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

Abstract

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

SAXS Evaluation of Size Distribution for Nanoparticles

“…Jia et al [27] have recently evaluated thickness distribution of the hard segment domains for supramolecular elastomers (starblocks of soft polyisobutylene and hard oligo(β − alanine) segments). The molecule is a novel type of supramolecule as schematically shown in Figure 15 where the green chains are soft polyisobutylene.…”

“…Black dots are for the experimentally obtained SAXS profile, and red curve is the calculated SAXS profile. The inset shows the evaluated thickness distribution [27].…”

Towards a Supertough Thermoplastic Polyisoprene Elastomer Based on a Biomimic Strategy

“…[12][13][14][15][16][17] In particular, rare-earth catalyst systems gave high cis content and high incorporation ratio of polar monomers simultaneously. [19] And it is also reported that oligo-alanine formed b-sheet [20] is part of hard segment of silk, which is mechanically strong and thermally stable. Considering potential large-scale manufacturing in the future,arare-earth catalytic system Nd(VA) 3 /Al(i-Bu) 3 /Al(i-Bu) 2 Cl was adopted in this work (Supporting Information, Scheme S2), which has already been successfully utilized in the industrial field.…”

“…[19] And it is also reported that oligo-alanine formed b-sheet [20] is part of hard segment of silk, which is mechanically strong and thermally stable. [19] And it is also reported that oligo-alanine formed b-sheet [20] is part of hard segment of silk, which is mechanically strong and thermally stable.…”

“…Themolecular weights of two samples are high enough to ensure the mechanical properties.Then proper functional groups need be attached on polar sites to introduce reversible crosslinking.Inspired by the high strength and toughness of spider silk and also considering the non-miscibility between peptide and polyisoprene chain, it is envisioned that aggregation of oligopeptide could function as physical crosslinking without changing the elasticity of rubber owing to strong phase separation. [19] And it is also reported that oligo-alanine formed b-sheet [20] is part of hard segment of silk, which is mechanically strong and thermally stable. Therefore tetrapeptide (ala-ala-ala-ala) groups were attached on B-OH-PIP and R-OH-PIP to generate B-4A-PIP and R-4A-PIP.T he attachment of peptides on hydroxy groups is close to quantitative and their structures are characterized by 1 HNMR spectra (Supporting Information, Figures S8-S12).…”