Solvation dynamics in viscous polymer solution: Propylene carbonate confined by poly(methylmethacrylate)

Solvation dynamics of a triplet state probe is used to explore the dynamics of supercooled propylene carbonate (PC) when modified by the presence of poly(methyl methacrylate) (PMMA) in viscous polymer solution. In the PMMA weight fraction range 0 to 0.32, the relaxation time for dipolar solvation increases by a factor of approximately 1500, if evaluated at a constant temperature. This is equivalent to a shift of the PC glass-transition temperature Tg by +6.4 K as a result of geometrical restriction by the presence of 32 wt. % PMMA. In terms of the estimated average PC-PMMA distance, the relaxation time approaches the bulk value much more rapidly compared with size effects of confinement in porous glasses or microemulsion droplets. The interpretation of this feature is that a reduced PMMA concentration not only increases the average PC-PMMA distance, but also changes from a solid to a more open topology of the confining material. Accordingly, the slowest dynamics in these mixtures are not found near a single polymer chain, but only in the more concentrated polymer environments where a larger fraction of the cooperative volume is immobilized by macromolecules.