MODELING OF FREE-RADICAL POLYMERIZATION WITH CROSS-LINKING - MONORADICAL ASSUMPTION AND STATIONARY-STATE HYPOTHESIS

The validity of the monoradical assumption and the stationary-state hy pothesis in modeling of free-radical polymerization with branching and /or cross-linking was evaluated using the method of moments. The polym erization system involved the reactions of chain transfer to polymer a nd radical recombination. Therefore, the system was capable of gelatio n. The gelation behavior was controlled by the three groups of paramet ers: K(fp)M0/K(t)R, K(tc)/K(t), and K(p)/K(t). It can be shown that po lyradical chains accumulate only in the vicinity of the gel point and beyond. The presence of polyradical chains gives higher chain growth r ates and thus promotes gelation. The monoradical assumption delays the gel point while the stationary-state hypothesis causes it to occur ea rlier. However, significant errors due to these assumptions were found only when the value of K(p)/K(t) was larger than 10(-3). Therefore, t hese assumptions should be considered valid for systems with K(p)/K(t) < 10(-3). The same conclusions are also applicable for free-radical c opolymerizations involving divinyl monomers.