Multiphase Polymer Networks with Shape-Memory
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Multiphase Polymer Networks with Shape-Memory Steffen Kelch1, Marc Behl2, Stefan Kamlage2 and Andreas Lendlein2 1 Sika Technology AG, Tüffenwies 16, CH-8048 Zürich, Switzerland 2 Center for Biomaterial Development, Institute of Polymer Research, GKSS Research Center Geesthacht GmbH, Kantstr. 55, 14513 Teltow, Germany ABSTRACT Tailoring of properties and functions of shape-memory polymer networks to the requirements of specific applications demands a knowledge-based approach. A comprehensive database enabling the analysis of structure-property relationship is obtained by the systematic variation of molecular parameters. Here, we investigated the influence of the nature of thermal transition on the shape-memory behavior of polymer networks. Furthermore, additional amorphous phases were introduced enabling tailoring of elastic properties especially in the temporary shape. The structure property relationships were derived for different designs of such multiphase polymer network architectures.
INTRODUCTION A recent development in shape-memory polymer technology is the design of shape-memory polymers as multifunctional materials. While the intrinsic properties of a material are determined by its molecular structure, the functionality of material arises from the combination of a suitable polymer architecture and a specific process [1]. Multifunctionality is the unexpected combination of two or more functions of a material. While usually functionalities are combined on purpose, the term unexpected results from the fact that such combinations are not apparent. An interesting example of such multifunctional materials are hydrolytically degradable shape-memory polymers, which combine the functionalities degradability and the shape-memory capability. While degradability could be obtained by the introduction of easily cleavable bonds, the shape-memory capability requires a suitable polymer network architecture in combination with an appropriate programming procedure. Several previous articles described the programming process and the characterization of the shape-memory effect and gave definitions for shape fixity (Rf) and shape recovery rates (Rr) [2-6]. In this article, we focused on the design of suitable polymer networks architectures enabling the shape-memory capability and the parameters to control the shape-memory properties. For a better comparability of the results presented, we will limit our considerations to polymer networks based on macrodimethacrylates. DISCUSSION Polymer network architectures Suitable polymer networks structures having shape-memory capability are displayed in Scheme 1. General parameters for controlling the shape-memory behaviour of covalently crosslinked polymer networks are the functionality of the crosslinks, the network chain segment length, the nature of the switching segment and the number of phases. The functionality of crosslinks and the chain segment length control the crosslink density and influence in this way the mechanical properties while the nature of the switching se
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