Studies On Direct Synthesis Of Poly(Lactic Acid) And Its Copolymer Through Melt Polycondensation

Polylactic acid was a well-known biocompatible and biodegradable polymer, which was being widely used as the scaffold of tissue engineering, carrier for the controlled release systems and absorbable sutures.In this study, PDLLA was synthesized by direct melt polycondensation using D,L-LA as monomer. In order to improve hydrophilicity of PLA, PLGA was synthesized in the same process using D,L-LA and GA as monomers. Properties of all productions were measured and obtained through FTIR,1H-NMR,DSC,XRD,GPC. The specific researches and results were listed as follows:(1) The kinetics of direct polycondensation was studied under condition of no catalyst and atmospheric pressure. The kinetic equation of the D,L-LA direct polycondensation was lnr=-11.03+2.958lnc at 122℃, with reaction order n=2.958 and the reaction rate constant k=1.61×10-5 L2·mol-2·min-1. According to reaction rate constant k at different temperatures, the reactive energy(E=104.34 kJ/mol) was obtained. The kinetic equation of the D,L-LA/GA polycondensation at 130℃was In r=-10.09+2.403lnc, with the reaction order n=2.403 and the reaction rate constant k=4.13×10-5L2·mol-2·min-1. According to reaction rate constant k at different temperatures, the reactive energy(E=92.45 kJ/mol) was obtained。(2) PDLLA was synthesized by direct melt polycondensation using D,L-LA as monomer. Under the optimal synthetic condition of SnCl2 0.6%(mass faction to monomer), polymerization temperature 160℃, polymerization pressure 1000 Pa, polymerization time 10 hours, PDLLA was obtained with the viscosity-average molecular weight 15032.(3) PLGA was synthesized by direct melt polycondensation using D,L-LA and GA as monomer. Under the optimal synthetic condition of SnCl2 0.5%(mass faction to perpolymer), polymerization temperature 165℃, polymerization time 9 hours, the PLGA70/30 was obtained with the viscosity-average molecular weight 9247. Through analysis of the water static contact angle, the hydrophilicity of the polymer was obviously improved via introducing GA segmer, and the value of static contact angle was reduced from 76°to 63°.