This is a simple tool that strips YouTube viewing of all of the distractions of related videos, comments, and promoted videos. To use it, copy the link of a video into the "purifier," click purify, and your video will be displayed on a blank white background. You can also install the View Pure bookmarklet to accomplish the same goal.
"The premise of their site is to take YouTube videos and strip away all the other 'nonsense' that you don't need when watching a tube video in class. There are no coments, no embedding or sharing options, no related videos - just the video you want."