Electron Paramagnetic Resonance Application to Polymers. IV. The Segmental Volume of Poly(Phenylacetylene) Using Different Nitroxide Spin Probes

• Published in: Polymer (Guilford) 1991-02, Vol.32 (2), p.231-234
• Main Authors: Hwang, J S, Saleem, M M, Tsonis, C P
• Format: Article
• Language: English
• ISSN: 0032-3861

Electron paramagnetic resonance studies of T sub 50G of poly(phenylacetylene) have been carried out at X-band as a function of spin probe size over a wide range of temperatures. It was found that T sub 50G increased with increasing probe size. The polymer glass transition temperature T sub g , determined from the break on the plot of ln T sub G vs. 1/T for tempone in poly(phenylacetylene), was 296K. The apparent activation enthalpy for the T sub g relaxation process increased with increasing probe size, while the segmental size of the polymer appeared to be independent of the nitroxide used, and has a range of 898-922 A exp 3 . The segmental volume measured by the spin probe technique is in excellent agreement with the volume of 970 A exp 3 of 10 repeat units on an average chain based on number-average molecular weight of 960. Thus results showed that there are 17-20 backbone atoms in the segment of poly(phenylacetylene). Assuming the polymer segment to be of spherical shape, the diameter of the sphere was found to have a range of 11.7-12.4 A. Spectra, Graphs. 7 ref.--AA