The structure of solid polymers

It is possible, under well-defined conditions, to cause normally simple linear polymer molecules to grow into branched chains. When this branching is extensive, the solid polymer shows a considerable interlocking of the branched chains and this gives a material that is both denser and stronger than the unbranched form. 

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The main factor that defines interconnection of local order and the fractal nature of the structure of solid polymers is the fact that both these features are a reflection of the key property of these polymers- their thermodynamical non-equilibrium nature. The scales of fractal behaviour and indicated above correspond very well to cluster structure border sizes - to statistical segment length - to distance... 

Section 8 deals with reactions which occur at gas—solid and solid—solid interfaces, other than the degradation of solid polymers which has already been reviewed in Volume 14A. Reaction at the liquid—solid interface (and corrosion), involving electrochemical processes outside the coverage of this series, are not considered. With respect to chemical processes at gas-solid interfaces, it has been necessary to discuss surface structure and adsorption as a lead-in to the consideration of the kinetics and mechanism of catalytic reactions. 

Both solution-state and solid-state NMR spectroscopy are important analytical tools used to study the structure and dynamics of polymers. This analysis is often limited by peak overlap, which can prevent accurate signal assignment of the dipolar and scalar couplings used to determine structure/property relationships in polymers. Consequently, spectral editing techniques and two- or more dimensional techniques were developed to minimize the effect of spectral overlap. This section highlights only a few of the possible experiments that could be performed to determine the structure of a polymer. 

The morphology of solid polymers is also an important parameter. Thus, radiation-induced changes can be expected to differ in crystalline and amorphous regions — but in what way and to what extent "Crystallinity" and "amorphous" are not absolute terms and as more becomes known about the solid-state structure of polymers this should be related to radiation degradation. 

We shall conclude with some remarks on the structure of glassy polymers. If one frequently speaks of glass structures, this does not mean that there exists one definite glass structure similar to a crystal. In a macromolecular solid-e.g., the polystyrene-plasticizer system, entirely different glasses are obtainable, the macroscopic composition of which is always the same (8). In Figure 10 the full... 

If the drug and polymer are miscible in their Luid state, then as discussed in Section Thermodynamic Perspective of Miscibility and Phase Separation in Solid Dispersions, the mixture may or may not undergo phase separation during solidiLcation, thereby inLuencing the structure of solid dispersion. 

On the basis of several analytical studies (differential thermal analysis, fluorescence, CPMAS solid-state NMR spectroscopy and others) [56-58] two models have been proposed to describe the structure of HCN-polymers, the Umemoto [59] and the Volker models [60]. In the Volker model, HCN polymerizes to extensive double-ladder rod-like structures, while a simpler mono-ladder pattern was hypothesized by Umemoto (Fig. 1). Irrespective of the structure assumed by HCN-polymers, a large panel of purine, imidazole and pyrimidine derivatives can be obtained by hydrolysis of these materials. In 1963, Lowe described the first example of acidic hydrolysis of the HCN-polymer (boiling 6.0 N HC1) to yield amino acids, carboxylic acids, adenine and hypoxanthine (Scheme 4). 

It should be mentioned that light scattering is not restricted to solutions. In fact, the technique can be used to obtain information about the super molecular structure of solid polymers. 

The data of Table II have been reexamined in terms of the two models proposed for the structure of flexible polymers at the solid/liquid interface, and the pertinent data are listed in Table III. In the first column are given the areas per monomer unit of the completely uncoiled polystyrene... 

What are the structures of conductive polymers, and what is the mechanism for electronic transport in the solid-state ... 

High-resolution solid-state NMR spectroscopy, combined with quantum chemistry, provides detailed information on the structure and electronic structures of solid polymers through the observation of the NMR chemical shift [11-... 

