both in the natural world in such materials as wool, hair, silk and sand, and in the world of synthetic materials in nylon, rubber, plastics, Styrofoam, and many other materials.
    • Polymers are extremely large molecules composed of long chains, much like paper clips that are linked together to make a long strand. The individual subunits, which can range from as few as 50 to more than 20,000, are called monomers (from the Greek mono meaning one and meros meaning part). Because of their large size, polymers (from the Greek poly meaning many) are referred to as macromolecules.
    • ...21 more annotations...
    • Most synthetic polymers are made from the non-renewable resource, petroleum, and as such, the "age of plastics" is limited unless other ways are found to make them. Since most polymers have carbon atoms as the basis of their structure, in theory at least, there are numerous materials that could be used as starting points.
    • Disposing of plastics is also a serious problem, both because they contribute to the growing mounds of garbage accumulating everyday and because most are not biodegradable. Researchers are busy trying to find ways to speed-up the decomposition time which, if left to occur naturally, can take decades.
    • n order for monomers to chemically combine with each other and form long chains, there must be a mechanism by which the individual units can join or bond to each other. One method by which this happens is called addition because no atoms are gained or lost in the process. The monomers simply "add" together and the polymer is called an addition polymer.
    • The simplest chemical structure by which this can happen involves monomers that contain double bonds (sharing two pairs of electrons). When the double bond breaks and changes into a single bond, each of the other two electrons are free and available to join with another monomer that has a free electron. This process can continue on and on. Polyethylene is an example of an addition polymer.
    • The polymerization process can be started by using heat and pressure or ultraviolet light or by using another more reactive chemical such as a peroxide. Under these conditions the double bond breaks leaving extremely reactive unpaired electrons called free radicals. These free radicals react readily with other free radicals or with double bonds and the polymer chain starts to form.
    • ifferent catalysts yield polymers with different properties because the size of the molecule may vary and the chains may be linear, branched, or cross-linked. Long linear chains of 10,000 or more monomers can pack very close together and form a hard, rigid, tough plastic known as high-density polyethylene or HDPE
    • Shorter, branched chains of about 500 monomers of ethylene cannot pack as closely together and this kind of polymer is known as low-density polyethylene or LDPE.
    • The ethylene monomer has two hydrogen atoms bonded to each carbon for a total of four hydrogen atoms that are not involved in the formation of the polymer. Many other polymers can be formed when one or more of these hydrogen atoms are replaced by some other atom or group of atoms.
    • Natural and synthetic rubbers are both addition polymers. Natural rubber is obtained from the sap that oozes from rubber trees. It was named by Joseph Priestley who used it to rub out pencil marks, hence, its name, a rubber. Natural rubber can be decomposed to yield monomers of isoprene.
    • It was sticky and smelly when it got too hot and it got hard and brittle in cold weather. These undesirable properties were eliminated when, in 1839, Charles Goodyear accidentally spilled a mixture of rubber and sulfur onto a hot stove and found that it did not melt but rather formed a much stronger but still elastic product. The process, called vulcanization, led to a more stable rubber product that withstood heat (without getting sticky) and cold (without getting hard) as well as being able to recover its original shape after being stretched. The sulfur makes cross-links in the long polymer chain and helps give it strength and resiliency, that is, if stretched, it will spring back to its original shape when the stress is released.
    • A second method by which monomers bond together to form polymers is called condensation.
    • Unlike addition polymers, in which all the atoms of the monomers are present in the polymer, two products result from the formation of condensation polymers, the polymer itself and another small molecule which is often, but not always, water.
    • One of the simplest of the condensation polymers is a type of nylon called nylon 6.
    • All amino acids molecules have an amine group (NH2) at one end and a carboxylic acid (COOH) group at the other end. A polymer forms when a hydrogen atom from the amine end of one molecule and an oxygen-hydrogen group (OH) from the carboxylic acid end of a second molecule split off and form a water molecule. The monomers join together as a new chemical bond forms between the nitrogen and carbon atoms. This new bond is called an amide linkage.
    • The new molecule, just like each of the monomers from which it formed, also has an amine group at one end (that can add to the carboxylic acid group of another monomer) and it has a carboxylic acid group at the other end (that can add to the amine end of another monomer). The chain can continue to grow and form very large polymers.
    • Polymers formed by this kind of condensation reaction are referred to as polyamides.
    • Nylon became a commercial product for Du Pont when their research scientists were able to draw it into long, thin, symmetrical filaments. As these polymer chains line up side-by-side, weak chemical bonds called hydrogen bonds form between adjacent chains. This makes the filaments very strong.
    • Another similar polymer of the polyamide type is the extremely light-weight but strong material known as Kevlar. It is used in bullet-proof vests, aircraft, and in recreational uses such as canoes. Like nylon, one of the monomers from which it is made is terephthalic acid. The other one is phenylenediamine.
    • Polyesters are another type of condensation polymer, so-called because the linkages formed when the monomers join together are called esters.
    • Probably the best known polyester is known by its trade name, Dacron.
    • Dacron is used primarily in fabrics and clear beverage bottles. Films of Dacron can be coated with metallic oxides, rolled into very thin sheets (only about one-thirtieth the thickness of a human hair), magnetized, and used to make audio and video tapes. When used in this way, it is extremely strong and goes by the trade name Mylar. Because it is not chemically reactive, and is not toxic, allergenic, or flammable, and because it does not promote blood-clotting, it can be used to replace human blood vessels when they are severely blocked and damaged or to replace the skin of burn victims.
    Becky Kriger

