MODELING OF CROSS-LINKING AND CYCLIZATION IN FREE-RADICAL COPOLYMERIZATION OF VINYL DIVINYL MONOMERS

The Tobita-Hamielec kinetic model of the crosslink density distributio n is further elaborated and extended to incorporate divinyl loop forma tion. Divinyl loop formation, primary and secondary cyclization, and t heir effects on the elastically effective crosslink density distributi on are extensively examined as a function of cyclization parameters an d double bond reactivities. Under conditions of equal double bond reac tivity and negligible cyclization, primary chains born at different co nversions have the same crosslink density. The variance of the crossli nk density distribution is mainly due to unequal reactivities of doubl e bonds and secondary cyclization. Divinyl loop formation and primary cyclization contribute neither to gelation nor to network elasticity a nd have an insignificant effect on the variance of the crosslink densi ty distribution.