Molecular environment effects on polymerization rates in diepoxide–binary amines compositions by dielectric studies

• Published in: Chemical physics 1999-04, Vol.242 (2), p.283-291
• Main Authors: Johari, G.P., Wasylyshyn, D.A.
• Format: Article
• Language: English
• ISSN: 0301-0104
• DOI: 10.1016/S0301-0104(99)00019-1

Dielectric studies during the polymerization of a diepoxide mixed with binary amines of different compositions have shown that the reaction kinetic characteristics of individual amines vanish in the mixed state. When the ratio of the two amines, one forming linear chains on reaction with the diepoxide and the second a network structure, was changed, the reaction kinetics changed as if the polymerization temperature or pressure had been changed. The distribution of relaxation times has been attributed to the rapid slowing of the dipole's or reacting group's environment's fluctuation, as in Anderson–Ullman's fluctuating environment theory [J.E. Anderson, R. Ullman, J. Chem. Phys. 47 (1967) 2178] for the origin of the relaxation spectrum shapes, with the difference that as polymerization progresses this slowing occurs in a continuous manner. Both, the change in molecular dynamics from a single relaxation time Debye-type spectrum to a broad distribution of relaxation times spectrum and the change from reaction kinetics from a single reaction rate constant to a time-dependent rate constant, occur when the viscosity increases during the macromolecular growth. The rate of fluctuation of a reacting group's environment controls the dispersive nature of the reaction kinetics, as in the Plonka–Paszkiewicz treatment [A. Plonka, A. Paszkiewicz, J. Chem. Phys. 96 (1992) 1128]. This interpretation has two more testable consequences: (1) reaction kinetics with a single rate constant will become dispersed when the liquid's viscosity is increased by cooling or compression; and (2) two independent reactions with different average rate constants will show a broad dispersion of kinetics when the liquid's viscosity is increased similarly, or by the occurrence of the reaction.