Synthesis and characterization of solvent free acrylic copolymer for polyurethane coatings

Solvents play a huge role in the manufacturing of various acrylic resins due to their ability to control the molecular weight, reduce the viscosity and enhance the flow and levelling of the coatings. However, they contribute significantly to volatile organic content (VOC) which is a key parameter in the field of coatings industry. In view to minimise VOC, various polyols have been studied as reactive diluents/solvents to replace conventional solvents in acrylic polyol synthesis. In this manuscript, 1,3-propanediol oligomer, a 100 % bio-based oligomer has been used to completely replace the conventional solvent in the acrylic polyol synthesis. 1,3-propanediol not only acts as a solvent but also takes part in the curing process by reacting with polyurethane (PU) cross-linkers. To achieve the same properties as solvent based acrylic polyol resins, suitable monomers, initiators and reaction conditions were explored. Most of our designs exhibited viscosity in the range of Z6 to Z8 on Gardener scale at 25 °C. A solitary design resulted in a viscosity of Z4-Z5, which was well within our required parameters. This acrylic polyol resin based on 1,3-propanediol was cross-linked with PU cross-linkers in clear coat. The obtained film was then studied using various analytical techniques such as dynamic mechanical analyser (DMA), thermogravimetric analysis (TGA), gel permeation chromatography (GPC) and fourier transform infrared (FTIR) spectroscopy. The advantage with 1,3-propanediol based solvent free acrylic polyol resin is the reduction of VOC from 400 g/L to ∼ 160 g/L. It is observed that the coatings obtained from this acrylic polyol resin exhibited comparable performance in two component (2 K) PU coatings to that of in-house solvent borne acrylic systems having high VOCs.