END-FUNCTIONALIZED BLOCK-COPOLYMERS OF STYRENE AND ISOPRENE - SYNTHESIS AND ASSOCIATION BEHAVIOR IN DILUTE-SOLUTION

The dilute solution properties of di- and triblock copolymers of isopr ene and styrene having a highly polar sulfozwitterion group on one or both ends of the chain were studied in the nonpolar solvent carbon tet rachloride (a good solvent for polystyrene and polyisoprene) by low-an gle laser light scattering. The copolymers were prepared by anionic po lymerization using high-vacuum techniques with [3-(dimethylamino)propy l]lithium as initiator. The dimethylamino end group of the chain was t ransformed to a zwitterion by reaction with cyclopropanesultone. The m onofunctional zwitterion-capped copolymers were found to associate in carbon tetrachloride, whereas the difunctional versions formed gels ev en below the coil overlap concentration, c. The aggregation number wa s found to decrease with increasing base molecular weight due to the e xcluded volume repulsions of the copolymeric tails. Comparison with th e corresponding omega-zwitterionic polyisoprene homopolymers in cycloh exane and in carbon tetrachloride shows that for the same base molecul ar weight the materials with the homopolymeric tails aggregate more st rongly. Aggregation numbers for the copolymers are of the same order o f magnitude as the degree of association measured for a zwitterion-cap ped polystyrene. The presence of the phenyl rings in the copolymer cha in seems to reduce the extent of aggregation. The effect of position a nd number of the functional groups on the strength of the association is also discussed.