Precision polymer synthesis by living cationic polymerization

Abstract

Cationic polymerization is a variant of electrophilic addition reactions of carbocations toward alkenes (vinyl compounds). With a variety of acidic initiators such as protonic acids and metal halides (BF3 etherate, A1C13, etc.), over 500 monomers may readily be polymerized into polymers and oligomers.1 Though effective for some purposes, the process has traditionally been considered among the least suited for the synthesis of polymers of well-designed or precisely controlled architectures, primarily because of the inherently favoured chain transfer, isomerization, and termination reactions of the carbocationic growing species. Cationic polymerizations under conventional conditions, for example, mixing styrene or an alkyl vinyl ether with tin tetrachloride in a solvent at around 0°C, are almost instantaneous, often poorly reproducible, and result in polymers of relatively low and uncontrolled molecular weights and with broad molecular weight distributions (MWDs). Thus, massscale industrial polymer syntheses via cationic polymerization include only a few, among which butyl rubber production from isobutene at crvogenic temperatures is the most important.