    Polymer Tutorial - 0 views

    www.chemistryland.com/...PolymerTutorial.htm

    shared by Becky Kriger on 08 Dec 08 - Snapshot
    • "Poly" means "many" and "mer"
      means "parts.
    • The parts are usually the same part used repeatedly in a chain-like manner.
      Polymers are also referred to as plastics
    • Nature has many examples of polymers. Cotton fibers are made
      of sugar molecules that are repeated in a chain-like manner. Hair, wool,
      and other natural fibers are polymers.
    • ...15 more annotations...
    • Now be aware that one of the connecting sticks
      can spring open. To see animation of this, move cursor
      over the image.       As long as cursor is over image, animation repeats
    • 1) We start with several pairs of balls each with two connecting
      sticks. 2) Something causes one of the connecting sticks to fling open. It then
      connects to another ball, but in doing so, causes one of its connecting sticks
      to fling open. 3) In moments all of the pairs of balls are now connected. Move cursor over image to see animation.
    • Sometimes heat, high energy light, or something else causes
      the double-bond to break and two of the middle 4 electrons split up and
      end up on the two outer ends of the molecule. These electrons are unpaired,
      which makes them eager to join with another electron.
    • (place
      cursor over the image to see animated version)
    • The unpaired electron
      triggers the ethylene molecule that bumps into it, to shift the inside electron
      to pair with it. That then causes the newly unpaired
      inner electron to move to the outside and it is now an unpaired
      electron ready to cause the next ethylene molecule to repeat the process.
    • The name of this polymer is appropriately
      called, polyethylene.
    • This is called high density polyethylene
      (HDPE).
    • High density polyethylene HDPE is used for bottles, buckets, jugs, containers,
      toys, even synthetic lumber, and many other things.
    • Sometimes the chains get up to 500,000 carbons long. Here
      they are tough enough for synthetic ice, replacement joints and bullet-proof
      vests. This is called Ultra High
      Molecular Weight
      PolyEthylene
      or UHMWPE.
    • low density polyethylene (LDPE).
    • It is made by causing the long chains of ethylene to branch.
      That way they cannot lie next each other, which reduces the density of
      the polyethylene. This makes the plastic lighter and more flexible.
    • Low density polyethylene is used to make plastic bags,
      plastic wrap, and squeeze bottles, plus many other things.
    • The favorite properties of plastics are that they are inert
      and won't react with what is stored in them. They also are durable and won't
      easily decay, dissolve, or break apart. These are great qualities for things
      you keep, but when you throw them away, they won't decompose.
    • The answer is to recycle the plastics. Here we see a bunch
      of CDs getting recycled.
    • Here are
      two recycle code drawings. You already know about HDPE and LDPE.
    • Becky Kriger
      Becky Kriger on 08 Dec 08
       
      A simply explained introduction to polymers.
    Becky Kriger

    Biopolymers and Bioplastics - 0 views

    www.biobasics.gc.ca/...View.asp

    shared by Becky Kriger on 08 Dec 08 - Snapshot

    • Biopolymers are polymers which are present in, or created by, living organisms. These include polymers from renewable resources that can be polymerized to create bioplastics.


      Bioplastics are plastics manufactured using biopolymers, and are biodegradable.

    • There are two main types of biopolymers: those that come from living organisms; and, those which need to be polymerized but come from renewable resources. Both types are used in the production of bioplastics
    • Biopolymer
      Natural Source
      What is it?

      Cellulose
      Wood, cotton, corn, wheat, and others
      This polymer is made up of glucose. It is the main component of plant cell walls.

      Soy protein
      Soybeans
      Protein which naturally occurs in the soy plant.

      Starch
      Corn, potatoes, wheat, tapioca, and others
      This polymer is one way carbohydrates are stored in plant tissue. It is a polymer made up of glucose. It is not found in animal tissues.

      Polyesters
      Bacteria
      These polyesters are created through naturally occurring chemical reactions that are carried out by certain types of bacteria.
    • ...9 more annotations...
    • Biopolymer
      Natural Source
      What is it?

      Lactic Acid
      Beets, corn, potatoes, and others
      Produced through fermentation of sugar feedstocks, such as beets, and by converting starch in corn, potatoes, or other starch sources. It is polymerized to produce polylactic acid -- a polymer that is used to produce plastic.

      Triglycerides
      Vegetable oils
      These form a large part of the storage lipids found in plant and animal cells. Vegetable oils are one possible source of triglycerides that can be polymerized into plastics.

    • Using Fermentation to Produce Plastics


      Fermentation, used for hundreds of years by humans, is even more powerful when coupled with new biotechnology techniques.

