Multiple-shape memory polymers from benzoxazine–urethane copolymers

Abstract

In this research, multiple-shape memory polymers were prepared from benzoxazine (BA-a) resin and a urethane prepolymer (PU). The effects of BA-a resin content on the thermal, mechanical and multiple-shape memory properties were investigated by differential scanning calorimetry (DSC), thermogravimetric analysis, dynamic mechanical analysis, a flexural test and a multiple-shape memory test. The results revealed that the suitable curing conversions of BA-a:PU resin mixtures affect the shape memory behaviors. The BA-a/PU copolymers demonstrated an increase in flexural strength and flexural modulus at various deformation temperatures with an increase in the BA-a mass ratio from 55%–80%, whereas the thermal properties of these binary systems, i.e. glass transition temperature (Tg), degradation temperature (Td) and char yield, were also found to increase with an increase in BA-a content. In addition, the two-step bending test was carried out using a universal testing machine to evaluate the multiple-shape memory properties. The results revealed that the BA-a/PU samples exhibited high values of shape fixity (70%–96% for the first temporary shape and 83%–99% for the second temporary shape) and shape recovery (88%–96% for the first temporary shape and 97%–99% for the original shape).