Poly , exclusion

Formaldehyde homopolymer is composed exclusively of repeating oxymethylene units and is described by the term poly oxymethylene (POM) [9002-81-7]. Commercially significant copolymers, for example [95327-43-8] have a minor fraction (typically less than 5 mol %) of alkyUdene or other units, derived from cycHc ethers or cycHc formals, distributed along the polymer chain. The occasional break in the oxymethylene sequences has significant ramifications for polymer stabilization. 

Molybdenum Oxides. Molybdenum was one of the first elements used to retard the flames of ceUulosics (2). Mote recently it has been used to impart flame resistance and smoke suppression to plastics (26). Molybdic oxide, ammonium octamolybdate, and zinc molybdate ate the most widely used molybdenum flame retardants. Properties ate given in Table 5. These materials ate recommended almost exclusively for poly(vinyl chloride), its alloys, and unsaturated polyesters (qv). 

Poly(ethylene oxide). The synthesis and subsequent hydrolysis and condensation of alkoxysilane-terniinated macromonomers have been studied (39,40). Using Si-nmr and size-exclusion chromatography (sec) the evolution of the siUcate stmctures on the alkoxysilane-terniinated poly(ethylene oxide) (PEO) macromonomers of controlled functionahty was observed. Also, the effect of vitrification upon the network cross-link density of the developing inorganic—organic hybrid using percolation and mean-field theory was considered. 

Figure 4c illustrates interfacial polymerisation encapsulation processes in which the reactant(s) that polymerise to form the capsule shell is transported exclusively from the continuous phase of the system to the dispersed phase—continuous phase interface where polymerisation occurs and a capsule shell is produced. This type of encapsulation process has been carried out at Hquid—Hquid and soHd—Hquid interfaces. An example of the Hquid—Hquid case is the spontaneous polymerisation reaction of cyanoacrylate monomers at the water—solvent interface formed by dispersing water in a continuous solvent phase (14). The poly(alkyl cyanoacrylate) produced by this spontaneous reaction encapsulates the dispersed water droplets. An example of the soHd—Hquid process is where a core material is dispersed in aqueous media that contains a water-immiscible surfactant along with a controUed amount of surfactant. A water-immiscible monomer that polymerises by free-radical polymerisation is added to the system and free-radical polymerisation localised at the core material—aqueous phase interface is initiated thereby generating a capsule sheU (15). 

Heat resistance is an important characteristic of the bond. The strength of typical abrasive stmctures is tested at RT and at 300°C. Flexural strengths are between 24.1 and 34.4 MPa (3500—5000 psi). An unmodified phenoHc resin bond loses about one-third of its room temperature strength at 298°C. Novolak phenoHc resins are used almost exclusively because these offer heat resistance and because the moisture given off during the cure of resole resins results in undesirable porosity. Some novolaks modified with epoxy or poly(vinyl butyral) resin are used for softer grinding action. 

The most innovative photohalogenation technology developed in the latter twentieth century is that for purposes of photochlorination of poly(vinyl chloride) (PVC). More highly chlorinated products of improved thermal stabiUty, fire resistance, and rigidity are obtained. In production, the stepwise chlorination may be effected in Hquid chlorine which serves both as solvent for the polymer and reagent (46). A soHd-state process has also been devised in which a bed of microparticulate PVC is fluidized with CI2 gas and simultaneously irradiated (47). In both cases the reaction proceeds, counterintuitively, to introduce Cl exclusively at unchlorinated carbon atoms on the polymer backbone. 

Phthahc anhydride (1) is the commercial form of phthaUc acid (2). The worldwide production capacity for the anhydride was ca 3.5 x 10 metric tons ia 1993, and it was used ia the manufacture of plasticizers (qv), unsaturated polyesters, and alkyd resins (qv) (see Polyesters, unsaturated). Sales of terephthahc acid (3) and its dimethyl ester are by far the largest of any of the benzenepolycarboxyhc acids 14.3 x 10 t were produced in 1993. This is 80% of the total toimage of ah. commercial forms of the benzenepolycarboxyhc acids. Terephthahc acid is used almost exclusively for the manufacture of poly(ethylene terephthalate), which then is formed into textiles, films, containers, and molded articles. Isophthahc acid (4) and trimehitic anhydride (5) are commercial products, but their worldwide production capacities are an order of magnitude smaller than for terephthahc acid and its dimethyl ester. Isophthahc acid is used primarily in the production of unsaturated polyesters and as a comonomer in saturated polyesters. Trimehitic anhydride is used mainly to make esters for high performance poly(vinyl chloride) plasticizers. Trimesic acid (6), pyromehitic dianhydride (7), and hernimehitic acid (8) have specialized commercial apphcations. The rest of the benzenepolycarboxyhc acids are not available commercially. 

