Dynamic
covalent bonds (DCBs), which can undergo reversible cleavage
and reformation upon exposure to readily useable stimuli, have attracted
dramatic attention, but the library of such bonds still remains to
be developed. Herein, we report molecular structures, dynamic behaviors,
and healability of bis(2,2,6,6-tetramethylpiperidin-1-yl)trisulfide
(BITEMPS-S3) to compare with its disulfide analogue (BITEMPS-S2) exchanged
at moderate temperature. Unsymmetrical cleavage of trisulfide linkage
induced relatively rapid disproportionation to di- and tetrasulfide
derivatives. In the bulk, poly(hexyl methacrylate) networks partially
containing the BITEMPS-S3 moiety as a cross-linking point afforded
nearly quantitative damage healability only by simple hot pressing
at 110 °C under mild pressure. A slightly higher healability
of BITEMPS-S2 compared to that of BITEMPS-S3 would be due to the differences
in the chain-transfer reaction for the trisulfide linkage during free-radical
polymerization rather than thermal exchangeability of the BITEMPS-S3
moiety. Therefore, not only BITEMPS-S2 but also BITEMPS-S3 should
be regarded as one of DCBs triggered upon exposure to mild external
stimuli.
This paper describes the synthesis of highly sterically hindered piperidinyl trisulfide with four spirocyclohexyl moieties, bis(2,6-bis[spirocyclohexyl]piperidine-1-yl)trisulfide (BIBSCPS-S3), from commercially available starting materials in short steps and its application as a...
Although micro-Raman spectroscopy is a useful method as a strain probe with high spatial resolution, this method can not be applied to certain isotropic materials, such as less oriented polymers. To overcome the limitation diacetylene-containing copolymers, which were shown to have Raman band shift with tensile strain, were coated on substrates as an optical strain gage. In this study, diacetylene-containing copolyurethanes were prepared from new compositions by employing polycaprolactone instead of poly(propylene glycol). A solution of the copolymer was coated onto a single filament of an aramid fiber and cross-polymerized by heat treatment. And then, Raman spectra from the coating and the fiber substrate at the same point were measured simultaneously during a tensile test. The Raman frequency of the carbon triple bond (C ≡ C) in the cross-polymerized polymer coated on the fiber was found to follow closely the local strain of the fiber substrate. The Raman frequency of the coated polymer shifted with strain at a rate of −6.6cm −1 /% and held an approximate linear relationship up to 2% strain. Both of the shifting rate and the linear range were improved by replacing ether bonds with ester bonds in the copolyurethanes used as matrices.
Investigations of distribution of the carbon carbon triple bond in the moldings were carried out by measurement of Raman spectra. The moldings were prepared by reactive processing of poly (ε caprolactone) (PCL) , bis (4 hydroxymethylphenyl) acetylene(SU)and multifunctional isocyanates (MFI) . The signal derived from SU was changed by the addition method of MFI. When the moldings were prepared without MFI, aggregation of SU to the surface of the molding was observed. The moldings prepared by simultaneous addition of MFI, SU, and PCL showed good dispersibility of SU. In contrast, when the moldings were prepared by addition of prepolymer(synthesized by reaction between MFI and SU)to PCL, heterogeneous distribution of SU which seems to come from aggregation between prepolymers was observed. In addition, the intensity of SU signal in the moldings was not changed by microtome treatment when MFI was used. These results suggested that the distribution of the functional additive in the molding depended on the molding method.
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