Reflection crosslinking

The gel time of a 2000 ppm Flocon 4800 (a Pfizer xanthan polymer) in 2% NaCl solution was measured with various Cr(III) crosslinkers at room temperature (Table II). In this series of experiments Cr(III) concentration was 90 ppm. The most reactive Cr(III) species were dates derived from Cr(N0 )g with one and two equivalents of NaOH. Gels formed within 5 minutes and the reaction rate appeared to be diffusion-controlled. Cr(N03)3 without NaOH required 48 hours to gel the polymer solution. This reflects the time needed to hydrolyze CrCNOg) in Equation 3. 

X-ray diffraction pictures taken with a flat-film camera show that crosslinked SE-BR samples crystallize on stretching. Sharp reflections are observed at an extension ratio of 4 1 (Figure 4). With samples having different degrees of stereoregularity the order for increasing strain-induced crystallization is the same as the order for the rate of low temperature crystallization. 

The phantom network behaviour corresponding to volumeless chains which can freely interpenetrate one through the other and thus to unrestricted fluctuations of crosslinks should be approached in swollen systems or at high strains (proportionality to the Mooney-Rivlin constant C-j). For suppressed fluctuations of crosslinks, which then are displaced affinely with the strain, A for the small-strain modulus (equal to C1+C2) approaches unity. This situation should be characteristic of bulk systems. The constraints arising from interchain interactions important at low strains should be reflected in an increase of Aabove the phantom value and no extra Gee contribution to the modulus is necessary. The upper limit of the predicted equilibrium modulus corresponds therefore, A = 1. 

The formation of crosslinks in silk fibroin increases the tenacity and resistance to deformation of the fibres, as reflected in the initial modulus and the yield point. This protective effect conferred by fixation of the bifunctional dye Cl Reactive Red 194 was not shown by the monofunctional Orange 16, which is unable to form crosslinks. The loss in tenacity of undyed silk that is observed on treatment at 90 °C and pH 7 for 2 hours is attributable to lowering of the degree of polymerisation (DP) by hydrolysis of peptide bonds. The crosslinking action of bifunctional dyes tends to compensate for this loss in DP and provides an intermolecular network that helps to maintain the physical integrity of the fibre structure [124] ... 

The response of crosslinkers 1-4 to pTSA catalysis as a function of acid concentration is shown in Figure 2 for a 75°C/1 minute softbake and 105°C/1 minute hardbake cycle. The concentration of acid required to crosslink these films to a given LP is an indication of the relative resist sensitivities, while the steepness of the LP curves reflects resist contrast. Crosslinkers 3 and 4 are about twice as sensitive to pTSA catalysis as 1, while 2 requires a higher concentration of pTSA for crosslinking. Furthermore, the steepness of the curve for 3 suggests that it would show higher contrast in a resist formulation. 

These absorptions may reflect the degree of crosslinking and/or the degree of degradation which is proportional to the amount of residual free radicals. The relative absorptions per thickness at 10.6 pm are plotted against the discharge frequency as shown in Fig. 5. The absorptions near 10 pm of the film formed in region HL... 

Thus, the effect of introducing flexible crosslinked units into DAP resins was reflected in the improved flexibility. In particular, PEGBAP having a long-chain glycol unit showed a remarkable effect ... 

We have prepared a synthetic protein polymer based on repeat sequence Lys-25 to investigate the effect of uniformity of crosslink placement on the physical properties of a polymer hydrogel (Figure 1). The design of Lys-25 reflects two essential structural requirements for formation of polymer hydrogels (1) a flexible, hydrated (polyamide) backbone and... 

The plastic deformation in several amine and anhydride cured epoxy resins has been studied. The experimental results have been reasonably interpreted by the Argon theory. The molecular parameters determined from the data based on the theory reflect the different molecular structures of the resins studied. However, these parameters are in similar enough range to also show the structural similarity in these DGEBA based systems. In general, the mechanisms of plastic deformation in epoxy resins below T are essentially identical to those in amorphouE thermoplastics. The yield stress level being related to the modulus that controls the intermolecular energy due to molecular deformation will, however, be affected by the crosslinks in the thermosets. 

Atomic force microscopy and attenuated total reflection infrared spectroscopy were used to study the changes occurring in the micromorphology of a single strut of flexible polyurethane foam. A mathematical model of the deformation and orientation in the rubbery phase, but which takes account of the harder domains, is presented which may be successfully used to predict the shapes of the stress-strain curves for solid polyurethane elastomers with different hard phase contents. It may also be used for low density polyethylene at different temperatures. Yield and rubber crosslink density are given as explanations of departure from ideal elastic behaviour. 17 refs. 

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