U.S. capacities, given ia Table 19, show considerable stability both as to the producers and the amount produced. There have been no entrances or exits from the producer Hst since the 1970s. Amoco is totally a merchant suppHer, whereas the other producers are poly(ethylene terephthalate) producers who exclusively or mosdy satisfy their own requirements. 

Nucleophilic Substitution Route. Commercial synthesis of poly(arylethersulfone)s is accompHshed almost exclusively via the nucleophilic substitution polycondensation route. This synthesis route, discovered at Union Carbide in the early 1960s (3,4), involves reaction of the bisphenol of choice with 4,4 -dichlorodiphenylsulfone in a dipolar aprotic solvent in the presence of an alkaUbase. Examples of dipolar aprotic solvents include A/-methyl-2-pyrrohdinone (NMP), dimethyl acetamide (DMAc), sulfolane, and dimethyl sulfoxide (DMSO). Examples of suitable bases are sodium hydroxide, potassium hydroxide, and potassium carbonate. In the case of polysulfone (PSE) synthesis, the reaction is a two-step process in which the dialkah metal salt of bisphenol A (1) is first formed in situ from bisphenol A [80-05-7] by reaction with the base (eg, two molar equivalents of NaOH),... 

Poly(vinyl acetate) latex paints are the first choice for interior use (149). Their abihty to protect and decorate is reinforced by several advantages belonging exclusively to latex paints they do not contain solvents so that physiological harm and fire ha2ards are eliminated they are odorless they are easy to apply with spray gun, roUer-coater, or bmsh and they dry rapidly. The paint can be thinned with water, and bmshes or coaters can be cleaned with soap and tepid water. The paint is usually dry in 20 minutes to two hours, and two coats may be applied the same day. 

Ninety-six percent of the EDC produced in the United States is converted to vinyl chloride for the production of poly(vinyl chloride) (PVC) (1) (see Vinyl polymers). Chloroform and carbon tetrachloride are used as chemical intermediates in the manufacture of chlorofluorocarbons (CECs). Methjiene chloride, 1,1,1-trichloroethane, trichloroethylene, and tetrachloroethylene have wide and varied use as solvents. Methyl chloride is used almost exclusively for the manufacture of silicone. Vinylidene chloride is chiefly used to produce poly (vinylidene chloride) copolymers used in household food wraps (see Vinylidene chloride and poly(vinylidene chloride). Chloroben2enes are important chemical intermediates with end use appHcations including disinfectants, thermoplastics, and room deodorants. 

The calciaed or meta kaolin is used almost exclusively ia poly(vinyl chloride) wire iasulation because it enhances the electrical resistivity of the compound. 

Most moisture-curing hot-melt adhesives utilize a crystallizable backbone and are based almost exclusively on monomeric MDI at NCO/OH ratios of 1.5 to 2.2. Poly(hexamethylene adipate) polyol is the workhorse of the curing hot-melt adhesives. 

Figure 3 Reversed-phase chromatography of products after alkaline hydrolysis of /3-poly(L-malate), Discrete polymer products are formed, which differ in length by several units of L-malate. The absorbance at 220-nm wavelength was measured, (a) /3-Poly(L-malate) before hydrolysis, (b) After 10-min incubation in 20 mM NaOH at 37°C. (c) After 15 h in 20 mM NaOH at 37°C. (d) After I h in 500 mM NaOH at 100°C. High pressure chromatography (HPLC) on Waters reversed-phase Ci8- i-Bondapak. The methanol gradient (in water-trifluoro acetic acid, pH 3.0) was programmed as follows 0-40 min 0.3-23%, 40-47 min 23-40%, 47-49 min 40%, 49-54 min 40-0%. (d) Inset size exclusion chromatography after 3-min alkaline hydrolysis at pH 10.2. BioSil SEC 250 column of 300 mm x 7.8 mm size, 0.2 M potassium phosphate buffer pH 7.0.

