Association of End-Functionalized Block Copolymers. Light Scattering and Viscometric Studies

The dilute solution properties of diblock and triblock copolymers of styrene and isoprene with one dipolar sulfobetaine group at either or both ends of the chain were examined in carbon tetrachloride by static and dynamic light scattering as well as by viscometry. The copolymers were prepared by anionic polymerization techniques using [3-(dimethylamino)propyl] lithium as initiator. The tertiary amine groups were converted to sulfobetaines by reaction with cyclopropanesultone. Aggregation numbers derived from static and dynamic methods are in good agreement and decrease with increasing molecular weight of the polymeric tail. Aggregates seem to be polydisperse and stable for long periods of time. Although aggregation is reduced when small amounts of 2-methylcyclohexanol are added, in CCl₄ solutions, it persists even at concentrations of alcohol as high as 5% (v/v). Gels, formed by the difunctional species, are also destroyed by addition of alcohol. There is evidence for intramolecular association in very dilute solutions of the difunctional species. The hydrodynamic behavior of the aggregates, formed by the monofunctional species, resembles that of star polymers in general. Comparisons with theoretical predictions show that the behavior of the aggregates is best described by the linear head-packing model.