A Study On The Synthesis And Crystallization Properties Of Polyglycolide

Polyglycolide?PGA?has excellent degradability,biocompatibility,gas barrier properties and excellent mechanical properties.Currently it has great market prospects in medical degradable materials and packaging materials.However,the synthesis of high molecular weight PGA is still a difficult point in the current synthesis.In addition,the research on the crystallization of PGA is not sufficient,and there is still a large amount of basic research work needs to be done.In this paper,I synthesized PGA using high purity glycolide?GA?as the raw material,stannous octoate?Sn?Oct?2?as the catalyst and1,4-butanediol?BDO?as the initiator.Moreover,I explored the ring-opening polymerization process of PGA and I analyzed and characterized the polymer product.Furthermore,I prepared PGA with different molecular weights and studied their thermal property,crystallization kinetics,crystal morphology and crystal structure.First,PGA polymerization process was studied.The effects of different reaction temperatures and catalyst contents on the conversion,polymerization rate,intrinsic viscosity,and thermal stability of PGA were investigated.In the polymerization process,the conversion rate is high in the early stage of polymerization,and the subsequent conversion rate changes little.Increasing polymerization temperature will accelerate the decomposition of initiator,thus it will increase conversion and polymerization rate.When the polymerization temperature is 170°C and the catalyst content is n?GA?:n?Sn?Oct?2?=6×10⁴,the catalytic effect on the reaction is best.Conversion.The intrinsic viscosity[?]of PGA synthesized under this condition is biggest and its value is 0.97.At the same time,the monomeric glycolide?GA?and the polymerization product were characterized by infrared spectroscopy?FTIR?,and PGA ring-opening polymerization has been shown to be a first-order kinetic reaction.Secondly,the isothermal crystallization process of PGA with different molecular weights was studied.When the isothermal crystallization temperature is 160-180°C,the PGA crystallization induction time t₀ and the half crystallization time t_1/2 increase as the crystallization temperature increases.When the viscosity of PGA is within 0.06-0.70,PGA of high molecular weight can complete crystallization in a shorter time.The phenomenon of melting double peaks that occurred during the subsequent heating process was explored which was produced by melt recrystallization.I used Avrami equation to study the isothermal crystallization kinetics of PGA with different molecular weights.The Avrami index n is between 2-3,and the value of n is close to 3.It is mainly determined that the main nucleation method of PGA is heterogeneous nucleation.The growth mode is three-dimensional spherulites or two-dimensional discotic crystals.As the crystallization temperature increases,the Avrami exponent n and the crystallization rate constant k decrease,and the PGA crystallization induction time t₀ and the half-crystallization time t_1/2increase.POM indicates that the nucleation density of PGA crystals becomes smaller as the isothermal crystallization temperature increases,and the high molecular weight PGA has a higher nucleation density and a smaller crystal size.Finally,the non-isothermal crystallization process of PGA with different molecular weights was researched.As the cooling rate increases,the exothermic peak of melt crystallization corresponding to the PGA moves to a lower temperature region and the entire crystallization temperature range broadens.High molecular weight of PGA has a higher crystallization temperature T_mc.X_c highlights the excellent crystalline properties of PGA which reaches 63.1%-39.4%.The non-isothermal crystallization kinetics of PGA with different molecular weights were analyzed by the Jeziomy method.The Avrami index n was also between 2 and 3.With the increase of the cooling rate,n decreased,and the crystallization constant of the zirconia k_c increased.When the viscosity of PGA is within0.06-0.70,high molecular weight PGA has a larger k_c value.At the same time,POM shows that the crystal size of PGA decreases as the cooling rate increases.