Electron Spin Resonance Study on Dynamic Heterogeneity in Miscible Blend of Poly(cyclohexyl methacrylate) and Poly(cyclohexyl acrylate)

Electron spin resonance (ESR) was applied to estimate the segmental dynamics of poly(cyclohexyl methacrylate) (PCHMA) and poly(cyclohexyl acrylate) (PCHA) in their miscible blend. The PCHMA and PCHA chains were labeled with nitroxide radicals, and the temperature-dependent ESR spectra of the spin-labels selectively reflected the segmental dynamics of the labeled chains in the blend. The ESR result showed different mobility between PCHMA and PCHA chains even though their blend showed a single glass transition in any composition by a calorimetric measurement. The WLF treatment demonstrated that a transition temperature, T 5.0mT, at which the extreme separation width due to 14 N anisotropic hyperfine splitting was 5.0 mT, reflected the glass transition observed at a frequency of the ESR. The T 5.0mT of poly(CHMA- random -CHA) was dependent on the composition; namely, the mobility of the spin-labels was sensitive to the composition around them. The self-concentration model suggested by Lodge and McLeish [Lodge, T. P.; McLeish, T. C. B. Macromolecules 2000, 33, 5278] was used to interpret the segmental dynamics of the PCHMA and PCHA in the blend estimated by the ESR. The Lodge−McLeish model provided the excellent prediction of the segmental dynamics of the PCHMA in the blend. The segmental dynamics of the PCHA chain in the blend was also explained well by the Lodge−McLeish model although the experimental values were slightly higher than the predicted ones. The mobility of the nitroxides labeled to the PCHA chains might be restricted by the rigid PCHMA component in the blend. These results imply that the dimension of a region observed by the ESR method is comparable to the cube of the Kuhn length suggested by Lodge and McLeish.