Synthesis And Properties Of The Biodegradable Material-polylactide Acid And Its Copolymers

Poly(lactic acid)(PLA) is a typical green polymer since it is produced from renewableresources, starch，and can be degraded to lactic acid and finally to carbon dioxide and water. PLAis widely applied in biomedical polymer material for its advantageous properties ofbiocompatibility, mechanical property and degradation ability. However, the performance defectslimit the application of PLA in biomedical field due to PLA surface hydrophobicity whichreduces its biocompatibility and degradability. And also, the degradation product is acidicmaterial which results in non infectious inflammation in the implanted part. In order to overcomethe limitations, people made many researches on PLA to improve the hydrophilicity anddegradability.In this paper, glycolide (GA), polyethylene glycol (PEG) and ε-caprolactone (CL) wereused to copolymerize with lactide (LA) to prepare the PLA copolymers in order to improve theperformance of PLA. The main research contents and results are as follows:(1) Polyglycolide (PGA), Poly(L-lactide)(PLLA) and Poly(L-lactide-co-glycolide)(PLGA)were prepared by bulk ring-opening polymerization at high temperature and high vacuum usingstannous octoate as catalyst and1,4-butanediol as initiator. The chemical structures of thepolymers were characterized by infrared spectroscopy (FT-IR), H nuclear magnetic resonance(1H NMR), gel permeation chromatography (GPC), differential scanning calorimetry (DSC),thermogravimetric analyzer (TGA) and X-ray diffraction (XRD). The results of GPC showedthat PLGA and PLLA had high molecular weight and narrow molecular weight distribution. Theresults of rheological property showed that the melts of PGA, PLLA and PLGA wereshear-thinning fluids, while PGA and PLLA had higher storage modulus and PLGA had higherloss modulus. Amorphous PLGA was much more easily purified than PGA and PLLA which hadhigher crystallinity, thus PLGA was more suitable for biodegradable material.(2) Amphipathic poly (D,L-lactide-co-glycolide)-polyethylene glycol-poly(D,L-lactide-co-glycolide)(PLGA-PEG-PLGA) triblock copolymers were synthesized viabulk ring-opening polymerization with D,L-LA, GA, PEG as raw materials and Sn(Oct)2ascatalyst. The chemical structure of PLGA-PEG-PLGA was characterized by FT-IR,1H NMR,GPC, DSC, TGA and rheometer. The results showed that phase inversion temperature (PIT) increased and solid phase range became narrow with the decreasing of copolymers concentrationand the increasing of molecular weight of PEG, and the PIT decreased and solid phase rangebecame narrow with the increasing of the mass ratio of D,L-LA/GA. The studies of drug releaseproperties of hydrogel containing ceftibuten indicated a higher initial release followed by aslower pattern up to120h.(3) Ploy(CL-co-LA)-PEG-ploy(CL-co-LA)(PCLA-PEG-PCLA) triblock prepolymers weresynthesized via bulk ring-opening polymerization with L-LA, CL, PEG as raw materials andstannous octoate as catalyst. The hexamethylene diisocyanate-1,4-butanediol-hexamethylenediisocyanate (HDI-BDO-HDI) as chain extender was reacted with triblock prepolymers toprepare biodegradable polyurethane. The polyurethane films were prepared by solventevaporation method. The chemical structure of polyurethane was characterized by FT-IR,1HNMR, DSC, TGA and GPC and the mechanical property of polyurethane films was researchedby materials testing machine. The results indicated that the mechanical properties of the filmswere mainly affected by the ratio of soft segments (prepolymers) and hard segments (chainextender). When the content of hard segment in polyurethane was21wt%(soft segments content:79wt%; hydrophilic segments content:29.6wt%), the films had the best mechanical properties.The elongation at break and fracture strength could be up to1237%and10.9MPa, respectively.The degradation properties of polyurethane films in physiological saline, acidic buffersolution and alkaline buffer solution were studied. The results showed that the degradation rateof films increased with the increasing hydrophilic segments (PEG) content in polyurethane.