Polyglycolide Prepared By Ring-opening Polymerization And Its Degradation Behavior Under Temperature And Humidity Conditions

Polyglycolide(PGA),one of the biodegradable polymer materials,has been applied in the biomedicine,food packaging,shale gas exploitation,and other fields.Due to its excellent biocompatibility,mechanical properties,gas barrier properties and other excellent properties.Ring-opening polymerization of glycolide is the most common method to synthesize PGA with high molecular weight.However,due to the fast reaction rate of the ring-opening polymerization of glycolide,the viscosity in the system increases rapidly,leading to the difficulty in mass and heat transfer in the later stage of polymerization.Thus,it is difficult to achieve the ring-opening polymerization of glycolide through traditional stirring reactors.This paper aims to synthesize high molecular weight PGA by ring-opening polymerization in the reactive extrusion process.First,the effects of temperature,raw material purity,catalyst type,and initiator content suitable for the reactive extrusion system on the ring-opening polymerization process of glycolide were explored.Then,a continuous process of ring-opening polymerization to synthesize PGA was designed,and the process conditions of prepolymerization,final polymerization,and devolatilization in the process were explored.Finally,the synthesized high molecular weight PGA was used to study its degradation behavior under different temperatures and humidity conditions.The specific research results are as follows:(1)The process conditions affecting the ring-opening polymerization process were systematically investigated.The results show that the polymerization temperature suitable for the continuous synthesis of PGA should be around 210℃.Obtaining high molecular weight PGA requires that the purity of glycolide should be above 99.5%.Compared with stannous octoate,stannous chloride as a catalyst has a shorter reaction induction period and a faster reaction rate,which is more conducive for reactive extrusion systems.Lauryl alcohol as the initiator has little effect on the reaction rate of glycolide ring-opening polymerization under high temperature,while it is capable to control the molecular weight of PGA.(2)The continuous "prepolymerization-final polymerization-devolatilization"process to produce PGA by ring-opening polymerization was designed,and the optimal process parameters were obtained by exploring the effects of prepolymerization,final polymerization and devolatilization.The optimal conditions are as follows:the prepolymerization temperature is 110℃,and the prepolymerization time does not exceed 30 min;the final polymerization temperature is 210℃,and the reaction time is 6-8 min.In order to avoid the degradation of PGA,the devolatilization time is 1 min.Using this process condition,PGA with molecular weight higher than 200,000 and content of monomer and oligomer less than 1%was synthesized.(3)The effect of temperature and humidity on the degradation behavior of PGA is very significant when PGA is stored in air.After PGA is placed in high temperature and high humidity air at 35℃ and RH 90%,respectively for 48 h,the intrinsic viscosity is reduced by 42.4%.Therefore,the storage conditions should be as dry as possible.The degradation of PGA under high temperature and humidity is related to its crystal structure.At the initial stage of degradation,degradation mainly occurs in the amorphous region of PGA,result in the fast degradation.As the amorphous region degrades and falls off,the crystalline region begins to degrade,slowing down the degradation rate.