4.7 Article

Supramolecular Elastomers: Self-Assembling Star Blocks of Soft Polyisobutylene and Hard Oligo(β-alanine) Segments

期刊

MACROMOLECULES
卷 48, 期 4, 页码 1077-1086

出版社

AMER CHEMICAL SOC
DOI: 10.1021/ma502322n

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资金

  1. National Science Foundation of USA [CHE-1266442]
  2. University of Akron
  3. Ministry of Education, Culture, Sports, Science, and Technology of Japan [25102524]
  4. Direct For Mathematical & Physical Scien
  5. Division Of Chemistry [1266442] Funding Source: National Science Foundation
  6. Grants-in-Aid for Scientific Research [25102524] Funding Source: KAKEN

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A series of novel self-assembling star-blocks consisting of M-w = 29 000 g/mol 3-arm polyisobutylene (PIB) stars and oligo(beta-alanine) end segments were synthesized and characterized. Starblocks containing beta-alanine dimers are viscous liquids, while those with tri-, tetra-, and penta(beta-alanine)s are elastic solids. According to IR spectroscopy, the beta-alanine dimer is partially hydrogen-bonded, while the trimer, tetramer, and pentamer are fully hydrogen-bonded and form beta-sheets. DSC suggests crystalline beta-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(beta-alanine) segment. Transmission electron microscopy, wide-angle X-ray diffraction, and small-angle X-ray scattering of star-blocks containing tetra(beta-alanine) indicate stacks of hydrogen-bonded beta-sheets dispersed in a soft continuous PIB phase. The crystalline phases form fibrous lamellae with lengths up to similar to 200 nm, widths up to similar to 20 nm, and thicknesses of similar to 2 nm, which is the length of beta-alanine tetramer. Although the oligo(beta-alanine) contents are very low (from 1.5 to 3.6 wt % in the series), the static and dynamic mechanical properties of the starblocks are very different. The elastic moduli of the TPEs increase 5-fold with increasing beta-alanine content. Evidently, the oligo(beta-alanine) domains provide not only physical cross-links but also act as fillers.

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