Comparison of memory effects in multiblock copolymers and covalently crosslinked multiphase polymer networks composed of
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Comparison of memory effects in multiblock copolymers and covalently crosslinked multiphase polymer networks composed of the same types of oligoester segments and urethane linker Li Wang1, 2, Ulrich Nöchel1, Marc Behl1, Karl Kratz1, Andreas Lendlein1, 2 1 Institute of Biomaterial Science and Berlin-Brandenburg Centre for Regenerative Therapies (BCRT), Helmholtz-Zentrum Geesthacht, 14513 Teltow, Germany 2 Institute of Chemistry, University Potsdam, 14476 Potsdam, Germany * Corresponding Author: [email protected]
ABSTRACT Phase-segregated multiblock copolymers (MBC) as well as covalently crosslinked multiphase polymer networks, which are composed of crystallizable oligo(ε-caprolactone) (OCL) and oligo(ω-pentadecalactone) (OPDL) segments have been recently introduced as degradable polymer systems exhibiting various memory effects. Both types of copolyesterurethane networks can be synthesized via co-condensation of the respective hydroxytelechelic oligomers and 2,2(4),4-trimethyl-hexamethylene diisocyanate (TMDI) as aliphatic linker. In this work the dual-shape properties as well as the temperature-memory capability of thermoplastics and covalently crosslinked copolyesterurethanes containing OCL and OPDL domains are explored. Both copolyesterurethane networks exhibited excellent dual-shape properties with high shape fixity ratios Rf t 93% and shape recovery ratios in the range of 92% to 100% determined in the 2nd and 3rd test cycle, whereby the dual-shape performance was substantially improved when covalent crosslinks are present in the copolymer. A pronounced temperature-memory effect was achieved for thermoplastic as well as crosslinked copolyesterurethanes. Hereby, the switching temperature Tsw could be adjusted via the variation of the applied deformation temperature Tdeform in the range from 32 °C to 53 °C for MBC and in the range from 29 °C to 78 °C for multiphase polymer networks. INTRODUCTION In recent years different memory effects such as dual-, triple-, or multi-shape effect or temperature-memory effect (TME), where a material can memorize the temperature at which it was deformed before, have been reported for various thermo-sensitive polymers [1, 2, 4, 16]. These memory effects are characterized by a controlled shape change in a predefined way, when the response temperature of a material is exceeded, and therefore these materials are of great technological interest for the realization of actively moving intelligent devices [3, 4]. Polymers, which are capable to memorize defined shapes or temperatures, have two structural elements in common: netpoints, which stabilize the original, permanent shape and reversible crosslinks related to a thermal transition (e.g. a glass or melting transition) acting as switching domains and in this way enabling on the one hand side the fixation of temporary shapes as well as the entropy driven recovery of the original shape. The netpoints in thermo-sensitive polymers can be either of chemical (covalently crosslinked polymer networks) or physical (thermoplastics) nature.
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