Raman spectral changes during the solid‐state polymerization of diacetylenes

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Abstract
Raman spectral changes resulting from the solid‐state 1,4‐addition polymerization of conjugated diacetylenes are reported. The monomers show an intense CC stretching frequency near 2260 cm−1, where as the polymers showed two strong bands, a CC vibration near 2100 cm−1 and a CC vibration near 1500 cm−1. The presence of both double and triple bonds in the polymers suggests the backbone structure (CCCC)n. The alternate mesomeric structure (CCCC)n can be eliminated as a possibility by the presence of the strong CC vibration in the polymer. Sequential Raman spectra obtained during radiation‐induced polymerization revealed intermediate spectral states between the initial monomer and final polymer. Intermediate‐state vibrations first increase and then decrease in intensity as polymerization proceeds. However, the observed vibtrational frequencies of intermediate states were not dependent upon the extent of polymerization. Whether polymerization occurred thermally or as a result of radiation did not appear to influence the spectrum of the final polymer, but the observed number of intermediate states differed. Polymerization mechanisms, required molecular motions, and resulting structural changes are discussed.