Polymers commercial

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. 

Poly(vinyl pyrrolidone). Another commercial polymer with significant usage is PVP (7). It was developed ia World War II as a plasma substitute for blood... 

The incidence of these defects is best determined by high resolution F nmr (111,112) infrared (113) and laser mass spectrometry (114) are alternative methods. Typical commercial polymers show 3—6 mol % defect content. Polymerization methods have a particularly strong effect on the sequence of these defects. In contrast to suspension polymerized PVDF, emulsion polymerized PVDF forms a higher fraction of head-to-head defects that are not followed by tail-to-tail addition (115,116). Crystallinity and other properties of PVDF or copolymers of VDF are influenced by these defect stmctures (117). 

Polysulfone. Polysulfone is a commercial polymer that is a product of bisphenol A and 1,1 -sulfonylbis (4-chlorobenzene) (see Polymers... 

Butyl mbber, a copolymer of isobutjiene with 0.5—2.5% isoprene to make vulcanization possible, is the most important commercial polymer made by cationic polymerization (see Elastomers, synthetic-butyl rubber). The polymerization is initiated by water in conjunction with AlCl and carried out at low temperature (—90 to —100° C) to prevent chain transfer that limits the molecular weight (1). Another important commercial appHcation of cationic polymerization is the manufacture of polybutenes, low molecular weight copolymers of isobutylene and a smaller amount of other butenes (1) used in adhesives, sealants, lubricants, viscosity improvers, etc. 

The molecular weight and the distribution of multiple molecular weights normally found within a commercial polymer influence both the processibiUty of the material and its mechanical properties. Eor a few well-defined homopolymers, an analysis of composition and molecular weight is sufficient to define the likely mechanical properties of the polymer. 

Acrylonitrile—Butadiene—Styrene. ABS is an important commercial polymer, with numerous apphcations. In the late 1950s, ABS was produced by emulsion grafting of styrene-acrylonitrile copolymers onto polybutadiene latex particles. This method continues to be the basis for a considerable volume of ABS manufacture. More recently, ABS has also been produced by continuous mass and mass-suspension processes (237). The various products may be mechanically blended for optimizing properties and cost. Brittle SAN, toughened by SAN-grafted ethylene—propylene and acrylate mbbets, is used in outdoor apphcations. Flame retardancy of ABS is improved by chlorinated PE and other flame-retarding additives (237). 

Small concentrations of vinylcarboxyhc acids, eg, acryhc acid, methacrylic acid, or itaconic acid, are sometimes included to enhance adhesion of the polymer to the substrate. The abihty to crystalline and the extent of crystallization are reduced with increa sing concentration of the comonomers some commercial polymers do not crystalline. The most common lacquer resins are terpolymers of VDC—methyl methacrylate—acrylonitrile (162,163). The VDC level and the methyl methacrylate—acrylonitrile ratio are adjusted for the best balance of solubihty and permeabihty. These polymers exhibit a unique combination of high solubihty, low permeabihty, and rapid crystallization (164). 

It is virtually impossible to manufacture commercial polymers that do not contain traces of hydroperoxides. The peroxide bond is relatively weak and cleaves homolyticaHy to yield radicals (eqs. 2 and 3). Once oxidation has started, the concentration of hydroperoxides becomes appreciable. The decomposition of hydroperoxides becomes the main source of radical initiators. 

Epichlorohydrin Elastomers without AGE. ECH homopolymer, polyepichlorohydrin [24969-06-0] (1), and ECH—EO copolymer, poly(epichlorohydrin- (9-ethylene oxide) [24969-10-6] (2), are linear and amorphous. Because it is unsymmetrical, ECH monomer can polymerize in the head-to-head, tail-to-tail, or head-to-tail fashion. The commercial polymer is 97—99% head-to-tail, and has been shown to be stereorandom and atactic (15—17). Only low degrees of crystallinity are present in commercial ECH homopolymers the amorphous product is preferred. 

The classification given in Table 1 is based on the process, ie, thermosetting or thermoplastic, by which polymers in general are formed into usehil articles and on the mechanical properties, ie, rigid, flexible, or mbbery, of the final product. AH commercial polymers used for molding, extmsion, etc, fit into one of these six classifications the thermoplastic elastomers are the newest. 

The lengths of these chains may be varied but in commercial polymers chains with from 1000 to 10000 of these methylene groups are generally encountered. These materials are of high molecular weight and hence are spoken of as high polymers or macromolecules. 

