Some Industrially Important Polymers

Frequently, the desired bulk properties cannot be achieved by using only one monomer and copolymers of glassy and rubbery polymers of different compositions are used. This is illustrated in general by the following list of some industrially important polymer families with their end-use areas ... 

The presence of ring molecrdes has to be taken into account in the manufacture of some commerdally-important polymers including linear poly(dimethylsiloxane), nylon-6 and poly(ethylene tere dithalate). Indeed much of the research carried out on cyclic concentrations in such polymers has been by woricers in Industry, who have been concerned to acquire detaited knowledge of the cydic contents of thdr products. 

Chlorination. Chlorination of PVC results in a resinous product having about 73% chlorine, which corresponds to the introduction of one chlorine per carbon atom. Such postchlorinated polymers have achieved some industrial importance because they have lower softening temperatures and increased solubility in a variety of solvents. They have been used in synthetic fibers in Germany and in solution coatings. 

Early industrial developments in the field of polymer science and technology were concerned with the modification and utilization of natural polymers. The commercial production of purely synthetic polymers was started in the early 1900s, when some commercially important polymers were prepared. It was the late 1930s and the beginning of the Second World War that saw the development of all but a handful of the wide variety of synthetic polymers now in commercial use. 

This chapter will deal with ionic chain growth polymerization for monomers which are of some industrial importance. It will deal mainly with those polymer reaction engineering aspects which are relevant for designing processes and products. As it cannot cover the entire subject, the systems dealt with are chosen as examples of the most important features of ionic polymerization. 

Section II is devoted exclusively to polysaccharide systems, but includes a fairly broad variety of polymers and applications. Kennedy et al. describe some industrially important polysaccharides, while Morris covers various bacterial-derived polysaccharides used in the food and agricultural industries. Carraher et al. describe some tin modified dextrans in the third Chapter of this Section. Some acidic, heparin-like, polysaccharides are described in the following Chapter (Linhardt, et al.) then Kobayashi reveals some cellulose derivatives which form liposomes and membranes. The final three papers of this Section deal with chitin and chitosan systems. Alkaline chitosan gels are presented by Hirano et al. Kikuchi and Kubota then describe some polyelectrolytes derived from chitosan derivatives. Finally, Seo and lijima consider the sorption behavior of chitosan gels. 

Some aspects of semicrystalline polymers were also discussed earlier in this article. See the paragraphs titled Tensile and Shear Properties, Semicrystalline Polymer Processing, Semicrystalline Pol3rmer Properties, and Thermoplastic Elastomer Properties in the section titled Practical Importance and Common Methods for Measurement. Crystallinity will, however, be discussed below in further detail because of the complexity of the interplay between the amorphous and crystalline phases and the role of this interplay in the processing and end use performance of a vast variety of industrially important polymers. 

In this section we examine some examples of cross-linked step-growth polymers. The systems we shall describe are thermosetting polymers of considerable industrial importance. The chemistry of these polymerization reactions is more complex than the hypothetical AB reactions of our models. We choose to describe these commercial polymers rather than model systems which might conform better to the theoretical developments of the last section both because of the importance of these materials and because the theoretical concepts provide a framework for understanding more complex systems, even if they are not quantitatively successful. 

Derivatives. The most important data for 2-methyl a siridine and 1-(2-hydroxyethy1)asiridine, which previously had some industrial significance, are given in Table 1. Like ethyleneimine, these compounds ate used in polymer form and as intermediates. The use of activated asiridines, eg, /V-acylasiridines, for amino ethylation, under alkaline conditions, is of preparative interest (1). 

Polymers are organic materials and are sensitive to natural or artificial UV sources. This is of primary importance for outdoor exposure of unprotected parts and for some industrial applications such as electrical welding, photocopier light exposure devices. .. 

Furthermore, polymer-assisted solution-phase syntheses also show several advantages over Merrifield-type syntheses. Fxcept for some industrially employed heterogeneous catalysts the requirement of high loading capacities for the sohd supports is not necessarily of prime importance for immobilized catalysts. Because not every site needs to react, lower loadings are acceptable. The recovered catalyst is often available for immediate reuse. A discussion on immobilized catalysts should also include a brief listing of obstacles associated with their use, particular in comparison to their soluble analogs ... 

Unlike other areas of chemistry, most of the basic research has been done in industry so that there is often a close tie between discoveries and their commercialization. Table 1.2 lists some of the dates of commercialization for some important polymer discoveries. 

Most monomers contain only one polymerizable group. There are some monomers with two polymerizable groups per molecule. Polymerization of such monomers can lead to more than one polymer structure. The polymerization of 1,3-dienes, of large industrial importance, is discussed in Sec. 8-6. 1-Substituted-l,2-dienes (allenes) undergo polymerization through both the substituted and unsubstituted double bonds... 

Much recent work on micellization in block copolymers has been focussed on this industrially important type of polymer. We therefore describe experiments on micellization in aqueous solutions of poly(oxyalkylene) diblocks and triblocks in some detail. This serves to illustrate many of the important features of micellization of block copolymers, also observed in other systems such as the styrenic block copolymers covered in the following section. 

Aqueous systems have been studied by a very large number of investigators. Economy, safety, convenience and quality of product have combined to make this the method of choice for commercial production of copolymers. The industrial importance of such end products as elastomers and acrylic fibers has been a special incentive to related fundamental studies. Furthermore, the relatively high solubility of acrylonitrile monomer in water coupled with insolubility of the polymer make it a convenient test monomer for studies of initiation by redox systems (6, 25, 102). Large numbers of homogeneous chemical initiators and some heterogeneous initiators have been studied as well as initiation by photochemical means, by ultrasonics and by ionizing radiation. It will not be possible here to review the enormous world literature. Several publications (/, 92, 117) refer in some detail to the older papers, and we shall restrict our comments to recent interpretations that have received support from several quarters. 

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