Synthesis And Properties Of Copolymers Derived From Lactide And Carbonate

Polylactic acid?PLA?has been widely used in biomedical applications due to its biocompapatibility and biodegradability.Hompolymer of lactide and copolymers derived from lactide and carbonate were synthesized using ring opening polymerization in this paper.Yield and viscosity-average molecular weights of PLA homopolymers were measured.The structures of obtained copolymers were characterized by fourier transform infrared spectroscopy?FTIR?and nuclear magnetic resonance?NMR?.Properties of obtained polymers were studied by means of differential scanning calorimetry?DSC?,thermogravimetric analysis?TGA?,X-ray diffraction?XRD?and tensile test.In addition,shape memory properties of obtained copolymers were also studied.Zirconium?IV?acetylacetonate[Zr?Acac?₄]and stannous octoate[Sn?OCt?₂]were respectively used as catalyst for polymerization of L-lactide in this paper.The effects of reaction temperature,reaction time and molar ratio of monomer/catalyst on yield and viscosity-average molecular weights in the LLA melting ring opening polymerization were studied.Results showed that the yield and viscosity-average molecular weights of poly?L-lactide??PLLA?were the highest when molar ratio of monomer/catalyst was 2000,the reaction temperature was 130°C and the reaction time was 72h.PDLLA was also synthesized in this reaction condition using Zr?Acac?₄ as catalyst.The obtained PLLA was crystalline polymer while PDLLA was in amorphous state in the reaction condition.The obtained PLLA and PDLLA showed good thermal stabilities and the thermal decomposition temperatures?T_d?were above 310°C.And the highest tensile strength of PLLA and PDLLA respectively reached32.44MPa and 29.63MPa,revealing good mechanical property.Copolymerspoly?L-lactide-1,3-trimethylenecarbonate?[P?LLA-TMC?]and poly?DL-lactide-1,3-trimethylene carbonate?[P?DLLA-TMC?]derived from lactide and1,3-trimethylene carbonate?TMC?were successfully synthesized using Zr?Acac?₄ as catalyst.NMR and DSC results showed that P?LLA-TMC?and P?DLLA-TMC?with different monomer molar raios were all random and the viscosity-average molecular weights were all above 2.54×10⁴g/mol.T_g and tensile strength decreased with decreasing of LA molar ratio.Howerer,elongation increased with decreasing of LA molar ratio.Therefore,the brittleness of PLA was improved.TGA results suggested that no weight loss below 200°C was observed and T_d of obtained polymers were all above 300°C,which showed good thermal stabilities.With the increasing of LA/TMC monomer molar ratio,the morphology of P?LLA-TMC?changed from crystalline to amorphous,while P?DLLA-TMC?were all amorphous and random.Terpolymers of P?LLA-TMC-GA??LTG?,P?DLLA-TMC-GA??DLTG?derived from lactide,1,3-trimethylene carbonate and glycolide?GA?and P?LLA-TMC-?-CL??LTCL?derived from lactide,1,3-trimethylene carbonate and?-caprolactone were synthesized by adding GA and?-CL respectively.The viscosity-average molecular weights of P?LLA-TMC-GA?were above 2.21×10⁴g/mol and all LTG terpolymers were random and amorphous.In addition,LTG terpolymers showed good thermal stabilities.The T_g values of the obtained terpolymers decreased and elongation increased with decreasing of LLA molar ratio.The elongation at break of LTG503020 was the largest,reaching 1446.71%.The viscosity-average molecular weights of DLTG were all above 3.08×10⁴g/mol.The T_g values decreased with decreasing of DLLA molar ratio.The tendency of the T_g value changes was in accordance with the T_g calculated by FOX.Elongations at break of DLTG were above 200%.Toughnesses of polymers were obviously improved by means of adding glycolide monomer.The viscosity-average molecular weights of LTCL were all above 2.93×10⁴g/mol.The morphology changed from crystalline to amorphous and the T_g value decreased with decreasing of LLA molar ratio.The LTCL801010 terpolymer was crystalline polymer and other LTCL terpolymers were amorphous.However,weak diffraction peaks appeared on XRD curves of LTCL601525 and LTCL502525and the intensities of diffraction peak increased with increasing of LLA molar ratio,indicating that crystallization of PLLA was induced by?-CL.Shape memory properties of copolymers derived from lactide and carbonate were studied.The optimum deformation temperatures of copolymers in different types were measured.Shape fixity ratio,shape recovery ratio and shape recovery time of copolymers were also measured at deformation temperature.Shape recovery ratios of different P?LLA-TMC?copolymers were greater than that of P?DLLA-TMC?.Shape fixity ratio and shape recovery ratio of LT8020 were both higher than other binary copolymers.Shape recovery time of LT8020 was 75.53s.Shape memory property of LT8020 was better than other LT and DLT copolymers.According to terpolymers of lactide and carbonate,it was found that monomer ratios of terpolymers affected shape memory property.The T_g values of LTCL were close to room temperature,so LTCL were all soft at room temperature,which led to bad shape recovery.Shape fixity ratio and shape recovery ratio of LTCL801010 were relatively high.It was found that LTCL801010 can be recovered from temporary to initial shape in 78.0s at 39°C.Shape fixity ratios of DLTG were above 90%except DLTG602020,which showed good shape fixation abilities.The DLTG702010 showed good shape memory property,which shape fixity ratio and shape recovery ratio of 96.58%and 90.27%respectively.As for LTG terpolymers,shape fixity ratio and shape recovery ratio were all above 95%and 90%respectively except LTG503020 and LTG602020.Shape recovery ratio of LTG701515 was 97.53%and shape recovery time was only 4.57s,which provided possibilities for medical applications in the field of bone implantation materials.