期刊
JOURNAL OF POLYMER SCIENCE PART B-POLYMER PHYSICS
卷 46, 期 13, 页码 1390-1399出版社
WILEY
DOI: 10.1002/polb.21473
关键词
dielectric relaxation; fragility; glass transition; light scattering; mechanical spectroscopy; polyisobutylene; Raman spectroscopy; structure-property relationship
The influence of molecular weight, M, on the fragility and fast dynamics in polyisobutylene (PIB) was studied using dielectric and mechanical relaxation spectroscopies, calorimetry, and Raman spectroscopy. The measurements indicate a decrease in fragility with increasing M for shorter chains, in the range of M where T-g is M-dependent. Such behavior is not observed for other polymers and is at odds with traditional theoretical models that predict an increase in fragility with chain length. These results confirm the unusual character of PlB, as evident in various properties including extremely low gas permeability, a low fragility, and a segmental relaxation spectrum much broader than expected for a low-fragility material. The reason for this anomalous behavior remains unclear, but might be related to the symmetric structure of the PIB repeat unit, together with comparable flexibility of both structural components, the backbone and side groups. (C) 2008 Wiley Periodicals, Inc.
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