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Structure and Dynamics of Syndiotactic Poly(n-Butyl Methacrylate) Near the Glass Transition

Published online by Cambridge University Press:  16 February 2011

G. D. Paiterson ,
P. K. Jue  and
J. R. Stevens
G. D. Paiterson
Affiliation:
Department of Chemistry, Carnegie Mellon University, Pittsburgh, PA 15213
P. K. Jue
Affiliation:
Department of Chemistry, Colgate University, Hamilton, NY 13346
J. R. Stevens
Affiliation:
Department of Physics, University of Guelph, Guelph, ON, Canada N1G2W1
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Abstract

An optically homogeneous sample of highly syndiotactic poly(n-butyl methacrylate) (PBMA) has been prepared. The glass transition temperature was observed to be Tg=55C. Measurements of the scattered intensity of the sample followed the expected behavior for a pure liquid above Tg. The intensity rose as the sample was cooled further towards the glass transition temperature for atactic PBMA. These results illuminate the importance of regions of different stereoisomers in methacrylate polymers. Measurements of the Rayleigh- Brillouin spectrum were carried out from -15 to 130 C. The ratio of the the central peak intensity to the Brillouin intensities at temperatures above Tg was consistent with a viscoelastic liquid and had a magnitude near 3. The Brillouin linewidth remained large near Tg. and decreased continuosly with no apparent change in slope in the glass transition region. The presence and importance of rapid motions in polymers near the glass transistion is demonstrated by these results. Slowly relaxing density fluctuations near Tg. were measured by photon correlation spectroscopy. Relaxation functions were obtained from 10−6 to 10 s. Average relaxation times <τ> were obtained from the integral of the relaxation function and were found to follow the relation <τ>=Aexp(B/(T−T0)), where for our sample B=2940K and T0=273K. The observed relaxation function decayed over a wider time range as the sample was cooled. Quantitative analysis of this effect using the Williams-Watts empirical function yielded a decrease in β from 0.35 at 90 C to 0.18 at 65 C. The relaxation functions were also analyzed to give a distribution of relaxation rates. The observed distributions were bimodal at 70 and 80 C. The two features behaved in a manner consistent with the primary and secondary relaxations observed for methacrylate polymers by other techniques.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 215: Symposium R2 – Structure, Relaxation and Physical Aging of Glassy Polymers , 1990 , 37
Copyright
Copyright © Materials Research Society 1991

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