Study On Hydrolysis And Thermal Stability Of Poly(Glycolide)

Poly（glycolide）（PGA）has excellent biodegradability,biocompatibility,gas isolation and good mechanical properties.it is a promising medical device,tissue engineering and packaging material.However,the problem of poor hydrolysis stability and thermal stability of PGA has not been well solved,and a lot of research work needs to be done.Firstly,high purity glycolide（GA）was used as raw material,stannous octoate Sn（Oct）₂ as catalyst,1,4-butanediol（BDO）and pentaerythritol（PTO）as initiators.Poly（glycolide）（PGA）,with different catalyst content and structure was prepared by ring-opening polymerization.the polymerization products were detected and characterized.Then the effect of the presence of glycolide on the hydrolysis performance of PGA was studied.The weight loss rate,water absorption,intrinsic viscosity,micromorphology and crystallinity of PGA splines with different glycolide content in a certain degradation period were measured.it was found that the hydrolysis performance of PGA became worse with the increase of GA content.The presence of lactide promoted the hydrolysis of PGA.The degradation rates of PGA splines with 5%,10%and 15%GA content in deionized water were6.87%,12.7%and 16.15%respectively after 32 days of degradation.The degradation rates were 8.08%,13.01%and 16.66%in 0.01mol/LHCl aqueous solution and 8.66%,14.05%and17.68%in 0.01mol/LNaOH aqueous solution.The results showed that the hydrolysis rate of PGA increased with the increase of glycolide content,and the PH value of degradation medium also had a great influence on the hydrolysis of PGA.With the hydrolysis,the intrinsic viscosity of linear PGA is decreasing and the content of carboxyl group is increasing,both of which show a good linear relationship.Through the characterization of micromorphology,it was found that glycolide formed a porous structure in PGA matrix during the degradation of PGA,which accelerated the entry of water molecules into the material matrix and promoted the hydrolysis process.The hydrolysis degradation of PGA follows the overall degradation mechanism,that is,the overall hydrolysis of the material occurs,and weightlessness will not occur until the whole molecular weight decreases to a critical value（intrinsic viscosity is0.04g/dl）.Finally,the effect of Sn（Oct）₂ content on the thermal stability of two different structures of PGA was studied,and the activation energy of thermal degradation of two kinds of PGA with different catalyst Sn（Oct）₂ content was solved by the same superthermal analysis.With the increase of conversion rate of PGA samples with different structures,the activation energy of thermal degradation corresponding to each conversion rate becomes smaller and smaller.with the decrease of catalyst content,the activation energy of thermal degradation of linear PGA becomes lower and lower.The activation energy of thermal degradation of linear PGA with catalyst Sn（Oct）₂ and initiator 1,4-butanediol hydroxyl molar ratio is 1:50,1:100,1:150,1:200,respectively,and the activation energy of thermal degradation is 91.68 kJ/mol,111.42kJ/mol,121.02 kJ/mol,134.87 kJ/mol.The activation energy of thermal degradation of 4-arm PGA with catalyst Sn（Oct）₂ and initiator pentaerythritol was 96.63 kJ/mol,98.05kJ/mol,109.54 kJ/mol,118.17 kJ/mol,respectively,when the molar ratio of catalyst to pentaerythritol hydroxyl group was 1:50,1:100,1:150 and 1:200,respectively.Through the thermal degradation experiment,it can be found that the existence of catalyst can promote the thermal degradation of PGA.