Supramolecular Elastomers: Self-Assembling Star鈥揃locks of Soft Polyisobutylene and Hard Oligo(尾-alanine) Segments

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• 作者：Joseph Scavuzzo ; Shogo Tomita ; Shiwang Cheng ; Hao Liu ; Min Gao ; Joseph P. Kennedy ; Shinichi Sakurai ; Stephen Z. D. Cheng ; Li Jia
• 刊名：Macromolecules
• 出版年：2015
• 出版时间：February 24, 2015
• 年：2015
• 卷：48
• 期：4
• 页码：1077-1086
• 全文大小：582K
• ISSN：1520-5835

文摘

A series of novel self-assembling star-blocks consisting of M_w = 29鈥?00 g/mol 3-arm polyisobutylene (PIB) stars and oligo(尾-alanine) end segments were synthesized and characterized. Star鈥揵locks containing 尾-alanine dimers are viscous liquids, while those with tri-, tetra-, and penta(尾-alanine)s are elastic solids. According to IR spectroscopy, the 尾-alanine dimer is partially hydrogen-bonded, while the trimer, tetramer, and pentamer are fully hydrogen-bonded and form 尾-sheets. DSC suggests crystalline 尾-alanine trimer tetramer and pentamer domains phase separated from the rubbery PIB. The melting temperature of the crystalline domains increases with the length of the oligo(尾-alanine) segment. Transmission electron microscopy, wide-angle X-ray diffraction, and small-angle X-ray scattering of star-blocks containing tetra(尾-alanine) indicate stacks of hydrogen-bonded 尾-sheets dispersed in a soft continuous PIB phase. The crystalline phases form fibrous lamellae with lengths up to 鈭?00 nm, widths up to 鈭?0 nm, and thicknesses of 鈭? nm, which is the length of 尾-alanine tetramer. Although the oligo(尾-alanine) contents are very low (from 1.5 to 3.6 wt % in the series), the static and dynamic mechanical properties of the star鈥揵locks are very different. The elastic moduli of the TPEs increase 5-fold with increasing 尾-alanine content. Evidently, the oligo(尾-alanine) domains provide not only physical cross-links but also act as fillers.