Microwave-assisted sodium borohydride/lanthanide rare earth chlorides system for reduction of terminal carboxyl groups in liquid fluoroelastomer

Liquid terminal carboxyl fluororubber (LTCFs) derived from poly(vinylidene fluoride-co-hexafluoropropylene) was efficiently converted to liquid terminal hydroxyl fluororubber (LTHFs) through a microwave-assisted reduction process employing NaBH₄/lanthanide chloride (MCl₃; M = La, Ce, Sm, Gd) catalytic systems. Comprehensive structural characterization via FTIR, UV–Vis, ¹H NMR, GPC, and titration analyses confirmed the transformation of terminal carboxyl groups (-COOH) to hydroxyl groups (-OH) while simultaneously reducing backbone carbon-carbon double bonds (-C = C-) to single bonds (-C-C-). Systematic evaluation revealed NaBH₄/CeCl₃, NaBH₄/SmCl₃, and NaBH₄/GdCl₃ systems achieved exceptional reduction efficiencies exceeding 80 %. Process optimization using the NaBH₄/SmCl₃ system established optimal parameters: 4 min microwave irradiation at 320 W power, SmCl₃/-COOH molar ratio of 2:1, and substrate/solvent ratio of 1:10 (g/mL), yielding 84.60 % conversion efficiency. The microwave methodology demonstrated remarkable temporal efficiency, achieving >80 % conversion within 4 min compared to conventional thermal methods requiring hours. This accelerated process significantly enhanced reaction kinetics while maintaining structural fidelity, as evidenced by comprehensive spectroscopic and chromatographic analyses. The work establishes a robust microwave-assisted platform for precise fluororubber functional group modification with potential applications in advanced fluoropolymer synthesis.