Does branching occur during free radical polymerization of ethylene even at high temperatures and pressure or only on other type of monomers using free radical polymerization at lower temperatures? I was reading this article: http://en.wikipedia.org/wiki/Polymerization It was not very clear on this part, "Free radical addition polymerization of ethylene must take place at high temperatures and pressures, approximately 300 °C and 2000 atm. While most other free radical polymerizations do not require such extreme temperatures and pressures, they do tend to lack control. One effect of this lack of control is a high degree of branching. Also, as termination occurs randomly, when two chains collide, it is impossible to control the length of individual chains. A newer method of polymerization similar to free radical, but allowing more control involves the Ziegler-Natta catalyst, especially with respect to polymer branching." To me, that makes it sound like high temperature and high pressure polymerization has more control and does not branch.