Synthesis of fluorinated gradient copolymers via in situ transesterification with fluoroalcohols in tandem living radical polymerization

Abstract

Fluorinated gradient copolymers were synthesized by the tandem catalysis of ruthenium-catalyzed living radical polymerization (LRP) and titanium alkoxide-mediated transesterification of methyl methacrylate (MMA) with fluoroalcohols. Although transesterification using less nucleophilic fluoroalcohols is generally regarded as difficult, we found that MMA was efficiently transesterified with fluoroalcohols (R_FOH) into fluorinated methacrylates (R_FMA) by Ti(Oi-Pr)₄ catalysts (2–8 mol%) in the presence of molecular sieves 4A (MS 4A). The yield of R_FMA increased with increasing the alkyl spacer (carbon number) between a hydroxyl group and a fluorinated alkyl segment in fluoroalcohols: propyl (4,4,5,5,5-pentafluoro-1-pentanol: 5FPOH) > ethyl (1H,1H,2H,2H-nonafluoro-1-hexanol: 9FHOH) > methyl (1H,1H-heptafluoro-1-butanol). Tandem polymerization of MMA was conducted with a ruthenium catalyst, a chloride initiator, and Ti(Oi-Pr)₄ in toluene/fluoroalcohol mixtures (1/1, v/v) at 80 °C. Typically, in the presence of 4 mol% Ti and MS 4A, transesterification of MMA with 5FPOH or 9FHOH was efficiently synchronized with LRP to produce well-controlled MMA/5FPMA or MMA/9FHMA gradient copolymers in high yield (Conv. >95%, M_w/M_n = 1.2).