Stability copolymers

Table I. Stabilizing Copolymers, Particle Sizes and Surface Coverage of PMMA Dispersions in Flocculation Experiments (9)...

Impact- Modified Copolymer Mineral- filled Copolymer Extrusion and Blow Molding Grade (Terpolymer) Copolymer with 2% Silicone Low Wear uv Stabilized Copolymer 20% Glass-reinforced Homopolymer 25% Glass- Coupled Copolymer 40% Long Glass Liber-reinforced 21% PTFE-filled homo- polymer 2-20% PTFE-filled Copolymer 1.5% PTFE-filled Homo- Polymer... 

One of the stages on the route was Ford s introduction of black rubber strips along the bumper in the 1973 Capri another was the addition of plastic end caps to chrome bumpers, at Fiat and VW. The mix of black and chrome persisted as a styling feature for a while. The plastic end cap idea had obvious benefits elimination of post-forming operations, the extension of wrap-around , with possibilities for styling variations, and conceivable benefits to pedestrians. Originally PUR was the selected material, particularly in Japan, with ABS and HOPE in use in Europe. However PP quickly took over everywhere, as UV stabilized copolymer grades. A common feature of low price cars for many years was the matt black bumper in rolled steel with PP wrap-around end caps. 

Their good electrical and high mechanical properties, notably their UL electrical rating for 100 C (212 F), qualify these plastics for electrical parts requiring long-time stability. Copolymers have excellent resistance to chemicals and solvents. For example, samples... 

Table II. Compositions of the Steric Stabilized Copolymer Latexes...

Emulsion copolymerizations can be carried out using batch, semi-continuous, or continuous processes. The copolymers made by these processes differ according to the process used, the copoly-meriztion reactivity ratios of the monomers, and the monomer solubilities in the aqueous phase. To show the difference between batch and semi-continuous polymerization, the latex particle size, surface characteristics, latex stability, copolymer properties, and latex film morphology were investigated for the vinyl acetate-butyl acrylate system (37). The water solubilities are 290 mM and llmM for vinyl acetate and butyl acrylate, respectively, and the copoly-merization reactivity ratios of = 0-0.04 and r 2 show... 

Lamination of Paper and Board. Adhesives based on starch, dextrin, glutin and poly(vinyl alcohol), and also emulsion adhesives, mainly polyfvinyl acetate), are used for the lamination of paper and board. Only when high initial tack and a lay-flat effect are required are hot glues based on glutin still in use. Starch-based adhesives modified with silicate, casein-stabilized copolymer dispersions, and rubber latices are used in the lamination of paper to aluminum foils. Modified polyacrylate solutions and reactive polyurethane adhesives are used mainly for paper-to-plastic lamination. 

While polystyrenes can also be used non-stabilized, copolymers with butadiene content, such as ABS, must be protected against thermal-oxidative damage by antioxidants alone or in combination with synergists. The most important antioxidants here are phenolic antioxidants and BHT (butylated hydroxy toluene). Phosphites are used as synergists and long-chain thiodipropionates as thiosynergists, respectively. The butadiene content determines the antioxidant or the mixture of antioxidant pius synergist needed, see Table 3.3 [86]. 

Perfluoroalkylvinylethers (PAVE) forms an important class of monomers in that they are comonomers of choice for the modification of the properties of ho-mofluoropolymers in addition to their broad use in the structure of copolymers of TFE. They are capable of suppressing the crystallization of polytetrafluoroeth-ylene efficiently, which imparts useful mechanical properties to lower molecular weight PTFE polymers. The advantage of PAVEs as modifiers over hexafluoropropylene is their remarkable thermal stability. Copolymers of PAVEs andtetrafluoroethylene are as thermally stable as PTFE homopolymers. 

Polymeric vinylidene chloride generally produced by free radical polymerization of CH2 = CCl2. Homopolymers and copolymers are used. A thermoplastic used in moulding, coatings and fibres. The polymers have high thermal stability and low permeability to gases, and are self extinguishing. 

An important industrial example of W/O emulsions arises in water-in-crude-oil emulsions that form during production. These emulsions must be broken to aid transportation and refining [43]. These suspensions have been extensively studied by Sjoblom and co-workers [10, 13, 14] and Wasan and co-workers [44]. Stabilization arises from combinations of surface-active components, asphaltenes, polymers, and particles the composition depends on the source of the crude oil. Certain copolymers can mimic the emulsion stabilizing fractions of crude oil and have been studied in terms of their pressure-area behavior [45]. 

Finally, we briefly mention interactions due to adsorbing polymers. Block copolymers, witli one block strongly adsorbing to tire particles, have already been mentioned above. Flere, we focus on homopolymers tliat adsorb moderately strongly to tire particles. If tliis can be done such tliat a high surface coverage is achieved, tire adsorbed polymer layer may again produce a steric stabilization between tire particles. 

Copolymer. Acetal copolymers are prepared by copolymerization of 1,3,5-trioxane with small amounts of a comonomer. Carbon-carbon bonds are distributed randomly in the polymer chain. These carbon-carbon bonds help to stabilize the polymer against thermal, oxidative, and acidic attack. 

These monomers provide a means for introducing carboxyl groups into copolymers. In copolymers these acids can improve adhesion properties, improve freeze-thaw and mechanical stability of polymer dispersions, provide stability in alkalies (including ammonia), increase resistance to attack by oils, and provide reactive centers for cross-linking by divalent metal ions, diamines, or epoxides. 

The formation of copolymers involves the reaction of (at least) two kinds of monomers. This means that each must be capable of undergoing the same propagation reaction, but is is apparent that quite a range of reactivities is compatible with this broad requirement. We shall examine such things as the polarity of monomers, the degree of resonance stabilization they possess and the steric... 

