Sustainable, upscaled synthesis of pinene-derived (meth)acrylates and their application as high Tg monomers in styrene/acrylic-based bioderived copolymer coatings

Abstract

An 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 the 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 an analogous fashion. The obtained polymer latexes had particle sizes between 65 and 90 nm and very low polydispersities (<0.08) and were stable for several years without any coagulum formation. Gradient liquid chromatography indicated that all copolymers had relatively uniform chemical composition distributions. The n-butyl acrylate containing copolymers (P1–P3) were obtained with high molar masses (M_n > 40 000 and M_w > 400 000), very high dispersities (Ð > 9.5), and low glass transition temperatures (T_g < −5 °C). The styrene-based copolymers (P4–P6) had slightly lower molar masses (M_n > 40 000 and M_w > 150 000), lower dispersities (Ð > 3) and high glass transition temperatures (95 °C < T_g < 120 °C). Preliminary testing of the n-butyl acrylate-based materials demonstrated the potential of these copolymers for use in coating 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 that the properties of these polymers may be further tailored towards a range of coating applications.