This work examines the stereochemical control and polymerizability of exo-methylene-lactide (MLA) or (6S)-3-methylene-6-methyl-1,4-dioxane-2,5-dione, a chiral monomer derived from l-lactide, toward vinyl-addition and ring-opening polymerization (ROP) pathways, respectively. Currently, no information on the stereochemistry of the vinyl-addition polymerization of MLA is known, and the possible ROP pathway is unexplored. Accordingly, this work first investigated the stereochemical control and other characteristics of the radical polymerization of MLA and its copolymerization with an analogous exo-methylene-lactone, -methyl--methylene--butyrolactone (MMBL), and di-methylene-lactide (DMLA) or 3,6-dimethylene-1,4-dioxane-2,5-dione. The MLA homopolymerization produced optically active, but atactic, vinyl-type polymers having a specific rotation of [](23)(D)=-42 +/- 4 degrees, a high T-g from 229 to 254 degrees C, and a medium (M-w=76.3 kg/mol, D=1.16) to high (M-w=358 kg/mol, D=2.83) molecular weight, depending on the solvent. The copolymerization of MLA with MMBL afforded copolymers exhibiting enhanced thermal stability, while its copolymerization with DMLA led to cross-linked polymers. The results obtained from the model reactions designed to probe the possible ROP indicate that the nonpolymerizability of MLA by initiators or catalysts comprising acidic, protic, and/or nucleophilic reagents is due to the high sensitivity of MLA toward such common ROP reagents that trigger decomposition or other types of transformations of MLA forming nonpolymerizable derivatives. (c) 2015 Wiley Periodicals, Inc. J. Polym. Sci. Part A: Polym. Chem. 2015, 53, 1523-1532