Influence of functionality of novolac phenol-formaldehyde resins on the kinetics of the curing of epoxy resins

摘要

Oligophenols produced by the condensation of phenol and formaldehyde, in particular the novolac resins (NPFRs) [1], are widely used as curing agents for epoxy resins in different areas of applicaton [2-5]. Information on their use largely concerns the properties of the final curing products. Questions of the kinetics and mechanism of the reaction, with the aim of establishing the optimum production regimes with their participation, have been studied inadequately [6,7]. In particular, there are no data on the influence of the molecular weight or functionality of NPFRs on the kinetics of the process of their interaction with epoxides, although it is known [8] that the functionality of NPFRs has a considerable influence on the physicomechanical properties of epoxy-novolac polymers. The question of the influence of this factor on the reactivity of phenolic groups of the curing agent and on the physicomechanical properties of epoxy-novolac polymers. The question of the influence of this factor on the reactivity of phenolic groups of the curing agent and on the completeness of their coversion remains unanswered. It is known [9] that, by using polyphenols as curing agents, the topological limit of curing of the final crosslinked polymer is lowered (a_infinity=0.85) by comparison with the topological limit for epoxy-amine polymers (a_infinity=0.95 [10]. This result is explained [9] by the stronger steric hindrances for the interacton of functional groups in epoxy-phenol systems.