Subject synthetic polymers

The preparation of synthetic polymers is hardly suitable for the ordinary organic laboratory. However, a few simple demonstration experiments are described below which, it is hoped, will provide an elementary introduction to the subject. 

Modem synthetic polymers are the subject of increasing research by conservation scientists. Not only does their frequent use in conservation treatments require a better understanding of their long term stabiUty, but also many objects, including those in collections of contemporary art and in history and technology museums, are made out of these new materials. 

Fabrics composed of synthetic polymer fibers are frequendy subjected to heat-setting operations. Because of the thermoplastic nature of these fibers, eg, polyester, nylon, polyolefins, and triacetate, it is possible to set such fabrics iato desired configurations. These heat treatments iavolve recrystaUization mechanisms at the molecular level, and thus are permanent unless the fabrics are exposed to thermal conditions more severe than those used ia the heat-setting process. 

Nowadays, a strategic area of research is the development of polymers based on carbohydrates due to the worldwide focus on sustainable materials. Since the necessary multi-step synthesis of carbohydrate-based polymers is not economical for the production of commodity plastics, functionalization of synthetic polymers by carbohydrates has become a current subject of research. This aims to prepare new bioactive and biocompatible polymers capable of exerting a temporary therapeutic function. The large variety of methods of anchoring carbohydrates onto polymers as well as the current and potential applications of the functionalized polymers has been discussed recently in a critical review [171]. Of importance is that such modification renders not only functionality but also biodegradability to the synthetic polymers. 

The first of the thermoplastic synthetic polymers to be developed was celluloid, made by combining nitrated cellulose (pure cotton subjected to nitric acid) and camphor (C10H16O), a plasticizer. The motivation was a search for a replacement for the ivory used in making billiard balls. It became a commercial product circa 1865, and is still used for making ping-pong balls. 

The use of PCA for the classification of both natural and synthetic polymers was demonstrated by Vazquez et al. [119]. In their work, the researchers recorded Totai X-Ray Fluorescence (TXRF) spectra of scleroglucan, xanthan, glucomannan, poly(ethylene oxide), and polyacrylamide and subjected the resulting spectral data to PCA. To the naked eye, the X-ray fluorescence spectra of the polymers look virtually identical. However, when subjected to PCA it could be shown that the first two principal components contain approximately 96% of the variance in the dataset. When plotting the scores of the two components against each other, six distinct clusters are observed, which clearly differentiate the individual polymers. 

Various criteria can be considered in the classification of the SEC applications. The most important are the analytical SEC procednres. The preparative applications, which encompass the purification of complex samples before their further treatment, draw rather wide attention. In this latter case, analytes are preseparated by SEC according to the size of their components and either macromolecular or low molecular fractions are subject to further analyses by other methods. The production oriented SEC did not find wide application in the area of synthetic polymers due to both the high price of organic solvents and the ecological considerations. 

Chemical Stability. Chemical stability is just as important as the physical stability just discussed. In general, chemical deterioration of the polymers is no problem, and they can be stored at room temperature for years. However, the polymeric surfaces are subjected to an extreme variety of chemicals during the accumulation process. Some of these may react with the polymer. For example, reactions of styrene-divinylbenzene polymers and Tenax with the components of air and stack gases have been documented (336, 344, 540). The uptake of residual chlorine from water solutions has also been observed in my laboratory and elsewhere (110, 271, 287). Although the homogeneous nature of synthetic polymers should tend to reduce the number of these reactions relative to those that occur on heterogeneous surfaces of activated carbons, the chemical reaction possibility is real. In the development of methods for specific chemicals, the polymer stability should always be checked. On occasion, these checks may lead to... 

The use of synthetic polymers in medicine and biotechnology is a subject of wide interest. Polymers are used in replacement blood vessels, heart valves, blood pumps, dialysis membranes, intraocular lenses, tissue regeneration platforms, surgical sutures, and in a variety of targeted, controlled drug delivery devices. Poly(organosiloxanes) have been used for many years as inert prostheses and heart valves. Biomedical materials based on polyphosphazenes are being considered for nearly all the uses mentioned above. 

Polymers are large molecules (macromolecules) that consist of one or two small molecules (monomers) joined to each other in long, often highly branched, chains in a process called polymerization. Both natural and synthetic polymers exist. Some examples of natural polymers are starch, cellulose, chitin (the material of which shells are made), nucleic acids, and proteins. Synthetic polymers, the subject of this chapter, include polyethylene, polypropylene, polystyrene, polyesters, polycarbonates, and polyurethanes. In their raw, unprocessed form, synthetic polymers are sometimes referred to as resins. Polymers are formed in two general ways by addition or by condensation. 

The possibility of grafting synthetic polymers to cellulose immediately attracted worldwide attention as a new and exciting way to modify cellulose and extend its uses against the rapidly growing competition from synthetic polymers themselves. The well known phrase attributed to Theodore Roosevelt, "if you can t beat them, join them", if somewhat trite, seems particularly appropriate at this point. Research in the field blossomed quickly and is still an extremely active subject of study. For example, in a very recent (and the first) book on the subject by Hebeish and Guthrie (4) more than one thousand references are quoted. 

Silicones are a class of synthetic polymers having the general formula (RmSi(0)4 m/2) , where m = 1-3 and n> 2. The most common example is polydimethylsiloxane (PDMS). This polymer has a repeating (CH3)2SiO unit. Silicones and silanes are the subject of many reviews.12 22 It is not possible to cover adequately the many uses to which silicones have been put. However, a summary of the most important properties and representative applications that utilize these properties are provided in the literature.23 24... 

Synthetic polymer materials are so ubiquitous in modem life that we now take them for granted. But, the first commercially significant, completely synthetic plastic was only introduced at the beginning of the 20th century. This was Bakelite, invented by Leo Baekeland and a short account of his contributions will form the subject of one of our Polymer Milestones in the next chapter. The introduction of this new material was preceded by roughly 40 years of the development of what can be called semi-synthetics based on chemically modified forms of cellulose. 

This introductory text is intended as the basis for a two- or three-semester course in synthetic polymers. It can also serve as a self-instruction guide for engineers and scientists without formal training in the subject who find themselves working with polymers. For this reason, the material covered begins with basic concepts and proceeds to current practice, where appropriate. 

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