ON THE ORIGIN OF THERMOCHROMISM IN CROSS-POLYMERIZED DIACETYLENE-FUNCTIONALIZED POLYAMIDES

The thermochromic behavior of a cross-polymerized diacetylene-functionalized polyamide, poly(hexamethylene-10,12-docosadiyne-1,22-diamide) (PADA 6,22), has been investigated with infrared and C-13 solid-state NMR spectroscopy. The polymer was rendered thermochromically active by exposure to UV or electron beam radiation which creates polydiacetylene cross-links across the host polyamide chains. The NMR data indicate that the thermochromic transition of this material is associated with a temperature-induced gauche to trans conformational transition of the methylene groups pendant to the polydiacetylene cross-links. FTIR results showed that the hydrogen bonds of the host polymer remain intact during the transition, thereby ensuring its reversibility. Retention of the hydrogen-bonded network was also found to be strongly linked to the conformational transition triggered in the methylene groups nearest to the polydiacetylene backbone.