    • Today, fermentation can be carried out with genetically engineered microorganisms, specially designed for the conditions under which fermentation takes place,
    • Fermentation, in fact, is the process by which bacteria can be used to create polyesters. Bacteria called Ralstonia eutropha are used to do this. The bacteria use the sugar of harvested plants, such as corn, to fuel their cellular processes. The by-product of these cellular processes is the polymer.
    • Lactic acid is fermented from sugar, much like the process used to directly manufacture polymers by bacteria. However, in this fermentation process, the final product of fermentation is lactic acid, rather than a polymer. After the lactic acid is produced, it is converted to polylactic acid using traditional polymerization processes.
    • Plants are becoming factories for the production of plastics. Researchers created a Arabidopis thaliana plant through genetic engineering. The plant contains the enzymes used by bacteria to create plastics. Bacteria create the plastic through the conversion of sunlight into energy. The researchers have transferred the gene that codes for this enzyme into the plant, as a result the plant produces plastic through its cellular processes. The plant is harvested and the plastic is extracted from it using a solvent. The liquid resulting from this process is distilled to separate the solvent from the plastic.
    • Currently, fossil fuel is still used as an energy source during the production process. This has raised questions by some regarding how much fossil fuel is actually saved by manufacturing bioplastics. Only a few processes have emerged that actually use less energy in the production process.
    • Energy use is not the only concern when it comes to biopolymers and bioplastics. There are also concerns about how to balance the need to grow plants for food, and the need to grow plants for use as raw materials. Agricultural space needs to be shared. Researchers are looking into creating a plant that can be used for food, but also as feedstock for plastic production.
    • Biopolymers and bioplastics are the main components in creating a sustainable plastics industry. These products reduce the dependence on non-renewable fossil fuels, and are easily biodegradable. Together, this greatly limits the environmental impacts of plastic use and manufacture. Also, characteristics such as being biodegradable make plastics more acceptable for long term use by society. It is likely that in the long term, these products will mean plastics will remain affordable, even as fossil fuel reserves diminish.
    Becky Kriger

    OChem- Biopolymers - 0 views

    www.usm.maine.edu/...BiopolymersI.html

    shared by Becky Kriger on 08 Dec 08 - Snapshot
    • The red lines connecting the 4th carbon atom
      of one isoprene unit with the 1st carbon of the next indicate that
      latex is an addition polymer that results from the 1,4-addition of
      one isoprene unit to the next. Note the head-to-tail pattern in
      which the isoprene units are connected. Note, too, that the
      stereochemistry is the same at each double bond, namely
      cis.



    • Synthetic
      Rubber



      In 1839 Charles Goodyear discovered,
      literally by accident, that heating natural rubber with elemental
      sulfur altered the properties of the polymer, most notably making
      it tougher and more elastic. Goodyear's discovery led to the
      development of synthetic rubber, a material that found its most
      profitable application in the manufacture of automobile tires.
      Investigation of the structure of synthetic rubber revealed that
      the sulfur had formed disulfide bonds that linked one polyisoprene
      chain to the next. As Figure 2 demonstrates, these cross-links
      serve to restore the polymer to its original shape after it has
      been deformed by the application of a force.



      Figure
      2



      Bouncing
      Back





    • Not surprisingly, the desireable properties
      of natural as well as synthetic rubber led to investigations of
      the polymerization of structural analogs of isoprene. One notable
      success came from the polymerization of 2-chloro-1,3-butadiene,
      sometimes called chloroprene. Polychloroprene is known
      commercially as neoprene rubber. It is widely used in the
      automotive industry for the manufacture of oil-resistant hoses.
      Neoprene that contains entrapped air has good insulating
      properties and is used in the production of wet suits.
    Becky Kriger

    Thermosetting plastic - Plastics Wiki - 0 views

    plastics.inwiki.org/Thermosetting_plastic

    shared by Becky Kriger on 08 Dec 08 - Snapshot
    Becky Kriger

    Plastics - 0 views

    nobelprize.org/...readmore.html

    shared by Becky Kriger on 08 Dec 08 - Snapshot
    • lastics are synthetic materials, which means that they are artificial, or manufactured.
    • he building blocks for making plastics are small organic molecules - molecules that contain carbon along with other substances. They generally come from oil (petroleum) or natural gas, but they can also come from other organic materials such as wood fibers, corn, or banana peels! Each of these small molecules is known as a monomer ("one part") because it's capable of joining with other monomers to form very long molecule chains called polymers ("many parts")
    • 1. Crude oil, the unprocessed oil that comes out of the ground, contains hundreds of different hydrocarbons, as well as small amounts of other materials. The job of an oil refinery is to separate these materials and also to break down (or "crack) large hydrocarbons into smaller ones.



      2. A petrochemical plant receives refined oil containing the small monomers they need and creates polymers through chemical reactions.



