Incorporation of drying oils into emulsion polymers for use in low-VOC architectural coatings

Abstract

The use of vegetable oil macromonomers (VOMMs) as co-monomers in emulsion polymerization enables good film formation without the use of traditional coalescing solvents which constitute volatile organic compounds (VOCs). However, the allylic protons associated with the fatty acid double bonds can result in extensive chain transfer, reduced rates of polymerization, and potential gel content. Different vegetable oils were derivatized to yield their respective VOMMs which were subsequently polymerized into latexes with conventional (meth)acrylate monomers. The degree of ambient crosslinking was related to the extent of chain transfer for the various vegetable oils. The retention of VOMM unsaturation depended on reaction temperature, and the greatest variability between high and low temperatures was exhibited by the linseed oil macromonomer (the highest level of unsaturation). Lower reaction temperatures minimized the negative impact of the chain transfer reactions, yielding latexes with higher molecular weights and greater retention of allylic unsaturation. Core–shell polymers were characterized by bimodal particle size distribution indicating that the presence of VOMM-rich droplets contributed little to homogeneous VOMM distribution. Optimized single-stage polymerizations resulted in significant preservation of unsaturation, good film-forming qualities, rapid drying, and improved solvent resistance. The resulting latexes exhibited potential for use in higher performance application than conventional latexes. This study has demonstrated that drying oils can be incorporated into emulsions in limited quantities as effective reactive monomers for internal plasticization and auto-oxidative crosslinking after application. Broader ranges of incorporation require further study of VOMM reaction kinetics as a function of structure and improved process methods for macromonomer incorporation into emulsion polymers.