Polymerization of acrylonitrile

To the extent that the data allow, suggest where these substituents might be positioned in Table 7.3. The following reactivity ratios describe the polymerization of acrylonitrile (Ml) with the monomers listed ... 

Dimethylformamide [68-12-2] (DME) and dimethyl sulfoxide [67-68-5] (DMSO) are the most commonly used commercial organic solvents, although polymerizations ia y-butyrolactoae, ethyleae carboaate, and dimethyl acetamide [127-19-5] (DMAC) are reported ia the hterature. Examples of suitable inorganic salts are aqueous solutioas of ziac chloride and aqueous sodium thiocyanate solutions. The homogeneous solution polymerization of acrylonitrile foUows the conventional kinetic scheme developed for vinyl monomers (12) (see Polymers). 

Bulk Polymerization. The bulk polymerization of acrylonitrile is complex. Even after many investigations into the kinetics of the polymerization, it is stiU not completely understood. The complexity arises because the polymer precipitates from the reaction mixture barely swollen by its monomer. The heterogeneity has led to kinetics that deviate from the normal and which can be interpreted in several ways. 

Although bulk polymerization of acrylonitrile seems adaptable, it is rarely used commercially because the autocatalytic nature of the reaction makes it difficult to control. This, combined with the fact that the rate of heat generated per unit volume is very high, makes large-scale commercial operations difficult to engineer. Lastiy, the viscosity of the medium becomes very high at conversion levels above 40 to 50%. Therefore commercial operation at low conversion requires an extensive monomer recovery operation. 

HydroxyethyUiydrazine (11) is a plant growth regulator. It is also used to make a coccidiostat, furazoHdone, and has been proposed, as has (14), as a stabilizer in the polymerization of acrylonitrile (72,73). With excess epoxide, polysubstitution occurs and polyol chains can form to give poly(hydroxyaLkyl) hydrazines which have been patented for the preparation of cellular polyurethanes (74) and as corrosion inhibitors for hydrauHc fluids (qv) (75). DialkyUiydrazines, R2NNH2, and alkylene oxides form the very reactive amineimines (15) which react further with esters to yield aminimides (16) ... 

Polymerization and Spinning Solvent. Dimethyl sulfoxide is used as a solvent for the polymerization of acrylonitrile and other vinyl monomers, eg, methyl methacrylate and styrene (82,83). The low incidence of transfer from the growing chain to DMSO leads to high molecular weights. Copolymerization reactions of acrylonitrile with other vinyl monomers are also mn in DMSO. Monomer mixtures of acrylonitrile, styrene, vinyUdene chloride, methallylsulfonic acid, styrenesulfonic acid, etc, are polymerized in DMSO—water (84). In some cases, the fibers are spun from the reaction solutions into DMSO—water baths. 

Acrylonitrile-butadiene rubber (also called nitrile or nitrile butadiene rubber) was commercially available in 1936 under the name Buna-N. It was obtained by emulsion polymerization of acrylonitrile and butadiene. During World War II, NBR was used to replace natural rubber. After World War II, NBR was still used due to its excellent properties, such as high oil and plasticizer resistance, excellent heat resistance, good adhesion to metallic substrates, and good compatibility with several compounding ingredients. 

Silver nitrate and/or cuppric nitrate [50] can photoinitiate the polymerization of acrylonitrile in a dimethyl formamide (DMF) medium. The photoactive species is the complex formed between the monomer and salt molecules ... 

Ce4+ is a versatile one-electron oxidizing agent (E° = - 1.71 eV in HC10466 capable of oxidizing sulfoxides. Rao and coworkers66 have described the oxidation of dimethyl sulfoxide to dimethyl sulfone by Ce4+ cation in perchloric acid and proposed a SET mechanism. In the first step DMSO rapidly replaces a molecule of water in the coordination sphere of the metal (Ce v has a coordination number of 8). An intramolecular electron transfer leads to the production of a cation which is subsequently converted into sulfone by reaction with water. The formation of radicals was confirmed by polymerization of acrylonitrile added to the medium. We have written a plausible mechanism for the process (Scheme 8), but there is no compelling experimental data concerning the inner versus outer sphere character of the reaction between HzO and the radical cation of DMSO. 

