Molecular weight effects on the mechanical properties of novel epoxy thermoplastics

Abstract

A series of epoxy thermoplastics (ETPs) with varying molecular weights were synthesized from a difunctional diglycidyl ether of bisphenol-A (DGEBA)-based epoxy resin and an aromatic secondary diamine. The materials possessed glass transition temperatures varying between 73.61 and 85.36°C. The ETP series was characterized for fracture toughness, flexural, and compression properties. In general, fracture properties increased with increasing molecular weight and yet were consistently shown to decrease when higher molecular weight values were the result of increased branching. Flexural ultimate strength and strain-at-break increased with increasing molecular weight while flexural modulus decreased to a plateau. Compression properties were relatively unaffected by changes in molecular weight over the range of materials synthesized.