In-plane orientation in Langmuir-Blodgett multilayers of a partly converted flexible poly(p-phenylenevinylene) precursor polymer

The dimethoxy-substituted precursor poly(p-phenylenevinylene) (prec-DMePPV) was partly converted to dimethoxy-PPV by exposing the precursor solution in chloroform to daylight. The monolayer and transfer behavior of this partly converted precursor (pc-DMePPV) was studied with the Langmuir-Blodgett technique. In contrast to prec-DMePPV, an excellent transfer behavior was found for pc-DMePPV, and it was possible to build up multilayer films. The observed Z-type transfer behavior was peculiar, because the transfer ratio was higher than 1, and after deposition the monolayer expanded. Although the pc-DMePPV is not a rigid-rod-like polymer, an in-plane orientation of the chain in the transfer direction was found in the multilayers. We assume that, due to hydrophobic intra- and intermolecular interactions between the conjugated parts in the chains, the monolayer of pc-DMePPV can be considered as a 2D physical network, and the obtained orientation in the dipping direction is due to the stretching of this network during deposition. After each dip the monolayer relaxes, restoring the free volume again as observed by the expansion of the film. After full conversion to dimethoxy-PPV (DMePPV) by thermal treatment of the multilayer, the dipping-induced in-plane orientation was preserved.