Study Of Melt Copolycondensation Of PDLLLA And Solid Phase Post-polymerization

Poly-lactic acid（PLA） as a new biodegradable commodity polymer,with related copolymer developing in biological materials field,the research and development of poly-lactic acid has been valued increasing,especially applied as fracture fixation material,drug delivery material,tissue engineering scaffolds material,etc.There are two synthesis methods of poly-lactic acid:direct poly-condensation and ring-opening polymerization.For ring-opening polymerization,the synthesis technology is complex, very difficult to achieve industrialization.The synthesis technology of direct poly-condensation was easy.However,the high molecular weight of poly-lactic acid was relatively difficult to be obtained.This paper focused on the conditions of synthesis technology to get high molecular weight poly-lactic acid.In order to increase molecular weight of poly-lactic acid,three aspects were studied in this work:Firstly,L-lactic acid and DL-lactic acid were used as raw materials,the melt poly-condensation method to synthesis poly-DL,L-lactic acid（PDLLLA） was used firstly and the polymerization product influenced by reactant ratio（LLA:DLA） and synthesis technology was investigated.Secondly,for increasing relative weight,based on melt poly-condensation,the solid phase polymerization was introduced to study relative molecular weight of polymerization product impacted by solid-state polymerization time and catalyst amount,etc.Thirdly,the PDLLLA and PDLLLA-TMPTA materials wereγ-radiated by ⁶⁰Co-γray source in the lower range doses（D≤25kGy,the common dose range to sterilization for food and medicine requirements）.The influence of PDLLLA relative molecular weight and radiation stability byγ-radiation was studied.The main results were obtained in the following:（1） The molecular weight of PDLLLA was high while the Monomer mass ratio was 80:20,which synthesized by direct melt copolycondensation.（2） When the catalyst amount is 0.5wt%of PDLLLA which synthesized by direct melt copolycondensation,pre-polymerized at 130℃for 6 hours at first,then the temperature is down to 100℃under vacuum state for 18 hours,the high molecular weight polymer may be obtained.（3） In the observation dose rang（0-25kGy）,viscosity-average molecular weight of PDLLLA which synthesized by direct melt co-poly-condensation was decreased with increasing the absorbedγ-radiation dose（D）,when the D was 25kGy,the （（?）_η） of PDLLLA was downed by 51%compared to non-radiation.（4） It was found that TMPTA has a good cross-link sensitization effect on PDLLLA underγ-radiation.When the TMPATA content was 3wt%,whenγ-radiation dose was 10kGy,the（?）_ηreached up to about 27,000,doubled compared to non-radiation.（5） FT-IR analysis showed that the synthesized polymer has the structural character of poly-lactic,and.the structure of PDLLLA was not changed significantly impacted byγ-radiation.And TG analysis shows thatγ-radiation could improve epitaxial temperature of PDLLLA and its thermal stability.（6） The thermal gravimetric analysis,x-ray diffraction,Polarizing microscope results shown that PDLLLA synthesized in this paper was non-crystal polymers, so were polymers which treated by solid-phase polymerization andγ-radiation.