Synthesis And Properties Of The Biodegradable Polyester-polyurethanes

The biodegradable polyester-polyurethanes have been used in wide range of applications,owning to their good degradability, biocompatibility, blood compatibility, and excellent mechanical properties, easy processing and forming. The degradation products of polyesterpolyurethanes prepared from aliphatic diisocyanates were non-harmful to human body, which thus made them good candidates for further biomedical applications. With the demands of biomedical materials, the development for biodegradable polyester-polyurethanes will be urgent,and the studies of synthesis methods will be the direction of the research.In this paper, different kinds of polyester-polyurethanes materials were preparedby changing the hydrophilic segments inpolyurethanes, chain extender, and the formation methods of soft segments. The main research contents and results are as follows:(1) The prepolymer of poly-(?-caprolactone-co-L-lacticacid)-poly(ethyleneglycol)-poly-(?-caprolactone-co-L-lactic acid)(PCLA-PEG-PCLA) was synthesized via bulk ring-opening polymerization with PEG as an initiator and L-lactide(L-LA), ?-caprolactone(?-CL) as monomers. Then, the prepolymer was chain-extended with an isocyanate-terminated urethane triblock to give the polyurethanes(PU-1, PU-2, PU-3) with different hydrophilic segments(PEG). The structure and properties of prepolymer, chain extender, and PUs were characterized by1 H NMR,13 C NMR, GPC, FT-IR, HR-TOF-MS, XRD, TGA and DSC. In the study on thermal properties of PUs, two glass transition temperatures(Tg) were observedin DSC thermograms, which proved the structure of micro-phase separation in PUs. The synthesized PUs exhibited good mechanical properties, which embodied in elongation at break(942%- 1061%),the maximum stress(17.5- 23.5 MPa) and the initial modulus(15.1- 21.5 MPa). In vitro degradation studied showed the PUs having excellent degradation properties: the degradation rate increased with the increasing content of hydrophilic segments in PUs. The biological evaluation indicated that the PUs synthesized in this experiment conformed with nationalstandard, which could be used in the biological medical field.(2) The prepolymer of poly-(?-caprolactone-co-L-lactic acid)(PCLA) was prepared via bulk ring-opening using 1,4-butanediol(BDO) as initiator, L-LA, ?-CL as monomers and stannous octoate as catalyst. By chain extension of PCLA with different diisocyanate chain extender(HBH, HDI-BDO-HDI-BDO-HDI, HDI, IPDI, TDI, MDI), six kinds of polyurethanes materials were prepared(PU-I, PU-II, PU-III, PU-IV, PU-V, PU-VI). The structure and properties of prepolymer, chain extender, and polyurethanes were characterized by1 H NMR, 13 C NMR, FT-IR,GPC, HR-TOF-MS, DSC and TGA. With the long uniform hard segments, the polyurethanes materials had two Tg in the DSC thermograms, which showed micro-phase separation. The similar thermo-stability of the six kinds of polyurethanes materials indicated that the hard segments content had little impact on the thermo-stability. The polyurethanes chained by segmented chain extender had better mechanical properties: the elongation at break for PU-I and PU-II was 669 % and 601 %, the maximum stress was 35.4 MPa and 24.8 MPa, and the initial modulus was 41.7 MPa and 31.9 MPa, respectively. In vitro degradation showed that the time of the PU-I and PU-II films becoming fragments was 60 and 53 days, respectively. The polyurethanes chained by MDI had lower degradation rate, the time of the PU-VI films becoming fragments was 68 days.(3) A new approach for synthesizing biomedical SPU based on PEG, PCLA and diurethane diisocyanates(HBH) with long uniform hard segments was developed. By chain extension of the mixture of PEG diol and PCLA diol with HBH, three SPUs with different hydrophilic segments(PEG) content and hard segments content were obtained. The chemical structures of the chain extender, PCLA and SPUs were confirmed by 1H NMR, 13 C NMR, FT-IR, HR-TOF-MS and GPC. The SPU films exhibiting similar thermostability indicated that the hard segments content had little influence on the thermostability. Two Tg being observed in DSC thermograms demonstrated micro-phase separation in SPU films. These SPU films exhibited satisfactory mechanical properties and degradation properties. The degradation rate increased with the increasing content of hydrophilic segments in SPU. Studies of in vitro drug release were carried out using vitamin B1 as model drug, which indicated the films exhibited good release properties.Cytotoxicity test in the film extracts and cell attachment on the film surface were conducted with L929 mouse fibroblasts, and the results indicated that the SPU films possess excellent cytocompatibility and cell adhesive ability.