RELAXATION PROCESSES IN A POLY(CYCLOHEXYL METHACRYLATE) ADDITIVE SYSTEM AS STUDIED BY PHOTON-CORRELATION, DIELECTRIC-RELAXATION, AND MECHANICAL RELAXATION SPECTROSCOPY

Dynamic light scattering (PCS), mechanical relaxation (MR), and dielectric (DR) relaxation techniques are employed to examine the effect of the additive di(2-ethylhexyl) phthalate (DOP) on the primary and secondary relaxations of high molecular weight poly(cyclohexyl methacrylate) (PCHMA) in the glassy and rubbery states within the temperature range 133-430 K and with DOP content up to 15%. The results indicate that the primary (alpha) glass-rubber relaxation is shifted to lower temperatures with increasing DOP content, and the width of the distribution of relaxation times is insensitive to composition variations. When the same data analysis is employed, an agreement between PCS and MR results is observed, whereas the interrelation of the primary relaxation times from PCS and DR measurements on plasticized PCHMA is subject to some uncertainties in the description of the dipole autocorrelation functions with increasing DOP composition. The average primary relaxation times exhibit a strong temperature dependence, and when the same data analysis is employed, we found a quantitative agreement between PCS and MR times, whereas the agreement between PCS and DR times was rather semiquantitative. Sub-T(g) or beta-relaxation was enchanced with additive content in contrast to the gamma-relaxation associated with the chair-to-chair inversion of the cyclohexyl ring. The latter relaxation times exhibit an Arrhenius temperature dependence with activation parameters independent of the additive content and of the technique used. The secondary (gamma) intensity suppression effect, reported in some polymer/additive systems, was not observed in the PCHMA/DOP system.