MODEL MONO-OMEGA-FUNCTIONALIZED, DI-OMEGA-FUNCTIONALIZED, AND TRI-OMEGA-FUNCTIONALIZED 3-ARM STAR POLYBUTADIENES - ASSOCIATION BEHAVIOR IN DILUTE-SOLUTION BY DYNAMIC LIGHT-SCATTERING AND VISCOMETRY

The dilute solution properties of three-arm star polybutadienes with o ne, two, aad three dimethylamino or sulfobetaine end groups were studi ed in tetrahydrofuran (THF) and cyclohexane by dynamic light scatterin g and viscometry. The polymers were prepared by anionic polymerization techniques using [3-(dimethylamino)propyl]lithium or sec-BuLi as init iator and methyltrichlorosilane as linking agent. The dimethylamino gr oups were converted to highly polar sulfozwitterion groups by reaction with cyclopropanesultone. In the case of the amine-capped polybutadie nes, the hydrodynamic behavior in cyclohexane and THF was almost the s ame, meaning the absence of any appreciable association in cyclohexane . For the zwitterionic polymers, the hydrodynamic, RH, and viscometric radii, Rv, in cyclohexane are larger than those for the corresponding amine-capped samples, showing the existence of aggregation. The diffe rence decreases as the number of functional groups increases, which is in agreement with previous static methods results. The micelles forme d by the monofunctional species behave hydrodynamically as star polyme rs with functionality equal to 2N(w), where N-w is the weight-average degree of association. The R(v)/R(H) ratio is lower than unity (0.51-0 .89), meaning that during the flow in the viscometer there is some dis association of the aggregates.