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Updated: Jul 12, 2026

Visualizing Single Molecular Complexes In Vivo Using Advanced Fluorescence Microscopy
Published on: September 8, 2009
The glass transition time scale and configurational entropy in polymers: an experimental molecular view
J E Wolak1, X Jia, Jeffery L White
1Department of Chemistry, North Carolina State University, Campus Box 8204, Raleigh, North Carolina 27695-8204, USA.
Abstract:
We report direct experimental observation of local conformational dynamics in a polymer chain at the calorimetric glass transition temperature Tg. Variable-temperature two-dimensional (2D) solid-state exchange NMR, at natural abundance, reveals segmental dynamics in pure polyisobutylene (PIB) occurring on a time scale of several seconds over the Tg range observed by DSC (203-208 K). To our knowledge, this is the first direct observation of molecular-level conformer interchange (trans-trans/trans-gauche/gauche-gauche) at the caloric glass transition temperature. Our results provide a chronologically accurate and pedagogically advantageous demonstration of molecular processes during a polymer phase transition, relative to traditional bulk mechanical and calorimetric techniques. More importantly, we use a miscible blend to demonstrate a general strategy for quantitative evaluation of configurational entropy changes via combination of temperature-dependent 2D exchange NMR and Adams-Gibbs theory. Our results on the Tg time scale are directly relevant to fundamental understanding of the Tg length scale, i.e., the dimension of cooperatively rearranging regions.
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