Time-Resolved Luminescence Anisotropy Studies of the Relaxation Behavior of Polymers. 1. Intramolecular Segmental Relaxation of Poly(methyl methacrylate) and Poly(methyl acrylate) in Dilute Solutions in Dichloromethane

• Published in: Macromolecules Vol. 29; no. 14; pp. 4931 - 4936
• Main Authors: Soutar, Ian, Swanson, Linda, Christensen, Ronald L, Drake, Rodney C, Phillips, David
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 01.07.1996
• Subjects: Applied sciences; Exact sciences and technology; Organic polymers; Physicochemistry of polymers; Properties and characterization; Solution and gel properties; Organic solution; Dilute solution; Methyl methacrylate polymer; Experimental study; Segmental movement; Molecular relaxation; Activation energy; Methyl acrylate polymer; Fluorescence spectrometry
• ISSN: 0024-9297; 1520-5835
• DOI: 10.1021/ma951671y

The intramolecular segmental relaxation behaviors of poly(methyl methacrylate) (PMMA) and poly(methyl acrylate) (PMA) in dilute dichloromethane solutions have been studied using time-resolved fluorescence anisotropy measurements (TRAMS). TRAMS have been made on two different spectrometers, incorporating a picosecond laser source and synchrotron, respectively, as excitation sources. Excellent agreement was achieved between the resultant relaxation data, generating confidence both in the spectroscopic procedures involved and in the various forms of analytical data retrieval applied. The relaxation characteristics of each polymer, over the temperature range 230−310 K, was adequately described by an exponential model for the anisotropy, for both acenaphthylene- and 1-vinylnaphthalene-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 kJ mol-1 for PMMA and PMA, respectively, in dichloromethane. These values are considerably reduced compared to those which have been reported for either polymer in other solvents. The differences in activation parameters are too great to be explained on the assumption that the solvents 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 the macromolecular dynamics might experience specific interactions with the dichloromethane which distort the apparent behavior of the polymer.