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°C to 100°C. However, the addition of cyclopentadiene exhibited the color change at a significantly higher temperature, ranging from 180°C to 200°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°C for the PCDA and 72.37°C for PCDA in combination with cyclopentadiene, as recorded by the DSC. It is believed that a chemical bond between PCDA and cyclopentadiene 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°C and 194.88°C for PCDA and PCDA with cyclopentadiene, respectively. Because the color change involves CC bond rotation of side groups, stressing π‐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°C. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011