Multifunctional coupling agents for living cationic polymerization .6. Synthesis of multiarmed and end-functionalized poly(alpha-methylstyrene) with multifunctional silyl enol ethers

Tri- and tetraarmed polymers (3-P and 4-P) of alpha-methylstyrene (alpha MeSt) and their end-functionalized versions (12) [R(4-m)C{CH2OC6H4COCH2-(alpha MeSt)(n)-CHMeOCH(2)CH(2)-X}(m) (Me = CH3); arm number m = 3 (R = Me), 4; X = Cl, OCOMe, OCOCMe=CH2] have been synthesized by coupling reactions of living poly(alpha MeSt) with multifunctional silyl enol ethers [R(4-m)C{CH2OC6H4C(OSiMe(3)) = CH2}(m); 3, m = 3, R = Me; 4, m = 4]. The living poly(alpha MeSt) was prepared by living cationic polymerization in methylene chloride solvent at -78 degrees C with the hydrogen chloride-vinyl ether adduct [Cl-CHMe(OCH2-CH2-X)] as initiator in conjunction with tin tetrabromide (SnBr4). Subsequently, the living chains were allowed to react with 3 or 4 in the presence of N-ethylpiperidin to give the target multiarmed polymers in high yield (>90%). Specifically for alpha MeSt, it proved crucial that N-ethylpiperidine and similar nucleophiles should be added into the living polymer solution for its efficient coupling to occur. In the end-functionalized polymers (12), each of the four poly(alpha MeSt) arms carries a terminal function X, which would provide a novel cross-linking agent [X = OH (from OCOMe)] or a tetraarmed macromonomer (X = methacryloyl).