STERIC HINDRANCE EFFECTS ON DIELECTRIC-RELAXATION AND POLYMERIZATION KINETICS OF A MONOAMINE-TRIEPOXIDE MIXTURE, THERMOCHEMISTRY, AND DIFFUSION CONTROL

Calorimetry and dielectric relaxation spectroscopy during the growth o f a polymer network in the stoichiometric mixture of a triepoxide with 4-chloroaniline have been performed in separate experiments to invest igate the increase in the relaxation time with the number of covalent bonds. A comparison with the corresponding study of triepoxide-aniline and triepoxide-3-chloroaniline mixtures shows that steric hindrance o f the amine group by chlorine slows the molecular dynamics and the rel axation time of the state containing a fixed number of bonds. The poly merization kinetics measured during ramp heating does not yield a reli able activation energy. A recent empirical relation between the relaxa tion time and the extent of polymerization, and the condition for the onset of diffusion-control kinetics have been examined using the data for these three polymerizing mixtures. The results show substantial de viations from the empirical relation and appear to conflict with our b asic understanding of the polymerization process. It is shown mathemat ically that features attributed to the onset of diffusion-controlled k inetics can arise from thermochemical behavior alone, without referenc e to the molecular dynamics. An earlier theory for the change in the k inetics of an addition reaction from mass control to diffusion control has been considered, and is seen as relevant to the polymerization re actions. It is argued that the dielectric relaxation rate does not dir ectly indicate the chemical reaction fate because the reorientational motion of the dipolar entities may not be coupled to the rotational an d translational diffusion that brings the sterically hindered chemical ly reacting sites together. (C) 1998 John Wiley & Sons, Inc.