Synthesis and Characterization of Hydroxy-telechelic Four-arm Star-shaped Oligo(tetrahydrofuran), Their Crosslinking, an
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Synthesis and Characterization of Hydroxy-telechelic Four-arm Star-shaped Oligo(tetrahydrofuran), Their Crosslinking, and Thermomechanical Investigation of the Poymer Network K. K. Yang1,2, J. Zotzmann1, A. Lendlein1,3, and M. Behl1,3 1 Center for Biomaterial Development and Berlin Brandenburg Center for Regenerative Therapies (BCRT), Institute of Polymer Research, Helmholtz-Zentrum Geesthacht, Kantstr.55, 14513 Teltow, Germany 2 National Engineering Laboratory of Eco-Friendly Polymeric Materials (Sichuan), College of Chemistry, Sichuan University, Wangjiang Road 29, Chengdu 610064, P. R. China 3 Tianjin University-Helmholtz-Zentrum Geesthacht, Joint Laboratory for Biomaterials and Regenerative Medicine, Kantstr. 55, Teltow, Germany ABSTRACT Here the synthesis of hydroxy-telechelic four-arm star-shaped oligotetrahydrofuran (4PTHF) with controllable molecular weight was explored, which was perfomed as living cationic ringopening polymerization of THF using pentaerythritol and trifluoromethanesulfonicanhydride as initiation system. The molecular weights of the 4PTHF were a function of the reaction time. A polymer network was prepared from the hydroxy-telechelic 4PTHF precursor by crosslinking with diisocyanate and the shape-memory properties were determined. High values for Rf and Rr > 98% were obtained even at high programmed elongations, which suggest the 4PTHF-network as a promising shape-memory material. These materials might have a great potential, as the upscaling of synthesis could be successfully demonstrated. INTRODUCTION Shape-memory polymers (SMPs) respond to various external stimuli such as heat, or light or electric and magnetic fields by changing their shape [1-5]. This unique characteristic of SMPs could enable various potential applications such as intelligent biomedical applications [6-10]. SMPs can be deformed by external stress and fixed in a second, temporary shape. They recover their original, permanent shape when they were exposed to an appropriate stimulus. The permanent shape of SMP is determined by netpoints, which can be covalent cross-links or physically in nature [11-16]. SMP networks having covalent crosslinks can serve as model systems for fundamental studies of the shape-memory effect (SME) as covalent crosslinks are more defined than crosslinks based on physical interaction. However, this requires polymer networks of a precise architecture and therefore defined precursors, which they are based on. SMP polymer networks of defined architecture can be can be easily obtained by crosslinking star-shaped precursors with a diisocyanate. Thus far SMP networks based on star-shaped precursors were prepared from biodegradable polyesters such as poly([rac-lactide]-co-glyocolide), poly([rac-lactide]-co-[pdioxanone]), or poly(Ȧ-pentadecalactone) [11, 14-16]. We have explored, whether such SMP networks of defined architecture could also be prepared from polytetrahydrofuran. Here, polytetrahydrofuran (PTHF) was selected as it is a polyether, which has been applied in various polyetherurethanes of good
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