Thermal and photoinduced polymerization of thin diacetylene films. 1. Phthalimido-substituted diacetylenes

A series of phthalimido-substituted (Pht) diacetylenes with the structure Pht-(CH2)n-CC-CC-(CH2)m-R was synthesized. The influence of the length of the alkyl spacer n between the phthalimido group and the diacetylene group, the length of the alkyl spacer m and an additional polar group R on the thermal and UV-induced polymerization was investigated by systematic variation of n, m, and R (for R = H and m = 8, n = 1, 3, 4, 5, 8, 9; for n = 9 and m = 3, R = H, CH2OH, COOH). All synthesized compounds underwent thermal polymerization. The polymerization temperature increased with longer n spacer or shorter m spacer, and no effect was observed on variation of R. For UV-induced polymerization, a spacer length n of more than four carbon atoms was necessary. Introduction of a hydrogen-bond-forming hydroxyl or carboxyl group at the other side of the diacetylene yielded polymers with a significantly higher degree of conjugation and also improved film formation on quartz enormously.