Investigation On Star-Shaped Shape Memory Polyurethane

Recently, shape memory polyurethane (SMPU) were researched widely for various kinds of raw materials, bigger adjustable compositions and broader transition temperature. Usually, SMPU are a kind of thermoplastic block copolymers. The shape memory effect of SMPU is based on two phase structure:one is fixed phase which memory the initial shape and give entropy elasticity for recovery; another is switch phase which is for the fix and recover of temporary shape. Star-shaped polyurethane (SPU) is a kind of polymer that exploiting star-shaped polycaprolactone (SPCL) reacting with4,4’-diphenylmethane diisocyanate (MDI) and diol. In comparison with corresponding linear polymers, SPU has unique properties due to its well-defined branched structures, a large number of functional groups available in a small volume, controlled functionality and composition and thus can endure polymer more excellent shape memory effect. Further we used1,4-butanediol (BDO) for crosslinking to make the crosslinking SPU.This paper also research in this respect, the main results are as follows:Firstly, a series of star-shaped polycaprolactone(SPCL) were prepared. The glycerol (G), pentaerythritol (PE) and dipentaerythriol (DPE) were used as initiator to initiate the ε-caprolactone (CL) for ring opening reaction. By regulating the ratio of CL and hydroxyl group (-OH), the number average molecular weight (Mn) per arm is about1500mol/g.’H-NMR was done to demonstrate the structure and calculate the Mn of SPCL. The thermal properties and crystallization properties were analyzed by Differential Scanning Calorimetry (DSC) and X-ray Diffractometry (XRD).Then, the SPU were prepared by reacting SPCL with MDI and BDO after pre-polymerization and chain-extending reaction. Through adjusting the mole ratio among SPCL, MDI and BDO, we obtain the SPCL with soft segment comppsitions for55%,60%and65%. The SPU were characterized by Fourier Transform Infrared Spectroscopy (FT-IR), Nuclear Magnetic Resonance (NMR), DSC, XRD, Static Tensile Test, Dynamic Mechanical Thermal Analysis (DMA), In Vitro Cytotoxicity Assay. DMA and circle thermomechnical analysize demonstrated six-arm SPU (6S-PU) has a better shape memory effect than four-arm SPU (4S-PU) and three-arm SPU (3S-PU) with the same ratio of hard segment. Cytotoxicity analysis demonstrates that the polymer possess good cytocompatibility. Finally, we fabricated a kind of crosslinking SPU. In order to endor the material better hydrophile, six-arm star-shaped poly(ethylene glycol)(6S-PEG) was used as the initiator to initiate the CL for ring-opening reaction. After pre-polymerization and chain-extending reaction, a pinch of BDO was put into the reaction system for crosslinking. The final product were detected by DSC, XRD, DMA and Static Tensile Test and so on.