      3. A plastics factory buys the end products of a petrochemical plant - polymers in the form of resins - introduces additives to modify or obtain desirable properties, then molds or otherwise forms the final plastic products.
    • ...13 more annotations...
    • One such molecule is the ethylene monomer, the starting point for a variety of plastics. Ethylene is a small hydrocarbon consisting of four hydrogen atoms and two carbon atoms.
    • Polymerization is often started by combining the monomers through the use of a catalyst - a substance that aids a chemical reaction without undergoing any permanent chemical change itself. During the chemical reaction, hundreds or thousands of monomers combine to form a polymer chain, and millions of polymer chains are formed at the same time. The mass of polymers that results is known as a resin.
    • Polyethylene is made from just ethylene monomers - but it's also possible to create polymers from two or more different monomers. You can make hundreds of different polymers depending on which monomers and catalysts you use.
    • Cellulose, the basic component of plant cell walls is a polymer, and so are all the proteins produced in your body and the proteins you eat. Another famous example of a polymer is DNA - the long molecule in the nuclei of your cells that carries all the genetic information about you.
    • lastics are classified into two categories according to what happens to them when they're heated to high temperatures. Thermoplastics keep their plastic properties: They melt when heated, then harden again when cooled. Thermosets, on the other hand, are permanently "set" once they're initially formed and can't be melted. If they're exposed to enough heat, they'll crack or become charred.
    • The linear chains are crosslinked - strongly chemically bonded. This prevents a thermoplastic object from being melted and reformed.

    • Thermoplastics have long, linear polymer chains that are only weakly chemically bonded, or connected, to each other. When a thermoplastic object is heated, these bonds are easily broken, which makes the polymers able to glide past each other like strands of freshly cooked spaghetti. That's why thermoplastics can readily be remolded.


      The weak bonds between the polymers reform when the plastic object is cooled, which enable it to keep its new shape.

    • The most common method for making plastics is molding. To make a thermoplastic object, plastic granules known as resin are forced into a mold under high heat and pressure. When the material has cooled down, the mold is opened and the plastic object is complete. When making plastic fibers, the molten resin is sprayed through a strainer with tiny holes.

    • Thermosets are produced in two steps:



      1. Linear polymers are formed.


      2. The linear polymers are forced into a mold where "curing" takes place. This may involve heating, pressure, and the addition of catalysts. During this process, a cross-linked or networked structure forms, creating a permanently hard object that is no longer meltable or moldable.

    • For most applications, the ideal polymer is a long, straight chain with a highly regular molecular structure. Early synthetic polymers, however, often exhibited odd little branches and other irregularities. In the 1950s, German chemist Karl Ziegler (1898–1973) discovered that an entirely different type of catalyst - a combination of aluminum compounds with other metallic compounds - could solve some of these annoying problems and increase the length of a polymer chain, producing superior plastics.
    • olymers often have short side chains, which can occur on either side of the main chain. If side branches occur randomly to the left or right, the polymer has an irregular structure. Italian chemist Giulio Natta (1903–1979) discovered that some Ziegler catalysts led to a uniform structure in which all the side branches are on the same side.
    • Firstly, there is an environmental impact from plastics production; however the plastics industry has worked hard to reduce energy and water use, as well as waste generation during the manufacturing processes.
    • Secondly, during their lives, plastic products can save energy and reduce carbon dioxide emissions in a variety of ways. For example, they're lightweight, so transporting them is energy efficient. And plastic parts in cars and airplanes reduce the weight of those vehicles and therefore less energy is needed to operate them and lower emissions are created.
    Becky Kriger

    7 Misconceptions About Plastic and Plastic Recycling - 0 views

    www.ecologycenter.org/...misconceptions.html

    Recylcing plastics

    shared by Becky Kriger on 08 Dec 08 - Snapshot
    • Plastics that go into a curbside recycling bin get recycled. Not necessarily.
    • In fact, none of the recovered plastic containers from Berkeley are being made
      into containers again but into new secondary products such as textiles, parking
      lot bumpers, or plastic lumber – all unrecyclable products. This does not reduce
      the use of virgin materials in plastic packaging.
    • Curbside collection will reduce the amount of plastic landfilled. Not
      necessarily. If establishing collection makes plastic packages seem more
      environmentally friendly, people may feel comfortable buying more.
    • ...14 more annotations...
    • Since only a fraction of certain types of plastic could realistically be
      captured by a curbside program, the net impact of initiating curbside collection
      could be an increase in the amount of plastic landfilled. The Berkeley pilot
      program showed no reduction of plastic being sent to the landfill in the areas
      where the curbside collection was in operation.
    • A chasing arrows symbol means a plastic container is recyclable. The arrows are
      meaningless. Every plastic container is marked with the chasing arrows symbol.
      The only information in the symbol is the number inside the arrows, which
      indicates the general class of resin used to make the container.
    • Packaging resins are made from petroleum refineries’ waste. Plastic resins are
      made from non-renewable natural resources that could be used for a variety of
      other applications or conserved. Most packaging plastics are made from the same
      natural gas used in homes to heat water and cook.
    • Using plastic containers conserves energy. When the equation includes the energy
      used to synthesize the plastic resin, making plastic containers uses as much
      energy as making glass containers from virgin materials, and much more than
      making glass containers from recycled materials. Using refillables is the most
      energy conservative.
    • Our choice is limited to recycling or wasting. Source reduction is preferable
      for many types of plastic and isn’t difficult. Opportunities include using
      refillable containers, buying in bulk, buying things that don’t need much
      packaging, and buying things in recyclable and recycled packages
    • Plastic packaging has economic, health, and environmental costs and benefits.
    • Plastic container producers do not use any recycled plastic in their packaging.
      Recycled content laws could reduce the use of virgin resin for packaging.
      Unfortunately, the virgin&endash;plastics industry has resisted such
      cooperation by strongly opposing recycled -content legislation, and has defeated
      or weakened consumer efforts to institute stronger laws.

