Polystyrene styrene/acrylonitrile copolymers

Shapras and Claver [38] have described a gas chromatographic method for the determination of various volatiles in polystyrene, styrene-acrylonitrile copolymers, styrene-butadiene, styrene-acrylonitrile-butadiene terpolymers and other co-polymers. In this procedure, the polymer is dissolved in dimethyl formamide containing a known amount of toluene as internal standard. A portion of this solution is injected into two columns in series comprising 20% Tween 81 on Chromosorb W, followed by 10% Resoflex-446 on Chromosorb W. Using a hydrogen flame ionisation detector, less than 10 ppm of various monomers and other volatile impurities can be determined in the polymer by this procedure. Shapras and Claver state that the polymer present in the solution injected into the gas chromatographic column deposits on the injection block and is removed by reaming after every 50 sample injections. 

Compared to straight polystyrene, styrene-acrylonitrile copolymers have a higher softening point and improved impact strength. (See Table 3.1.) They are also transparent but tend to have a slight yellow tint. Because of the polar nature of acrylonitrile, the copolymers are more resistant to hydrocarbons and oils than... 

Many important polymers are made commerdally via suspension polymerization of vinyl monomers. These include poly(vinyl chloride), poly(methyl methacrylate), expandable polystyrene, styrene-acrylonitrile copolymers and a variety of ion-exchange resins and specialist materials. The annual polymer production from suspension processes is very high. 

Other Polymers. Besides polycarbonates, poly(methyl methacrylate)s, cycfic polyolefins, and uv-curable cross-linked polymers, a host of other polymers have been examined for their suitabiUty as substrate materials for optical data storage, preferably compact disks, in the last years. These polymers have not gained commercial importance polystyrene (PS), poly(vinyl chloride) (PVC), cellulose acetobutyrate (CAB), bis(diallylpolycarbonate) (BDPC), poly(ethylene terephthalate) (PET), styrene—acrylonitrile copolymers (SAN), poly(vinyl acetate) (PVAC), and for substrates with high resistance to heat softening, polysulfones (PSU) and polyimides (PI). 

The valuable characteristics of polyblends, two-phase mixtures of polymers in different states of aggregation, were also discussed in the previous chapter. This technique has been widely used to improve the toughness of rigid amorphous polymers such as PVC, polystyrene, and styrene-acrylonitrile copolymers. 

In addition to polystyrene and high-impact polystyrene there are other important styrene-based plastics. Most important of these is ABS, with a global capacity of about 5 X 10 t.p.a. and production of about 3 X 10 t.p.a. The styrenic PPO materials reviewed in Chapter 21 have capaeity and production figures about one-tenth those for ABS. Data for the more specialised styrene-acrylonitrile copolymers are difficult to obtain but consumption estimates for Western Europe in the early 1990s were a little over 60000 t.p.a. 

The important features of rigidity and transparency make the material competitive with polystyrene, cellulose acetate and poly(methyl methacrylate) for a number of applications. In general the copolymer is cheaper than poly(methyl methacrylate) and cellulose acetate, tougher than poly(methyl methacrylate) and polystyrene and superior in chemical and most physical properties to polystyrene and cellulose acetate. It does not have such a high transparency or such food weathering properties as poly(methyl methacrylate). As a result of these considerations the styrene-acrylonitrile copolymers have found applications for dials, knobs and covers for domestic appliances, electrical equipment and car equipment, for picnic ware and housewares, and a number of other industrial and domestic applications with requirements somewhat more stringent than can be met by polystyrene. 

In the late 1940s, the demand for styrene homopolymers (PS) and styrene-acrylonitrile copolymers (SAN) was drastically reduced due to their inherent brittleness. Thus, the interest was shifted to multiphase high-impact polystyrene (HIPS) and rubber-modified SAN (ABS). In principle, both HIPS and ABS can be manufactured by either bulk or emulsion techniques. However, in actual practice, HIPS is made only by the bulk process, whereas ABS is produced by both methods [132,133]. 

PS (polystyrene), PVC [poly(vinyl chloride)], PC (bisphenol A polycarbonate) PMMA [poly (methyl methacrylate)], PB (polybutadiene), SAN (styrene-acrylonitrile copolymer),NBR (acrylonitrile-butadiene rubber), PPE (polyphenylene ether), SBR (styrene-butadiene rubber)... 

Similar grafting experiments by the emulsion technique were described (34) in the system vinyl chloride/copolymer butyl methacrylate-methacrylic acid and in the reverse system, and also in the system styrene/polyvinyl chloride. In this last case again as in homogenous medium, the inverse process failed (vinyl chloride on polystyrene). Grafted acrylonitrile copolymers were also prepared in order to improve their dyeability, by polymerizing acrylonitrile in emulsion in the presence of many different polymers as polyvinyl alcohol, polymethacrylamide and polyvinylpyrrolidone (119, 120, 121), polyvinyl acetate and polyacrylic acid (115), wool (224,225), proteins (136), etc. 

