Electron paramagnetic resonance application to polymers: 4. The segmental volume of poly(phenylacetylene) using different nitroxide spin probes

• Published in: Polymer (Guilford) 1991, Vol.32 (2), p.231-234
• Main Authors: Hwang, J.S., Saleem, M.M., Tsonis, C.P.
• Format: Article
• Language: English
• Subjects: e.p.r; poly(phenylacetylene); segmental volume; spin probe
• ISSN: 0032-3861; 1873-2291
• DOI: 10.1016/0032-3861(91)90007-6

Electron paramagnetic resonance (e.p.r.) studies of T 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 50G increased with increasing probe size. The polymer glass transition temperature T g, determined from the break on the plot of ln T R versus 1 T for tempone in poly(phenylacetylene), was 296 K. The apparent activation enthalpy for the T 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 Å 3. The segmental volume measured by the spin probe technique is in excellent agreement with the volume of 970 Å 3 of 10 repeat units on an average chain based on number-average molecular weight of 960. Thus our 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 Å.