TIME-RESOLVED LUMINESCENCE ANISOTROPY STUDIES OF THE RELAXATION BEHAVIOR OF POLYMERS .1. INTRAMOLECULAR SEGMENTAL RELAXATION OF POLY(METHYLMETHACRYLATE) AND POLY(METHYL ACRYLATE) IN DILUTE-SOLUTIONS IN DICHLOROMETHANE

The intramolecular segmental relaxation behaviors of poly(methyl metha crylate) (PMMA) and poly(methyl acrylate) (PMA) in dilute dichlorometh ane solutions have been studied using time-resolved fluorescence aniso tropy measurements (TRAMS). TRAMS have been made on two different spec trometers, incorporating a picosecond laser source and synchrotron, re spectively, as excitation sources. Excellent agreement was achieved be tween the resultant relaxation data, generating confidence both in the spectroscopic procedures involved and in the various forms of analyti cal data retrieval applied. The relaxation characteristics of each pol ymer, over the temperature range 230-310 K, was adequately described b y an exponential model for the anisotropy, for both acenaphthylene- an d 1-vinylnapthalene-based labels. The associated correlation times for segmental motion exhibited an Arrhenius dependence in the temperature range studied, giving activation energies of the order of 14 and 11 k J mol(-1) for PMMA and PMA, respectively, in dichloromethane. These va lues are considerably reduced compared to those which have been report ed for either polymer in other solvents. The differences in activation parameters are too great to be explained on the assumption that the s olvents function to provide frictional resistance alone to the polymer dynamics. It is tentatively suggested that both PMMA and PMA exhibit specific interactions with dichloromethane and/or other solvents, such as toluene. Alternatively; the naphthyl labels used to interrogate th e macromolecular dynamics might experience specific interactions with the dichloromethane which distort the apparent behavior of the polymer .