Dielectric and steric hindrance effects on step-polymerization of a diepoxide with monoamines

Abstract

The step-polymerization reaction between monoamines and diepoxide has been investigated by measuring the permittivity and dielectric loss as a function of reaction time, t_re, at different temperatures. Hexylamine and cyclohexylamine were used both in stoichiometric and non-stolichiometric (amine-rich) compositions with the diglycidyl ether of bisphenol-A. The dielectric consequences of increase in the growth of the macromolecule during the step-polymerization are analogous to the frequency dependence of a chemically invariant substances. The reaction-time dependence of ε* has the functional form: Φ(t)= exp –[t/τ(t_re)]^γ where γ= 0.3–0.4. Steric hindrance of the NH₂ group in cyclohexylamine slowed the rate of polymerization and the ε* features were shifted towards longer t_re. Excess amine accelerated the polymerization process, but shifted the dielectric features towards longer reaction time. Although the reaction reached completion, the mixture did not vitrify. In this respect the dielectric behaviour differs from that of network polymerization. Reaction temperature, time, composition and chemical structure of the monoamine, all affected the strength of the sub-glass transition temperature (T_g) relaxations of the polymerized product.