| Abstract: | Changes in TG-DSC diagrams and X-ray diffraction patterns in the course of four-center-type photopolymerization of 2,5-distyrylpyrazine (DSP) and thermal depolymerization of poly-DSP were investigated. It has been found that as-polymerized poly-DSP crystal with high molecular weight does not melt but depolymerizes into the oligomer in the crystalline state. The crystal change found in the depolymerization was just the reverse of that in the polymerization. From the results a reversible topochemical process, which comprises monomer lattice-controlled photopolymerization and polymer lattice-controlled thermal depolymerization, has been established between DSP and poly-DSP. Quantitative thermal analysis reveals that both of the two endotherms of poly-DSP crystal include the heat of crystallization as well as that of depolymerization. Several specific properties of a topochemical product of as-polymerized poly-DSP crystal, such as nonreproducibility of the original crystal structure by recrystallization and superior stabilities to thermal depolymerization and photooxidation, are discussed in comparison with natural cellulose. |
