Ralph A. Mosher

Conformational recovery of poly(vinyl chloride) glasses prepared under pressure

The recovery of polyvinyl chloride glasses prepared at high temperature and pressure (120 °C, 7 kbar) have been observed using Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC). Changes in absorbance associated with conformational reequilibration occur above 80 °C, the normal glass temperature of polyvinyl chloride (PVC). Peaks are observed in Cp 15–20 °C below Tg which are attributed to relaxation of volume strain or holes. Since the enthalpy and the conformational recovery occur at different temperatures and time scales, we conclude that neither free volume models nor flexed bond models are adequate to explain the properties of glasses prepared at high pressure.

Remnant Cis Bonds in “Trans”-Polyacetylene

Abstract We report the infrared spectra of “trans”-polyacetylene that has been thermally prepared from c/s-(CH)x. The minimum of 5-7 percent residual 740 cm−1 absorption observed for all cases studied is suggested to be due to isolated remnant c/s linkages. It is shown that these remnant cis linkages may confine the neutral soliton and hence affect the neutral soliton diffusion coefficient. Implications for the soliton generation mechanisms and for conjugation lengths derived from Raman spectra are pointed out.

Thermal Isomerization of Polyacetylene Films

Abstract Isomerization of the as-formed (-78°C) cis-polyacetylene to the trans isomer is relevant to the electronic structure, the crystal structure and the electrical properties of this prototypical conductive polymer. We have studied the process using Fourier transform infrared (FTIR) and 13C magic angle nuclear magnetic resonance (NMR) spectroscopies at temperatures between 80 and 110°C. The observed kinetics will be discussed in terms of three basic processes: a second order process which randomly converts cis-cis-cis (CCC) sequences to trans-cis-trans (TCT) sequences via a pair of biradicals, a fourth order process that converts CTCC sequences to TCTT sequences via four biradicals, and two fourth order processes which allow sequential migration along the chain. The correlation of observed electron spin resonance and x-ray results, among others, with these mechanisms will be shown.