Linking Density Measurements

Cross-Link Density. Cross-link density measurements were determined on samples swollen to equilibrium in toluene after 24 h. Five specimens were tested for each sample. The volume fraction... 

A cured epoxy synthesised from a mixture of the diglycidyl ether of bisphenol A (DGEBA) and 1,3-phenylenediamine was studied by NMR spectroscopy including multiple pulse techniques and spin-lattice relaxation in the rotating frame. Tip. The study [28] focused on the water distribution based upon possible variation in the cross-link density measured by spin diffusion. From the analysis involving a combination of Tip and multiple... 

The reactivity of EPTMs in radical curing, predicted by these calculations, has been confirmed directly by cross-linking density measurements (Table 11) also carried out on EPM and some EPDMs vulcanized with dicumyl peroxide at 145 °C. 

The apparent structural parameters of the three-dimensional networks are presented in Table 3. Cross-link density analysis showed that vulcanizates contained both ionic bonds and covalent bonds. As we expected, addition of co-agents led to an increase of cross-Unk density (vj) of vulcanizates. The highest value was obtained for the sample containing acrylic acid and zinc oxide (7.55 10 mol/cm ) in contrary to the sample without co-agents (4.77 10 mol/ cm ). Thus, also the cross-link efficiency increased. It was foimd that non-covalent bonds are formed in the network structure and then break under the influence of ammonia vapoms. It reveals in a decrease of cross-link density measured on the basis of equilibrium swelling in toluene and ammonia vapours (vt+a)-... 

Vt- cross-link density measured on the basis of equilibrium swelling in toluene... 

Vt+a" cross-link density measured on the basis of equilibrium swelling in toluene and ammonia vapours Av/vt- non-covalent bonds content E- cross-link efficiency... 

Table 21.1 shows the recipe for obtaining NR specimen without filler. The specimen was cured at 145°C for 30 min. The cross-link density was measured by allowing it to swell in toluene and calculated to be 1.47 X 10 mol cm using the Flory-Rehner equation. The average number of... 

The rate of 7-radiation-induced cross-linking in the crystalline and amorphous regions of a crystallizable polychloroprene has been measured by Makhlis et al. [75] who have found a considerably lower cross-link density and less degradation in the crystalline portion of the rubber. The cross-links have been posmlated to be mainly intramolecular in crystalline regions and intermolecular in the amorphous phases. 

Determination of cross-link density from compression experiments is perhaps the most effective means of determining cross-link density as long as samples of the appropriate geometry can be prepared. When a hydrogel is subjected to an external force, it undergoes elastic deformation which can be related to the effective cross-link density of the network [63,99], Here the measurements made to extract cross-link density from polymer deformation are briefly discussed. 

The absorption of moisture critically affects other important resin properties, particularly those associated with low-dielectric and thermomechanical applications. Results of a 96-h boiling water immersion test are presented in Table 2.2. The moisture absorbed decreased substantially with fluoromethylene chain length from n = 3 to n = 6, followed by only modest decreases for n = 8 and 10. This latter behavior was somewhat unexpected and may be the effect of decreased cross-link density counteracting the increased fluorine content. These 100°C measurements are just above the glass transition and the situation may be different at room temperature. These measurements are in progress. 

Cross-link density, 10 415-416, 417-418 direct measurement of, 10 426 427 Cross-linked copolymers, 7 6 lOt Cross-linked high amylose starch, 13 742 Cross-linked hydrogels, 13 729-730 Cross-linked polymers, internal stresses and, 10 423 424 Cross-linked starches, 4 721 Cross-linked thermoset polymer structure, 10 418... 

Differing from the previous studies (5-7) where the parameters Goo, m, loay have been treated as constants, we find that they depend on cross-link density which is consistent with the measurements of Dickie and Ferry (4). Figure 5 shows the dependence of the viscoelastic relaxation on cross-link density. The solid curves are calculated from Equations 17, 19 and 20 by using a value of xq = 2.5 x 102 hrs at T = 25°C. Figure 5 resembles the corresponding figure in ref. 5. 

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