Strain Induced Crystallization in Stereoregular Poly[Methyl(3,3,3-Trifluoropropyl) Siloxane] Networks
| Autor: | John C. Saam, Robert L. Miller, Chung-Mien Kuo, Kevin P. Battjes |
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| Rok vydání: | 1997 |
| Předmět: | |
| Zdroj: | Rubber Chemistry and Technology. 70:769-780 |
| ISSN: | 1943-4804 0035-9475 |
| DOI: | 10.5254/1.3538459 |
| Popis: | Elastomeric networks based on poly[methyl(3,3,3-trifluoropropyl)siloxane] having a minimum level of stereo-regularity crystallize and self-reinforce when stretched at room temperature. The effect is especially pronounced in networks where the cross-links are uniformly spaced. The polymers are made by modification of a recently described anionic ring opening copolymerization of prescribed mixtures of cis- and trans-1,3,5-trimethyl-1,3,5-tris (3′, 3′, 3′-trifluoropropyl) cyclotrisiloxane. This provides polymers enriched in stereoregularity with nearly monodisperse molecular weight distributions and reactive groups at the chain ends. The end-linked networks show markedly enhanced mechanical properties due to self-reinforcement from strain-induced crystallization. In addition to applied strain, self-reinforcement depends on temperature and the amount of stereoregularity introduced to the polymer. Strained specimens having high levels of stereoregularity and pre-existing crystallinity exhibit plastic flow and, upon release of the applied strain, stress-hardening. Wide angle X-ray scattering (WAXS) on strained specimens establishes that, although the relative degree of crystallinity varies, the basic crystal structure is unaltered by cross-linking, amount of strain, or amount of stereoregularity. Unit cell parameters from WAXS indicate a monoclinic crystal and suggest a 4*11 chain conformation. |
| Databáze: | OpenAIRE |
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