Preparation And Properties Of Polylactic Acid And Its Copolymers

In this paper, lactides were synthesized by lactic acid with Sn(Oct)2 and ZnO as catalysts. The structures of the lactides were characterized by Fourier transformation infrared (FTIR) and mass spectroscopy. The results show that structure of the lactides is clear. The thermal property of the lactides was investigated by differential scanning calorimeter (DSC) analysis. It was found that the melting point of lactides was at 130℃, this was similar as the 128℃of literature report.PLA-b-PEG block copolymers were synthesized by solution polycondensation of lactic acid and poly(ethylene glycol) (PEG) in dimethylbenzene at 180℃. The structure of the PLA-b-PEG block copolymers was clear based on the analysis of nuclear magnetic resonance (1H-NMR). The molecular weight of PLA-b-PEG was measured by gel permeation chromatography (GPC). It was found that molecular weight increased through increasing reaction time. The results of differential scanning calorimeter showed that the glass transfer temperatures of PLA-b-PEG were controlled between 35.6 and 54.3℃by changing the ratio of LA and PEG due to formation and stability of the film. The transparent films of PLA-b-PEG block copolymers were prepared by membrane casting method. The hydrophilicity and tensile measurements of films were characterized by dynamic contact angle and universal testing machine. The contact angles were decreased from 87.69 oto 63.32 o, the water absorptions were increased from 0 % to 18 %, the hydrophilicities were increased, the tensile strengthes were from 10 MPa to 1.5 MPa, but the rupture elongates were from 1 % to 12.5 % through increasing amount of PEG in feed.Also, PLA-HEMA macromonomers were prepared by step polycondensation of lactic acid and ring-opening polymerization of lactides with Sn(Oct)2 as catalyst, separately. The structures of the PLA-HEMA were characterized by FTIR and 1H-NMR. It was found that the structures of PLA-HEMA were clear, and the double bond content could be reached 50%. PMPC graft PLA (PMPC-g-PLA) copolymers were prepared by radical copolymerization of 2-methacryloyloxyethyl phosphorylcholine (MPC) and PLA-HEMA macromonomer. The micelle of PMPC-g-PLA was prepared in the selective solvent such as DMF/H2O by self-assembly. The critical water content (CWC) was studied by ultraviolet spectroscopy for formation of micelles. The CWC was increased with amount of MPC and decreasing solution concentration of the copolymer.