Synthesis And Properties Of The Linear And Cross-linked Polymers From Methylated Polycarbonate

Biodegradable aliphatic polycarbonate materials have been widely used in biomedical applications such as surgical sutures,drug delivery system,and tissue engineering.Among them,polytrimethylene carbonate(PTMC)has received more and more attention due to its excellent performance.PTMC has good biocompatibility,biodegradability,and flexibility in vivo because of the low glass transition temperature below the human physiological temperature.Furthermore,no acid degradation products are produced during the degradation process,which will avoid aseptic inflammation caused by the low pH at the implant site.In recent years,modification has been performed to tailor the structure and properties of PTMC in order to meet the extend applications in medical fields.The design idea of this paper is to introduce-CH3 group into the structure of PTMC or obtain three-dimensional structure based on PTMC via chemical cross-linking to improve the properties of PTMC.It is expected to obtain novel biodegradable materials with low degradation rate and high form-stability,in order to meet the requirements for long-term applications.In the second chapter,a series of poly(trimethylene carbonate-co-2,2'-dimethyltrimethylene carbonate)P(TMC-co-DTC)copolymers with different molar ratios or molecular weights were synthesized by bulk ring opening copolymerization of trimethylene carbonate(TMC)and 2,2'-dimethyltrimethylene carbonate(DTC)under the catalysis of Sn(Oct)2.Their structure was characterized by FT-IR and 1H NMR.The Mn and polymer dispersity index(PDI)of the copolymers were measured by GPC.DSC and TGA results indicated that the Tg of the copolymers P(TMC-co-DTC)at a given molecular weight increased with the increase of DTC content in copolymer,while the Tg of the P(TMC-co-DTC)at a given molar ratio uplifted with the increase of molecular weight.The initial decomposition temperature of all the copolymers was higher than 211.4?,indicating the high thermal stability of P(TMC-co-DTC).The mechanical properties test results showed that P(TMC-co-DTC)had good flexibility.The tensile strength(Ts)and the breaking strength(Tsb)enhanced with the increase of the molecular weight.Then the degradation property of P(TMC-co-DTC)was investigated by in vitro degradation.The macroscopic morphology observation clearly displayed that P(TMC-co-DTC)with high molecular weight had better form-stability and the introduction of DTC segment could significantly increase the form-stability of PTMC homopolymer.SEM was used to observe the changes in surface morphology before and after degradation.The results showed that cracks and ho les appeared during the period of degradation,but the cross-section remained smooth and flat all the time.Meanwhile,the results of GPC indicated that the molecular weight of the samples didn't change substantially during the entire degradation process and remained constant.These results indicated that the degradation mechanism of P(TMC-co-DTC)could be surface erosion degradation.And the change trend of the mass loss of the sample indicated that the introduction of DTC segment could effectively reduce the degradation rate of PTMC.The pH monitoring results of the degradation medium verified that there was no acid degradation product in the degradation process.Subsequently,DSC and TGA were used to test the thermal properties of the samples during the degradation.In the third chapter,the crosslinker 2,2'-bis(trimethylene carbonate-5-yl)butyl ether(BTB)was synthesized firstly and its structure was verified by FT-IR and 1H NMR.Then a series of cross-linked P(TMC-co-DTC)networks NPTD with different molar ratios or crosslinker contents were prepared via the ring-opening copolymerization of BTB with TMC and DTC,under the catalysis of Sn(Oct)2.The cross-linking effect was proved by the swelling experiments.The experimental results showed that the gel percentage increased while the swelling degree decreased with the increase of the BTB amount for the NPTD at a given molar ratio of TMC to DTC.The results of thermal properties showed that the Tg of NPTD increased with the increase of DTC or BTB amount.While the effect of different molar ratios or BTB contents on Td was different and the thermal stability of the samples could be effectively improved by crosslinking.