Explain why a polymer such as polybutadiene can be cross-linked, however a polymer such as polyethylene cannot be cross-linked. Make reference to what it is about the chemistry of the repeating units that allows for the formation of cross-links.

Answer 1

butadiene is left with a second double bond when it polymerizes, making cross chains possible. Study these two images.

http://upload.wikimedia.org/wikipedia/commons/c/c6/1,3-Butadiene_Polymerization.PNG

http://www.google.com/imgres?imgurl=http://upload.wikimedia.org/wikipedia/commons/f/f7/Polyethylene-repeat-2D-flat.png&imgrefurl=http://en.wikipedia.org/wiki/File:Polyethylene-repeat-2D-flat.png&h=1052&w=1100&sz=21&tbnid=QtnQAgr3rIA1rM:&tbnh=93&tbnw=97&zoom=1&usg=__1PiU_qffpsFCTFUX8ulotS86Aik=&docid=rLW8JQHZ90znBM&sa=X&ei=giPfUIm1DOXg2gXymYHQBg&ved=0CGoQ9QEwBw&dur=2596