DYNAMICS IN CONCENTRATED-SOLUTIONS OF POLY(METHYL METHACRYLATE) BIS(2-ETHYLHEXYL PHTHALATE)

Photon correlation spectroscopy (PCS) and dielectric spectroscopy (DS) are employed to study the dynamics of density fluctuations at tempera tures above and below the glass transition temperature, T(g), and the dynamics of concentration fluctuations above T(g) in concentrated solu tions of poly(methyl methacrylate)/bis(2-ethylhexyl phthalate) (PMMA/D OP). The PCS measurements covered the temperature range between 252 an d 373 K, and the DS measurements were made between 200 and 398 K and i n the frequency range between 10(-2) and 10(5) Hz. Above T(g) the pola rized PCS correlation functions contain contributions from both densit y and concentration fluctuations for a range of temperatures. The conc entration fluctuations are characterized by a relatively narrow distri bution of relaxation times compared to the density fluctuations and di splay the usual q2-dependence. The dynamics of both processes conform to the Vogel-Fulcher-Tammann equation, and the coupling model of relax ation can explain their different temperature dependences. The alpha-r elaxation bifurcates into alpha- and beta-relaxations below T(g) which can be followed respectively by PCS and DS. The additive alters signi ficantly the dynamics of the alpha-relaxation and also has a small eff ect on the dynamics of the beta-relaxation which become faster. Increa sing plasticizer content enhances the dielectric beta-relaxation but w eakens the alpha-relaxation. At 20 % plasticizer content a single, alb eit broad, dielectric relaxation exists (beta-relaxation) which is due to the concerted motion of the polymer side group with the polar addi tive. Similarities with the internal plasticization of PMMA are discus sed.