Novel Synthesis of Carboxy-Functional Soybean Acrylic-Alkyd Resins for Water-Reducible Coatings

By Changchun Wang, Geng Lin, Joon-Hwan Pae, Frank N. Jones, Huijuan Ye, Weidian Shen

A new process was developed for synthesis of alkyd resins in which a conventional monoglyceride is reacted with a carboxy-functional acrylic copolymer. The novel products are called acrylic-alkyd resins. The carboxy-functional acrylic copolymers were synthesized by solution-free radical polymerization.

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 de-rived from a mixture of acrylic and methacrylic 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 prepared from soybean oil and trimethylol propane. The composition of the acrylic resin was adjusted to minimize phase separation [observed visually and by scanning probe microscopy (SPM)] within cast films.

The most satisfactory results were obtained with copolymers of 62-71 wt% of methyl methacrylate, 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 acrylic-alkyd resins based on these acrylics had excellent stability, with acid numbers changing less than 10% after nine months of storage.