Model ω-functionalized linear polystyrenes with one, two, and three sulfobetaine end groups:: Synthesis, characterization, and association behavior

Three series of omega-functionalized polystyrenes (PS) with different molecular weights, the first consisting of dimethylamino end-capped PSs and the other two of omega-branched PSs end-capped with two and three low-molecular-weight ((M) over bar (n) similar to 500 g.mol(-1)) dimethylamino omega-functionalized polybutadienes (PB), were synthesized by high-vacuum anionic polymerization techniques using the functional initiator ([3-(dimethylaminopropyl)] lithium) and chlorosilane linking chemistry. The omega-dimethylamino polymers (precursors) were molecularly characterized by size-exclusion chromatography, low-angle laser light scattering (LALLS), membrane osmometry, and NMR spectroscopy. The characterization results indicate a high degree of molecular and structural homogeneity. The dimethylamino end groups were transformed to the highly polar sulfozwitterionic ones (see Figure) by reaction with cyclopropanosultone. The mono-, di-, and tri-zwitterion capped polymers were found by LALLS, dynamic light scattering (DLS) and viscometry, to associate in carbon tetrachloride, a good nonpolar solvent for the PS tail. In contrast, results on dimethylamino-capped precursors show no evidence of aggregation. Aggregation numbers increase in decalin compared with those in carbon tetrachloride. At constant molecular weight of the parental PS, the degree of association increases with increasing number of functional groups and for a given number of functional groups with decreasing molecular weight of the PS tail. Temperature-dependent light scattering measurements in decalin indicate that aggregation persists at the highest temperature investigated.