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

Polycarbonates were synthesized by ring-opening copolymerizations of trimet hylene carbonate (TMC) with 1,2-O-isopropylidene-D-xylofuranose-3,5-carbona te(IPXTC). Subsequent deprotection of the ketal protecting groups gave cont rolled quantities of vicinal diol pendant groups. Studies of TMC/IPXTC copo lymerization showed that MAO and ZnEt2-0.5H(2)O were the preferred catalyst s. The reactivity ratios measured by the Fineman-Ross method and using ZnEt 2-0.5H(2)O as the catalyst were 0.31 and 0.20 for IPXTC and TMC, respective ly. Hence, even though IPXTC has bulky substituents, IPXTC was more reactiv e than TMC early in the copolymerization. Consistent with the above, the av erage IPXTC chain segment length was longer early in the copolymerization b ut decreased with increased conversion. H-1 and C-13 NMR were used to analy ze 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 CF3CO OH/H2O to give a novel polycarbonate with hydroxyl pendant groups. Longer d eprotection times led to higher extents of deprotection but lower molecular weight. Studies by differential scanning calorimeter (DSC) showed that cop olymers having from 8 to 83% IPXTC were all amorphous. In addition, a physi cal aging transition was apparent. The T-g of the copolymer increased with increasing IPXTC copolymer content. Furthermore, the experimental T-g value s were in good agreement with that calculated by the Fox equation. After de protection, the copolymer T-g decreased, which is consistent with the loss of the bulky ketal side group.