SELF-ASSEMBLING BEHAVIOR OF LIVING POLYMERS

In order to elucidate the structure of intermediate species present du ring the early stages of ''living'' anionic polymerization, the aggreg ation behavior of styryllithium head groups [RCH2CH-(C6H5)Li+] in benz ene was investigated by small angle neutron scattering(SANS). The mono functional lipophobic anionic head group was found to self-assemble in a first step to dimers and tetramers. The concentration dependent equ ilibrium between these species was quantitatively analyzed by using th e form factors of a Gaussian linear coil and star, respectively. These results seem to contradict a mechanistic viewpoint of anionic polymer ization that dates to 1960. Therein the dimer was assumed to be the ma ximum allowable aggregation state for this head group. In addition, th e 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 fo rm factor for a mass fractal structure recently proposed by Beaucage.