Free-radical copolymerization behavior of plant-oil-based vinyl monomers and their feasibility in latex synthesis

Abstract

Vinyl monomers from soybean, sunflower, linseed, and olive oils were copolymerized with styrene (St), methyl methacrylate (MMA), and vinyl acetate (VAc) to determine the reactivity of biobased monomers in radical copolymerization, as well as their feasibility in emulsion processes for the synthesis of biobased latexes. Radical copolymerization of plant-oil-based monomers is described with the classical Mayo-Lewis equation. Using emulsion (or miniemulsion) polymerization with MMA or VAc, stable aqueous polymer dispersions with latex particles measuring 80-160 nm and containing 3-35 wt % of biobased monomer units were successfully synthesized. The number-average molecular weight of the latex copolymers (20 000-150 000) decreases by increasing the degree of unsaturation in monomers and their content in the reaction feed. The presence of plant-oil-based fragments changes the Tg of resulting copolymers from 105 to 79 °C in copolymerization with MMA and from 30 to 11 °C in copolymerization with Vac. As a result, biobased units provide considerable flexibility (elongation at break of about 250%) and improve the toughness of the normally rigid and brittle poly(MMA). Even a small amount (2-5%) of biobased fragments incorporated into the structure of poly(VAc) significantly improves water resistance and provides hydrophobicity to the resulting polymer latex films. The obtained results clearly indicate that the vinyl monomers from plant oils can be considered as good candidates for internal plasticization of polymeric materials through reducing intermolecular interactions in copolymers.