Topochemical diacetylene polymerization in layered metal phosphate salts

UV- and X-ray induced polymerization of diacetylene groups in layered salts of 3,5-octadiyne bisphosphate (ODBP) with di- and trivalent metals (Zn, Mg, Mn, Ca, Cd, La, Y, and Sm) was studied. Diffuse reflectance UV-visible spectra were used to monitor the course of the polymerization reactions. From these spectra, it was found that the highest degree of polymerization was obtained with the Zn, Mg, and Mn salts; short-chain oligomers were formed with La, Y, and Sm, while the Ca and Cd salts had the lowest reactivity. These trends can be rationalized in terms of structural models for the juxtaposition of diacetylene groups in the monomeric salts and on the basis of the similarity of the spacing of phosphate coordination sites in the basal plane (4.8 Å for Zn, Mg, and Mg, and 5.6 Å for La, Y, and Sm) and the polydiacetylene repeat distance (4.93 Å). The nucleation and growth of the polymeric phase within these layered solids followed inverse exponential kinetics and could be fitted to the Avrami equation (M. Avrami, J. Chem. Phys. 7, 1103 (1939)).