Study On Properties And Melt Synthesis Of High Molecular Weight Poly(Lactic Acid) Chain-linked By Epoxy Compound

Direct melt polycondensation were employed to produce PLLA oligomer from L-lactic acid and high molecular weight PLLA were obtained by treating the oligomer with chain-extender—multifunctional epoxy compounds (ESO and Joncryl-ADR- 4370) in this work. The characterization of the obtained polymers was by the means of Gel permeation chromatography(GPC), fourier transform infrared spectrometry(FTIR), nuclear magnetic resonance spectrometer (NMR), differential scanning calorimeter (DSC) and some other classical chemical analysis to explore the structures and the properties. Furthermore, surface wettability, biodegradation and biocompatibility of the materials treated by Joncryl-ADR4370 were investigated in this work. The main research work and results are summarized as follow:(1) Catalytic effect of various catalysts on the polycondensation of PLLA oligomer was studied in this work. The results indicated that stannous chloride/para- toluenesulfonic acid(SnCl2·2H2O/TSA) as catalysts showed the best catalytic effect. Furthermore, the results proved that the suitable reaction temperature was 180℃and the suitable reaction time was 30 hours for the polycondensation. On the other hand, it is favorable for increasing the yield and improving the quality of the products that heightening the temperature step by step ( increased temperature from 80℃to 140℃for 5 hours and then increased to 180℃further).(2) Studies on the melt synthesis of PLLA chain-linked by ESO were performed in this work. The results revealed that the molecular weight of products increased as the increasing of the ratio of ESO, and the Mw reached 250000g/mol when the ratio of ESO achieved 8wt%. The products were characterized by FT-IR and NMR.(3) Kinetics of the reaction between ESO and PLLA oligomer were also studied in this work. The dates collected by detecting the content of the end-carboxyl and handled by statistical analysis showed that the reaction order for ESO and PLLA oligomer was 1 and 0.5 respectivelly. On the other hand, the purity of oligomer had no significant effect on the chain-linking reaction.(4) The molecular weight of products increased as the increasing of the ratio of ADR. The Mw reached 360000g/mol when the ratio of ADR achieved 1.5wt%, and the reactants turned to cross-linking when the ratio of ADR reached 2.0wt%. Chain-linking reaction carried out in 1 hour after ADR added, and the reactants turned to cross- linking when the reaction time extended 2 hours. On the other hand, the suitable reaction temperature for chain-linking was 160℃. The products were characterized by FT-IR and NMR.(5) Direct melt co-polycondensation of lactic acid and epoxy compounds were carried out in this work, and it can be called as"chain-linking from core". The results showed that the molecular weight of products was increased and the reaction time was shortened greatly through this way, especially for the melt co-polycondensation between lactic acid and ADR.(6) PLLA chain-linked by ADR and PLLA synthesized by direct melt polycondensation shared the close glass transition temperature(Tg), melt temperature (Tm) and thermal decomposition temperature. The experiment of Static water contact angle and water absorption ratio showed that the PLLA treated by ADR was hydrophobic materials. Degradation behavior of PLLA treated by ADR and PLLA synthesized by ring-opening as control were studied in vitro for 9weeks. The results revealed that the PLLA treated by ADR possessed better degradability than that of the PLLA synthesized by ring-opening. The degradation behavior of the PLLA treated by ADR can be summarized as 3 stages: adaption, acceleration and stabilization.(7)Biocompatibility of the PLLA chain-linked by ADR were studied by rats osteoblasts cultivation and MTT metholds preliminarily. The results revealed that osteoblasts growed well on the PLLA materials treated by ADR, and there were no significant difference of the cell growth and proliferation between PLLA and PLLA chain-linked by ADR. So it proved that PLLA chain-linked by ADR was biocompatible and was suitable to be used in biomedicial field.