In this study, we explore the functionalization of low-value fats from brown grease via transesterification and the thiol-ene reaction to afford polyol monomers capable of undergoing step-growth polymerization to form polyurethanes (PUs). The capability of this two-step functionalization process to develop copolymers from low-value fats will provide a route for other bio-derived molecules to be modified for step-growth polymerization.

Abstract

The valorization of waste-derived feedstocks for polymer synthesis represents a sustainable alternative to petroleum-based materials. In this study, brown grease, a low-value waste lipid source, is utilized as a precursor for polyol monomer synthesis via a two-step functionalization process. Transesterification of brown grease with allyl alcohol generates allyl esters, which are subsequently modified via thiol-ene click chemistry with 2-mercaptoethanol to yield hydroxyl-functionalized polyols (BG-diol). The thiol-ene reaction proceeds under mild UV-initiated conditions, achieving high conversion efficiency (>90%) while preserving the structural integrity of the derived polyol. BG-diol is further polymerized with 4,4′-methylene diphenyl diisocyanate (MDI) through step-growth polymerization to form brown grease-derived polyurethane (BG-PU). Comparative analysis of BG-PU with polyurethane (PU) synthesized from purified oleic acid (OLA-PU) demonstrates comparable molecular weight distributions (M _n = 14.4 kDa, M _w = 20.4 kDa for BG-PU) and thermal properties (T _g = 24 °C, T _d,5% = 270 °C for BG-PU). These results underscore the feasibility of brown grease as a cost-effective and renewable alternative to plant oil-based polyols, offering a pathway toward sustainable PU production while mitigating food security concerns. This approach exemplifies the potential of waste lipids in circular economy strategies for high-performance polymer synthesis.