MULTIFUNCTIONAL COUPLING AGENTS FOR LIVING CATIONIC POLYMERIZATION .3. SYNTHESIS OF TRIARMED AND TETRAARMED POLY(VINYL ETHERS) WITH TRIFUNCTIONAL AND TETRAFUNCTIONAL SILYL ENOL ETHERS

Tri- and tetrafunctional silyl enol ethers, Me4-nC[CH2OC6H4C(OSiMe3)=CH2]n (3: n = 3; 4: n = 4), proved efficient multifunctional coupling agents for the living polymer of isobutyl vinyl ether (IBVE) prepared by the hydrogen chloride/zinc chloride (HCI/ZnCl2) initiating system at -15-degrees-C in methylene chloride. The silyl enol ethers were readily synthesized by the silyl enolation of the corresponding multifunctional acetophenones (e.g., 6 and 8). Upon the coupling react' ions, the number-average molecular weights (M(n)BAR) of the products increased in accordance with the multiplicity of the coupling agents (e.g., 4-fold increase with 4), while the molecular weight distributions became even narrower (M(w)BAR/M(n)BAR < 1.1) than that of the original living polymer. The products were identified by IH NMR spectroscopy; 3 and 4 led to the tri- and tetraarmed polymers (3-P and 4-P, respectively), where the living polymer (arm) was connected to the coupling agent via an aromatic ketone linkage (CH2OC6H4COCH2-polymer). The coupling of a relatively short chain of living poly(IBVE) (DP(n)BAR approximately 10) occurred nearly quantitatively to give the multiarmed polymers (yield > 95%), but the yield decreased slightly (85-90%) with a longer living chain (DP(n)BAR approximately 50).