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. 

Nitrile mbber finds broad application in industry because of its excellent resistance to oil and chemicals, its good flexibility at low temperatures, high abrasion and heat resistance (up to 120°C), and good mechanical properties. Nitrile mbber consists of butadiene—acrylonitrile copolymers with an acrylonitrile content ranging from 15 to 45% (see Elastomers, SYNTHETIC, NITRILE RUBBER). In addition to the traditional applications of nitrile mbber for hoses, gaskets, seals, and oil well equipment, new applications have emerged with the development of nitrile mbber blends with poly(vinyl chloride) (PVC). These blends combine the chemical resistance and low temperature flexibility characteristics of nitrile mbber with the stability and ozone resistance of PVC. This has greatly expanded the use of nitrile mbber in outdoor applications for hoses, belts, and cable jackets, where ozone resistance is necessary. 

Thermal Oxidative Stability. ABS undergoes autoxidation and the kinetic features of the oxygen consumption reaction are consistent with an autocatalytic free-radical chain mechanism. Comparisons of the rate of oxidation of ABS with that of polybutadiene and styrene—acrylonitrile copolymer indicate that the polybutadiene component is significantly more sensitive to oxidation than the thermoplastic component (31—33). Oxidation of polybutadiene under these conditions results in embrittlement of the mbber because of cross-linking such embrittlement of the elastomer in ABS results in the loss of impact resistance. Studies have also indicated that oxidation causes detachment of the grafted styrene—acrylonitrile copolymer from the elastomer which contributes to impact deterioration (34). 

Emulsion Adhesives. The most widely used emulsion-based adhesive is that based upon poly(vinyl acetate)—poly(vinyl alcohol) copolymers formed by free-radical polymerization in an emulsion system. Poly(vinyl alcohol) is typically formed by hydrolysis of the poly(vinyl acetate). The properties of the emulsion are derived from the polymer employed in the polymerization as weU as from the system used to emulsify the polymer in water. The emulsion is stabilized by a combination of a surfactant plus a coUoid protection system. The protective coUoids are similar to those used paint (qv) to stabilize latex. For poly(vinyl acetate), the protective coUoids are isolated from natural gums and ceUulosic resins (carboxymethylceUulose or hydroxyethjdceUulose). The hydroHzed polymer may also be used. The physical properties of the poly(vinyl acetate) polymer can be modified by changing the co-monomer used in the polymerization. Any material which is free-radically active and participates in an emulsion polymerization can be employed. Plasticizers (qv), tackifiers, viscosity modifiers, solvents (added to coalesce the emulsion particles), fillers, humectants, and other materials are often added to the adhesive to meet specifications for the intended appHcation. Because the presence of foam in the bond line could decrease performance of the adhesion joint, agents that control the amount of air entrapped in an adhesive bond must be added. Biocides are also necessary many of the materials that are used to stabilize poly(vinyl acetate) emulsions are natural products. Poly(vinyl acetate) adhesives known as "white glue" or "carpenter s glue" are available under a number of different trade names. AppHcations are found mosdy in the area of adhesion to paper and wood (see Vinyl polymers). 

Chemical Resistance and Hydrolytic Stability. Modified ethylene—tetrafluoroethylene copolymers are resistant to chemicals and ... 

Copolymers of VF and a wide variety of other monomers have been prepared (6,41—48). The high energy of the propagating vinyl fluoride radical strongly influences the course of these polymerizations. VF incorporates well with other monomers that do not produce stable free radicals, such as ethylene and vinyl acetate, but is sparingly incorporated with more stable radicals such as acrylonitrile [107-13-1] and vinyl chloride. An Alfrey-Price value of 0.010 0.005 and an e value of 0.8 0.2 have been determined (49). The low value of is consistent with titde resonance stability and the e value is suggestive of an electron-rich monomer. 

Physical Stabilization Process. Cellulai polystyrene [9003-53-6] the outstanding example poly(vinyl chloride) [9002-86-2] copolymers of styrene and acrylonitrile (SAN copolymers [9003-54-7]) and polyethylene [9002-88-4] can be manufactured by this process. 

Cross-linked macromolecular gels have been prepared by Eriedel-Crafts cross-linking of polystyrene with a dihaloaromatic compound, or Eriedel-Crafts cross-linking of styrene—chloroalkyl styrene copolymers. These polymers in their sulfonated form have found use as thermal stabilizers, especially for use in drilling fluids (193). Cross-linking polymers with good heat resistance were also prepared by Eriedel-Crafts reaction of diacid haUdes with haloaryl ethers (194). 

Heat stabilizers protect polymers from the chemical degrading effects of heat or uv irradiation. These additives include a wide variety of chemical substances, ranging from purely organic chemicals to metallic soaps to complex organometaUic compounds. By far the most common polymer requiring the use of heat stabilizers is poly(vinyl chloride) (PVC). However, copolymers of PVC, chlorinated poly(vinyl chloride) (CPVC), poly(vinyhdene chloride) (PVDC), and chlorinated polyethylene (CPE), also benefit from this technology. Without the use of heat stabilizers, PVC could not be the widely used polymer that it is, with worldwide production of nearly 16 million metric tons in 1991 alone (see Vinyl polymers). 

The aqueous phase into which the monomer mix is dispersed is also prepared in a separate tank before transferring to the copolymerization ketde. It contains a catalyst, such as benzoyl peroxide [94-36-0], to initiate and sustain the polymerization reaction, and chemicals that aid in stabilizing the emulsion after the desired degree of dispersion is achieved. Careful adherence to predeterrnined reaction time and temperature profiles for each copolymer formulation is necessary to assure good physical durabiHty of the final ion-exchange product. 

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