To extract information on molecular orientation distribution from experimental data, the most widely known technique, the Legendre moment expansion approach can be taken. In this section, this approach will be discussed first, followed by methods to elucidate atomic resolution details of the structures of ordered polymers with orientation-dependent NMR interactions, such as those from chemical shielding, dipole-dipole and quadrupolar coupling. Then, solid-state NMR studies of the torsion angles of the peptide backbone of highly ordered silk fibroin fiber, a protein that has been studied extensively as a model for fibrous proteins, will be described. 

The structure of polyacenic polymers, one of the typical conducting polymers, has been studied by infrared (IR), X-ray diffraction and ESR [17, 18]. From these studies, it was found that polyacenic polymers obtained by heating resins are amorphous and their structures are very complicated. Therefore, their exact structures have not been clarified because of their amorphous nature and insolubility. Kurosu et al. [19] studied the relationship between the structure and electrical conductivity of polyacenic polymer samples by high resolution solid-state NMR spectroscopy. 

Polysilanes are a unique class of polymers in which the o--electrons are delocalized entirely along the sp -bonded silicon backbone, causing their electronic absorption properties to be strongly dependent on the conformation of silicon backbones [2]. This property has created much interest in the structure of these polymers in the solid state [3]. In spite of the usefulness of solid-state NMR, there are few systematic studies on the Si CP/MAS NMR of polysilanes [4-6]. Most recently, it has been demonstrated that the VT Si CP/MAS NMR experiment is very useful to study the conformational features of polysilanes in the solid state [7j. Measurements of the Si CP/MAS NMR spectra of poly (methylphenylsilane) (PMPS), in the solid state over a wide range of temperatures, are performed and the conformation... 

In previous papers [7, 17, 20], it has been demonstrated that VT Si CP/MAS NMR spectroscopy is a powerful means for characterizing the structures of solid-state polysilanes and other solid polymers [1, 30]. In this work, high-resolution Si NMR spectra and spin-lattice relaxation times, Ti, of CPTMPS/DMS in the solid state over a wide range of temperatures were measured and the conformational behavior and molecular motion of the main chain discussed. To discuss the experimental results in more detail, calculation of the Si shielding constants of the main Si atoms by means of FPT CNDO/2 MO framework was attempted. 

It has been demonstrated that solid state NMR spectroscopy provides useful information about the structure and dynamics of polymers in the bulk. At present, in polymer science, solid state NMR is recognized as one of the most powerful means for elucidating the structure and the dynamics of solid polymers in addition to X-ray diffraction. The history of solid state NMR, which has been used in polymer science, is very old. The appearance of new techniques in solid state NMR has certainly contributed to the development of polymer science and technology. 

The most commonly used type of inhibited films is produced by joint processing of thermoplastic polymers and highly dispersed Cl powders. When the melting points, as well as the sublimation and thermal destruction temperatures, of the Cl exceed the viscous flow temperature of the thermoplast, the film acquires the structure of a polymer composite filled with solid inhibitor particles [101]. The particles may partially dissolve in the polymer melt and exert a plasticizing effect on the polymer. Introduction of 1-2% of NBA into PE elevates melt flow by 1.5-1.8 times [10]. Aggregation of solid Cl particles may present essential difficulties for their joint processing with polymer melts and result in structural defects or impair the quality of the film as a whole [4]. 

Physico-structural inhomogeneity. In contrast to low-molecular substances, the reactivity of solid polymers depends greatlyon the structure of the electron shells and to a greater extent on molecular d3mamics and imperfections of the permolecular structure. Physical-structural inhomogeneity of polymers may bring about the following phenomena that are critical for tribochemical reactions [80]. 

The chemical analysis of the structure of crossllnked polymer networks Is complex In nature and various approaches have been given in an effort to understand these systems (1- ). The usual chemical or physical methods are limited because of the insolubility and infusibility of the system. However, recently CP/MASS (cross-polarlzatlon magic-angle satple spinning) has made It possible to obtain a high resolution NMR spectrum of these Insoluble solid polymers (9,10). 

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