LASER-DESORPTION MASS-SPECTROMETRY OF CHEMICALLY AND ELECTROCHEMICALLY PREPARED POLY(2-VINYLTHIOPHENE)

We have used laser desorption Fourier transform mass spectrometry to d etermine the molecular weight distributions of three forms of poly(2-v inylthiophene): polymer A, the classic, free radical-initiated form, p olymer B, produced as a precipitate during the anodic oxidation of the monomer, and polymer C, formed as an insoluble film on the anode duri ng the same oxidation. We have obtained molecular weight distributions for all three of these products in the form of Na+-attached species. Analysis of the mass spectral data allows us to reach several conclusi ons. For polymer A, initiation takes place by benzoate radicals, and t his reaction is faster than decomposition of benzoate radicals to phen yl radicals and carbon dioxide. Propagation takes place by the well-es tablished radical mechanism, and termination occurs mainly by chain tr ansfer to monomer with some disproportionation. For polymer B, two mec hanisms are consistent with the mass spectral data. The first involves free radical chain propagation involving loss of a proton after the i nitiation step. Termination can occur by combination, disproportionati on, or chain transfer. The second mechanism involves combination of tw o initially formed radical cations with subsequent cationic propagatio n. Termination involves the loss of two protons. The second mechanism alone does not adequately explain the data. For polymer C, infrared sp ectral data support a mechanism that involves initial ring-ring radica l coupling followed by loss of two protons and further oxidation of th e resulting dimer, leading to a polymer containing some cross-linking. The mass spectral data are consistent with this interpretation.