Poly excess

The ethylene glycol liberated by reaction (5.L) is removed by lowering the pressure or purging with an inert gas. Because the ethylene glycol produced by reaction (5.L) is removed, proper stoichiometry is assured by proceeding via the intermediate, bis(2-hydroxyethyl) terephthalate otherwise the excess glycol used initially would have a deleterious effect on the degree of polymerization. Poly(ethylene terephthalate) is more familiar by some of its trade names Mylar as a film and Dacron, Kodel, or Terylene as fibers it is also known by the acronym PET. 

HydroxyethyUiydrazine (11) is a plant growth regulator. It is also used to make a coccidiostat, furazoHdone, and has been proposed, as has (14), as a stabilizer in the polymerization of acrylonitrile (72,73). With excess epoxide, polysubstitution occurs and polyol chains can form to give poly(hydroxyaLkyl) hydrazines which have been patented for the preparation of cellular polyurethanes (74) and as corrosion inhibitors for hydrauHc fluids (qv) (75). DialkyUiydrazines, R2NNH2, and alkylene oxides form the very reactive amineimines (15) which react further with esters to yield aminimides (16) ... 

Poly(viayl acetate) emulsions or hot-melt adhesives are typically used to form the manufacturer s or glue lap joiat of the box. The main criteria for the adhesive is that it provide a strong and tough final bond and that it set up quickly enough to allow fast box production speeds. Production rates ia excess of 240 boxes per minute are not uncommon ia the iadustry. 

The overall yield of the process is at least 87 mol %, and 2.3 mol of methanol per mole of final product are needed, an excess of 15% over the 2.0 theoretical amount. The methanol can be recycled from the manufacture of poly(ethylene terephthalate). Reported utilities consumptions per kilogram of product are 1.2 kg of 1400-kPa steam, 420 kj of boiler fuel, and 0.5 kWh of electricity (72). 

The packaging (qv) requirements for shipping and storage of thermoplastic resins depend on the moisture that can be absorbed by the resin and its effect when the material is heated to processing temperatures. Excess moisture may result in undesirable degradation during melt processing and inferior properties. Condensation polymers such as nylons and polyesters need to be specially predried to very low moisture levels (3,4), ie, less than 0.2% for nylon-6,6 and as low as 0.005% for poly(ethylene terephthalate) which hydrolyzes faster. 

Manufacture. PVBs are manufactured by a variety of two-stage heterogeneous processes. In one of these an alcohol solution of poly(vinyl acetate) and an acid catalyst are heated to 60—80°C with strong agitation. As the poly(vinyl alcohol) forms, it precipitates from solution (77). Ethyl acetate, the principle by-product, is stripped off and sold. The precipitated poly(vinyl alcohol) is washed to remove by-products and excess acid. The poly(vinyl alcohol) is then suspended in a mixture of ethyl alcohol, butyraldehyde, and mineral acid at temperatures above 70°C. As the reaction approaches completion the reactants go into solution. When the reaction is complete, the catalyst is neutralized and the PVB is precipitated from solution with water, washed, centrifuged, and dried. Resin from this process has very low residual vinyl acetate and very low levels of gel from intermolecular acetalization. 

Drying of the poly(vinyl alcohol) is critical to both the color and solubiHty of the final product. Excessive drying temperatures result in high product color and an increase in the crystallinity, which in turn reduces the solubiHty of the product. Drying is initially subjected to a flash regime, where the solvent not contained within the particles is flashed off. This first phase is foUowed by a period where the rate is controUed by the diffusion rate of solvent from the poly(vinyl alcohol) particles. Because the diffusion rate falls as the material dries, complete drying is not practical. The polymer is therefore generally sold at a specification of 95% soHds. 

The PVA process is highly capital-iatensive, as separate faciUties are required for the production of poly(viayl acetate), its saponification to PVA, the recovery of unreacted monomer, and the production of acetic acid from the ester formed during alcoholysis. Capital costs are far in excess of those associated with the traditional production of other vinyl resins. 

