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 i n chloroform to daylight. The monolayer and transfer behavior of this partl y converted precursor (pc-DMePPV) was studied with the Langmuir-Blodgett te chnique. In contrast to prec-DMePPV, an excellent transfer behavior was fou nd for pc-DMePPV, and it was possible to build up multilayer films. The obs erved Z-type transfer behavior was peculiar, because the transfer ratio was higher than 1, and after deposition the monolayer expanded. Although the p c-DMePPV is not a rigid-rod-like polymer, an in-plane orientation of the ch ain in the transfer direction was found in the multilayers. We assume that, due to hydrophobic intra- and intermolecular interactions between the conj ugated parts in the chains, the monolayer of pc-DMePPV can be considered as a 2D physical network, and the obtained orientation in the dipping directi on is due to the stretching of this network during deposition. After each d ip the monolayer relaxes, restoring the free volume again as observed by th e expansion of the film. After full conversion to dimethoxy-PPV (DMePPV) by thermal treatment of the multilayer, the dipping-induced in-plane orientat ion was preserved.