Aliphatic polycarbonates with controlled quantities of D-xylofuranose in the main chain

Polycarbonates were synthesized by ring-opening copolymerizations of trimethylene carbonate (TMC) with 1,2-O-isopropylidene-D-xylofuranose-3,5-carbonate(IPXTC). Subsequent deprotection of the ketal protecting groups gave controlled quantities of vicinal diol pendant groups. Studies of TMC/IPXTC copolymerization showed that MAO and ZnEt2-0.5H(2)O were the preferred catalysts. The reactivity ratios measured by the Fineman-Ross method and using ZnEt2-0.5H(2)O as the catalyst were 0.31 and 0.20 for IPXTC and TMC, respectively. Hence, even though IPXTC has bulky substituents, IPXTC was more reactive than TMC early in the copolymerization. Consistent with the above, the average IPXTC chain segment length was longer early in the copolymerization but decreased with increased conversion. H-1 and C-13 NMR were used to analyze the repeat unit sequence distribution of copolymers. For copolymers with high IPXTC contents, three types of IPXTC linkages were found: head-head, tail-tail, and head-tail. The protecting ketal groups were removed by CF3COOH/H2O to give a novel polycarbonate with hydroxyl pendant groups. Longer deprotection times led to higher extents of deprotection but lower molecular weight. Studies by differential scanning calorimeter (DSC) showed that copolymers having from 8 to 83% IPXTC were all amorphous. In addition, a physical aging transition was apparent. The T-g of the copolymer increased with increasing IPXTC copolymer content. Furthermore, the experimental T-g values were in good agreement with that calculated by the Fox equation. After deprotection, the copolymer T-g decreased, which is consistent with the loss of the bulky ketal side group.