PS PSF PSU PTFE PU PUR PVA PVAL PVB PVC PVCA PVDA PVDC PVDF PVF PVOH SAN SB SBC SBR SMA SMC TA TDI TEFE TPA UF ULDPE UP UR VLDPE ZNC Polystyrene Polysulfone (also PSU) Polysulfone (also PSF) Polytetrafluoroethylene Polyurethane Polyurethane Poly(vinyl acetate) Poly(vinyl alcohol) poly(vinyl butyrate) Poly(vinyl chloride) Poly(vinyl chloride-acetate) Poly(vinylidene acetate) Poly(vinylidene chloride) Poly(vinylidene fluoride) Poly(vinyl fluoride) Poly(vinyl alcohol) Styrene-acrylonitrile copolymer Styrene-butadiene copolymer Styrene block copolymer Styrene butadiene rubber Styrene-maleic anhydride (also SMC) Styrene-maleic anhydride (also SMA) Terephthalic acid (also TPA) Toluene diisocyanate Ethylene-tetrafluoroethylene copolymer Terephthalic acid (also TA) Urea formaldehyde Ultralow-density polyethylene Unsaturated polyester resin Urethane Very low-density polyethylene Ziegler-Natta catalyst... 

In Contact with Organic Vapors. Finely divided polystyrene beads (22-48 mesh) supported on a screen suspended above the surface of pentane in a closed vessel absorb as much as 9.2% in 2 days at 30°C. In the same way, a styrene-acrylonitrile copolymer is rendered expandable by exposure to vapors of a 90/10 mixture of pentane and methylene chloride (5). 

The development of SAN was triggered by the idea of building a polar comonomer into polystyrene to improve its resistance to chemicals and to stress cracking. The relatively polar acrylonitrile presented itself as a suitable comonomer in this case. Styrene-acrylonitrile copolymers are further characterized by high rigidity and thermal shock resistance. Two parameters substantially determine the properties of SAN molecular weight and the proportion of acrylonitrile. 

The moisture resistance, low cost, and low-density closed-cell structure of many cellular polymers resulted in their acceptance for buoyancy in boats, floating docks, and buoys. Because each cell is a separate flotation unit, these materials cannot be destroyed by a single puncture. Foamed-in-place polyurethane between thin skins of high tensile strength is used in pleasure craft [98]. Other cellular polymers that have been used where buoyancy is needed are produced from polystyrene, polyethylene, poly(vinyl chloride), and certain types of rubber. Foams made from styrene-acrylonitrile copolymers are resistant to petroleum products [99,100]. 

There are a number of flame-retardant styrenic polymers that will be covered in this chapter. These include polystyrene itself, rubber-modified polystyrene [high-impact polystyrene (HIPS)] and rubber-modified styrene-acrylonitrile copolymer [acrylonitrile-butadiene-styrene (ABS)]. Blends with styrenic... 

Styrene acrylonitrile copolymers were synthesized by bulk free radical polymerization at 60°C and 40°C over a wide range of initial monomer compositions (10). Copolymer compositions were determined by gas chromatography and verified by H1 NMR spectroscopy. The narrow MWD polystyrene standards (Pressure Chemicals) and the SAN copolymers were purified prior to the analysis by dissolution in THF and precipitation from absolute methanol. 

In the annual figures (11) polystyrene resins are disclosed from 1942 through 1950. Styrene-acrylonitrile copolymers are disclosed in 1950. Care must be exercised in using these figures to see where styrenated alkyds are classified. Polystyrene polyesters are disclosed in 1945 polystyrene-maleic anhydride resins are disclosed in 1946 styrene-alkyd polyesters are disclosed in 1949 and 1950 polystyrene-butadiene copolymers are disclosed in 1949 and 1950. 

Composition (type of polymeric components). The base polymer (which is to be modified) may be an amorphous polymer [e.g., polystyrene (PS), styrene-acrylonitrile copolymer, polycarbonate, or poly(vinyl chloride)], a semicrystalline polymer [e.g., polyamide (PA) or polypropylene (PP)], or a thermoset resin (e.g., epoxy resin). The modifier may be a rubber-like elastomer (e.g., polybutadiene, ethylene-vinyl acetate copolymer, ethylene-propylene copolymer, or ethylene-propylene-diene copolymer), a core-shell modifier, or another polymer. Even smaller amounts of a compatibilizer, such as a copolymer, are sometimes added as a third component to control the morphology. 

Foams (cellular structures) made by expanding a material by growing bubbles in it [11]. A foam has at least two components. At a macroscopic scale, there are the solid and liquid phases. The solid phase can be a polymer, ceramic or metal. The fluid phase is a gas in most synthetic foams, and a liquid in most natural foams. At a microscopic scale, the solid phase may itself consist of several components. For example, the solid phase of an amorphous polystyrene foam has only one component. On the other hand, the solid phase of a polyethylene foam or a flexible polyurethane foam typically has two components. These components are the crystalline and amorphous phases in polyethylene foams, and the hard and soft phases formed by the phase separation of the hard and soft segment blocks in flexible polyurethane foams. The solid phase of a polyurethane foam may, in fact, have even more than two components, since additional reinforcing components such as styrene-acrylonitrile copolymer or polyurea particles are often incorporated [12,13]. The solid is always a continuous phase in a foam. Foams can generally be classified as follows, based on whether the fluid phase is co-continuous with the solid phase ... 

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