Dual-shape properties of triple-shape polymer networks with crystallizable network segments and grafted side chains

Abstract

Triple-shape materials have recently been introduced as a promising class of active polymers, that can change on demand from a first shape (A) to a second shape (B) and from there to a third shape (C). Here, the dual-shape capability of such a triple-shape polymer network system having two distinct melting transitions is investigated by cyclic, thermomechanical experiments. These multiphase polymer networks are synthesized by photopolymerization from poly(ethylene glycol) monomethyl ether monomethacrylate and poly(ε-caprolactone) dimethacrylate as crosslinker. While their permanent shape is determined by the chemical crosslinks formed during network preparation, the two different crystallizable phases can be used to fix other temporary shapes. When programmed appropriately in a two-step thermomechanical process these materials can exhibit a triple-shape effect. Here, one-step programming methods for dual-shape effects are applied to these polymer networks under variation of process parameters, especially thermal conditions. In this way, crystalline phases formed by both segments can be used either individually or simultaneously to fix a temporary second shape. The permanent shape can be recovered by heating, exceeding a specific switching temperature. This switching temperature correlates with the melting transition of the related domain, if one domain is used for fixation. If both domains are used, the switching temperature correlates with the higher melting temperature.