Aggregation of n-doped polystyrene-polyparaphenylene block-copolymers : a neutron scattering study

Summary form only given. The n-doping effect on the aggregation of polystyrene-potyparaphenylene (PS-PPP) block copolymers has been investigated through small-angle neutron scattering. A copolymer with a deuteriated PS sequence was synthesized and a 4% by weight solution in deuteriated tetrahydrofuran (d/sub 8/THF) was doped with potassium (K). K-doping was then performed in an aggregated structure and we were mainly interested in its influence on the PPP partial structure factor (the d/sub 8/THF scattering length density is close to that of PSd/sub 8/). Neutron scattering experiments show that both the size and relative arrangement of the PPP cores of PS-PPP aggregates are modified by K-doping. The size of PPP cores increases with the doping rate and an 80% change in volume is reached for the maximum rate. The packing of PPP chains inside cores of aggregates is therefore less compact with a coinsertion of solvent molecules. This is presumably related to a decrease in cristallinity. On the other hand, an increase of attractive interactions between aggregates is achieved by K-doping. Indeed, further associations were observed when PS-PPP aggregates were doped. Such a weak floculation effect corresponds to an increase in the polarizability due to an extended /spl pi/ electron delocalization, as observed by visible absorption spectroscopy. Doped PS-PPP aggregates have therefore a higher Hamaker constant, without localized charge. Finally, K-doped PS-PPP copolymers allow the production of fine conducting PPP dispersions in an insulating PS matrix.