Star-shaped polymers by living cationic polymerization. 3. Synthesis of heteroarm amphiphilic star-shaped polymers of vinyl ethers with hydroxyl or carboxyl pendant groups

Amphiphilic star-shaped polymers of vinyl ethers (VEs) (5) where separate sets of hydrophilic and hydrophobic arm chains are independently attached to a single core were prepared on the basis of living cationic polymerization. For example, a living polymer (DP(n)BAR = 30) of isobutyl VE (IBVE), prepared by the HI/ZnI2 system at -40-degrees-C in toluene, was allowed to react with a small amount of a divinyl ether [1; CH2=CHOCH2CH2OC6H4C(CH3)2C6H4OCH2CH2OCH=CH2] to give a star-shaped poly(IBVE) (3; M(w)BAR = 50 300, 10 arms). On addition of an ester-containing VE [AcOVE, CH2=CHOCH2CH2OCOCH3; VOEM, CH2=CHOCH2CH2CH(COOEt)2] to a solution of 3, quantitative polymerization of AcOVE or VOEM immediately ensued from the living active sites on the core and afforded "heteroarm" star polymers (4) with different arms on a single core. The concentration of the living ends, determined by the end-capping with the dibenzyl malonate anion [-CH(COOCH2C6H5)2], Was almost constant and equal to the initial HI concentration throughout the reaction. The product polymers were completely soluble in common organic solvents (toluene, CHCl3, etc.), and the observed DP(n)BAR of IBVE and AcOVE or VOEM arm chains were in good agreement with the calculated values. Hydrolysis of the ester functions of 4 gave a heteroarm amphiphilic star polymer 5 with hydroxyl or carboxyl pendant groups [H[-CH2CH(OiBu)]m-(core)-[-CH2CH(OCH2CH2X)]n-OCH3; 5a X, OH; 5b X, CH(COOH)2]. The star polymers 5a (m = 30, n = 20) and 5b (m = 30, n = 10) were completely soluble in toluene, chloroform, and methanol. H-1 NMR analysis showed that the star polymers 5 changed conformation with solvent polarity.