1997 Volume 13 Issue 2 Pages 273-278
The photoproducts obtained from p-phenylene diacrylic acid diethyl ester crystal with various photo-irradiation times were analyzed by liquid ionization (LI) mass spectrometry. It was found that hexadecane was an effective matrix for observing large oligomer ions, trifluoroacetic acid enhanced the protonated molecular peaks, and 2-aminoethanol was useful to produce stable adduct ions of oligomers. The molecular weight distributions were readily determined from the mass numbers of both protonated molecules and molecular adduct ions. Large oligomers up to the hexamer (M.W. 1644) were observed, even though they were insoluble in CHCl3. The topochemical photopolymerization via step-growth process was observed, as has been reported. The mass spectra of the oligomers produced with longer than 20min photo-irradiation, however, indicated that the reaction between two dimer molecules occurred also to result in formation of species having an even-numbered degree of polymerization, such as tetramer, hexamer and so on. The observed chain-growth may be attributed to the gradual change of molecular arrangement in the reacting crystal during the initial stage of topochemical reaction. The LI method gives detailed information about chemical reactions.
