Acrylonitrile monomers

In all manufacturing processes, grafting is achieved by the free-radical copolymerization of styrene and acrylonitrile monomers in the presence of an elastomer. Ungrafted styrene—acrylonitrile copolymer is formed during graft polymerization and/or added afterward. 

The monomer pair, acrylonitrile—methyl acrylate, is close to being an ideal monomer pair. Both monomers are similar in resonance, polarity, and steric characteristics. The acrylonitrile radical shows approximately equal reactivity with both monomers, and the methyl acrylate radical shows only a slight preference for reacting with acrylonitrile monomer. Many acrylonitrile monomer pairs fall into the nonideal category, eg, acrylonitrile—vinyl acetate. This is an example of a nonideality sometimes referred to as kinetic incompatibiUty. A third type of monomer pair is that which shows an alternating tendency. 

Another type of polyol often used in the manufacture of flexible polyurethane foams contains a dispersed soHd phase of organic chemical particles (234—236). The continuous phase is one of the polyols described above for either slab or molded foam as required. The dispersed phase reacts in the polyol using an addition reaction with styrene and acrylonitrile monomers in one type or a coupling reaction with an amine such as hydrazine and isocyanate in another. The soHds content ranges from about 21% with either system to nearly 40% in the styrene—acrylonitrile system. The dispersed soHds confer increased load bearing and in the case of flexible molded foams also act as a ceU opener. 

Pure polymeric acrylonitrile is not an interesting fiber and it is virtually undyeable. In order to make fibers of commercial iaterest acrylonitrile is copolymerized with other monomers such as methacrylic acid, methyl methacrylate, vinyl compounds, etc, to improve mechanical, stmctural, and dyeing properties. Eibers based on at least 85% of acrylonitrile monomer are termed acryHc fibers those containing between 35—85% acrylonitrile monomer, modacryhc fibers. The two types are in general dyed the same, although the type and number of dye sites generated by the fiber manufacturing process have an influence (see Eibers, acrylic). 

AH iagredients in the polymerization recipe are not always added at the beginning of the process. For example, better latex stabHity can sometimes be achieved by starting with only part of the emulsifier, saving the rest for later addition. Sometimes a portion of the modifier is held out for late addition to aHow higher final conversion without premature consumption of aH of it. OccasionaHy, if a low acrylonitrile product is the objective, part of the acrylonitrile monomer wiH be saved for late addition so that a chemically more uniform copolymer is produced, which can sometimes enhance properties in critical appHcations. 

Acetyl bromide Acrylonitrile monomer Allyl chloride Allyl chloroformate Allyl iodide... 

An example of the way in which process competition works in the manufacture of plastics is the story of acrylonitrile. The first process for the production of this plastic was based upon the reaction between hydrogen cyanide and acetylene, both hard to handle, poisonous, and explosive chemicals. The raw material costs were relatively low as compared to materials for other monomers, but the plant investment and manufacturing costs were too high. As a result, originally acrylonitrile monomer (1950s) sold for about 30 cents per pound and the future of the material looked dim as other plastics such as polyethylene became available at much lower prices due to their lower production costs. 

Analytical procedures sensitive to 2 ppm for styrene and 0.05 ppm or less for other items were used for examining the extracts. Even under these exaggerated exposure conditions no detectable levels of the monomers, of the polymer, or of other potential residuals were observed. The materials are truly non-food-additive by the FDA definitions. Hydrogen cyanide was included in the list of substances for analysis since it can be present at low levels in commercial acrylonitrile monomer, and it has been reported as a thermal decomposition product of acrylonitrile polymers. As shown here, it is not detectable in extracts by tests sensitive to... 

The heterogeneous copolymerization of styrene and acrylonitrile in various diluents as reported by Riess and Desvalois (22). Although the copolymer composition in these studies was not strongly influenced by the diluent choice, the preferential adsorption of acrylonitrile monomer onto the polymer particles shifted the azeotropic copolymerization point from the 38 mole % acrylonitrile observed in solution to 55 mole % acrylonitrile. 

