Sustainable, Upscaled Synthesis of Pinene-Derived (Meth)acrylates and their Application as High Tg Monomers in Styrene/Acrylic-Based Bioderived Copolymer Coatings

Abstract

The improved synthesis of the pinene-derived monomers (3-pinanyl acrylate 1 and 3-pinanyl methacrylate 2), replacing hazardous and/or expensive reagents from established methods with cheaper, more innocuous and sustainable reagents is reported; the monomers of high purity are obtained at up to 160 g scale, without need for chromatographic separation. Subsequently, these monomers (1 and 2) were successfully copolymerized with n-butyl acrylate/methacrylic acid or styrene/methacrylic acid using a radical semi-batch emulsion copolymerization process. For comparison, materials incorporating the more established terpene-derived monomer iso-bornyl methacrylate 3 were also prepared in analogous fashion. The obtained polymer latexes had particle sizes between 65 and 90 nm, very low polydispersities (<0.08) and were stable for several years without any coagulum formation. Gradient liquid chromatography indicated all copolymers had relatively uniform chemical composition distributions. The n-butyl acrylate containing copolymers (P1-P3) were obtained with high molar masses (Mn > 40 000, Mw > 400 000), very high dispersities (Ð > 9.5), and low glass transition temperatures (Tg < -5 °C). The styrene-based copolymers (P4-P6) had slightly lower molar masses (Mn > 40 000, Mw > 150 000), lower dispersities (Ð > 3) and high glass transition temperatures (95 °C < Tg < 120 °C). Preliminary testing of the n-butyl acrylate-based materials demonstrated the potential of these copolymers for use in coatings applications. The poly(n-butyl acrylate)/pinanyl methacrylate copolymer P2 was found to be harder (König hardness) and had better stain resistance properties towards water-based substances than the analogous n-butyl acrylate-based copolymers containing 3-pinanyl acrylate (P1) or iso-bornyl methacrylate (P3). Through further refinement of the copolymerization process we expect the properties of these polymers may be further tailored towards a range of coatings applications.