Investigations of Chromatic Transformations of Polydiacetylene with Aromatic Compounds

Thermochromic changes of 10,12-pentacosadiynoic acid (PCDA) were investigated in combination with four aromatic compounds, benzene, furan, thiophene, and cyclopentadiene, with subsequent exposure to UV radiation. Using Raman spectroscopy and solid-state Fluorometry, no differences were observed between benzene, furan, or thiophene from the PCDA itself, with respect to the blue to red color change, which took place from 80 degrees C to 100 degrees C. However, the addition of cyclopentadiene exhibited the color change at a significantly higher temperature, ranging from 180 degrees C to 200 degrees C. Lack of new products formed during the initial mixing period was ruled out by analysis using solid-state NMR MAS and differential scanning calorimetry (DSC), with only monomer peaks at 69.61 degrees C for the PCDA and 72.37 degrees C for PCDA in combination with cyclopentadiene, as recorded by the DSC. It is believed that a chemical bond between PCDA and cyclo-pentadiene is formed after polymerization from catalysis by the UV radiation. Solid-state NMR MAS revealed a chemical shift peak of 131.55 ppm for the PCDA and a much larger peak at 130.84 ppm for the PCDA and cyclopentadiene. The DSC exhibited melting point peaks at 193.26 degrees C and 194.88 degrees C for PCDA and PCDA with cyclopentadiene, respectively. Because the color change involves C-C bond rotation of side groups, stressing pi-bond overlap, the cyclopentadiene bond is thought to prevent rotation by steric hindrance until a higher temperature or melting occurs at the DSC stated temperature of 194.88 degrees C. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 120: 2809-2820, 2011