    • Processing used plastics often costs more than virgin plastic. As plastic
      producers increase production and reduce prices on virgin plastics, the markets
      for used plastic are diminishing. PET recyclers cannot compete with the virgin
      resin flooding the market.

    • 1. Reduce the use
      Source reduction Retailers and consumers can select
      products that use little or no packaging. Select packaging materials that are
      recycled into new packaging - such as glass and paper.
    • 2. Reuse containers
      Since refillable plastic containers can be reused
      about 25 times, container reuse can lead to a substantial reduction in the
      demand for disposable plastic, and reduced use of materials and energy
    • 3. Require producers to take back resins
    • Make reprocessing easier by limiting the number of container types and shapes,
      using only one type of resin in each container, making collapsible containers,
      eliminating pigments, using water-dispersible adhesives for labels, and phasing
      out associated metals such as aluminum seals.

    • 4. Legislatively require recycled content
      Requiring that all
      containers be composed of a percentage of post-consumer material reduces the
      amount of virgin material consumed.

    • 5. Standardize labeling and inform the public
      The chasing arrows
      symbol on plastics is an example of an ambiguous and misleading label.
      Significantly different standardized labels for "recycled," "recyclable," and
      "made of plastic type X" must be developed.

    Becky Kriger

    Recycling Plastics - How to Recycle Different Types of Plastic - 0 views

    environment.about.com/...recycleplastics.htm

    Plastics recycle

    shared by Becky Kriger on 08 Dec 08 - Snapshot
    • The easiest and most common plastics to recycle are made of polyethylene
      terephthalate (PETE) and are assigned the number 1. Examples include soda and
      water bottles, medicine containers, and many other common consumer product
      containers. Once it has been processed by a recycling facility, PETE can become
      fiberfill for winter coats, sleeping bags and life jackets. It can also be used
      to make bean bags, rope, car bumpers, tennis ball felt, combs, cassette tapes,
      sails for boats, furniture and, of course, other plastic bottles.
    • Number 2 is reserved for high-density polyethylene plastics. These include
      heavier containers that hold laundry detergents and bleaches as well as milk,
      shampoo and motor oil. Plastic labeled with the number 2 is often recycled into
      toys, piping, plastic lumber and rope.
    • Polyvinyl chloride, commonly used in plastic pipes, shower curtains, medical
      tubing, vinyl dashboards, and even some baby bottle nipples, gets number 3. Like
      numbers 4 (wrapping films, grocery and sandwich bags, and other containers made
      of low-density polyethylene) and 5 (polypropylene containers used in Tupperware,
      among other products), few municipal recycling centers will accept it due to its
      very low rate of recyclability.
    • ...2 more annotations...
    • Number 6 goes on polystyrene (Styrofoam) items such as coffee cups, disposable
      cutlery, meat trays, packing “peanuts” and insulation. It is widely accepted
      because it can be reprocessed into many items, including cassette tapes and
      rigid foam insulation.
    • Usually imprinted with a number 7 or nothing at all, these plastics are the most
      difficult to recycle and, as such, are seldom collected or recycled.
    Becky Kriger

    How Plastics Are Made - 0 views

    www.mindfully.org/...How-Plastics-Made.htm

    plastics

    shared by Becky Kriger on 08 Dec 08 - Snapshot
    • The term "plastics" encompasses organic materials, such as the elements carbon
      (C), hydrogen (H), nitrogen (N), chlorine (Cl) and sulfur (S), which have
      properties similar to those naturally grown in organic materials such as wood,
      horn and rosin.
    • The plastic production process begins by heating the hydrocarbons in a "cracking
      process." Here, in the presence of a catalyst, larger molecules are broken down
      into smaller ones such as ethylene (ethene) C2H4,
      propylene (propene) C3H6, and butene C4H8
      and other hydrocarbons.

    • Other
      examples of thermoset plastics and their product applications are:

      • Polyurethanes: mattresses, cushions, insulation, ski boots, toys
      • Unsaturated Polyesters: lacquers, varnishes, boat hulls, furniture, 
      • Epoxies: glues, coating electrical circuits, helicopter blades

    • ...13 more annotations...

