KINETIC MODELING OF NETWORK FORMATION IN STYRENE BUTADIENE EMULSION COPOLYMERS - A COMPARATIVE-STUDY WITH THE GENERALIZED FORM OF FLORY THEORY OF GELATION

A theoretical model is proposed for the distribution of molecular weight, branching and crosslinking in styrene-butadiene emulsion copolymers. The main objective is to compute the instantaneous distributions of primary macroradicals and primary dead chains with zero, one, two or more crosslinks as the reaction proceeds. The amount of gel is calculated on the assumption that each chain with at least two (or three) crosslinks is withdrawn from the sol fraction. The network thus formed is characterized by its crosslink density and number average length of the primary chains. This model has been compared with a mean field theory of network formation derived recently by Hamielec et al. Both models were used to predict the extent of gel versus conversion and the crosslink density of the gel polymer, differentiating between elastically active and inactive crosslinking points. The same value of the adjustable parameter (i.e. reactivity ratio of the butadiene pendent double bond) can be used in the two models to account for gel formation with fairly good accuracy.