Abstract
Abstract Topochemical photopolymerization of 4-[2-(unsubstituted and methyl-substituted pyrazinyl)ethenyl]cinnamates and -thiocinnamates were carried out in the crystalline state. Upon photoirradiation, ethyl 4-[2-(unsubstituted and methyl-substituted pyrazinyl)ethenyl]cinnamates and S-ethyl 4-[2-(unsubstituted and methyl-substituted pyrazinyl)ethenyl]thiocinnamates gave α-hetero-type crystalline linear polymers, whereas methyl 4-[2-(methyl-substituted pyrazinyl)ethenyl]cinnamates afforded mixtures of β-type oligomers. The X-ray crystallographic analyses of the monomers revealed that the thioesters were more favorable monomers than the corresponding esters from the viewpoint of close packing in a crystal. The following factor(s) would play an important role in determining their molecular arrangements: 1) The close contact between the central 1,4-phenylene ring and the alkoxy oxygen of the ester group or the alkylthio sulfur of the thioester group, 2) the hydrogen bond between the interstacked pyrazinyl groups, and/or 3) the gearing of the alkyl group in the ester moiety with the methylpyrazinyl group.
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