Acrylonitrile polymerization, initiation

Yerusalimskii has demonstrated a similar mechanism for acrylonitrile polymerization initiated by Grignard reagents (13). We were unable at the time to investigate the isotactic polymerization initiated by t-BuMgBr in toluene as it was too fast for classical techniques. We have now developed techniques which can follow this reaction. 

The literature contains descriptions of acrylonitrile polymerization initiated by three different phosphorus bases, triethyl phosphine, triphenylphosphine, and triethyl phosphite. 

Acryhc stmctural adhesives have been modified by elastomers in order to obtain a phase-separated, toughened system. A significant contribution in this technology has been made in which acryhc adhesives were modified by the addition of chlorosulfonated polyethylene to obtain a phase-separated stmctural adhesive (11). Such adhesives also contain methyl methacrylate, glacial methacrylic acid, and cross-linkers such as ethylene glycol dimethacrylate [97-90-5]. The polymerization initiation system, which includes cumene hydroperoxide, N,1S7-dimethyl- -toluidine, and saccharin, can be apphed to the adherend surface as a primer, or it can be formulated as the second part of a two-part adhesive. Modification of cyanoacrylates using elastomers has also been attempted copolymers of acrylonitrile, butadiene, and styrene ethylene copolymers with methylacrylate or copolymers of methacrylates with butadiene and styrene have been used. However, because of the extreme reactivity of the monomer, modification of cyanoacrylate adhesives is very difficult and material purity is essential in order to be able to modify the cyanoacrylate without causing premature reaction. 

Samal et al. [25] reported that Ce(IV) ion coupled with an amide, such as thioacetamide, succinamide, acetamide, and formamide, could initiate acrylonitrile (AN) polymerization in aqueous solution. Feng et al. [3] for the first time thoroughly investigated the structural effect of amide on AAM polymerization using Ce(IV) ion, ceric ammonium nitrate (CAN) as an initiator. They found that only acetanilide (AA) and formanilide (FA) promote the polymerization and remarkably enhance Rp. The others such as formamide, N,N-dimethylformamide (DMF), N-butylacetamide, and N-cyclohexylacetamide only slightly affect the rate of polymerization. This can be shown by the relative rate (/ r), i.e., the rate of AAM polymerization initiated with ceric ion-amide divided by the rate of polymerization initiated with ceric ion alone. Rr for CAN-anilide system is approximately 2.5, and the others range from 1.04-1.11. 

Polyacrylics are produced by copolymerizing acrylonitrile with other monomers such as vinyl acetate, vinyl chloride, and acrylamide. Solution polymerization may be used where water is the solvent in the presence of a redox catalyst. Free radical or anionic initiators may also be used. The produced polymer is insoluble in water and precipitates. Precipitation polymerization, whether self nucleation or aggregate nucleation, has been reviewed by Juba. The following equation is for an acrylonitrile polymer initiated by a free radical ... 

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) ... 

We have considerable latitude when it comes to choosing the chemical composition of rubber toughened polystyrene. Suitable unsaturated rubbers include styrene-butadiene copolymers, cis 1,4 polybutadiene, and ethylene-propylene-diene copolymers. Acrylonitrile-butadiene-styrene is a more complex type of block copolymer. It is made by swelling polybutadiene with styrene and acrylonitrile, then initiating copolymerization. This typically takes place in an emulsion polymerization process. 

Acrylonitrile polymerization is similarly complicated by addition reactions of the initiator and/or propagating nucleophiles with the nitrile group [Berger and Adler, 1986 Tsvetanov, 1979 Vankerckhoven and Van Beylen, 1978]. 

The most recent and most puzzling example of anionic initiation is that which seems to take place when monomer is subjected to ionizing radiation at low temperatures. Acrylonitrile polymerizes rapidly at temperatures well below 0° (and even in the solid at —196°) when irradiated with X-rays or with electrons. Since it is now known that cationic polymerization may be induced by radiation, there has been speculation that similar anionic polymerization might be occurring with acrylonitrile (87, 121). This subject has been discussed recently by Magat (95) who quotes unpublished work of Bensasson and of Tabata and Hiroshi. 

