Polymers organic

Polymers are molecular compounds, either natural or synthetic, that are made up of many repeating units called monomers. The physical properties of these so-called macromolecules differ greatly from those of small, ordinary molecules. 

Once the structures of these macromolecules were understood, the way was open for the synthesis of polymers, which now pervade almost every aspect of our daily lives. About 90 percent of today s chemists, including biochemists, work with polymers. In this section, we will discuss the reactions that result in polymer formation and some of the natural polymers that are important to biology. 

Polyniecs lypicaly have v (y high mobr masses—soinetinies thousands or even millions of grams. 

Some of the other properties that suggested a highmolar-mass solute were low osmotic pressure and negigiUe freezing nt depression. These are kncwvn as a gaUve properties [Mt Chapter 13]. 

Organic polymers attracted considerable interest for hydrogen storage when uptake capacities of 6-8 wt% were reported for polyaniline (PAni) and polyprrrole (Ppy) at room temperature [64, 65], Unfortunately, these results could not be reproduced independently, instead room temperature values of less than 0.5 wt% at pressures up to 94bar were subsequently observed for similar samples [66, 67]. 

The advantages of microporous organic molecules are that they consist of very light atoms (C, H, N, O), and that they can possess high specific surface areas and 

By infrared studies Spoto et al. showed that the adsorption ofhydrogen on a porous poly(styreneco-divinylbenzene)polymer involves the specific interaction of the H2 molecule with the phenyl ring with an interaction energy of 0.4 kJ mol which is comparable with the interaction energy between H2 and activated carbon [71]. This interaction may be increased in narrower pores where hydrogen can interact with more than one pore wall, as suggested by Wood et al. [10]. 

The hydrogen storage values of PIMs and HCPs are still smaller than for many porous carbon samples. However, PIMs and HCPs have only recently been investigated for H2 adsorption and further modifications of these materials can lead to an enhancement of their hydrogen storage capacity at cryogenic temperatures. 

From the photoconductivity induced by vacuum ultraviolet light, the band gap. Eg, of several simple polymers was determined. The data are summarized in Table 7. 

A number of excellent books and reviews have been published on the subject of polymeric gas separating membranes, which are recommended to the interested reader [266-272]. It is the purpose of this chapter to supply the reader with a basic background that is important for the understanding of the transport mechanism of gases through polymers, to introduce those polymers that are currently of commercial importance and finally to give an outlook on interesting developments in this field. 

The simplest model used to explain and predict gas permeation through non-porous polymers is the solution-diffusion model. In this model it is assumed that the gas at the high-pressure side of the membrane dissolves in the polymer and diffuses down a concentration gradient to the low pressure side, where the gas is desorbed. It is further assumed that sorption and desorption at the interfaces is fast compared to the diffusion rate in the polymer. The gas phase on the high- and low-pressure side is in equilibrium with the polymer interface. The combination of Henry s law (solubility) and Picks law (diffusion) leads to 

The selectivity of a polymer to gas A relative to another gas B can be expressed in terms of an ideal selectivity Uab defined by the relation 

1) The permeability coefficient is most commonly given in Barrei defined as 10 cm cm/cm s cm Hg and named after 

It can be seen that the diffusion coefficient of the large pentane molecule is 3.6 times smaller than the diffusion coefficient of oxygen. However, the solubility of pentane is about 200 times larger than the solubility of oxygen. This solubility selectivity outnumbers the reverse diffusion selectivity. As a result, silicone rubber is much more permeable for pentane than for oxygen. 

These transformations may add new molecular species that are not initially produced by organisms [5]. 

Finally there are the composite materials that are not uniform but do have identifiable component parts. These component parts can usually be separated and analyzed individually. However, this is not always the chosen procedure for their analysis. Analytical pyrolysis has been applied to composite materials as well as to uniform polymers, depending on the purpose of the analysis. Some examples of the pyrolytic analysis of natural organic composite materials are presented in Part 3 of this book. 

Niimura, T. Miyakoshi, J. Onodera, T. Higuchi, J. Anal. Appl. Pyrol., 37 (1996) 199. 

Voorhees, Analytical Pyrolysis, Techniques and Applications, Butterworths, London, 1984. 

