Living Cationic Copolymerization of Isobutyl Vinyl Ether with P-Methoxystyrene by Hydrogen Iodide/Iodine Initiating System

Abstract

Living cationic copolymerization of isobutyl vinyl ether with p-methoxystyrene was effected by an equimolar mixture of hydrogen iodide and iodine (HI/I2 initiator) at −15°C in nonpolar solvents (carbon tetrachloride and toluene). Isobutyl vinyl ether reacted faster than p-methoxystyrene. The products were random copolymers with a nearly monodisperse molecular weight distribution (MWD) (Mw/Mn=1.1–1.2). Their number-average molecular weight (Mn) increased in proportion to total monomer conversion. The iodine-initiated copolymerization under similar conditions led to long-lived (but not perfectly living) copolymers with a narrow MWD (Mw/Mn=1.2–1.3). In contrast, boron trifluoride etherate induced a conventional transfer-dominant copolymerization. The Mn of the copolymers obtained with the HI/I2 initiator was almost independent of the monomer feed ratio, but in the BF3OEt2-initiated non-living process, the polymer molecular weight decreased sharply with increasing isobutyl vinyl ether content in the feed. These findings show the living copolymerization by HI/I2 to be free from the cross-transfer usually involved in the conventional cationic copolymerization of vinyl monomers.