Synthesis Of High Isotactic Poly(L-Lactic Acid)with High Active Biogenic Creatinine-based Catalysts System

In recent years,with the wide use and excessive production of petroleum-based plastics,white pollution aggravates increasely.With the strengthening awareness of environmental protection which mankind live on,the research and utilization of environmentally-friendly polymers based on renewable resources has aroused widespread concern.As a synthetic biodegradable polyester,poly(lactic acid)(PLA)is the most valuable and potential one to replace the petroleum-based plastics,and shows high biological safety and conpatibility.Currently,the synthesis of PLLA is catalyzed by the Sn(II),but Sn(II)compounds display cytotoxicity and it is difficult to remove from the resulting polymer.Synthesis of biodegradable PLA using non-toxic organic catalyst is a new challenge in the field of biodegradable materials.This thesis,used the biomass-organic guanidine as the main catalyst,adding the non-toxic lewis acid-trifluoromethane sulfonic acid as the co-catalyst,to synthesize the biodegradable material-PLLA which has high optical purity,high molecular weight,high thermal stability via controlled polycondensation.(1)Isotactic melt polycondensation of L-Lactic acid(L-La)was successfully realized under the conditions of 180 ? and 10 torr with biogenic creatinine and trifluoromethanesulfonic acid as catalysts.The product of melt polycondensation poly(L-Lactic acid)(PLLA)possesses high isotacticity(97.9%)and optical purity(e.e.96.1?98.7%),as well as narrow molecular weight distribution(PDI 1.54?1.88).Meanwhile,the kinetic of CR-HOTf-catalyzed L-La polycondensation was studied,and the mechanism of the creatinine-catalyzed polycondensation was proposed based on the experimental investigation of active catalytic species.(2)High molecular weight polymers of PLLA(Mw 2.22×105)was successfully synthesized via isotactic melt-solid polycondensation(MP-SSP)using high active catalysts system based on biogenic creatinine.The products of MP-SSP polycondensation PLLA possess high melting point(180.8 ?)and high optical purity(e.e.97.2%).Thermogravimetric(TG)analysis demonstrated that the decomposition temperatures(Td,init 250.3 ?)of PLLA synthesized with the designed catalysts system are over 50? above those of PLLA synthesized with catalyst SnCl2·2H2O.