Finally, in a recent study by Walling and El-Taliawi (216) it was shown that solvolytically generated vinyl cations may be reduced by Fe ions in solution to the corresponding vinyl radical. When 2-buten-2-yl triflate was solvolyzed in concentrated ferrous perchlorate solution in the presence of acrylonitrile monomer, polymerization of the acrylonitrile was observed. No such polymerization occurred under identical conditions in the absence of Fe ions. It seems that the polymerization of acrylonitrile was initiated by the vinyl radicals formed by reduction of the intermediate vinyl cation by Fe as follows (216) ... 

The polymerization rates of styrene and acrylonitrile monomer are not equal. If we were to initiate polymerization in an equimolar solution of the two monomers, the styrene monomer would initially be depleted at a faster rate than the acrylonitrile. Thus, the copolymer molecules initially produced would contain a higher concentration of styrene than acrylonitrile. As the reaction progressed, the styrene would be depleted from the solution and the comonomer ratio in the copolymer would gradually shift towards a higher acrylonitrile content. The final product would consist of polymer chains with a range of comonomer compositions, not all... 

Residual acrylonitrile monomer may also occur in commercially-made polymeric materials used in rugs and other products. Estimated levels include acrylic and modacrylic fibers (less than 1 mg acrylonitrile/kg polymeric material), acrylonitrile-based resins (15 to 50 mg/kg), and nitrile rubber and latex (0 to 750 mg/kg) (IARC 1979 Miller and Villaume 1978). It is possible that acrylonitrile may evaporate into air or leach into water from these products, but no data on this topic were located. 

Synonyms Acritet Acrylon Acrylonitrile monomer AI3-00054 AN BRN 0605310 Carbacryl Caswell No. 010 CCRIS 8 Cyanoethene Cyanoethylene EINECS 203-466-5 ENT 54 EPA pesticide chemical code 000601 Fumigrain Miller s fumigrain NCI-C50215 Nitrile NSC 6362 Propenenitrile 2-Propenenitrile RCRA waste number U009 TL 314 UN 1093 VCN Ventox Vinyl cyanide. 

Acrylonitrile monomer when masticated in the presence of polymer leads to the formation of pseudocrosslinked block copolymers by mechanical scission of soluble block copolymers. The aggregation of the polyacrylonitrile chains of the block copolymer fraction results in the formation of swollen gels when the polymerization products are extracted with solvents from the initial polymer (78-80). 

Originally, processes were common that involve the feeding of a solution of rubber in a mixture of styrene and acrylonitrile monomers to the polymerization mixture. These processes have the inherent limitation in that they cannot produce polymers with a high rubber content. This occurs because in spite the rubber dissolves readily in styrene. However, its solubility in a mixture of styrene and acrylonitrile monomers decreases with the concentration of acrylonitrile. 

The data agree well with theoretical data obtained from the Barton equation (21). For copolymers and specifically for the styr-ene/AN system, the glass transition temperature is dependent on the amounts of the dyads SS,AS, AA occurring in the a copolymer, where S denotes a styrene monomer and A denotes a acrylonitrile monomer, as (22)... 

In order to make libers of commercial interest acrylonitrile is eopolymer-ized with other monomers such as inethacrylic acid, methyl methacrylate, vinyl compounds, etc., to improve mechanical, structural, and dyeing properties. Fibers based on at least 85% of acrylonitrile monomer are termed... 

Step 2—Polybutadiene rubber is further polymerized, but in the presence of styrene and acrylonitrile monomers. This is done in low-pressure reactors under a nitrogen atmosphere. In this operation, the monomers are grafted onto the rubber backbone through the residual unsaturation remaining from the first step. 

The general literature on acrylonitrile monomer, its reactions, its polymerization and the technical applications of its polymers have been summarized in a recent book listing 1454 references (7). These topics will not be discussed here except as they bear on polymerization mechanisms. Copolymerization is mentioned only as it throws light on... 