Similarly, Garcia-Rubio and Hamielec (17) conducted bulk polymerizations of acrylonitrile at various temperatures and initiator levels in glass ampoules. Their plots of the rate of polymerization as a function of conversion are typical of the extensive radical occlusion in this very glassy polymer. 

In addition, Bamford, Jenkins and coworkers (19) previously reported on the behavior of occluded radicals in the heterogeneous polymerizations of acrylonitrile, methyl acrylate, methyl methacrylate and vinylidene chloride. From their electron spin resonance studies, they concluded that the degree of occlusion was ... 

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) ... 

Recently Mosher and Driscoll 2 have noted that the polymerization of acrylonitrile can be observed during the chromic acid oxidation of 2,2-dimethyl-l-phenyl-l-propanol. The polymerization is caused by radicals formed during the oxidation of benzaldehyde (which is one of the cleavage product of phenyl-1-butylcarbinol). The oxidation of benzaldehyde is due to the chromium(IV), most probably, or chromiun(V) intermediates. 

Two different emulsion polymerization reactions were Investigated. One was the polymerization of acrylonitrile and methylacrylate (75/25 AN/MA) In the presence of an acrylonitrile elastomer (70/30 BD/AN) to produce a graft resin, llie second was the copolymerization oiE acrylonitrile and styrene (70/30 AN/S). Chromatographic analyses of latex solutions were conducted periodically during both types of polymerization reactions, using acetonitrile as latex solvent and chromatographic mobile phase. 

Anionic polymerization of acrylonitrile is less important in commercial production than the radical process. 

Deaths from cancer of the stomach were statistically elevated in one study of six manufacturing plants in the United Kingdom involved in the polymerization of acrylonitrile and the spinning of acrylic fibers (Werner and Carter 1981). No quantitative data on the exposure levels to acrylonitrile were given and the numbers of expected deaths was too small to provide confidence in the results. 

Although benzoyl peroxide will initiate the polymerization (by a radical chain reaction) of either styrene or acrylonitrile, -methoxy- -nitrobenzoyl peroxide will not initiate polymerization efficiently in the latter monomer because it is too rapidly destroyed by the polar decomposition. Acrylonitrile, but not styrene, causes the polar decomposition to predominate, and the intermediates of the polar decomposition are not catalysts for the polymerization of acrylonitrile. 

Poly(acrylic acid) is not soluble in its monomer and in the course of the bulk polymerization of acrylic acid the polymer separates as a fine powder. The conversion curves exhibit an initial auto-acceleration followed by a long pseudo-stationary process ( 3). This behaviour is very similar to that observed earlier in the bulk polymerization of acrylonitrile. The non-ideal kinetic relationships determined experimentally in the polymerization of these two monomers are summarized in Table I. It clearly appears that the kinetic features observed in both systems are strikingly similar. In addition, the poly(acrylic acid) formed in bulk over a fairly broad range of temperatures (20 to 76°C) exhibits a high degree of syndiotacticity and can be crystallized readily (3). 

The bulk polymerization of acrylonitrile has been studied by numerous workers (for a literature survey on the problem see ref. j O and JL1J. The kinetic features of this reaction at room temperature are summarized in Table I. It is one of the typical examples of polymerization under heterogeneous conditions in which the anomalies are generally assumed to arise as a result of non-stationary conditions caused by the "occlusion" of growing chains in the precipitated polymer (10). The presence of occluded radicals was indeed demonstrated by 5R measurements (12) and by... 

