ASSOCIATION BEHAVIOR OF LINEAR OMEGA-FUNCTIONALIZED POLYBUTADIENES INCYCLOHEXANE

The dilute solution properties of linear polybutadienes with dimethyla mine and zwitterionic end groups were studied by membrane osmometry (M O), low-angle laser light scattering (LALLS), viscometry, and dynamic light scattering (DLS) in cyclohexane. The polymers were prepared by a nionic polymerization, under high vacuum conditions using [3-(dimethyl amino)propyl]lithium as initiator. The dimethylamine groups were conve rted to zwitterions by reaction with cyclopropane sultone. No evidence of association was found for the amine-capped polymers, whereas the z witterionic samples exhibited strong association in cyclohexane. The d egrees of association increase by decreasing molecular weight of the b ase polymer due to the excluded volume repulsions. These aggregation n umbers are of the same order as those found for omega-functionalized p olyisoprenes, with the same polar groups in the same solvent. The hydr odynamic properties, measured by viscometry and dynamic light scatteri ng, supported the conclusions drawn by LALLS and provide strong eviden ce that the aggregates behave hydrodynamically as star polymers. Compa rison with theoretical models shows that the association behavior is b est described by the linear head packing model. (C) 1996 John Wiley & Sons, Inc.