Association Behavior in End-Functionalized Polymers. 1. Dilute Solution Properties of Polyisoprenes with Amine and Zwitterion End Groups

The dilute solution properties of linear polyisoprenes with a highly polar sulfo-zwitterion group on one end of the chain were examined in several solvents by osmometry, light scattering, and viscometry. The polymers were prepared by anionic polymerization with initiation by (3-(dimethylamino)propyl)lithium. The terminal tertiary amine groups were converted to zwitterions by treatment with cyclopropane sultone. A few linear and star materials with all ends functionalized were also prepared. The zwitterion-capped polymers were found to associate strongly in aliphatic hydrocarbons. Solutions of monofunctional zwitterion polymers were highly aggregated in cyclohexane. The multifunctional versions (two or more zwitterions per molecule) formed gels which, however, readily dissolved when small amounts of alcohol were added. Considerably less association of the zwitterion-capped chains was found in aromatic or more highly polar solvents. The number of molecules per zwitterion aggregate in cyclohexane decreased with increasing chain length, a characteristic that we have attributed to excluded volume repulsions of the polymeric tails. The aggregates were found to resemble star polymers in behavior. Some tentative conclusions are drawn about aggregate lifetimes, polar core geometry, and the concentration dependence of aggregation in these systems.