The cfata presented in Table I show that the kinetic features of the bulk polymerization of acrylonitrile are very similar to those observed with acrylic acid. It therefore seems pertinent to query whether atrix effect could not arise in the polymerization of acrylonitrile through a regular orientation of monomer molecules along the polymeric matrix involving dipole interaction of the -CsN groups (structure IV). 

Several recent studies carried out in these laboratories did provide evidence for a matrix effect operating in the polymerization of acrylonitrile. These include ... 

The bulk polymerization of acrylonitrile in this range of temperatures exhibits kinetic features very similar to those observed with acrylic acid (cf. Table I). The very low over-all activation energies (11.3 and 12.5 Kj.mole-l) found in both systems suggest a high temperature coefficient for the termination step such as would be expected for a diffusion controlled bimolecular reaction involving two polymeric radicals. It follows that for these systems, in which radicals disappear rapidly and where the post-polymerization is strongly reduced, the concepts of nonsteady-state and of occluded polymer chains can hardly explain the observed auto-acceleration. Hence the auto-acceleration of acrylonitrile which persists above 60°C and exhibits the same "autoacceleration index" as at lower temperatures has to be accounted for by another cause. 

Figure 8. Arrhenius diagram of the gamma-ray initiated polymerization of acrylonitrile in bulk 1161 Curve 1 Initial rates" curve 2 Pseudostationary rates. ...

Polymerization of acrylonitrile adsorbed on polyacrylonitrile" An intimate mixture of polyacrylonitrile solvated by its monomer is obtained if one melts acrylonitrile crystals which have been subjected to high energy radiation at low temperatures. The polymer forms under irradiation within the crystal lattice and upon melting, a gel-like phase is obtained in which the individual polymer molecules do not aggregate, presumably because most of the CN groups are then associated in pairs with the -CN groups of the monomer. Such a polyacrylonitrile solvated by its monomer should indeed be an ideal medium for the matrix effect to operate. 

Figure 10. Polymerization of acrylonitrile at 20°C in an intimate mixture with a highly divided polyacrylonitrile obtained by pre-irradiation of the crystalline monomer at 95°C (20). Doses of pre-irradiation of 0.11 Mrad (curve 2) to 3.14 Mrad (curve 12). The broken curve 1 pertains to the polymerization of pure acrylonitrile curve 13 is obtained in the presence of polyacrylonitrile pre-poly-...

Polymerization of acrylonitrile in polar solvents. Polar solvents are expected to interfere with the association of nitrile groups in pairs and to replace the nitrile-nitrile association complex by a nitrile-solvent association. Under such conditions structures such as IV should no longer arise and the "matrix effect" should disappear. 

Further experiments were therefore carried out with polar solvents which do not dissolve the polymer. Most striking results were obtained with trichloroacetic acid. The polymerization of acrylonitrile in this solvent was found to proceed under precipitating conditions at all concentrations. In spite of this, the conversion curves were perfectly linear in solutions containing 60 volume per cent monomer or less (18). Moreover, these systems exhibit marked post-polymerization showing the presence of long-lived radicals. 

Phase-transfer techniques are widely used for the preparation of polymers. For example, potassium fluoride is used to produce poly(etherketone)s under phase-transfer conditions (Scheme 10.18). Use of this reagent allows the chloroaro-matics to be used as starting material as opposed to the more expensive flu-oroaromatics that are usually employed [23]. This method is suitable for the synthesis of high molecular weight semicrystalline poly(ether ketone)s, although the presence of excess potassium fluoride in the reaction mixture can lead to degradation reactions. The use of a phase transfer catalyst can allow the use of water-soluble radical initiators, such as potassium peroxomonosulfate used to promote the free-radical polymerization of acrylonitrile [24],... 

Polymerization of acrylonitrile (AN) in tol uene/water was studied using hexadecyltrimethyl-ammonium bromide as the phase transfer catalyst (12). 

Graft polymerization of acrylonitrile and styrene on a preformed polybutadiene elastomer... 

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