Novel synthesis of carboxy-functional soybean acrylic-alkyd resins for water-reducible coatings

A new process was developed for synthesis of alkyd resins in which a conven tional monoglyceride is reacted with a carboxy-functional acrylic copolymer . The novel products are called acrylic-alkyd resins. The carboxy-functiona l acrylic copolymers were synthesized by solution-free radical polymerizati on. Gelation during alkyd resin synthesis was avoided by: (1) limiting the molecular weight of the acrylic copolymers to Mn 3500-5000 and (2) limiting the number average functionality about 6.5-10 carboxyl groups per molecule . Further, the carboxyl groups were derived from a mixture of acrylic and m ethacrylic acids (1/1.2 mol ratio) in the expectation that this would help control the process. Three series of acrylic copolymers were prepared from various combinations of acrylic monomers and reacted with a monoglyceride p repared from soybean oil and trimethylol propane. The composition of the ac rylic resin was adjusted to minimize phase separation [observed visually an d by scanning probe microscopy (SPM)] within cast films. The most satisfact ory results were obtained with copolymers of 62-71 wt% of methyl methacryla te, 5-21 wt% of lauryl methacrylate, 7.2 wt% of acrylic acid, and 10.3 wt% of methacrylic acid. In preliminary tests, waterborne coatings made from ac rylic-alkyd resins based on these acrylics had excellent stability, with ac id numbers changing less than 10% after nine months of storage.