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A number of friction studies have been carried out on organic polymers in recent years. Coefficients of friction are for the most part in the normal range, with values about as expected from Eq. XII-5. The detailed results show some serious complications, however. First, n is very dependent on load, as illustrated in Fig. XlI-5, for a copolymer of hexafluoroethylene and hexafluoropropylene [31], and evidently the area of contact is determined more by elastic than by plastic deformation. The difference between static and kinetic coefficients of friction was attributed to transfer of an oriented film of polymer to the steel rider during sliding and to low adhesion between this film and the polymer surface. Tetrafluoroethylene (Telfon) has a low coefficient of friction, around 0.1, and in a detailed study, this lower coefficient and other differences were attributed to the rather smooth molecular profile of the Teflon molecule [32]. 

Nagasawa Y, Passino S A, Joo T and Fleming G R 1997 Temperature dependence of optical dephasing in an organic polymer glass J. Chem. Phys. 106 4840-52... 

McClellan s and Hamsberger s survey, which embraced a considerable variety of solids including carbons, metal oxides and organic polymers such as polythene, arrived at a mean value of 20-2 A, with a standard deviation of 1-6 A. Other more recent results, likewise based on = 16-2 A, ... 

Wynne-Jones and Marshfound somewhat similar results with a number of carbons made by pyrolysis of eight organic polymers at a series of temperatures. The isotherms of Nj at 77 K and of COj at 195 K were measured, and the apparent surface area calculated by the usual BET procedure. (Owing to the microporous nature of the solids, these figures for area will be roughly proportional to the uptake at saturation and therefore... 

Organic polymer glass Organic sequestrants Organic sulfides Organic sulfur... 

G. Beamson and D. Briggs, High Resolution XPS of Organic Polymers,]ohxi Wiley Sons, Inc., New York, 1992. 

Subliming ablators are being used in a variety of manufacturing appHcations. The exposure of some organic polymers to pulsed uv-laser radiation results in spontaneous ablation by the sublimation of a controUed thickness of the material. This photoetching technique is utilized in the patterning of polymer films (40,41) (see PHOTOCHEMICAL TECHNOLOGY). 

With the exception of glass fiber, asbestos (qv), and the specialty metallic and ceramic fibers, textile fibers are a class of soHd organic polymers distinguishable from other polymers by their physical properties and characteristic geometric dimensions (see Glass Refractory fibers). The physical properties of textile fibers, and indeed of all materials, are a reflection of molecular stmcture and intermolecular organization. The abiUty of certain polymers to form fibers can be traced to several stmctural features at different levels of organization rather than to any one particular molecular property. 

The materials of attention in promoting fire safety are generally organic polymers, both natural, such as wood (qv) and wool (qv), and synthetic, nylon (see Polyamides), vinyl, and mbber (qv). Less fire-prone products generally have either inherently more stable polymeric stmctures or fire-retardant additives. 

The detection of organic polymers in solution represents a more difficult problem, especially in industrial water and wastewater. In theory, charged polymers react with polymers of the opposite charge in solution and such reactions can be used to titrate the concentration of polymer present. There are a number of techniques using this method (65). 

The presence of carbon—fluorine bonds in organic polymers is known to characteristically impart polymer stabiUty and solvent resistance. The poly(fluorosibcones) are siloxane polymers with fluorinated organic substituents bonded to siUcon. Poly(fluorosibcones) have unique appHcations resulting from the combination provided by fluorine substitution into a siloxane polymer stmcture (see Silicon compounds, silicones). 

The wide range of soHd lubricants can generally be classified as either inorganic compounds or organic polymers, both commonly used in a bonded coating on a matching substrate, plus chemical conversion coatings and metal films. Since solid-film lubricants often suffer from poor wear resistance and inabihty to self-heal any breaks in the film, search continues for improved compositions. 

Ceramic, Metal, and Liquid Membranes. The discussion so far implies that membrane materials are organic polymers and, in fact, the vast majority of membranes used commercially are polymer based. However, interest in membranes formed from less conventional materials has increased. Ceramic membranes, a special class of microporous membranes, are being used in ultrafHtration and microfiltration appHcations, for which solvent resistance and thermal stabHity are required. Dense metal membranes, particularly palladium membranes, are being considered for the separation of hydrogen from gas mixtures, and supported or emulsified Hquid films are being developed for coupled and facHitated transport processes. 

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