Polymers/polymerization/plastics

Raw Materials. PVC is inherently a hard and brittle material and very sensitive to heat it thus must be modified with a variety of plasticizers, stabilizers, and other processing aids to form heat-stable flexible or semiflexible products or with lesser amounts of these processing aids for the manufacture of rigid products (see Vinyl polymers, vinyl chloride polymers). Plasticizer levels used to produce the desired softness and flexibihty in a finished product vary between 25 parts per hundred (pph) parts of PVC for flooring products to about 80—100 pph for apparel products (245). Numerous plasticizers (qv) are commercially available for PVC, although dioctyl phthalate (DOP) is by far the most widely used in industrial appHcations due to its excellent properties and low cost. For example, phosphates provide improved flame resistance, adipate esters enhance low temperature flexibihty, polymeric plasticizers such as glycol adipates and azelates improve the migration resistance, and phthalate esters provide compatibiUty and flexibihty (245). 

Uses. Neopentyl glycol is used extensively as a chemical intermediate in the manufacture of polyester resins (see Alkyd resins), polyurethane polyols (see Urethane polymers), synthetic lubricants, polymeric plasticizers (qv), and other polymers. It imparts a combination of desirable properties to properly formulated esterification products, including low color, good weathering and chemical resistance, and improved thermal and hydrolytic stabiUty. 

Plasticizers. Monomeric (mol wt 250—450) plasticizers (qv) are predominantiy phthalate, adipate, sebacate, phosphate, or trimeUitate esters. Organic phthalate esters like dioctyl phthalate (DOP) are by far the most common plasticizers in flexible PVC. Phthalates are good general-purpose plasticizers which impart good physical and low temperature properties but lack permanence in hot or extractive service conditions and are therefore sometimes called migratory plasticizers. Polymeric plasticizers (mol wt up to 5000 or more) offer an improvement in nonmigratory permanence at a sacrifice in cost, low temperature properties, and processibiHty examples are ethylene vinyl acetate or nitrile polymers. 

Different types of PVC exist on the market. The two principle types are suspension and paste-forrning PVC the latter includes the majority of emulsion PVC polymers. The plasticizer appHcations technologies associated with these two forms are distinctly different and are discussed separately. Details of the polymerization techniques giving rise to these two distinct polymer types can be found in many review articles (5,28) (see ViNYLPOLYMERS, (VINYL Cm ORIDE POLYPffiRS)). 

Polymers are examples of organic compounds. However, the main difference between polymers and other organic compounds is the size of the polymer molecules. The molecular mass of most organic compounds is only a few hundred atomic mass units (for reference, atomic hydrogen has a mass of one atomic mass unit). The molecular masses of polymeric molecules range from thousands to millions of atomic mass units. Synthetic polymers include plastics and synthetic fibers, such as nylon and polyesters. Naturally occurring polymers include proteins, nucleic acids, polysaccharides, and rubber. The large size of a polymer molecule is attained by the repeated attachment of smaller molecules called monomers. 

The production of monomers and their reaction to form polymers account for more than half of the chemical industry, and the polymers and plastics industries are among the major employers of chemical engineers. Many of the reactions we have considered previously were concerned with methods of preparing the small molecule monomers that are used in preparing polymers. In this chapter we consider the reactors used to polymerize these molecules into polymers. We will see that the reactions we are trying to manage are sufficiently different so that the reactors needed for polymerization processes are qualitatively different than for other chemical processes. 

Later, a polymerized zinc electrode was developed [322] using wetting polymer and plastically shaping polymer materials, which improved the performance of batteries for many cycles. 

Beniska and Staudner (55) described a different method for the grafting of vinyl polymers on plasticized rubber. In a first stage they performed a degradation at 20-25° C in the presence of oxygen and hydroperoxide groups. The hydroperoxides are decomposed by heat (at 90, 100, and 120°C) with formation of macroradicals which initiate polymerization of monomers. It is claimed that with increasing time of plasticizing and temperature, the conversion of monomers increased. 

In addition to the effects on physical properties, an effect on ballistic properties may also be observed. If the polymer does not fill the entire space not occupied by the solids, when ignited the flame front may proceed by connected voids to yield an uncontrolled combustion condition. A porous condition can have an effect on the sensitivity to detonation as discussed in Chapter 10. The attractive forces between polymer and solids are probably the major contributing factor that causes differences in physical properties of propellant and causes one polymeric or polymer-plus-plasticizer system to be preferred over another. 

