Syntheses And Properties Of Homo And Copolymers Of Novel Biodegradable Polycarbonates

Biodegradable polycarbonates are a class of important biomedical materials. Aliphatic polycarbonates have surface erosion property, and good biocompatiblity and biodegradability because they decompose into carbon dioxide and neutral diols after degradation. Various main chain structures and functional pendent groups enable biodegradable polycarbonates to possess versatile physiochemical and biological properties in order to meet needs in biomedical applications. Nowadays, they have been extensively used as bioabsorbable sutures, bone fixing materials and drug controlled release carriers. In this paper, the recent development of biodegradable polycarbonates are briefly reviewed with emphasis on their structures, syntheses, properties and applications.Synthesis of novel biodegradable polymers has attracted a lot of research interest in recent years. A novel six-membered cyclic carbonate monomer, 2, 2-ethylenedioxy-1, 3-propanediol carbonate (EOPDC), based on dihydroxyacetone with ethylene ketal protected carbonyl group was prepared for first time. The monomer EOPDC can be obtained by a four-step reaction including oxidation, protection, reduction and ring-closing, starting from diethyl malonate. Poly(2,2-ethylenedioxy 1,3-propanediol carbonate) (PEOPDC) was obtained by the ring-opening polymerization of EOPDC in bulk using Al(OBu)₃ or Sn(Oct)₂ as a catalyst. The effects of different reaction conditions on the polymerization were investigated. The monomer and polycarbonates obtained were characterized by FT IR, ¹H NMR, ¹³C NMR, GPC and DSC. The PEOPDC were obtained with yield of 48.3-92.6%. The number average molecular weight of PEOPDC ranges from 1.47× 10⁴ to 5.50×10⁴ with the polydispersity ranging from 1.29 to 1.81. The properties of PEOPDC including in vitro cytotoxicity, hydrolytic degradation property, thermal stability and drug controlled release property were investigated. The results show that PEOPDC is a kind of biodegradable aliphatic polycarbonate with surface erosion degradation property, good biocompatibility and satisfactory mechanical properties. PEOPDC is expected to have promising applications in biomedical fields such as drug controlled release, and tissue engineering.Biodegradable polycarbonates with pendent functional groups are of particular importance. Another novel six-membered cyclic carbonate monomer, 2,2-dimethoxy-1,3-propanediol carbonate (MOPDC) based on dihydroxyacetone with methanol ketal protected carbonyl group was prepared. Monomer MOPDC can be obtained by a two-step reaction including protection and ring-closing, starting from dihydroxyacetone. Poly(2,2-dimethoxy 1,3-propanediol carbonate) (PMOPDC) was obtained by the ring-opening polymerization of MOPDC in bulk using Sn(Oct)2 as a catalyst. The effects of different reaction conditions on the polymerization were investigated. The monomer and polycarbonates obtained were characterized by FT IR, *H NMR, I3C NMR, GPC and DSC. The PMOPDC was obtained with the yield of 58.9-91.0%. The number average molecular weight of PMOPDC is 1.4-14X 104 with a polydispersity of 1.31-1.91. The protecting ketal group was partly removed by hydrolysis using 50% trifluroacetic acid as a catalyst to give a functional polycarbonate containing 70% ketone carbonyl group, which improved the hydrophilicity of this polycarbonate. The polycarbonate degraded completely after 5 days in PBS at 37 °C.To improve the properties of polycarbonates, the random copolymers of DTC and EOPDC were synthesized in bulk at 120 °C using Sn(Oct)2 as a catalyst. The polycarbonates obtained were characterized by FT IR, ]H NMR, 13C NMR, GPC and DSC. The copolymers were obtained with yield of 78.7-98.7%, The number average molecular weight of the copolymer is 5.5-15.1 X 104 with a polydispersity of 1.61-1.97. The mechanical properties and drug controlled release properties of copolymers were investigated.The random copolymers of L-LA and EOPDC were synthesized in bulk at 120 °C using Sn(Oct)2 as a catalyst. The poly(LA-co-EOPDC)s obtained were characterized by FT IR, 'H NMR, I3C NMR, GPC and DSC. The copolymers were obtained with yield of 87.9-95.6%, The number average molecular weight of the copolymer is 1.85-6.18X 104 with a polydispersity of 1.41-1. 73. The properties of the copolymer including the enzymatic degradation by proteinase K and drug controlled release property were also investigated. The results show that the degradation rate of the copolymers increases with increasing LA content in the copolymers.The random copolymers of 1,4-dioxane-2-one(DON) and EOPDC were synthesized in bulk at 120 °C using Sn(Oct)2 as a catalyst. The poly(DON-co-EOPDQs obtained were characterized by FT IR, !H NMR, 13C NMR, GPC and DSC.The copolymers were obtained with yield of 55.4-98%. The number average molecular weight of the copolymer is 0.49-4.18 X104 with a polydispersity of 1.52-1. 68. The hydrolytic degradation of the copolymer in PBS was also investigated. The results showed that both the hydrophilicity and degradation rate of the copolymers increase with increasing DON content in the copolymers.The random copolymers of e -caprolacfone(CL) and EOPDC were synthesized in bulk at 120°C using Sn(Oct)2 as a catalyst. The poly(CL-co-EOPDC)s obtained were characterized by FT IR, *H NMR, I3C NMR, GPC and DSC. The copolymers were obtained with yield of 84.2-97.8%, The number average molecular weight of the copolymer is 2.75-7.76 X104 with a polydispersity of 1.52-1. 68. The properties of the copolymer including the enzymatic degradation by Pseudomonas Cepacia lipase and drug controlled release property were also investigated. The results showed that rate of degradation of the copolymer and release of tegafur in the copolymers increase with increasing CL content in the copolymers.The PEOPDC has a relatively high glass transition temperature and improved mechanical properties. However it degraded relatively slowly. In order to enhance the degradation rate, The random copolymers of cyclic phosphate (2-ethoxy-2-oxo-l,3 -dioxaphosphoriane ) (EEP) and EOPDC were synthesized in bulk at 130 °C using Al(O'Bu)3 as a catalyst. The poly(EEP-co-EOPDC)s obtained were characterized by FT IR, 'H NMR, 13C NMR, GPC and DSC. Both the hydrophilicity and degradation rate of the copolymers increase with increasing EEP content in the copolymers.