Polyacrylonitrile solvents

The residue consists mainly of polyacrylonitrile and copper or copper salts. It is slowly soluble in acetone, more readily soluble in polyacrylonitrile solvents such as dimethylformamide or dimethyl sulfoxide, especially when warmed. 

Resin and Polymer Solvent. Dimethylacetamide is an exceUent solvent for synthetic and natural resins. It readily dissolves vinyl polymers, acrylates, ceUulose derivatives, styrene polymers, and linear polyesters. Because of its high polarity, DMAC has been found particularly useful as a solvent for polyacrylonitrile, its copolymers, and interpolymers. Copolymers containing at least 85% acrylonitrile dissolve ia DMAC to form solutions suitable for the production of films and yams (9). DMAC is reportedly an exceUent solvent for the copolymers of acrylonitrile and vinyl formate (10), vinylpyridine (11), or aUyl glycidyl ether (12). 

The first reported synthesis of acrylonitrile [107-13-1] (qv) and polyacrylonitrile [25014-41-9] (PAN) was in 1894. The polymer received Htde attention for a number of years, until shortly before World War II, because there were no known solvents and the polymer decomposes before reaching its melting point. The first breakthrough in developing solvents for PAN occurred at I. G. Farbenindustrie where fibers made from the polymer were dissolved in aqueous solutions of quaternary ammonium compounds, such as ben2ylpyridinium chloride, or of metal salts, such as lithium bromide, sodium thiocyanate, and aluminum perchlorate. Early interest in acrylonitrile polymers (qv), however, was based primarily on its use in synthetic mbber (see Elastomers, synthetic). 

In the case of solvent spinning, ie, secondary acetate, polyacrylonitrile, and poly(vinyl chloride), the FWA is added to the polymer solution. An exception is gel-whitening of polyacrylonitrile, where the wet tow is treated after spinning in a washbath containing FWA. 

Worldwide demand for DMF in acryhc fiber production has held up better than in the United States. The high solubiUty of polyacrylonitrile in DMF, coupled with DMF s high water miscibility, makes it an attractive solvent for this appHcation. Its principal competition in this area comes from DMAC. 

Polymer Solvent. Sulfolane is a solvent for a variety of polymers, including polyacrylonitrile (PAN), poly(vinyhdene cyanide), poly(vinyl chloride) (PVC), poly(vinyl fluoride), and polysulfones (124—129). Sulfolane solutions of PAN, poly(vinyhdene cyanide), and PVC have been patented for fiber-spinning processes, in which the relatively low solution viscosity, good thermal stabiUty, and comparatively low solvent toxicity of sulfolane are advantageous. Powdered perfluorocarbon copolymers bearing sulfo or carboxy groups have been prepared by precipitation from sulfolane solution with toluene at temperatures below 300°C. Particle sizes of 0.5—100 p.m result. 

Statistics for the production of basic dyes include those products hsted as cationic dyes, eg, cyanines, for dyeing polyacrylonitrile fibers and the classical triaryhnethane dyes, eg, malachite green, for coloring paper and other office apphcations (2,53). Moreover, statistics for triaryhnethane dyes are also hidden in the production figures for acid, solvent, mordant, and food dyes, and also organic pigments. Between 1975 and 1984, the aimual production of basic dyes in the United States varied from 5000—7700 t. However, from 1985—1990, aimual production of basic dyes varied from 5000—5700 t, and the annual sales value increased from 56 to 73 million per year. 

Solution Polymerization These processes may retain the polymer in solution or precipitate it. Polyethylene is made in a tubular flow reactor at supercritical conditions so the polymer stays in solution. In the Phillips process, however, after about 22 percent conversion when the desirable properties have been attained, the polymer is recovered and the monomer is flashed off and recyled (Fig. 23-23 ). In another process, a solution of ethylene in a saturated hydrocarbon is passed over a chromia-alumina catalyst, then the solvent is separated and recyled. Another example of precipitation polymerization is the copolymerization of styrene and acrylonitrile in methanol. Also, an aqueous solution of acrylonitrile makes a precipitate of polyacrylonitrile on heating to 80°C (176°F). 

