Epoxy‐cyanate ester shape memory thermoset: some aspects of phase transition, viscoelasticity and shape memory characteristics

Abstract

A shape memory thermoset comprising of a co‐reacted system of epoxy resin (diglycidylether of bisphenol A), cyanate ester (bisphenol A dicyanate ester) and phenol telechelic poly(tetramethylene oxide) (PTOH) was investigated for its morphology, viscoelasticity and shape memory characteristics at the transition temperature regime. The system exhibited a switching temperature (Tswitch) centered at about 105°C. Atomic force microscopy analyses at different temperatures provided evidences for the existence of a discrete phase at Tswitch regime. Polarized light microscope images gave evidence for the birefringence and tubular crystal formation due to PTOH segments in the shape memory thermoset. It is concluded that the Tswitch has its origin from melting transition of PTOH and Tg of the thermoset matrix, the latter being lowered through plasticization by PTMO segments. Reversibility of Tswitch, and stress relaxation behavior of the blend were investigated by dynamic mechanical analysis (DMA). The reversibility of transition temperature was ascertained by cyclic DMA. Temperature dependency of shape memory properties implied fast recovery of original shape above the Tswitch. The cured system manifests shape memory properties even below Tswitch though it is a slow process. The extent of shape recovery increased with temperature and became faster in league with the trend in temperature dependency of stress relaxation of the polymer. Copyright © 2013 John Wiley & Sons, Ltd.

Thermoset shape memory polymers and their composites

“…Various manipulations of cyanate-based SMPs have been investigated, and most of these studies have used polybutadiene (Wang et al, 2014a; Xie et al, 2014; Zhao et al, 2014), PEG (Xie et al, 2014), and epoxy (Biju et al, 2012a; Biju and Reghunadhan Nair, 2014; Rajendran et al, 2013; Santhosh Kumar et al, 2014; Wang et al, 2014a) as mobile flexible segments. Xie et al (2014) prepared a series of cyanate-based high-temperature SMPs using functional PEG or polybutadiene/acrylonitrile (PBAN).…”

Shape‐memory effect in hyperbranched poly(ethyleneimine)‐modified epoxy thermosets

“…Biju and Nair reported the synthesis of a shape‐memory epoxy network based on a diglycidyl ether of bisphenol A (DGEBA) cured with a pyromellitic dianhydride for possible use in smart actuator systems. Rajendran et al synthesized an epoxy‐cyanate system by coreacting a DGEBA, cyanate ester and phenol telechelic poly(tetramethylene oxide) and studied the correlation between the viscoelastic and shape‐memory properties. Wei at al .…”

Mechanically strong and resilient shape memory polyurethane with hexamethylene diisocyanate as mixing segment

“…Peak stress was observed at zero time, which suggests the rigidity of the material due to hard-aromatic segments present. Higher the tension, the stiffness of the section decreases and low stress increase the material’s flexibility (Rajendran et al, 2013).…”

“…It was observed that the stress value did not decrease to zero; instead, it approached a plateau. The plateau stress is the stored internal energy of the net-points, responsible for the recovery of the original shape during the shape memory effect (Rajendran et al, 2013).…”

“…At 36°C, a steady rise in the fixity with strain % is observed, since the SMPU experience restriction in segmental motion at room temperature. Therefore, the polymer does not get enough time to memorise its deformed shape when cooled (Rajendran et al, 2013). However, the increase is more significant at higher strain (200%), and high temperature (70°C), owing to rapid molecular rearrangement.…”