To broaden the application scope of lactic acid polymers, a new miniemulsion of poly(alkyl methacrylate-graft-lactic acid)s has been developed. The graft copolymer synthesis was based on a poly(lactic acid) macromonomer having a methacryloyl polymerizable group. The macromonomer and a comonomer of n-butyl methacrylate together with a suitable surfactant formed a miniemulsion of the comonomers in water. A radical copolymerization of the comonomers took place to produce the graft copolymer as a stable miniemulsion. The copolymer showed elastic polymer properties. The miniemulsion system may find useful applications as a new biobased polymer material that is environmentally desirable.

For developing broader application of biobased polymers, graft copolymers and comb polymers having poly(lactic acid) (PLA) side chains have been synthesized by using a macromonomer technique. PLA macromonomers (MMm) having a methacryloyl polymerizable group with different PLA chain length with an average length m = 4, 6, 8, 12, 18, and 30 were prepared via ring-opening polymerization of l-lactide using hydroxyethyl methacrylate (HEMA) initiator catalyzed by Sn(Oct)(2). Radical polymerization behaviors of these macromonomers were examined. Radical copolymerization of MMm (m = 4, 6, and 8), with vinyl monomers like n-butyl methacrylate (BMA) and n-butyl acrylate (BA) in water as the reaction medium, gave stable miniemulsions of poly[n-butyl (meth)acrylate-graft-lactic acid]s [PB(M)A-g-PLAm]. MMm with m value higher than 12, however, gave aggregate products in a minor amount besides miniemulsions in a major amount, producing not a stable emulsion system of graft copolymers. The solution copolymerization, on the other hand, produced a wider variety of the graft copolymers, where a wider range of MMm (even m ≥ 12) can be employed. In a 1,4-dioxane solution, the radical copolymerization of MMm with BMA and methyl methacrylate (MMA) gave various graft copolymers [PB(M)MA-g-PLAm]. A new type of comb polymers (PMMm) having PLAm as pendant side chains were obtained by radical homopolymerization of MMm in a 1,4-dioxane solution. The graft copolymers and comb polymers obtained here are amorphous. Physical properties of the polymers from miniemulsions suggested them to be applicable for coatings or elastic materials which are environmentally desirable as a new class of biobased polymers. In addition, the present approach provided fundamental information on relationships between the length of PLA side chain and the bulk properties of the product polymers.

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