    • Other
      examples of thermoplastics are:


      • Polyethylene:
        packaging, electrical insulation, milk and water bottles, packaging film, house
        wrap, agricultural film



      • Polypropylene:
        carpet fibers, automotive bumpers, microwave containers, external prostheses



      • Polyvinyl
        chloride (PVC): sheathing for electrical cables, floor and wall coverings,
        siding, credit cards, automobile instrument panels

    • These monomers are then chemically bonded into chains called polymers.
    • The resulting resins may be molded or formed to produce several different kinds
      of plastic products with application in many major markets. The variability of
      resin permits a compound to be tailored to a specific design or performance
      requirement.
    • Polymers are created by the chemical bonding of many identical or related basic
      units and those produced from a single monomer type are called homopolymers.
      These polymers are specifically made of small units bonded into long chains.
      Carbon makes up the backbone of the molecule and hydrogen atoms are bonded along
      the carbon backbone.
    • In order to achieve a commercial product, the plastic is subject to further
      treatment and the inclusion of additives which are selected to give it specified
      properties
    • Additives are incorporated into polymers to alter and improve their basic
      mechanical, physical or chemical properties. Additives are also used to protect
      the polymer from the degrading effects of light, heat, or bacteria; to change
      such polymer properties as flow; to provide product color; and to provide
      special characteristics such as improved surface appearance or reduced friction.
    • Types of Additives:
           antioxidants:       for outside
      application, 
           colorants:
      for colored plastic parts, foaming agents: for Styrofoam
      cups, 
           plasticizers: used
      in toys and food processing equipment
    • A Thermoset is a polymer that solidifies or "sets" irreversibly when heated.
      Similar to the relationship between a raw and a cooked egg, once heated, a
      thermoset polymer can't be softened again and once cooked, the egg cannot revert
      back to its original form.
    • A Thermoplastic is a polymer in which the molecules are held together by weak
      secondary bonding forces that soften when exposed to heat and return to its
      original condition when cooled back down to room temperature. When a
      thermoplastic is softened by heat, it can then be shaped by extrusion, molding
      or pressing. Ice cubes are a common household item which exemplify the
      thermoplastic principle. Ice will melt when heated but readily solidifies when
      cooled.
    • In this method, a separate molding and cooling station on the equipment allows
      the parison to be continuously formed.  This technique is used mainly for
      small thin-walled parts ranging up to containers with five gallon
      capacities.  Parison programming can be used to vary the wall
      thickness.  Continuous extrusion also allows the use of heat-sensitive
      materials due to streamlined flow areas and die designs.
    • This technique is performed in three basic ways --reciprocating, ram
      accumulator, and accumulator head systems.  All three vary in machine
      design and the flow of molten resin through the die for parison forming. 
      However, each system is designed to produce larger, heavier, and thicker parts
      than continuous extrusion.
    • Blow moldable grades of material are initially injection molded into preform
      shapes.  These preforms are then thermally conditioned and then stretched
      (utilizing pneumatically operated stretch rods) low pressure air, followed by
      high pressure air up to 40 bar to form axially oriented parts with molded in
      necks.  The process is used to manufacture PET bottles.
    • This process utilizes various thermoplastic materials in a solid pelletized
      state and converts these materials by way of heat, pressure and compressed air
      into a finished good stat.

      The pellitized raw material is conveyed to the
      feed section of a plasticating extruder by way of a vacuum loader or auger
      screw.  The raw material is then conveyed forward through the extruder and
      is plastisized to a molten state of between 350 degrees and 500 degrees F. by
      way of a feed screw and external heating elements.

      The material in a melt
      state is then reshaped into a round hollow geometry termed a parison.  This
      parison is then extruded vertically from the head section of the machine through
      a round die at various outside and inside diameters.

      After extrusion of
      the parison between the two halves of a mold the press section closes
      encapsulating the parison inside the mold halves.  Upon mold close
      compressed air is entered into the parison by way of a centrally located air
      pipe or by piercing air needles.

      The molds are chilled with cooled water
      which transfers the hear form the now formed part inside the mold.  Upon
      complete part cooling the press section opens and the finished product is
      removed.  The material which is pinched off outside the mold cavity, or the
      flash, is then fed into a granulator which cops the flash into a granule size
      which can be fed back to the feed section of the extruder.
    Becky Kriger

    Special Properties of Polymers - 0 views

    pslc.ws/three.htm

    polymers

    shared by Becky Kriger on 08 Dec 08 - Snapshot
    • why these polymers, these macromolecules, act differently from small
      molecules.
    • Remember now that most polymers are linear polymers;
      that is, they are molecules whose atoms are joined in a long line to form a huge
      chain. Now most of the time, but not always, this chain is not stiff and
      straight, but is flexible. It twists and bends around to form a tangled mess.
    • ...4 more annotations...
    • when a polymer is molten, the chains will act like spaghetti tangled up on a
      plate. If you try to pull out any one strand of spaghetti, it slides right out
      with no problem. But when polymers are cold and in the solid state, they act
      more like a ball of string.
    • intermolecular forces affect polymers just like small molecules. But with
      polymers, these forces are greatly compounded. The bigger the molecule, the more
      molecule there is to exert an intermolecular force. Even when only weak Van der
      Waals forces are at play, they can be very strong in binding different polymer
      chains together. This is another reason why polymers can be very strong as
      materials. Polyethylene, for example is very nonpolar. It
      only has Van der Waals forces to play with, but it is so strong it's used to
      make bullet proof vests.

