13C NMR and ESR Studies on a Polydiacetylene Having Acetylenic Carbons in the Side Chains

The 13C NMR spin-lattice relaxation times and ESR spectra were measured for a polydiacetylene obtained by the solid-state polymerization of a tetrayne with n-C14H29 alkyl substituents (14-4A-14). Poly(14-4A-14) has two different side chains. One side chain contains two conjugated acetylenic bonds directly bound to the main backbone conjugated system; the other is an alkyl chain. Although the unpaired electron density of poly(14-4A-14) measured by ESR is less than that in trans-polyacetylene, paramagnetic effects may contribute to the long 13C relaxation times of unsaturated carbons, which provides insight concerning the π-electron structure on the conjugated system.