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Details van artikel 18 van 63 gevonden artikelen
| Titel: |
Gelation and dynamic mechanical behavior of liquid crystalline networks |
| Auteur: |
Valentova, H. Bouchal, K. Nedbal, J. Ilavsky, M. |
| Verschenen in: |
Journal of macromolecular science. Part B, Physics |
| Paginering: | Jaargang 38 (1999) nr. 1-2 pagina's 51-66 |
| Jaar: |
1999-01-01 |
| Inhoud: |
The dynamic mechanical behavior of polyurethane networks based on liquid crystalline (LC) diol, 6,6'-[ethylenebis(1,4-phenyleneoxy)]dihexanol (D), 2(4)-methyl-1,3-phenylene diisocyanate (DI), and poly(oxypropylene)triol (T) at the stoichiometric molar ratio of isocyanate (NCO) and hydroxy (OH) groups was studied. Samples were prepared at various initial molar ratios of the reactive groups [OH]T/[NCO]DI/[OH]D from 1/1/0 to 1/40/39. The gelation studies during the curing reaction in the LC and isotropic states showed that the critical gel structure at the sougel transition exhibits a power-law mechanical behavior; the relaxation exponent in the LC state is always higher than that in the isotropic state. From viscoelastic results, it follows that formation of the LC mesophase enhances the connectivity of the molecular structure at the gel point. Introduction of chemical cross-links in fully cured networks reduces the flexibility of the elastically active network chains (EANCs) and inhibits conformational arrangements required for LC ordering. Increasing the content of LC diol in networks, which leads to an increase of the length of EANCs, increases the concentration of permanent physical interactions (trapped entanglements) in the systems; the intensity of the slow relaxation process in the rubbery region also increases. |
| Uitgever: |
Taylor & Francis |
| Bronbestand: |
Elektronische Wetenschappelijke Tijdschriften |
Details van artikel 18 van 63 gevonden artikelen
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