Fully renewable limonene-derived polycarbonate as a high-performance alkyd resin

Limonene-derived polycarbonate-based alkyd resins (ARs) have been prepared by copolymerization of limonene dioxide with CO₂, catalysed by a β-diiminate zinc–bis(trimethylsilyl)amido complex, and subsequent chemical modification with soybean oil fatty acids using triphenylethylphosphonium bromide as the catalyst. This quantitative partial modification was realized via epoxy–carboxylic acid chemistry, affording ARs with higher oil lengths, lower polydispersities and higher glass transition temperatures (T_g) in comparison to a conventional polyester AR based on phthalic acid, multifunctional polyol pentaerythritol and soybean fatty acid. The novel limonene polycarbonate AR and the conventional polyester AR were evaluated as coatings and both the physical drying (without the presence of the oxidative drying accelerator Borchi® Oxy Coat) and chemical curing (with Borchi® Oxy Coat) processes of these coatings were monitored by measuring the König hardness and complex modulus development with time. A better performance was obtained for the alkyd paint containing polycarbonates modified with fatty acids (FA-PCs), which showed a faster chemical drying, a higher König hardness and a higher T_g in coating evaluation, demonstrating that the fully renewable FA-PCs are promising resins for alkyd paint applications.