Effect of hard segment architecture on shape memory properties of polycaprolactone-based polyurethane containing azobenzene

Abstract

In this work, we synthesized two kinds of polyurethanes with azobenzene as hard segments in the side chains and in the main chains. Their thermal stabilities were high enough for their shape memory application. For polyurethane with azobenzene in the side chain (PU), the azobenzene has more distinctly effect on inhibiting crystallization of polycaprolactone (PCL) because of irregular orientation of azobenzene. For polyurethane with azobenzene in the main chain (PUR), the crystallinity of PCL is mainly affected by its molecular weight. PU-3500 and PUR-3500 exhibit perfect shape fixing ability of 99 % with recovery ratio of 98 % at 50 % strain. The recovery ratio is decreased for PU-3500 and increased for PUR-3500 as the applied strain increased. The mechanism of the hard segment structures effect on the shape memory behavior is briefly discussed. Importantly, the two molecules behave trans–cis isomerization under UV irradiation. This work is crucially important for the structural design of shape memory polyurethane and applications in the smart devices.