The polyelectrolyte catalysis of chemical reactions involving ionic species has been the subject of extensive investigations since the pioneering studies of Morawetz et al. [12] and Ise et al. [13-17]. The catalytic effect or the ability of poly-electrolytes to enhance or retard reaction rates is mainly due to concentration or exclusion of either or both of the ionic reactants by the polyions added to the reaction systems. For example, the chemical reaction between ionic species carrying the same charge is enhanced in the presence of polyions carrying the opposite charge. This enhancement can be attributed to an increase in the local concentration... 

However, Pacansky and his coworkers77 studied the degradation of poly(2-methyl-l-pentene sulfone) by electron beams and from infrared studies of the products suggest another mechanism. They claim that S02 was exclusively produced at low doses with no concomitant formation of the olefin. The residual polymer was considered to be essentially pure poly(2-methyl-l-pentene) and this polyolefin underwent depolymerization after further irradiation. However, the high yield of S02 requires the assumption of a chain reaction and it is difficult to think of a chain reaction which will form S02 and no olefin. 

A typical Ziegler-Natta catalyst is the complex prepared from titanium tetrachloride and triethylaluminium. It is fed into the reaction vessel first, after which ethylene is added. Reaction is carried out at low pressures and low temperatures, typically no more than 70 °C, with rigorous exclusion of air and moisture, which would destroy the catalyst. The poly(ethylenes) produced by such processes are of intermediate density, giving values of about 0.945 g cm. A range of relative molar masses may be obtained for such... 

Before analyzing in detail the conformational behaviour of y9-peptides, it is instructive to look back into the origins and the context of this discovery. The possi-bihty that a peptide chain consisting exclusively of y9-amino acid residues may adopt a defined secondary structure was raised in a long series of studies which began some 40 years ago, on y9-amino acid homopolymers (nylon-3 type polymers), such as poly(/9-alanine) 3 [14, 15], poly(y9-aminobutanoic acid) 4 [16-18], poly(a-dialkyl-/9-aminopropanoic acid) 5 ]19], poly(y9-L-aspartic acid) 6 ]20, 21], and poly-(a-alkyl-/9-L-aspartate) 7 [22-36] (Fig. 2.1). 

Vinyl chloride is used exclusively for the preparation of plastics, by homopolymerization to poly(vinyl chloride) (PVC) and by copolymerization with other vinyl (-CH2=CH-) compounds. 

Even though poly(ortho esters) contain hydrolytically labile Linkages, they are highly hydrophobic materiads and for this reason are very stable and can be stored without careful exclusion of moisture. However, the ortho ester linkage in the polymer is inherently thermally unstable and at elevated temperatures is believed to dissociate into an alcohol and a ketene acetal (33). A possible mechanism for the thermal degradation is shown below. This thermal degradation is similar to that observed with polyurethanes (34). 

Whereas conventional poly (amino acids) are probably best grouped together with proteins, polysaccharides, and other endogenous polymeric materials, the pseudopoly (amino acids) can no longer be regarded as "natural polymers." Rather, they are synthetic polymers derived from natural metabolites (e.g., a-L-amino acids) as monomers. In this sense, pseudopoly (amino acids) are similar to polylactic acid, which is also a synthetic polymer, derived exclusively from a natural metabolite. 

In the previous Sections, the properties of acids and bases in macrocycles and other concave structures have been compared. A number of factors have been recognized which influence the acidity or basicity of an acid or base (i) hydrogen bonds, (ii) hindered solvation (exclusion of solvent), (iii) formation of tight ion pairs (high microacidity but low overall acidity), and (iv) Coulomb forces when poly anions are formed. A fifth influence, (v) steric hindrance, still has to be discussed. 

Poly(2,6-dimethyl-l,4-oxyphenylene) (poly(phenylene oxide), PPG) is a material widely used as high-performance engineering plastics, thanks to its excellent chemical and physical properties, e.g., a high 7 (ca. 210°C) and mechanically tough property. PPO was first prepared from 2,6-dimethylphenol monomer using a copper/amine catalyst system. 2,6-Dimethylphenol was also polymerized via HRP catalysis to give a polymer exclusively consisting of 1,4-oxyphenylene unit, while small amounts of Mannich-base and 3,5,3, 5 -tetramethyl-4,4 -diphenoquinone units are always contained in the chemically prepared PPO. 

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