DIFFUSION-CONTROLLED KINETICS OF CROSS-LINKING

Reactions of polymer formation and crosslinking become diffusion controlled when, during the reaction, the increasing glass transition temperature T(g) comes close to the reaction temperature. the reaction still goes on below T(g) but the reaction rate decreases steeply. A theory is presented relating the apparent rate constant to the difference between the reaction temperature and T(g) based on the free volume or the Adam-Gibbs theory of glass transition. The theory is correlated with experiments on curing of diglycidyl ether of bisphenol A with 1,3-propanediamine. The implications for formation of protective films chemically crosslinked are discussed. The presence of a solvent and its evaporation affects the reaction rate through a change in concentrations of reactants as well as in T(g).