Aqueous systems have been studied by a very large number of investigators. Economy, safety, convenience and quality of product have combined to make this the method of choice for commercial production of copolymers. The industrial importance of such end products as elastomers and acrylic fibers has been a special incentive to related fundamental studies. Furthermore, the relatively high solubility of acrylonitrile monomer in water coupled with insolubility of the polymer make it a convenient test monomer for studies of initiation by redox systems (6, 25, 102). Large numbers of homogeneous chemical initiators and some heterogeneous initiators have been studied as well as initiation by photochemical means, by ultrasonics and by ionizing radiation. It will not be possible here to review the enormous world literature. Several publications (/, 92, 117) refer in some detail to the older papers, and we shall restrict our comments to recent interpretations that have received support from several quarters. 

Graft ABS polymers were prepared by the reaction of an approximate azeotropic mole ratio of styrene-acrylonitrile monomer mixture in the presence of different weights of diene substrate latex. Initiator, chain transfer agent, and soap levels were constant. Grafting reactions were... 

Mixtures of liquid vinyl monomers and polymer powders serve as a basis for a special group of engineering materials. Vinyl acetate and acrylonitrile monomers are injected into polymer powders to accelerate swelling and gel formation. Styrene is added to improved the molding characteristics of reactive mixtures. Polystyrene, poly(vinyl acetate), poly(vinyl chloride), etc. are the most commonly used polymer powders. 

Acrylonitrile monomer (for synthesis) obtained from E. Merck was extracted with 6-8 aqueous sodium hydroxide solution three times in a separation funnel for removing inhibitor. The liquid monomer was then washed with distilled water several times and dried over anhydrous calcium chloride. 

Graft Copolymerization. Dried bamboo sample (0.25 g) was first swollen in 40 ml distilled water for at least 15 minutes at room temperature in a 50 ml, stoppered, Erlenmeyer flask. The flask was then placed in a thermostated water bath maintained at 40 i 1°C. By adding 0.8 ml of dilute nitric acid (0.005 M) and 1.25 ml of acrylonitrile monomer into the flask with stirring, followed by the adding of a... 

Carr et al.119 investigated grafting via reactive extrusion of starch with cationic methacrylate, acrylamide and acrylonitrile monomers. Starch, monomer and CAN initiator were metered into a twin-screw extruder at starch contents of approximately 35% solids. The cationic methacrylate monomer showed poor reactivity during extrusion, with essentially no add-on. Acrylamide-starch systems (1 1 w/w) gave conversions of approximately 20% and add-ons of 16% to 18%. Acrylonitrile displayed the greatest reactivity during extrusion, with conversions of 74% and 63% for 1 1 and 1 2 w/w acrylonitrile/starch ratios, respectively. The corresponding add-ons were 27% and 42%. 

The ratio ki/fkp can be estimated from published data in the following way. The primary radical formed by decomposition of azodiisobutyro-nitrile is structurally similar to the terminal unit of a polymethacrylonitrile radical, and we can therefore assume that its reactivity towards acrylonitrile is similar. Designating acrylonitrile monomer and radical with the subscript 1 and methacrylonitrile with subscript 2, we can write... 

PAN, a synthetic fiber, is a polymer of acrylonitrile monomers. Worldwide, 2.73 million tons of PAN are produced per year, of which over 98% are processed as filament yarn serving as material in the textile industry (Tauber et al., 2000). PAN usually has a molecular weight of 55,000-70,000 g mol and is most commonly a copolymer produced by radical polymerization from acrylonitrile, 5-10 mol% vinyl acetate (or similar nonionic comonomers) to disrupt the regularity and crystallinity, and ionic comonomers, such as sulfuric or sulfonic acid salts. PAN is a hydrophobic polymer that affects the processability of the fibers. The surface is not easily wetted. 

Compositional control in suspension systems can be achieved with a corrected batch process. A suspension process has been described where styrene monomer is continuously added until 75 —85% conversion, and then the excess acrylonitrile monomer is removed by stripping with an inert gas... 

Vinyl,- acrylic, etc.7 as well as acrylonitrile monomers 413-415 are readily obtained from Mannich bases. Further examples coneeming analogous derivatives are reported in Chap. II, A.2. Deuterated compound.s are also ineluded among aery lie acid derivatives along with several variously functionalized compounds. 

---