Cationic polymerization of isobutyl vinyl ether in aqueous media: physical chemistry tricks to fight against thermal runaway

Abstract

Cationic polymerization of isobutyl vinyl ether (IBVE) in aqueous media (suspension, dispersion or emulsion), using mainly BF₃OEt₂ as a co-initiator is reported. A high exotherm was observed while carrying out the polymerization in aqueous suspension, whereas in dispersion (mixture of water and n-hexane as reaction medium) or in emulsion particularly, efficient heat transfer decreased thermal runaway. Poly(isobutyl vinyl ether)s with M_n up to 8600 g mol⁻¹ and relatively broad molecular weight distribution (M_w/M_n = 2.5–3.5) in high yield (>85%) were synthesized in aqueous dispersion. In direct emulsion, using BRIJ®98 (7 wt% to monomer) as a surfactant, polymers of low molecular weight (M_n ≤ 2000 g mol⁻¹) and relatively narrow molecular weight distribution (M_w/M_n = 2.0–2.5) were obtained in moderate yields (50–60%), whereas, in inverse emulsion (water–n-hexane as a reaction medium), higher yields (85–96%) and higher molecular weights (M_n = 4500–5500 g mol⁻¹) were reached. Chain-end analyses by means of ¹H NMR spectroscopy revealed that most of the chains contain acetal end groups (typically ≥80%), while aldehyde (12–16%) and alkenal (0.5–3.5%) end groups were found in minor proportions.