Elastomeric mechanism

The individual fibres of an elastomeric fabric must be completely covered with a thin film of an elastic material without any fibre-to-fibre bonding. The film causes a high degree of recovery from deformations owing to its particular structure of widely spaced crosslinks. 

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Uny et also reported the chemical synthesis of protein polymers based on the (Val-Pro- Ala-Val-Gly) repeat sequence in which glycine is replaced by the D-alanine residue. The hetero-chiral Pro- Ala diad would be erqrected on the basis of stereochemical considerations to adopt a type-II p-tum conformation. Stmctural analyses of small-molecule "Pro- Ala turn models support the formation of the type-II p-mm conformation in solution and the solid state. Polymers based on the (Val-Pro- Ala-Val-Gly) repeat sequence display a thermo-reversible phase transition similar to the corresponding polypeptides derived from the parent (Val-Pro-Gly-Val-Gly) sequence, albeit with a shift of the Tt to approximately 5-10 ° G below the latter due to a slight inaease in hydrophobic character due to the presence of the alanine residue. NMR spectroscopic analyses of the (Val-Pro- Ala-Val-Gly) polymer suggest that the repeat unit retains the p-tum stmcture on the basis of comparison to the corresponding behavior of the (Val-Pro-Gly-Val-Gly) polymer. Stress-strain measurements on cross-linked matrices of the (Val-Pro- Ala-Val-Gly) polymer indicate an elastomeric mechanical response in which the elastic modulus does value in comparison to the (Val-Pro-Gly-Val-Gly) polymer. These smdies of glycine suhstitution support the hypothesis that type-II p-tum formation can he associated with the development of elastomeric behavior with native elastins and elastin-derived polypeptide sequences. Several investigators have proposed that the (Val-Pro-Gly-Val-Gly) pentapeptide represents the minimal viscoelastic unit... 

One of the unique characteristics of AA-PEA hbers is their elastomeric mechanical behavior, similar to Spandex and natural rubber materials, enabling them to be stretched to several times their length. Figure 11.5 shows the breaking stress and strain of one type of Phe-based PEA monohl-ament hbers, which support their elastomeric behavior. The AA-PEA-based... 

For the last two decades, interest in the polymerization of 1,3-disilacyclobutanes has shifted to the applied research due to high elastomeric, mechanical, and thermostable characteristics of polysilmethylenes and -trimethylenes [71, 72], These polycarbosilanes are also of interest as precursors for production of photoresists and Si-C-ceramics [71, 72], Therefore, many papers and patents have been devoted to the elaboration of effective methods of polymer syntheses. For example, traditional thermal initiation was used in the case of 1,3-dimethyl-1,3-diphenyl-... 

Cured fluoroelastomers can withstand prolonged exposure to high temperatures and retain their elastomeric, mechanical, chemical, and electrical properties better than other elastomers. Continuous service at 450 F is common intermittent exposure at 600 F is possible. Although resistance to compression set is excellent at 400-450 F, low temperature properties (including compression set) are poor, compared to silicones and fluorosilicones. 

There is interest in tailor making model oligomers of the hard and soft segments of thermoplastic elastomers because it is desirable to control the combined thermoplastic processing properties and elastomeric mechanical properties of the materials, especially as they are influenced by chain length distributions. Model urethane hard segment oligomers from 1,4-butanediol and 4,4 -methylenebis(phenyl isocyanate) (MDI) (can form H bonds) (15), and from 1,4-butanediol and... 

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