Biomacromolecules, Vol.5, No.1, 209-218, 2004
Novel biodegradable aliphatic poly(butylene succinate-co-cyclic carbonate)s with functionalizable carbonate building blocks. 1. Chemical synthesis and their structural and physical characterization
This study presents chemical synthesis, structural, and physical characterization of novel biodegradable aliphatic poly(butylene succinate-co-cyclic carbonate)s P(BS-co-CC) bearing functionalizable carbonate building blocks. First, five kinds of six-membered cyclic carbonate monomers, namely, trimethylene carbonate (TMC), 1-methyl-1,3-trimethylene carbonate (MTMC), 2,2-dimethyl-1,3-trimethylene carbonate (DMTMC), 5-benzyloxytrimethylene carbonate (BTMC), and 5-ethyl-5-benzyloxymethyl trimethylene carbonate (EBTMC), were well prepared from ethyl chloroformate and corresponding diols at 0 degreesC in THF solution with our modified synthetic strategies. Then, a series of new P(BS-co-CC)s were synthesized at 210 degreesC through a simple combination of polycondensation and ring-opening-polymerization (ROP) of hydroxyl capped PBS macromers and the prepared carbonate monomers, and titanium tetraisopropoxide Ti(i-OPr)(4) was used as a more suitable catalyst of 5 candidate catalysts which could concurrently catalyze polycondensation and ROP. By means of NMR, GPC, FTIR, and thermal analytical instruments, macromolecular structures and physical properties have been characterized for these aliphatic poly(ester carbonate)s. The experimental results indicated that novel biodegradable P(BS-co-CC)s were successfully synthesized with number average molecular weight (M) over bar (n) ranging from 24.3 to 99.6 KDa and various CC molar contents without any detectable decarboxylation and that the more bulky side group was attached to a cyclic carbonate monomer, the lower reactivity for its copolymerization would be observed. The occurrences of C-13 NMR signal splitting of succinyl carbonyl attributed to the BS building blocks could be proposed due to the randomized sequences of BS and CC building blocks. FTIR characterization indicated two distinct absorption bands at 1716 and 1733similar to1735 cm(-1), respectively, stemming from carbonyl stretching modes for corresponding BS and CC units. With regard to their thermal properties, it is seen that the synthesized P(BS-co-CC)s exhibited thermal degradation temperatures 10similar to20 degreesC higher than that of PBS. On the basis of the synthesized P(BS-co-BTMC)s, new aliphatic poly(butylene succinate-co-5-hydroxy trimethylene carbonate)s were further synthesized, bearing hydrophilic hydroxyl pendant functional groups through an optimized Pd/C catalyzed hydrogenation. These semicrystalline new biodegradable aliphatic copolymers with tunable physical properties and functionalizable carbonate building blocks might be expected as potential new biomaterials.