Permanence. The permanence of a plasticizer-i.e., its tendency to remain in the plasticized material, depends on the size of the plasticizer molecule and on its rate of diffusion in the polymer. The larger the plasticizer molecule, the lower its vapor pressure, or volatility and, therefore, the greater its permanence. This accounts for the popularity of certain polymeric plasticizers, such as polyesters, in spite of their relatively high price. Other factors, such as polarity and hydrogen bonding, will also, of course, affect the vapor pressure of the plasticizer. 

This approach is very useful for polymer-plasticizer systems, and especially for cases where polymeric plasticizers, which evidently cannot be treated as volatile liquids, are being considered. 

Polymaric plasticizars can ba mada by (1) Internal plasticization whoroby a monomor is copolymorizod with on which tends to yield soft polymers by itself (2) Mechanical mixing of a polymerizable monomer with a polymer, followed by polymerization (3) Mechanical blending of two compatible polymers. In many cases It Is necessary to combine the polymeric plasticizer with a liquid plasticizer because the compatibility of polymers with each other is generally limited. From the industrial polymeric plasticizers, especially polyesters of low degree of polymerization and several copolymers of butadiene with acrylonitrile, acrylic add esters and fumaric add esters were studied. These polymeric plasticizers are characterized by good compatibility and improved cold resistance of the final product. 

The principal polymeric plasticizers are the polymer hydrocarbons and the polyesters. The condensation products of diols and dicarboxylic acids, belonging to the polyester group, are most important. Higher functional compounds, like triols and tricarboxylic acids, are less important as are polyethers, polyacetals, and polymeric acids. 

The application of polymeric plasticizers can be effected by mixing a preformed polymer mechanically with a polymerizable monomer containing the catalyst and subsequent polymerization. But side reactions, like grafting, must be expected. Generally, this method has not found wide application because the resulting products are likely to show poor mechanical properties. Besides, mixing the monomer on the rolls or in the extruder leads to losses by evaporation and causes unpleasant odors. Furthermore, some of the more important monomers, like the acrylates, show poor compatibility with many polymers. For instance, PVC is not sufficiently plasticizable with acrylates. 

If the polymers and the polymeric plasticizers are prepared by emulsion polymerization, incorporating the plasticizer can be simplified if the mixture of both emulsions is coagulated and processed further. 

The extraordinary versatility of this polymeric plastic material, which has made it one of the most widely used of the myriad of polymers and copolymers available today, is demonstrated by its range of end uses. PVC products have properties that combine strength, lightness, and inertness with a wide range of resilience, excellent color acceptance, electrical insulating properties, crystal-like clarity, and the ability to be processed easily by many methods into a tremendous variety of forms. 

Both polymeric and silica-based columns are in common use.The polymeric columns are heavily used in the analysis of synthetic polymers and plastics where organic solvents are required. Silica-based columns with hydrophilic bonded phases are used to separate aqueous solutions of macromolecules. Finally, polymeric size-separation columns with hydrophilic phases are available for separation of polysaccharides, peptides, and very small proteins. 

Mixing principles are relevant to many disciplines what makes mixing polymeric materials unique is their exceptionally high viscosity. There are numerous texts (1-5) that are entirely devoted to the complex problem of mixing of polymers and plastics, and we refer the reader to them for further reading. 

Blending of polymers is an attractive method of producing new materials with better properties. Blends of aliphatic polyesters, especially of poly(e-CL), have been investigated extensively and have been the subject of a recent review paper [170]. Poly(e-CL) has been reported to be miscible with several polymers such as PVC, chlorinated polyethylene, SAN, bisphenol A polycarbonate, random copolymers of Vdc and VC, Vdc and AN, and Vdc/VAc, etc. A single composition-dependent Tg was obtained in the blends of each of these polymers with poly(e-CL). This is of interest as a polymeric plasticizer in these polymers. Blends of PVC and poly(e-CL) with less than 50 wt % of poly(e-CL) were homogeneous and exhibited a single Tg. These blends were soft and pliable because the inherent crystallinity of poly(e-CL) was destroyed and PVC was plasticized... 

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