MULTIFUNCTIONAL COUPLING AGENTS FOR LIVING CATIONIC POLYMERIZATION .5. SYNTHESIS OF AMPHIPHILIC TETRAARMED STAR POLY(VINYL ETHERS) BY COUPLING REACTIONS WITH TETRAFUNCTIONAL SILYL ENOL ETHER

Amphiphilic tetraarmed star poly(vinyl ethers), where each arm carries alkyl (hydrophobic) and alcohol (hydrophilic) pendant groups, have been synthesized by the coupling reaction of AB-block living poly(vinyl ethers) (4; arm chain) with a tetrafunctional silyl enol ether 1, C[CH2OC6H4-p-C(OSiMe(3))=CH2](4). The living arm chains 4 were prepared by the sequential living cationic polymerization of an alkyl vinyl ether (CH2=CHOR(1); R(1) = iBu, CH2CH2Cl) and a functionalized vinyl ether (CH2=CHOCH2-CH(2)R(2); R(2) = OCOCH3, OSi(t)BuMe(2)) with hydrogen chloride/zinc chloride initiating system in methylene chloride at -15 degrees C. The treatment of 4 with the silyl enol ether 1 led to tetraarmed block copolymers 5. The yield of 5 (93-73%) depended on the structure and the polymerization sequence of the monomer pair for the arm chain 4. The best result (93% yield) was obtained with the AB-block polymer of 2-chloroethyl vinyl ether (R(1) = CH2CH2Cl; CEVE) and 2-acetoxyethyl vinyl ether (R(2) = OCOCH3; AcOVE) where CEVE was polymerized first. Separate coupling experiments with the homopolymers of these vinyl ethers showed that the coupling yield was higher for monomers with less bulky pendant groups. Subsequent quantitative deprotections of the acetoxy of tert-butyldimethylsilyl groups in 5 into hydroxyl groups gave the amphiphilic tetraarmed polymers 6. By changing the polymerization sequence of the monomer pair, the hydrophilic polyalcohol segments could be placed either inside or outside the tetraarmed structure. For pairs of such inner- and outer-alcohol. versions with identical segmental compositions, solubility and arm-chain conformation (by H-1 NMR) were compared.