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Keywords:

  • photopolymerization;
  • differential scanning calorimetry (DSC);
  • fluorescence;
  • Raman spectroscopy;
  • NMR

Abstract

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 C[BOND]C 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