Based On The Series Of Polybutadiene Block Copolymer Synthesis, Phase Behavior And Related Biomedical Research Performance

Medical polyurethanes have been widely used in the medical field as a good blood compatible polymer biofunctional material. However, in the long-term clinical practice the polyurethane materials have been found to have many urgent problems to resolve and to improve, for instance degradation, cytotoxicity and micellar stability etc. Therefore, to further enhance and improve the performance of biomedical polyurethane materials bears an important theoretical research value and practical value for improving physicochemical properties, and promoting their wide applications. In this context, polyurethane copolymers with novel architecture have been designed and synthesized to acquire the PU materials with excellent physicochemical and biomedical performances. The specific work is caarried out focusing on the following aspects:1. Two types of polyurethanes with specific sequence structure and properties, viz. alternating (HTPB-alt-PEG) and random (HTPB-co-PEG) block copolymers were designed and synthesized by changing ways and charging sequence, with polyethylene glycol (PEG) with various molecular weights (MW) and hydroxyl-terminated polybutadiene oligomers as soft segments, and hexamethylene diisocyanate (HDI) as hard segment via a coupling reaction route between hydroxyl groups and isocyanate groups. The chemical and crystal structures were characterized by Fourier transform infrared spectra (FTIR) and X-ray diffraction (XRD).2. Microphase separation behavior of PU block copolymers was qualitatively and quantitatively examined by scanning electron microscope (SEM), and differential scanning calorimetry (DSC) based on the as-synthesized two PU copolymers with different sequence architectures. The biodegradation of these PU copolymers was carried out in a simulated human body fluid and was investigated through thermogravimetric analysis (TGA) mass loss, SEM and FTIR. The experimental results indicated that all polyurethane samples bore the microphase separation structure, and the separation degree depended on their sequence structure and MW of PEG, and further affected their in-vitro degradation. The driving force was related to the restricted movement of molecular segments, the crystallization of soft/hard phases and/or the hydrogen bonding interactions between hard segments. The surface morphological change of the degraded samples further demonstrated that the degradation became serious with increasing the MW of PEG, and the random block copolymers were more easily decomposed than the alternating copolymers. The block polymer materials are expected to find specific applications in related biomedical fields.3. Micelle-type star-shaped polyurethane (PU) block copolymers consisting of hydroxyl-functionalized carboxyl-terminated poly(butadiene-co-acrylonitrile)(f-CTBN) as the hydrophobic cores and methoxy poly(ethylene glycol)(MPEG) as the hydrophilic branched blocks were synthesized via an esterification and coupling reaction route, and characterized by FTIR, NMR and GPC. The micelle-type block copolymers could easily self-assemble to form core-shell type micelle nanoparticles in various media. The micelles bear the critical micelle concentration (CMC) was in the range from0.088to6.310mg L-1. The TEM and dynamical laser scattering (DLS) findings revealed that the micelles were almost spherical and narrow-size-distribution, with TEM mean diameters from13to24nm, and average hydrodynamic diameter about120-200nm. All these depend on the chain length and compositional ratios of hydrophilic MPEG blocks. The PU copolymer nanomicelles were very stable even in PBS solutions. The drug loading and in vitro release results indicated that the self-assembled micelles can effectively load hydrophobic prednisone, with encapsulation efficiency of30%, and the drug release from the nanoparticles was dependent on environmental media, MPEG chain length and the molar ratio of f-CTBN to MPEG. Cytotoxicity assays showed that the as-prepared micelle-type star-shaped block copolymers exhibit good biocompatibility, and could be employed as potential drug controlled release carriers.