Effect of Topological Constraint and Confined Motions on the Viscoelasticity of Polyrotaxane Glass with Different Interactions between Rings
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- 作者：Kazuaki KatoTomoki Mizusawa ; Hideaki Yokoyama ; Kohzo Ito
- 刊名：Journal of Physical Chemistry C
- 出版年：2017
- 出版时间：January 26, 2017
- 年：2017
- 卷：121
- 期：3
- 页码：1861-1869
- 全文大小：568K
- ISSN：1932-7455
文摘
A series of polyrotaxane glasses composed of poly(ethylene glycol) backbones and threaded α-cyclodextrins (α-CDs) with different substituents were found to exhibit unique viscoelasticities attributed to their interlocked structures, beyond a mere miscible blend of the different components. Differences in the interactions between CDs, which occupied 80 wt % or more of the materials, brought about wide variations in the glass transition temperature and also influenced the cooperativity of segmental motions of the polyrotaxanes near Tg. These polyrotaxane melts typically showed negligible cooperativity compared to conventional polymers, behaving as so-called “strong” glass formers. The cooperativity gradually emerged with increasing interaction strength between CDs, and elimination of the threading polymer resulted in “fragile” glass formers. These results suggest that the cooperative motion can be shielded by the topological constraint of the threading polymer, whereas the increasing dominance of conventional interactions between CDs develops unavoidable cooperativity. Strong secondary relaxation was observed for all of the polyrotaxane glass samples, and they exhibited considerably higher activation energies than glass made of CD alone. The common secondary relaxation dynamics insensitive to the substituents on the CDs indicate large-scale motion of minor backbone polymers under confinement by similar frozen CD frameworks in the glass state.