Poly(phenylene sulfide) (PPS) is another semicrystalline polymer used in the composites industry. PPS-based composites are generally processed at 330°C and subsequently cooled rapidly in order to avoid excessive crystallisation and reduced toughness. The superior fire-retardant characteristics of PPS-based composites result in appHcations where fire resistance is an important design consideration. Laminated composites based on this material have shown poor resistance to transverse impact as a result of the poor adhesion of the fibers to the semicrystalline matrix. A PPS material more recently developed by Phillips Petroleum, AVTEL, has improved fiber—matrix interfacial properties, and promises, therefore, an enhanced resistance to transverse impact (see PoLYAffiRS containing sulfur). 

Hard lenses can be defined as plastic lenses that contain no water, have moduli in excess of 5 MPa (500 g/mm ), and have T well above the temperature of the ocular environment. Poly(methyl methacrylate) (PMMA) has excellent optical and mechanical properties and scratch resistance and was the first and only plastic used as a hard lens material before higher oxygen-permeable materials were developed. PMMA lenses also show excellent wetting in the ocular environment even though they are hydrophobic, eg, the contact angle is 66°. 

Suspension Polymerization. This method (10) might be considered as a number of bulk polymerizations carried out simultaneously in the monomer droplets with water acting as a heat-transfer medium. A monomer-soluble initiator, eg, a peroxide or azo compound, and a protective coUoid like poly(vinyl alcohol) or bentonite, are requited. After completion of the polymerization, the excess of monomer(s) is steam stripped, and the beads of polymer are collected and washed on a centrifiige or filter and dried on a vibrating screen or by means of an expeUer—extmder. 

Latex Types. Latexes are differentiated both by the nature of the coUoidal system and by the type of polymer present. Nearly aU of the coUoidal systems are similar to those used in the manufacture of dry types. That is, they are anionic and contain either a sodium or potassium salt of a rosin acid or derivative. In addition, they may also contain a strong acid soap to provide additional stabUity. Those having polymer soUds around 60% contain a very finely tuned soap system to avoid excessive emulsion viscosity during polymeri2ation (162—164). Du Pont also offers a carboxylated nonionic latex stabili2ed with poly(vinyl alcohol). This latex type is especiaUy resistant to flocculation by electrolytes, heat, and mechanical shear, surviving conditions which would easUy flocculate ionic latexes. The differences between anionic and nonionic latexes are outlined in Table 11. 

About 60% of the ethylene oxide produced is converted to ethylene glycol by reaction of ethylene oxide ia the presence of excess water and an acidic catalyst at 50—70°C. This is followed by hydrolysis at relatively high temperatures (140—230°C) and 2—4 MPa (20—40 bar) (see Glycols, ethylene glycol). When the water concentration is lowered, poly(ethylene glycol) is obtained. 

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)... 

As with the polysulphones, the deactivated aromatic nature of the polymer leads to a high degree of oxidative stability, with an indicated UL Temperature Index in excess of 250°C for PEEKK. The only other melt-processable polymers in the same league are poly(phenylene sulphides) and certain liquid crystal polyesters (see Chapter 25). 

Whilst the Tg of poly(dimethylsiloxane) rubbers is reported to be as low as -123°C they do become stiff at about -60 to -80°C due to some crystallisation. Copolymerisation of the dimethyl intermediate with a small amount of a dichlorodiphenylsilane or, preferably, phenylmethyldichlorosilane, leads to an irregular structure and hence amorphous polymer which thus remains a rubber down to its Tg. Although this is higher than the Tg of the dimethylsiloxane it is lower than the so that the polymer remains rubbery down to a lower temperature (in some cases down to -100°C). The Tg does, however, increase steadily with the fraction of phenylsiloxane and eventually rises above that of the of the dimethylsilicone rubber. In practice the use of about 10% of phenyldichlorosilane is sufficient to inhibit crystallisation without causing an excess rise in the glass transition temperature. As with the polydimethylsilox-anes, most methylphenyl silicone rubbers also contain a small amount of vinyl groups. 

The chemical name for such materials is poly(bisbenzimid-azobenzophenan-throlines) but they are better known as BBB materials. Such polymers have a Tg in excess of 450°C and show only a low weight loss after aging in air for several hundred hours at 370°C. Measurements using thermal gravimetric analysis indicate a good stability to over 600°C. The main interest in these materials is in the field of heat-resistant films and fibres. 

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