ASSOCIATION BEHAVIOR OF LIVING ANIONIC LIPOPHOBIC HEAD-GROUPS IN HYDROCARBON MILEAU

The commercial applications of anionic polymerization have become wide -spread with regard to the preparation of linear and star shaped homop olymers and block copolymers (Diene-35(TM) Kraton(TM), Vector(TM), Sol prene(TM), K Resin(TM) and ShellVis(TM)). Furthermore, randomized styr ene/butadiene linear copolymers (Solprene(TM)) and low molecular weigh t, 10K or less, polybutadienes (Lithenes(TM)) of various microstructur es are commercially available. Recently Liquid Kratons(TM) with OH fun ctional units in place on one or both chain ends have become items of commerce. The lithium based systems yield materials of uniform composi tion and molecular weights with virtually monodisperse molecular weigh t distributions. Both molecular weight and composition are tunable via the simple expedient of manipulating the monomer/initiator ratio. Alt hough the synthetic aspects of these anionic systems have been well-ma stered and exploited over the years the mechanistic features have rema ined controversial; issues which revolve around active center aggregat ion behavior and the reactivity (or its absence) of these self-assembl ed anionic lipophobic head-groups. Thus a study of these systems was u ndertaken using modem scattering techniques and data analysis procedur es. Small angle neutron scattering (SANS) in combination with dynamic and static light scattering, DLS and SLS, has been used to evaluate th e association behavior of the styryl-and dienyllithium head-groups in benzene and cyclohexane solutions. Both types of lipophobic active cen ters were found to aggregate as dimers which in turn can self-assemble to yield large-scale wormlike micelles (prolate ellipsoids). These sy stems thus emulate the behavior of diblock copolymers and surfactants in their capacity to form flexible cylindrical micelles. It was also f ound for ail head-groups that the combination of long chain lengths an d high polymer concentrations favored the presence of the dimer struct ure. This commonality of aggregation state is in consonance with resul ts given in 1964.