Preparation Of Polyglycolide And Poly(Lactic-Co-glycolic Acid) Via Ring-opening Polymerization And Their Characteristics

Polyglycolid(PGA)can be applied to biomedicine,packaging,mining and other fields due to its excellent mechanical strength,good gas barrier properties,biocompatibility and biodegradability.However,because of its high melting point and high crystallinity,PGA is difficult to be processed and molded.On top of that,its fast degradation process exacerbates wear and tear.Copolymerizing with other monomers can improve its processing characteristics,and control the degradation rate and degradation cycle.In order to solve the problem of poor solubility of PGA,this thesis first proposed a pretreatment method which can effectively reduce the crystallinity of PGA and increase its solubility in hexafluoroisopropanol(HFIP)for following analysis and characterization.Then,the ring-opening polymerization of process glycolide and lactide and product characteristics were investigated.Finally,the melt crystallization and degradation behavior of PGA and the copolymer(PLGA)of glycolide and lactide were studied.The results are as follows:(1)A pretreatment method for reducing the crystallinity of PGA by combining rapid pressure relief with liquid nitrogen quenching was proposed to achieve the solubility of PGA in HFIP.The effects of pretreatment pressure,gas atmosphere,heat treatment time and temperature on the crystallinity of PGA and its dissolution in HFIP were systematically investigated.The best method for pretreatment process is a melting process in a CO2 pressure of 10 MPa and 230? for 5 minutes,followed by a rapid cooling process via rapid pressure relief and liquid nitrogen quenching.(2)The ring-opening polymerization process of glycolide was studied.The effects of reaction temperature and reaction time on the polymerization process and product characteristics were investigated.It was found that the reaction equilibrium can be reached in 30 minutes under 140 or 160?.When the temperature is raised by 20?,the reaction rate can be increased by 35%.(3)The bulk ring-opening copolymerization process of glycolide and lactide was studied.The effects of reaction time,reaction temperature and feeding ratio on the molecular weight and distribution,and copolymerization molar composition of PLGA were investigated.The higher the content of lactide in the feeding ratio,the slower the reaction rate,but the higher the molecular wight of PLGA.(4)By comparing the melt crystallization behavior of PGA and PLGA obtained by ring-opening polymerization,it was found that the introduction of lactide could slow down the crystallization rate of PGA without changing the nucleation and growth mode of PGA.When PGA and PLGA were degraded in alkaline solution,the higher the molecular weight was,the easier it was to degrade.Moreover,the amorphous zone of polymer was easier to degrade.The introduction of lactide had little effect on the proportion of lactide and glycolide segments in the degradation products.