The role of β relaxations in controlling compressive properties in hyperbranched polymer-modified epoxy networks

Abstract

In this work, a largely miscible second-generation aliphatic polyester hyperbranched polymer (HBP) is used as a modifier in a cured epoxy amine network to explore molecular mobility in the glassy state and its impact on compressive properties. The β relaxation determined by dynamic mechanical analysis is used as a measure of short-range motion in the glassy state and is related to the compressive modulus and yield properties. The parameters explored include an increased HBP concentration, enhanced HBP, and epoxy matrix interactions through pre-reaction via a rigid covalent linkage and a modified epoxy network of flexible butanediol diglycidyl ether (BDDGE) and highly crosslinkable tetraglycidyl diamino diphenyl methane (TGDDM). The β relaxation peaks are analyzed in terms of their area, FWHM, and position (Tβ) and are observed to correlate strongly with changes in the modulus, yield stress, and strain.