Effect of Phenol End Functional Switching Segments on the Shape Memory Properties of Epoxy-Cyanate Ester System

The effect of phenol end functional shape memory oligomers on the shape memory properties of an epoxy-cyanate ester resin system was examined. The basic resin system consisted of diglycidyl ether of bisphenol A (DGEBA) cured with bisphenol A dicyanate (BADC). For conferring the shape memory properties, the switching segment (SS) components selected are alpha, omega-phenol-terminated poly(tetramethyleneoxide) (PPTMO), poly(e-caprolactone) (PPCL), and poly(propylene glycol) (PPPG). Epoxy-cyanate ester blend of defined composition was analyzed for thermal, mechanical, thermo-mechanical, and shape memory properties at two concentrations of the three SSs. The transition temperature of heavily SS loaded matrix increased in the order: PPTMO < PPCL < PPPG commensurate with crystallizability of SS segments at ambient. For same reason flexural property showed an increasing trend. This is in league with the increased crystallizability of the shape memory polymer components. The shape fixity, recovery extent, and recovery time followed a reverse order: PPPG < PPCL < PPTMO. In contrast to the alcohol terminated shape memory components, phenol terminal groups were helpful in integrating the shape memory segments into the matrix by way of reaction with both epoxy and cyanate groups. The coreaction was conducive for achieving better shape memory properties and decreasing the transition temperature. A direct relation existed between the modulus ratio and the shape recovery property. Higher concentration of the SSs caused a diminution in transition temperature but enhanced the shape memory properties, though the mechanical properties were adversely affected. The shape recovery increased with increase in temperature. All polymers possessed good mechanical properties and thermal stability. (C) 2014 Wiley Periodicals, Inc.