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Elastomers structure determination

The technique of using the diffraction of X-rays to study the structure of fibres, plastics and elastomers, to determine the crystalline nature of such polymers, and to measure the particle size of finely divided materials. [Pg.72]

While the balance of evidence is therefore in favor of a cyclic formulation for all compounds (PNCU) except the elastomer, a direct crystal structure determination of the pentamer or higher polymer would be of great value. [Pg.369]

An important feature of polyurethane elastomers is that their elastomeric behaviour is highly sensitive to chemical and physical structure of the material, that are potentially under the control of the synthesist. For this advantage to be exploited more effectively, however, there is a need for deeper understanding of the mechanisms by which structure determines the properties of importance. [Pg.268]

The molecular structure determines the polymer properties. From the perspective of the application of polymers it can be differentiated into thermoplastics Qinear, branched), elastomers (slightly cross-linked, the chains between the connections are long, Tg is below room temperature), and thermosets (highly cross-linked, the chains between the connections are short, only a few monomer units, Tg is high) see Sect. 3.1. [Pg.23]

The use temperature of a polyolefin elastomer is determined by the range between the Tg and the Tm. These new OBCs have increased the use temperature range of olefin-based elastomers by > 40 ° C, enabling the introduction of these polymers to many new markets and applications where a polyolefin solution was previously unavailable. The extension of the tem-peramre plateau and network structure that is developed from the OBC s crystallinity translates to better high-temperature elastomeric properties for the OBCs. For example, the 70 °C... [Pg.731]

This book focuses on the relationships between the chemical structure and the related physical characteristics of plastics, which determine appropriate material selection, design, and processing of plastic parts. The book also contains an in-depth presentation of the structure-property relationships of a wide range of plastics, including thermoplastics, thermosets, elastomers, and blends. [Pg.418]

Today it is claimed that the surface fluorination of polymers using F2 gas mixtures enhances a wide range of properties, e.g., low permeability to nonpolar liquids4 improved permselectivity,5-6 excellent wettability and adhesion,7 low friction coefficient (especially for elastomers),8 and chemical inertness.9 Obviously, these properties depend on the chemical composition ofthe fluorinated layer, which in turn is determined by the chemical structure ofthe base polymer, the composition of the F2 gas mixture, and the fluorination parameters. [Pg.241]

Polymers are viscoelastic materials meaning they can act as liquids, the visco portion, and as solids, the elastic portion. Descriptions of the viscoelastic properties of materials generally falls within the area called rheology. Determination of the viscoelastic behavior of materials generally occurs through stress-strain and related measurements. Whether a material behaves as a viscous or elastic material depends on temperature, the particular polymer and its prior treatment, polymer structure, and the particular measurement or conditions applied to the material. The particular property demonstrated by a material under given conditions allows polymers to act as solid or viscous liquids, as plastics, elastomers, or fibers, etc. This chapter deals with the viscoelastic properties of polymers. [Pg.459]

By plotting the percentage of carbon particles separated from the vulcanizate versus the stress applied to the sample during extension, Hess et al. determined the stress at which the arbitrary quantity of 20% of the black had been separated from the matrix. This stress was indicated as the adhesion index. It appears (Fig. 12) that blacks of higher structures are associated with an increase of the adhesion index, i.e., with an enhancement of filler-elastomer interactions. [Pg.113]

The application of nuclear magnetic resonance (NMR) spectroscopy to polymer systems has contributed to significant advances in understanding of their structure and dynamical properties at the molecular level. From the analytical point of view, NMR spectroscopy is particularly suitable for a determination of the polymer structure by direct observation of the protons and carbons in different structural moieties. However, until the mid-1970s the application of this technique was limited to polymer solutions and to some elastomers in the solid state with a relatively high degree of the molecular mobility which allows the observation of the motionally narrowed absorption signals. [Pg.8]

The elastomers exhibited rubber-like behavior. From an examination of electron photomicrographs of cross sections of the elastomers, the fibrillar structure of the cellulose fibers apparently formed a network, and poly (ethyl acrylate) was distributed uniformly among the fibrils. The rigid crystalline regions of the cellulose fibers apparently stabilized the amorphous, grafted poly (ethyl acrylate) to determine the mechanical properties of the elastomers (43, 44). For example, typical elastic recovery properties for these elastomers are shown in Table X. [Pg.348]

Mechanical properties of crosslinked elastomers are influenced not only by the volume-average crosslink density but also by network heterogeneity. The influence of structural defects (such as residual sol, dangling chains, chain loops and the heterogeneity of the junction distribution) on the viscoelastic properties and the equilibrium swelling data is still under discussion. Local methods which probe molecular properties are very suitable for the determination of the degree of network heterogeneity [11]. [Pg.360]

A quantitative analysis of the shape of the decay curve is not always straightforward due to the complex origin of the relaxation function itself [20, 36, 63-66] and the structural heterogeneity of the long chain molecules. Nevertheless, several examples of the detection of structural heterogeneity by T2 experiments have been published, for example the analysis of the gel/sol content in cured [65, 67] and filled elastomers [61, 62], the estimation of the fraction of chain-end blocks in linear and network elastomers [66, 68, 69], and the determination of a distribution function for the molecular mass of network chains in crosslinked elastomers [70, 71]. [Pg.364]

A powerful technique for the study of orientation and dynamics in viscoelastic media is line shape analysis in deuteron NMR spectroscopy [1]. For example, the average orientation of chain segments in elastomer networks upon macroscopic strain can be determined by this technique [22-31]. For a non-deformed rubber, a single resonance line in the deuterium NMR spectrum is observed [26] while the spectrum splits into a well-defined doublet structure under uniaxial deformation. It was shown that the usual network constraint on the end-to-end vector determines the deuterium line shape under deformation, while the interchain (excluded volume) interactions lead to splitting [26-31]. Deuterium NMR is thus able to monitor the average segmental orientation due to the crosslinks and mean field separately [31]. [Pg.527]


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See also in sourсe #XX -- [ Pg.401 , Pg.402 , Pg.403 ]




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Structure elastomers

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