Crosslinked structure of pristine poly(p-phenylene vinylene) thin-films synthesized by chemical vapor deposition polymerization

The pristine conjugated polymers including poly(p-phenylene vinylene) (PPV) are often insoluble in organic solvents. In fact, PPV thin films prepared by chemical vapor deposition polymerization in this study were insoluble in common organic solvents as well. Although linear pristine conjugated polymers with saturated bonds and/or aromatics are often insoluble, the insolubility of CVDP-prepared PPV has never been studied. This study showed that the PPV film intentionally brominated to reduce the rigidity of polymer by saturating the vinylene groups in PPV was still insoluble indicating the crosslinking reaction occurred during polymerization. Insolubility of the precursor polymer was further confirmed and the swelling of the crosslinked polymers in various solvents was studied by optical microscopy. The presence of the diradical form of the activated monomer in the gas phase is proposed to explain the crosslinked structure.