Effect of polyradicals on gel formation in free radical polymer modification

The formation of polyradical chains is an important feature in free radical polymer modification with crosslinking. The effect of these polyradicals on the prediction of the gel point is theoretically investigated using the method of moments. The polyradical model derived gives a criterion for gelation, <x(r)over bar (W,0)> = 1, which fully agrees with the Flory-Stockmayer classical theory. The validity of the widely used monoradical assumption and the stationary state hypothesis in modeling of free radical gel formation is extensively examined by making comparisons to the polyradical model. It is found that both assumptions delay the prediction of the gel point. The magnitude of the discrepancies depends on the reaction conditions. Based on the calculations using a wide range of parameters, it is concluded that these two assumptions are acceptable provided R(in)/K-ha Y-1,Y-0 Y-1,Y-0 is smaller than 10(-7). However, this condition can be easily violated in a typical polymer modification system. Therefore, the use of polyradical models is suggested. (C) 1996 John Wiley & Sons, Inc.