Cross-linking density, characterization

In addition to the above techniques, inverse gas chromatography, swelling experiments, tensile tests, mechanical analyses, and small-angle neutron scattering have been used to determine the cross-link density of cured networks (240—245). Si soHd-state nmr and chemical degradation methods have been used to characterize cured networks stmcturaHy (246). H- and H-nmr and spin echo experiments have been used to study the dynamics of cured sihcone networks (247—250). 

Cross-link density and parameters relating to the network structure can be measured by NMR by analysis of the transverse relaxation decay (cf. Section 1.3) and the longitudinal relaxation in the rotating frame [67]. Combined with spatial resolution, the model-based analysis of relaxation yields maps of cross-link density and related parameters [68]. Often the statistical distribution of relaxation parameters over all pixels provides a reduced data set with sufficient information for sample characterization and discrimination [68]. 

In this paper the recently developed techniques to characterize the mar resistance of coating systems were presented. The techniques base on methods that create a single scratch onto a surface. Characteristic values like the critical load as a measure for the transition from plastic behaviour to brittle fracture can be determined and used to rank different clearcoat systems and to compare these results with other physical properties. In the field of mar resistance the cross-linking density of the... 

These relationships are commonly employed to determine Me in characterization studies of nonresponsive and responsive hydrogel preparations where the response does not lead to a change in cross-link density. 

The fatty acid residues of ESO triglycerides are flexible, and steric hindrance has little or no effect on the reactivity of the epoxy groups. ESO rubbers with diamines are therefore characterized by a higher cross-link density and polarity. 

It is seen in the figures that the magnetoelast shows ideal mechanical behavior in the studied deformation range. Similar ideal mechanical behavior was observed for other magneto elasts characterized by different cross-linking densities and different amount of fillers dispersed randomly in the elastic matrix. It has to be mentioned that within the experimental accuracy (5%) no hysteresis has been found. 

The aim of an investigation determines the method to obtain contrast " in NMR. Let us consider the case of evaluating the distribution of cross-linking density inside a network. By classical mechanical measurements, e.g., compression or stress-strain experiments, we can calculate a cross-linking density, which represents a mean value over the sample volume we used in measurements. NMR enables the characterization on a microscopic level if we can investigate the properties of network chains at different sample positions. 

Cross-link densities were characterized above T by equilibrium modulus measurements employing rubber elasticity theory. The results indicate that this method yields surprisingly reasonable values. 

Epoxy thermosets are typical densely cross-linked polymer materials. They are used in a wide variety of practical applications and thus have been studied extensively. However, the quantitative dependence of physical properties, such as strength, stiffness, and fracture toughness, on network microstructure are largely undetermined. This can be attributed, in part, to the lack of adequate techniques for characterizing densely cross-linked network structure. Several microstructiu e variables that have been studied with some success are (1) cross-link density,... 

This paper presents characterization studies performed on amine cured epoxy resins. Particular emphasis is placed on the characterization of the cross-link density, and on its influence on physical properties, especially the fracture toughness. 

Amine light stabilizer, melamlne-acryllo copolymer degradation, 281-83 Amine-cured epoxy networks cross-link density, 166-67,177-81 structure characterization, 172-73... 

Characterizing cross-linked networks according to molar mass is unrealistic in regard to their infinite size. Such cross-linked networks are classified according to the network chain length, kind of cross-link, and cross-link density. Here a cross-link point is defined as a group from which more than two network chains extend. A network chain corresponds to that portion of the chain which joins two cross-link points together. 

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