Cure kinetics modeling and thermomechanical properties of cycloaliphatic epoxy-anhydride thermosets modified with hyperstar polymers

Abstract

Hyperstar polymers (HSPs) with hyperbranched aromatic polyester core and arms consisting of block copolymers of poly(methyl methacrylate) and poly(hydroxyethyl methacrylate) have been used as polymeric modifiers in cycloaliphatic epoxy-anhydride formulations catalyzed with tertiary amines, with the purpose of enhancing the impact strength of the resulting materials without compromising other thermal and mechanical properties.> In this work, the effect of these polymeric modifiers on the curing kinetics, processing, thermal-mechanical properties and thermal stability has been studied using thermal analysis techniques such as DSC, TMA, DMA, and TGA. The morphology of the cured materials has been analyzed with SEM. The curing kinetics has been analyzed by isoconversional procedures and phenomenological kinetic models taking into account the vitrification during curing, and the degradation kinetics has been analyzed by means of isoconversional procedures, summarizing the results in a time-temperature-transformation (TTT) diagram. The results show that HSPs participate in the crosslinking process due to the presence of reactive groups, without compromising significantly their thermal-mechanical properties. The modified materials show a potential toughness enhancement produced by the formation of a nano-grained morphology. The TTT diagram is shown to be a useful tool for the optimization of the curing schedule in terms of curing completion and safe processing window, as well as for defining storage stability conditions. (C) 2014 Wiley Periodicals, Inc.