There is much evidence that weak links are present in the chains of most polymer species. These weak points may be at a terminal position and arise from the specific mechanism of chain termination or may be non-terminal and arise from a momentary aberration in the modus operandi of the polymerisation reaction. Because of these weak points it is found that polyethylene, polytetrafluoroethylene and poly(vinyl chloride), to take just three well-known examples, have a much lower resistance to thermal degradation than low molecular weight analogues. For similar reasons polyacrylonitrile and natural rubber may degrade whilst being dissolved in suitable solvents. 

Fig. 39.—Plots of c/c against c from the data of Masson and Melville for the following solvent-polymer pairs curve 1, polyacrylonitrile in dimethylformamide at 13.5° C curves 2 and 4, poly-(vinyl acetate) s in benzene at 20°C curve 3, polyacenaphthylene in benzene at 25°C curve 5, polyvinylxylene in benzene at 24°C curve 6, poly-(methyl methacrylate) in benzene at 16°C. All curves have been calculated from Eq. (13). Units correspond to those in Fig. 38. (Fox, Flory, and Bueche. )...

Wet spinning. This technique is characterized by spinning a filtered viscous polymer mass, dissolved in a suitable solvent, into contact with a precipitation or coagulation bath. Polyacrylonitrile, polyvinyl acetate, cellulose acetate, and other materials are processed by this method. Thermal requirements for pigments are less stringent than for melt spinning but pigments are expected to be fast to the solvents and chemicals used. 

However, DMF is a solvent for polyacrylonitrile and the polymerization occurs in a homogeneous medium for solutions containing 30 per cent monomer or less. This reduces the value of these experiments as an argument to show the influence of a matrix effect. Indeed the fact that auto-acceleration disappears when DMF is added to acrylonitrile was considered as a proof for the fact that precipitation of the polymer was the cause of autoacceleration. 

These results conclusively demonstrate that precipitation of polyacrylonitrile as a fine powder and occlusion of growing chains resulting in post-polymerization do not bring about autoacceleration if a highly polar solvent is present in the system. 

The individual values of vA, vB and vc have been excluded from Table 15 and indeed for this system the value of vB can only be measured in three solvents due to the insolubility of polyacrylonitrile in the others. For the purpose of calculating (vA - vB)/v, the value would have to be interpolated rather less accurately via Eq. (110). In the same order as the solvents listed in Table 15, the values of(t>A — vc)... 

Alkene polymers such as poly(methyl methacrylate) and polyacrylonitrile are easily formed via anionic polymerization because the intermediate anions are resonance stabilized by the additional functional group, the ester or the nitrile. The process is initiated by a suitable anionic species, a nucleophile that can add to the monomer through conjugate addition in Michael fashion. The intermediate resonance-stabilized addition anion can then act as a nucleophile in further conjugate addition processes, eventually giving a polymer. The process will terminate by proton abstraction, probably from solvent. 

Uses. Solvent for polyacrylonitrile present during rubber manufacturing... 

Surprising effects can also be observed when solvent mixtures are used to dissolve a polymer. There are examples where mixtures of two non-solvents act as a solvent vice versa, a mixture of two solvents may behave like a non-solvent. For example, polyacrylonitrile is insoluble in both, nitromethane and water, but it dissolves in a mixture of the two solvents. Similar behavior can be observed for polystyrene/acetone/hexane and poly(vinyl chloride)/acetone/carbon disulfide. Examples of systems where the polymer dissolves in two pure solvents but not in their mixture are polyacrylonitrile/malonodinitrile/dimethylforma-mide and poly(vinyl acetate)/formamide/acetophenone. These peculiarities are especially to be taken into account if one wants to adjust certain solution properties (e.g., for fractionation) by adding one solvent to another. 

For the case of acrylonitrile, there was an induction time of 24 h. This was attributed to the formation of cyanide radicals which are able to react with polyamidic macroradicals. The interpolymer is composed of two fractions one soluble in dimethyl formamide, whose properties are similar to polyacrylonitrile the other, insoluble in this solvent, whose properties are similar to those of the polyamide. No homopolymer was observed. The presence of acrylonitrile on the graft polymer was demonstrated by IR. 

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). 

Oxidation of the saturated heterocycle to sulfoxide and sulfone derivatives affords solvents for the preparation of polyacrylonitrile (62BEP613056), or corrosion inhibitors (e.g. 147)... 

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