Versatile copolymers from [L]-lactide and [D]-xylofuranose

The new monomer 1,2-o-isopropylidene-[D]-xylofuranose-3,5-cyclic carbonate (IPXTC) was prepared. The organometallic catalysts AlR3-H2O (R = ethyl, isobutyl), ZnEt2-H2O, and Sn(Oct)(2) were evaluated for the copolymerization of [L]-lactide ([L]-LA) with IPXTC. This work showed that Sn(Oct)(2) was preferred for the formation of high molecular weight copolymers. For example, a copolymerization ([L]-LA/IPXTC = 83:17 mol/mol) at 120 degrees C for 6 h gave poly([L]-LA-co-7 mol % IPXTC) with an M-n and polydispersity (M-w/M-n) of 78 400 and 1.9, respectively. The comonomer reactivity ratios were 4.15 and 0.255. respectively, for [L]-LA and IPXTC copolymerizations conducted at 120 degrees C, M/C = 200, and Sn(Oct)(2) as catalyst. Structural investigations by NMR revealed that [L]-LA/IPXTC copolymers had short average IPXTC repeat unit segment lengths. Increased copolymer IPXTC content resulted in products with lower melting transition temperatures but higher glass transition temperatures. To obtain hydroxyl functionalized P([L]-LA) copolymers, the pendant IPXTC ketal protecting group was removed. The deprotection was performed in CH2Cl2 using CF3COOH/H2O without substantial molecular weight decrease. Hence, an efficient route has been developed to synthesize high molecular weight PLA-based copolymers that consist of [L]-lactic acid and [D]-xylofuranose repeat units. The [D]-xylofuranose repeat units have vicinal diol groups that will facilitate further functionalization and modification of these copolymers. The "tailorability" of the new copolymers is expected to be of great value for the development of important new bioresorbable medical materials.