    • This is a fancy way of saying polymers move more slowly than small
      molecules do      . Imagine you are a first grade teacher, and it's time to go to
      lunch. Your task is to get your kids from the classroom to the cafeteria,
      without losing any of them, and to do so with minimal damage to the territory
      you'll have to cover to get to the cafeteria. Keeping them in line is going to
      be difficult. Little kids love to run around every which way, jumping and
      hollering and bouncing this way and that. One way to put a stop to all this
      chaotic motion is to make all the kids join hands when you're walking them to
      lunch. This won't be easy rest assured, as there's always going to be a lot of
      little boys who are too macho to hold the hands of the girls next to them in
      line, and some who are too insecure in their manhood to hold anyone's hand. But
      once you get them to do this, their ability to run around is severely limited.
      Of course, their motion will still be chaotic. The chain of kids will curve and
      snake this way and that on its way to eat soybean patties disguised as who knows
      what. But the motion will be a lot slower. You see, if one kid gets a notion to
      just bolt off in one direction, he or she can't do it because he or she will be
      bogged down by the weight of all the other kids to which he or she is bound.
      Sure, the kid can deviate from the straight path, and make a few other kids do
      so, but the deviation will be far less than you'd bet if the kids weren't all
      linked together.

      It's the same way with molecules.

    • So then how does this make a polymeric material different from a material made
      of small molecules? This slow speed of motion makes polymers do some very
      unusual things. For one, if you dissolve a polymer in a solvent, the solution
      will be a lot more viscous than the pure solvent.
    Becky Kriger

    Condensation Polymerization - 0 views

    www.materialsworldmodules.org/...4-condensation.html

    condensation polymers polymers

    shared by Becky Kriger on 08 Dec 08 - Snapshot

    • The monomers that are involved in condensation polymerization are not the
      same as those in addition polymerization. The monomers for condensation
      polymerization have two main characteristics:.
      Instead of double bonds, these monomers have functional groups (like
      alcohol, amine, or carboxylic acid groups).
      Each monomer has at least two reactive sites, which usually means two
      functional groups.

      Some monomers have more than two reactive sites, allowing for branching
      between chains, as well as increasing the molecular mass of the polymer.

    • Let's look again at the functional groups on these monomers. We've seen
      three:




      The carboxylic acid group
      The amino group

      The alcohol group

    • You might have learned in chemistry or biology class that these groups can
      combine in such a way that a small molecule (often H2O) is given off.

      The Amide Linkage:
      When a carboxylic acid and an amine react, a water
      molecule is removed, and an amide molecule is formed.

      Because of this amide formation, this bond is known as an amide
      linkage      .

      The Ester Linkage:
      When a carboxylic acid and an alcohol react, a water
      molecule is removed, and an ester molecule is formed.

      Because of this ester formation, this bond is known as an ester
      linkage      .

    • ...3 more annotations...

    • Example 1:
      A carboxylic acid monomer and an amine monomer can join in an
      amide linkage.

      As before, a water molecule is removed, and an amide linkage is formed.
      Notice that an acid group remains on one end of the chain, which can react with
      another amine monomer. Similarly, an amine group remains on the other end of the
      chain, which can react with another acid monomer.

      Thus, monomers can continue to join by amide linkages to form a long chain.
      Because of the type of bond that links the monomers, this polymer is called a
      polyamide.

    • Example 2:
      A carboxylic acid monomer and an alcohol monomer can join in an
      ester linkage.


      <form>A water molecule is removed as the ester linkage is formed. Notice the
      acid and the alcohol groups that are still available for bonding.</form>

    • Because the monomers above are all joined by ester linkages, the polymer
      chain is a polyester. This one is called PET, which stands for poly(ethylene
      terephthalate). (PET is used to make soft-drink bottles, magnetic tape, and many
      other plastic products.)

    Becky Kriger

    Polymer Structures - 0 views

    plc.cwru.edu/...textbook.htm

    shared by Becky Kriger on 08 Dec 08 - Snapshot
      • Becky Kriger
        Becky Kriger on 08 Dec 08
         
        To view the annotated contents of this page, click on the highlighted links to the left.

    • Although the fundamental property of bulk polymers is the degree of
      polymerization, the physical structure of the chain is also an important factor
      that determines the macroscopic properties.

    • Configuration
      refers to the order that is determined by chemical bonds. The configuration of a
      polymer cannot be altered unless chemical bonds are broken and reformed. Conformation
      refers to order that arises from the rotation of molecules about the single
      bonds. These two structures are studied below.
    • ...12 more annotations...

    • The two types of polymer configurations are cis and trans.
      These structures can not be changed by physical means (e.g. rotation). The
      cis configuration arises when substituent groups are on the same side of
      a carbon-carbon double bond. Trans refers to the substituents on opposite
      sides of the double bond.

