Polyaddition of p‐benzenedithiol to p‐diethynylbenzene in solid state under UV irradiation

A novel polyaddition of p‐benzenedithiol (BDT) to p‐diethynylbenzene (DEB) was studied in solid state under UV or γ‐ray irradiation at 25–99°C. Thin layer crystals of the 1:1 mixture of BDT and DEB mounted on a glass plate were prepared by a sublimation of an equimolar amount of the mixture of BDT and DEB at 45–80°C under a reduced pressure of nitrogen. The thin layer crystal of the 1:1 mixture of BDT and DEB and that of polymers exhibited almost similar and high crystalline diffraction patterns on x‐ray diagraph. Consequently, the polyaddition in the solid state was a topotactic reaction controlled by the crystal lattice of the 1:1 mixture of BDT and DEB. The arrangement of both compounds in the thin layer crystal of the 1:1 mixture of BDT and DEB is seemingly quite ordered induced by a molecular interaction between BDT and DEB, and this is supported on the basis of the broad absorption at 340–450 nm by the diffuse reflectance spectrum taken with the thin layer crystal of the 1:1 mixture of BDT and DEB. The melting point of the 1:1 mixture of BDT and DEB was 90–94°C. However, the polyaddition at 87°C proceeded in a molten state perhaps due to heat evolved in the polyaddition. In the solid state polyaddition Mn of polymers obtained was 3–4 × 103, whereas in the molten state polyaddition the crystallinity of polymers remarkably decreased, and Mn increased several times.