Other important polymers

Several other common industrial polymers are also used in biomedical applications [51]. Because of its low cost and easy processibility, polyethylene is frequently used in the production of catheters. High-density polyethylene is used to produce hip prostheses, where durability of the polymer is critical. Polypropylene, which has a low density and high chemical resistance, is frequently employed in syringe bodies, external prostheses, and other non-implanted medical applications. Polystyrene is used routinely in the production of tissue culture dishes, where dimensional stability and transparency are important. Styrene-butadiene copolymers or acrylonitrile-butadiene-styrene copolymers are used to produce opaque, molded items for perfusion, dialysis, syringe connections, and catheters. 

Poly(tetrafluoroethylene) (PTFE), more commonly known as Teflon (DuPont) and Goretex (expanded PTFE), is found in vascular grafts. The polymer has exceptionally good resistance to chemicals. 

Poly(vinyl chloride) and Poly[acrylonitrile-co-(vinyl chloride)] 

Poly(vinyl chloride) has excellent resistance to abrasion, good dimensional stability, and chemical resistance therefore, it is often used in medical tubing and catheter tubes. Poly[acrylonitrile-co-(vinyl chloride)]  

A commonly used linear polyester is polyfethylene terephthlate) (PET), which is synthesized by condensation of terephthalic acid and ethylene glycol, and produced under the trade name Dacron, 

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All of these facts indicate a strong reverse correlation beteen the hydroxyl population on the silica surface and the catalyst activity and termination rate. Possibly these hydroxyls coordinate to the active center and kill or at least retard it. Groeneveld et al. have reported that on barely activated samples, protons from surface hydroxyls later appear in the polymer (5,9). This may be evidence of interference by hydroxyls. Or perhaps the hydroxyls are not directly involved at all, but merely reflect some other important change such as the strain introduced onto the surface by their condensation. Whatever the reason, this relationship is used commercially to control MW and many other important polymer properties. 

Conventional GPC data processing is unable to determine other important polymer properties such as copolymer composition or copolymer molar mass. The reason is that the GPC separation is based on hydro-dynamic volume rather than the molar mass of the polymer and that molar mass calibration data are only valid for polymers of identical molecular structures. 

Other important polymers are Polyquaternium-11, a coplymer of vinylpyrroli-done and dimethylaminoethyl methacrylate quaternized with dimethyl sulfate. 

In spite of the great discoveries by Ziegler and Natta, most synthetic polymers are still made by free-radical reactions. Some of the important homopolymers are poly (vinyl chloride), poly (methyl methacrylate), polystyrene, and low-density polyethylene. Other important polymers made by free-radical reactions contain two or more monomers, for example, the styrene-butadiene rubbers, and the acrylonitrile-butadiene-styrene plastics. Most of these polymers are not stereoregular. A few that are represent the subject of this section. 

Other important polymers for the additives business include the styrenics and ABS, the polyesters PET and PBT, the polyamides, acrylics, thermoplastic polyurethanes and thermoplastic elastomers. Additives are widely used in blends too. 

These same considerations apply to other important polymer groups that must be dissolved at elevated temperature. They include polyacetals, polyvinylidene fluoride, polyetherketone (PEK), polyetheretherketone (PEEK), polyether sulfone, polyimide, and imide copolymers. Traditionally polyamides and polyesters also were analyzed at elevated temperature, but HFIP will dissolve them at room temperature (Fig. 17). 

The properties similar to polycarbonates show polyarylate resins, synthesized usually by polycondensation process from terephthalic acid, isophthalic acid chloride, and BPA (Fig. 7.18). Polyarylates exhibit good impact strength, high deflection temperature, good chemical, thermal, weather and UV resistance as well as the dimensional stability higher than that of polycarbonates. Other important polymers with industrial significance, derived from BPA, are unsaturated polyesters (e.g., epoxyfuma-rate resins) [78], polyetherimides and polyether ether ketones (Fig. 7.18). 

The field of step-growth polymers encompasses many polymer structures and polymerization reaction types. This chapter attempts to cover topics in step-growth polymerization outside of the areas reviewed in the other introductory chapters in this book, i.e., poly(aryl ethers), dendritic polymers, high-temperature polymers and transition-metal catalyzed polymerizations. Polyamides, polyesters, polycarbonates, poly(phenylene sulfides) and other important polymer systems are addressed. The chapter is not a comprehensive review but rather an overview of some of the more interesting recent research results reported for these step-growth polymers, including new polymerization chemistries and mechanistic studies. 

Used as fibres, particularly in textiles and film. Many other polyester polymers are of importance, e.g. unsaturated polyester resins from phthalic anhydride, propylene glycol and maleic anhydride used with reinforcement in boats, cars, etc. (alkyd resins). U.S. production 1983 1-7 megatonnes. 

We shall devote a considerable portion of this chapter to discussing the thermodynamics of mixing according to the Flory-Huggins theory. Other important concepts we discuss in less detail include the cohesive energy density, the Flory-Krigbaum theory, and a brief look at charged polymers. 

Two other important commercial uses of initiators are in polymer cross-linking and polymer degradation. In a cross-linking reaction, atom abstraction, usually a hydrogen abstraction, occurs, followed by termination by coupling of two polymer radicals to form a covalent cross-link ... 

One of the important attributes of alkyds is their good compatibiUty with a wide variety of other coating polymers. This good compatibiUty comes from the relatively low molecular weight of the alkyds, and the fact that the resin stmcture contains, on the one hand, a relatively polar and aromatic backbone, and, on the other hand, many aUphatic side chains with low polarity. An alkyd resin in a blend with another coating polymer may serve as a modifier for the other film-former, or it may be the principal film-former and the other polymer may serve as the modifier for the alkyd to enhance certain properties. Examples of compatible blends foUow. 

Polymerization Reactions. The polymerization of butadiene with itself and with other monomers represents its largest commercial use. The commercially most important polymers are styrene—butadiene mbber (SBR), polybutadiene (BR), styrene—butadiene latex (SBL), acrylonittile—butadiene—styrene polymer (ABS), and nittile mbber (NR). The reaction mechanisms are free-radical, anionic, cationic, or coordinate, depending on the nature of the initiators or catalysts (194—196). 

High impact strength, increased hardness, lower thermal expansion, and high fatigue strength are also important properties required of denture-base materials. To address these deficiencies, alternatives to the traditional PMMA dentures have been sought. These include the use of other base polymers and reinforced designed denture systems. 

Butyl rubber and other isobutylene polymers of technological importance iaclude various homopolymers and isobutylene copolymers containing unsaturation achieved by copolymerization with isoprene. Bromination or chlorination of the unsaturated site is practiced commercially, and other modifications are beiag iavestigated. 

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