The Effect of the Wavelength of an Exciting Light on Four-center-type Photopolymerization in the Crystalline State

Abstract The effect of the wavelength of an exciting light on four-center-type photopolymerization in the crystalline state has been investigated. 2,5-Distyrylpyrazine (DSP), 1,4-bis[β-pyridyl-(2)vinyl]benzene (P2VB), p-phenylenediacrylic acid (p-PDA) dimethyl ester were converted quantitatively into highly crystalline oligomers (pentamers on the average) on irradiation at the long-wavelength edge of the absorption of the monomer. On subsequent exposure to the light which is absorbed by each oligomer, the oligomer crystals as-polymerized were converted quantitatively into high polymer crystals. The polymer thus obtained was found to be identical with the polymer produced by the light of a xenon or a high-pressure mercury lamp. The quantum yields for the oligomerization and polymerization reactions of DSP and the p-PDA dimethyl ester were found to be between 1 and 2 on the basis of the number of olefinic double bonds consumed to form the cyclobutane ring. These results confirmed that the four-center-type photopolymerization in the crystalline state consists of two kinds of separable, step-by-step addition mechanisms: an oligomerization of the dioleflnic compound and a growth reaction of the terminal group in the growing chain. From the crystallographic information on the DSP oligomer, the oligomerization as well as the polymerization process of DSP were concluded to proceed by a monomer lattice-controlled mechanism.