Selective Single Monomer Addition in Living Cationic Polymerization: Sequential Double End-Functionalization in Combination with Capping Agent

Amine-functionalized and amine-carboxylate double-functionalized polymers (I and II, respectively) have been synthesized by a selective single addition of a protected 2-aminoethyl vinyl ether (BocVE) {CH2 = CH[OCH2CH2N(Boc)2]; Boc = t-butoxycarbonyl} onto a living cationic poly(n-butyl vinyl ether) [poly (NBVE)] initiated with the SnCl4/n-Bu4NCl system: (I) -(NBVE)(n)-CH2CH(OCH2CH2NH2)-H; (II) -(NBVE)(n)-CH2CH(OCH2CH2NH2)-CH2CO2H. The single addition was examined with a set of alkene monomers less reactive than NBVE, including BocVE, 2-chloroethyl vinyl ether, 2-vinyloxyethylphtalimide, and styrene (St). Upon addition of 10 molar excess of these alkenes onto the living ends, only BocVE led to the intended single adduct, and this was attributed to a chelating interaction of the two carboxylate groups in the terminal BocVE unit with the growing poly(NBVE) terminal, thus sterically hampering further propagation. A simple acid-catalyzed Boc-deprotection led to the amino-functionalized version I. Alternatively, an additional quenching the BocVE-capped living end (the precursor of I) with sodium malonate, followed by double deprotection of the Boc and the malonate groups gave the double-functionalized version II. The selective addition of a single monomer molecule is thus a new method for addressable or site-specific introduction of functional groups along polymer chains. (C) 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3375-3381, 2010