Polymer physical characteristics contrast

Rubbers have physical characteristics and a chemical composition that precludes their successful identification by infrared spectroscopy due to their inherent elasticity and highly filled composition. In contrast, no such difficulties are encountered with Py-GC. Crime scene rubber evidence from automotive tires and rubber vehicle components is found in hit-and-run cases and in soles of shoes worn by offenders in offenses against property. Discrimination of vehicle bumper rubbers by Py-GC has been reported. Volatile and polymeric components of rubbers and other polymers have been analyzed by Py-GC and the inorganic residue recovered for subsequent analysis. The technique may also be used to quantitate rubber blends by measuring the ratios of characteristic pyrolysis products. Figure 8.8 shows examples of the pyrograms of three common types of rubber. 

Attenuated total reflection (ATR) FTIR is one of the most useful tools for characterising the chemical composition and physical characteristics of polymer surfaces [53]. One useful application is the measurement of molecular orientation using polarised infrared ATR spectroscopy [54,55]. The polarised infrared ATR spectra normally include three-dimensional (e.g., machine, transverse, and thickness direction) orientational information in contrast to the polarised transmission infrared linear dichroism. In addition, band absorbance of less than 0.7 au is easily achieved, even with the strong absorption bands, because the penetration depth of ATR from sample surfaces can be adjusted to a few micrometers by changing the internal reflection element and/or the angle of incidence. If successful combination of the dynamic infrared spectroscopy and the ATR methods can be achieved, more useful dynamic orientational information can be obtained. 

A third major innovation in polymer physics during the past decade is the recognition that because they are quasi-one-dimen-sional materials, some polymers exhibit collective semiconducting ground states(5,8). In contrast to the pervasive effects of disorder in almost all polymers, however, the occurrence of collective phenomena is uncommon. Specifically, it is characteristic of macromolecules like polyacetylene which have experienced a symmetry-lowering structural modification that introduces a semiconductor gap into what would have been a metallic electronic excitation spectrum. Moreover, in such materials the consequences of disorder can be dramatically different from those noted in the previous lecture. Thus, in this third and final lecture we examine the destruction of the collective semiconducting ( Peierls ) ground state in doped polyacetylene by the interaction of the conduction electrons with a disordered array of donors or acceptors. 

These differences in physical structure are responsible for the different properties of foamed polymers containing varying proportions of open cells. In contrast to closed-cell foamed polymers, open-cell foamed plastics have a higher water and moisture absorptive capacity, a higher gas and vapor permeability, less pronounced electric and heat insulation characteristics but a stronger sound absorptive and damping power... 

Dendrimers are a relatively new class of macromolecules different from the conventional linear, crosslinked, or branched polymers. Dendrimers are particularly interesting because of their nanoscopic dimensions and their regular, well-defined, and highly branched three-dimensional architecture. In contrast to polymers, these new types of macromolecules can be viewed as an ordered ensemble of monomeric building blocks. Their tree-like, monodispersed structures lead to a number of interesting characteristics and features globular, void-containing shapes, and unusual physical properties [107-111]. 

In general a much wider use has been made of electrophilic substitution reactions with t-octylphenol from the reaction of diisobutene with phenol and rather less applications in the field of polymer chemistry. Thus for example, estenfication, nitration, phosphorylation, diazotisation, chlorination, sulphation, carboxylation, formylation and etherification have led to well-characterised derivatives (ref.93). Unlike t-nonylphenol, t-octylphenol [4-(1,1,3,3-tetra-methylbutyOphenoQ is a crystalline compound yielding characteristic crystalline derivatives as can be seen in the following instances. t-Nonylphenol by contrast is a mixture of sidechain isomers although predominantly a p-substituted compound. Its heterogeneity like that of many technical product undoubtedly enhances its physical properties in many of its industrial applications. Thus for... 

Finally a type of addition polymerization calling for the employment of stereospecific catalysts has recently aroused much interest in the laboratory as well as in industry. With the aid of such catalysts, an addition polymerization yields certain poljmers in which the main chain as well as tire chemical substituents are dtuated in a highly ordered spatial pattern. Polymers of physical and chemical characteristics are thus obtained which contrast markedly from those formed in normal polymerizations. 

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