A bifunctional monomer derived from lactide for toughening polylactide.

(6S)-3-Methylene-6-methyl-1,4-dioxane-2,5-dione was synthesized from L-lactide and used as the dienophile to prepare spiro[6-methyl-1,4-dioxane-2,5-dione-3,2'-bicyclo[2.2.1]hept[5]ene] via an exoselective and diastereofacial-selective Diels-Alder reaction. Polymerizations of this bifunctional lactide derivative were successfully carried out under ring-opening and ring-opening metathesis polymerization conditions to yield high molecular weight and high Tg polymers. We further demonstrated that by incorporating a small percentage of spiro[6-methyl-1,4-dioxane-2,5-dione-3,2'-bicyclo[2.2.1]hept[5]ene] into poly(1,5-cyclooctadiene) and copolymerizing it with DL-lactide, novel polymeric alloys of PLA can be created that have tremendous improvements in toughness over PLA and the corresponding binary blend of PLA and poly(1,5-cyclooctadiene).