It may also be mentioned that a number of commercial polymers are produced by chemical modification of other polymers, either natural or synthetic. Examples are cellulose acetate from the naturally occurring polymer cellulose, poly(vinyl alcohol) from polyfvinyl acetate) and chlorosulphonated polyethylene (Hypalon) from polyethylene. 

ELIAS, H.-G. and voHwiNKEL, E., New Commercial Polymers—2 (Chapter 14), Gordon and Breach, New York, London (1986)... 

Flow properties of polyethylene have been widely studied. Because of the wide range of average molecular weights amongst commercial polymers the viscosities vary widely. The most commonly used materials, however, have viscosities lower than for unplasticised PVC and polyfmethyl methacrylate) and higher than for the nylons. 

The monomer, 2-chlorobuta-1,3-diene, better known as chloroprene, is polymerised by free-radical emulsion methods to give a polymer which is predominantly (-85%) fr<2 s-l, 4-polychloroprene but which also contains about 10% cii-1,4- 1.5%, 1,2- and 1% of 3,4-structures (Figure 11.17). The commercial polymers have a Tg of about -A3°C and a of about 45°C so that at usual ambient temperatures the rubber exhibits a measure of crystallinity. 

The molecular weightsj or the bulk of commercial polymers are in the range... 

The properties of PVC may also he expected to depend on the molecular weight distribu n. Most commercial polymers, however, appear to have similar values for MJM and in any case there is little published information on effects of altering the parameter. It is perhaps rather surprising that there appears to be little work reported on the effect of blends of polymers of differing molecular weight on mechanical and rheological properties. 

With commercial polymers the major differences are, perhaps, not differences in molecular structure hut in the characteristics of the particle, i.e. its shape, size distribution and porosity. Such differences will considerably affect the processing behaviour of a polymer. 

The commercial polymers are mechanically similar to PTFE but with a somewhat greater impact strength. They also have the same excellent electrical insulation properties and chemical inertness. Weathering tests in Florida showed no change in properties after four years. The material also shows exceptional non-adhesiveness. The coefficient of friction of the resin is low but somewhat higher than that of PTFE. Films up to 0.010 in thick show good transparency. 

Poly(vinyl acetate) is too soft and shows excessive cold flow for use in moulded plastics. This is no doubt associated with the fact that the glass transition temperature of 28°C is little above the usual ambient temperatures and in fact in many places at various times the glass temperature may be the lower. It has a density of 1.19 g/cm and a refractive index of 1.47. Commercial polymers are atactic and, since they do not crystallise, transparent (if free from emulsifier). They are successfully used in emulsion paints, as adhesives for textiles, paper and wood, as a sizing material and as a permanent starch . A number of grades are supplied by manufacturers which differ in molecular weight and in the nature of comonomers (e.g. vinyl maleate) which are commonly used (see Section 14.4.4)... 

Substituents on the a-carbon atom restrict chain flexibility but, being relatively small, lead to a significantly higher Tg than with polyethylene. Differences in the Tg s of commercial polymers (approx. 104°C), syndiotactic polymers (approx. 115°C) and anionically prepared isotactic polymers (45°C) are generally ascribed to the differences in intermolecular dipole forces acting through the polar groups. 

As with the aliphatic polyamides, the heat deflection temperature (under 1.82 MPa load) of about 96°C is similar to the figure for the Tg. As a result there is little demand for unfilled polymer, and commercial polymers are normally filled. The inclusion of 30-50% glass fibre brings the heat deflection temperature under load into the range 217-231°C, which is very close to the crystalline melting point. This is in accord with the common observation that with many crystalline polymers the deflection temperature (1.82 MPa load) of unfilled material is close to the Tg and that of glass-filled material is close to the T. ... 

In addition to the commercial aromatic polyamides described above many others have been prepared but these have not achieved commercial viability. There are, however, a number of other commercial polymers that contain amide groups such as the polyamide-imides. The latter materials are discussed in Section 18.14. 

Most of the commercial polymers consist of polyether blocks separated by polyamide blocks. The polyether blocks may be based on polyethylene glycol, polypropylene glycol or, more commonly, polytetramethylene ether glycol. The polyamides are usually based on nylon 11 but may be based on nylons 6 or 66 even a copolymer, e.g. 6/11. 

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