Preparation and Characterization of Substituted Polylactides

We report the bulk polymerization of ethylglycolide (3,6-diethyl-1,4-dioxane-2,5-dione), isobutylglycolide (3,6-diisobutyl-1,4-dioxane-2,5-dione), and hexylglycolide (3,6-dihexyl-1,4-dioxane-2,5-dione) to high molecular weight polymers. The glycolides were prepared by two routes: the reaction of 2-bromoacyl bromides and α-hydroxy acids and the acid-catalyzed oligomerization of 2-hydroxy acids followed by thermal depolymerization of the oligomers in the presence of ZnO. Both methods gave the substituted glycolides as a mixture of diastereomers. The monomers were melt-polymerized using Sn(2-ethylhexanoate) 2, SnO, SnBr 2, SnBr 4, PbO, and Ph 4 Sn with alcohol initiators. The polymerization rates depend on the steric bulk of the monomer, and the kinetic data for polymerizations using Sn(2-ethylhexanoate) 2 can be fit to an equilibrium model. High molecular weight poly(ethylglycolide), poly(isobutylglycolide), and poly(hexylglycolide) have T g 's of 12, 22, and −37 °C, respectively. These polymers are amorphous and decompose to monomer above 300 °C.