| Abstract: | The photochemical reaction of m-phenylene diacrylic acid dimethyl ester (m-PDA Me) crystals and solutions has been studied to clarify the effects of the molecular shape on four-center type photopolymerization of diolefins. On irradiation, m-PDA Me crystals were converted into amorphous oligomers having more than two kinds of cyclobutane rings with respect to steric configuration. The characteristic oligomer formation is explained by considering a two-step mechanism: topochemical dimer formation in an ordered crystal lattice and subsequent random cycloaddition in a disordered crystal lattice. In m-PDA Me solution, reversible cyclobutane ring formation and cis–trans isomerization take place, depending on the concentration of m-PDA Me in solution and the wavelength of the irradiating light. The multiplicity of reactivity in various states has been established. |