    • Three distinct structures can be obtained. Isotactic
      is an arrangement where all substituents are on the same side of the polymer
      chain. A syndiotactic
      polymer chain is composed of alternating groups and atactic is
      a random combination of the groups. The following diagram shows two of the three
      stereoisomers
      of polymer chain.
    • The ability of an atom to rotate this way relative to the atoms which it joins
      is known as an adjustment of the torsional angle. If
      the two atoms have other atoms or groups attached to them then configurations
      which vary in torsional angle are known as conformations.
    • different conformation may represent different potential energies of the
      molecule. There several possible generalized conformations: Anti (Trans),
      Eclipsed (Cis), and Gauche (+ or -). The following animation illustrates the
      differences between them.
    • The geometric arrangement of the bonds is not the only way the structure of a
      polymer can vary. A branched
      polymer       is formed when there are "side chains" attached to a main
      chain. A simple example of a branched polymer is shown in the following diagram.
    • One of these types is called "star-branching".
      Star branching results when a polymerization starts with a single monomer and
      has branches radially outward from this point. Polymers with a high degree of
      branching are called dendrimers Often
      in these molecules, branches themselves have branches.
    • A separate kind of chain structure arises when more that one type of monomer is
      involved in the synthesis reaction. These polymers that incorporate more than
      one kind of monomer into their chain are called copolymers. There
      are three important types of copolymers. A random
      copolymer       contains a random arrangement of the multiple monomers. A block
      copolymer       contains blocks of monomers of the same type. Finally, a graft
      copolymer       contains a main chain polymer consisting of one type of
      monomer with branches made up of other monomers. The following diagram displays
      the different types of copolymers.
    • In addition to the bonds which hold monomers together in a polymer chain, many
      polymers form bonds between neighboring chains. These bonds can be formed
      directly between the neighboring chains, or two chains may bond to a third
      common molecule.
    • Polymers with a high enough degree of cross-linking have "memory." When the
      polymer is stretched, the cross-links prevent the individual chains from sliding
      past each other. The chains may straighten out, but once the stress is removed
      they return to their original position and the object returns to its original
      shape.
    • In vulcanization, a series of cross-links are introduced into an elastomer
      to give it strength. This technique is commonly used to strengthen rubber.
    • Elastomers,or
      rubbery materials, have a loose cross-linked structure. This type of chain
      structure causes elastomers to possess memory. Typically, about 1 in 100
      molecules are cross-linked
    • Natural and synthetic rubbers are both common examples of elastomers. Plastics are
      polymers which, under appropriate conditions of temperature and pressure, can be
      molded or shaped (such as blowing to form a film). In contrast to elastomers,
      plastics have a greater stiffness and lack reversible elasticity.
    Becky Kriger

    Polysaccharides - Chemistry Encyclopedia - 0 views

    www.chemistryexplained.com/...Polysaccharides.html

    shared by Becky Kriger on 08 Dec 08 - Snapshot
    • Polysaccharides are long polymers of monosaccharides and their derivatives. Unlike proteins or nucleic acids, these polymers can be either linear or branched, and they can contain only one type of monosaccharide (homopolysaccharides), or more than one (heteropolysaccharides)
    • Starch is a homopolysaccharide and has two forms: amylopectin and α-amylose. In nature, starch is approximately 10 to 30 percent α-amylose.
    • Starch is the main energy reserve in plants; glycogen is the main energy reserve in animals
    • ...10 more annotations...
    • In contrast to amylopectin, which comprises 70 to 90 percent of natural starch, α-amylose is a branching polysaccharide.
    • Branches occur at every twelve to thirty residues along a chain of α (1→4) linked glucoses. As a result, amylopectin has one reducing end and many nonreducing ends.
    • Amylopectin and α-amylose are broken down by the enzyme amylase. In animals, salivary α-amylase begins the digestion process in the mouth. Pancreatic α-amylase continues the process in the intestine.
    • Glycogen is the energy storage carbohydrate in animals. Glycogen is found mainly in the liver (where it is responsible for up to 10 percent of liver mass) and skeletal muscle (1 to 2 percent of skeletal muscle mass)
    • However, glycogen branches more abundantly than amylopectin, with branches at every eight to twelve residues. As a result, it has many more nonreducing ends. Glycogen is broken down at these nonreducing ends by the enzyme glycogen phosphorylase to release glucose for energy.
    • The primary structural homopolysaccharides are cellulose and chitin. Cellulose, a major component of plant cell walls, is the most abundant natural polymer on Earth.
    • Like α-amylose, cellulose is a linear polysaccharide composed entirely of glucose. However, in cellulose the glucose residues occur in β(1→4) linkage rather than α (1→4) (see Figure 1).
    • In addition, individual cellulose strands can form hydrogen bonds with one another to provide additional strength. Most animals, including humans, lack the enzymes necessary to dissolve α(1→4) linkages and so cannot digest cellulose
    • The animals that can (such as ruminants) do so via a symbiosis with bacteria that secrete cellulose-degrading enzymes.
    • The second most abundant polymer on Earth is chitin. Chitin comprises much of the exoskeletons of crustaceans, insects, and spiders, as well as the cell walls of fungi. Structurally, chitin is very similar to cellulose, except that its basic monosaccharide is N-acetylglucosamine
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