An IR study of poly-1,4-phenylenevinylene (PPV), the 2,5-dimethoxy derivative [(MeO)2-PPV], and their corresponding xanthate precursor polymers and monomers

A detailed comparison of the infrared (IR) spectra of poly-1,4-phenylenevinylene (PPV), its xanthate precursor polymer, and its bis-xanthate precursor monomer along with the corresponding 2,5-dimethoxy derivatives has provided a clearer basis for characterizing these species with regard to both structure and purity. All the xanthate precursor monomers and polymers exhibit characteristic intense absorptions typical of the xanthate group near 1220, 1110, and 1050 cm−1. Upon complete conversion of the precursor polymer to the vinylene linked final product, the intense IR peaks of the xanthate group have disappeared and new bands resulting from the vinylene linkages are found. The latter include a moderately strong band near 965 cm−1 due to the out-of-plane –CHCH– deformation of the trans-vinylene conjugated with and linking the phenyl rings into an optoelectronic polymer. Unfortunately, the corresponding C–H stretching vibration of this same group of atoms expected to appear near 3020 cm−1 falls in the same region of the spectrum as the aromatic C–H stretches of the phenyl rings. Similarly, for the 2,5-dimethoxy polymer derivative, [(MeO)2-PPV], the C–H stretching vibration near 3055 cm−1 contains contributions from both aromatic and vinylene C–H. Density functional theory (DFT) calculations on the monomers were instrumental in assigning the infrared spectra of these materials. This study provides a systemic means for verifying that the precursor monomer has been polymerized into the precursor polymer and that thermal conversion to the conjugated polymer is complete.

Figure optionsDownload as PowerPoint slideResearch highlights
► IR analysis of poly(p-phenylene vinylene) (PPV) made by xanthate precursor route.
► IR spectral comparison with dimethoxy derivative of PPV.
► Assignments made using density functional theory (DFT) calculations.
► Useful to verify that thermal conversion is complete.