Self-assembling behavior of living polymers

In order to elucidate the structure of intermediate species present during the early stages of "living" anionic polymerization, the aggregation behavior of styryllithium head groups [RCH(2)CH-(C(6)H(5))Li(+)] in benzene was investigated by small angle neutron scattering(SANS). The monofunctional lipophobic anionic head group was found to self-assemble in a first step to dimers and tetramers. The concentration dependent equilibrium between these species was quantitatively analyzed by using the form factors of a Gaussian linear coil and star, respectively. These results seem to contradict a mechanistic viewpoint of anionic polymerization that dates to 1960. Therein the dimer was assumed to be the maximum allowable aggregation state for this head group. In addition, the SANS technique has shown that the intermediate scale structures can also form large scale self-assembled aggregates (R(g) congruent to 10(3) Angstrom) whose scattering behavior can be analyzed in terms of a form factor for a mass fractal structure recently proposed by Beaucage.