Eur. Phys. J. E (2006) 20: 441-448
https://doi.org/10.1140/epje/i2006-10034-0

Regular Article

Molecular-weight dependence of the glass transition temperature of freely-standing poly(methyl methacrylate) films

Department of Physics and the Guelph-Waterloo Physics Institute, University of Guelph, N1G 2W1, Guelph, Ontario, Canada

^* e-mail: dutcher@physics.uoguelph.ca

Received: 17 May 2006
Accepted: 9 August 2006
Published online: 7 September 2006

Abstract

We have used transmission ellipsometry to measure the glass transition temperature, T_g, of freely-standing films of atactic and syndiotactic poly(methyl methacrylate) (PMMA). We have prepared films with different molecular weights, MW, (159×10³ < M _w < 1.3×10⁶) and film thicknesses, h, ( 30nm < h < 200 nm). For the high-MW ( M _w > 509×10³) atactic PMMA films, we find that T_g decreases linearly with decreasing h, which is qualitatively similar to previous results obtained for high-MW freely-standing polystyrene (PS) films. However, the overall magnitude of the T_g reduction is much less (by roughly a factor of three) for the high-MW freely-standing PMMA films than for freely-standing PS films of comparable MW and h. The observed differences between the freely-standing PMMA and PS film data suggest that differences in chemical structure determine the magnitude of the T_g reduction and we discuss the possible origins of these differences. Our analysis of the MW-dependence of the T_g reductions suggests that the mechanism responsible for the MW-dependent T_g reductions observed in the high-MW freely-standing films is different than that responsible for the MW-independent T_g reductions observed in the low-MW freely-standing and supported films.