MODEL MONO-OMEGA-FUNCTIONALIZED, DI-OMEGA-FUNCTIONALIZED, AND TRI-OMEGA-FUNCTIONALIZED 3-ARM STAR POLYBUTADIENES - SYNTHESIS AND ASSOCIATION IN DILUTE-SOLUTIONS BY MEMBRANE OSMOMETRY AND STATIC LIGHT-SCATTERING

Three-arm polybutadienes with one, two, and three functional end group s were prepared by anionic polymerization using [3-(dimethylamino)prop yl]lithium and sec-butyllithium as initiators and methyltrichlorosilan e as linking agent. Characterization carried out on the dimethylamine- capped polymers by size exclusion chromatography (SEC), in THF, low-an gle laser light scattering (LALLS) in THF, and membrane osmometry (MO) in toluene indicates a high degree of molecular and structural homoge neity. The 1,2 content, determined by NMR spectroscopy, of the arms ha ving the functional groups was higher (12-32%) than that of the arms w ithout the functional groups (7-10%), owing to the tertiary amine grou p of the initiator. The dimethylamine end groups were transformed to t he highly polar sulfozwitterionic ones by reaction with cyclopropanesu ltone. Association of the different omega-functionalized star polybuta dienes was studied in dilute solutions of cyclohexane by MO and LALLS. It was found that although the dimethylamine-capped polybutadienes do not associate, the corresponding zwitterionic species associate stron gly in this solvent. At fixed molecular weight of the arms, the degree of association increases with decreasing number of functional groups and, for the same number of functional groups, with decreasing molecul ar weight of the arms. The trifunctional species form gels at concentr ations needed for MO experiments. Comparison with linear omega-zwitter ionic polybutadienes in cyclohexane shows that the stars associate les s strongly, maybe due to the sterically hindered star structure (monof unctional species) and to intramolecular interactions (di- and trifunc tional species).