Measurements on a-Methylstyrene—Acrylonitrile. Polymerizations were carried out in dilatometers without solvent. Initiator was azobis-isobutyronitrile. At 100 °C the reaction was initiated thermally. At 0° and 20 °C the reaction was carried out in flasks in a thermally controlled room. Yields were below 5%. The composition of the copolymers was calculated from nitrogen determination (Kjeldahl method). In an older reference (29) polymerizations were carried out at 20°, 50°, 60°, and... 

The concept of PO macroinitiators centers on the introduction of an initiation moiety into an olefinic polymer chain for polymerization. The most effective route for preparing PO macroinitiators is by employing functional polyolefins containing hydroxyl groups or other reactive groups. These functional POs are prepared by copolymerization of olefins with functional monomers and post-polymerization reaction, as mentioned above. In the case where an initiation moiety was at the chain-end of the polyolefins, a block type copolymer is produced. It has been reported that thiol-terminated PP was used as polymeric chain transfer agent in styrene and styrene/acrylonitrile polymerization to form polypropylene-b/odc-polystyrene (PP-b-PS) and polypropylene-btock-poly(styrene-co-acrylonitrile) (PP-b-SAN) block copolymer [19]. On the other hand, polymer hybrids with block and graft structures can be produced if initiation moieties are in the polymer chain. 

An interesting polymerization that may involve an ion-radical initiation is the y-ray initiation of acrylonitrile polymerization at — 78° (42). Polymerization did not occur in solvents capable of accepting electrons, but did occur in dimethylformamide and amines. When styrene and acrylonitrile mixture was used, the polymer was essentially polyacrylonitrile. 

Tt is well known that the presence of precipitated polymer can influence the course of polymerization. In bulk acrylonitrile polymerization the effects are most dramatic and have been the subject of many studies. The literature on this subject has been reviewed by Bamford et al. (4) by Thomas (29), and by Peebles (23). Under conditions where the system becomes heterogeneous owing to precipitation of small particles of polymer, a protracted acceleration period is observed at the start of polymerization, and the final rate is found to depend on the 0.8 power of the concentration of free radical initiator. Unusual post-polymerization effects are observed in photoinitiated polymerization of acrylonitrile, owing to the presence of trapped radicals which can be detected by electron spin resonance. None of the detailed mechanisms proposed to... 

The rate of polymerization in the constant rate period is shown in Figure 5 as a function of AIBN concentration, both on logarithmic scales. At low concentrations of initiator (I) the rate varies as I0 89, but the slope drops as low as 0.33 at high rates of initiation. Similar results have been reported by Chapiro and Sebban-Danon (12) for polymerizations initiated by ionizing radiation at 19 °C. Initiator exponents significantly higher than the normal value of 0.5 have been reported by many workers (6, 10, 17, 25, 30, 31) for the polymerization of acrylonitrile under heterogeneous conditions. 

Tlie rubber latex is usually produced in batch reactors. The rubber can be polybutadiene [9003-17-2] or a copolymer of 1,3-butadiene [106-99-0] and either acrylonitrile [107-13-1] or styrene [100-42-5]. The latex normally has a polymer content of approximately 30 to 50% most of the remainder is water. In addition to the monomers, the polymerization ingredients include an emulsifier, a polymerization initiator, and usually a chain-transfer agent for molecular weight control. 

Before general acceptance of the co-catalysis mechanism for cationic polymerizations initiated by Friedel-Crafts halides, zwitterions were regarded as possible intermediates4-. However, Horner seems to have been first to correctly identify a polymerization in which zwitterions are formed. Horner, Jurgeleit and Klupfel7) studied the polymerization of acrylonitrile by triethylphosphine and reported their findings in 1955. 

The Fe3+/H202 system, known to generate oxygen which is an inhibitor of polymerization, is able to initiate the reaction the Fe(N03)3/H202 system at low pH (nitric acid) 54) serves as an example. During acrylonitrile polymerization, the reaction rate increases with increasing ferric salt or hydrogen peroxide concentration or... 

The rate of butadiene polymerization initiated by hydrogen peroxide and perchloric acid is of first order with respect to hydrogen peroxide and square root order with respect to HC104 71). A similar order has been found for butadiene-acrylonitrile copolymerization with H202 and BF3 etherate 70). On the contrary, for acrylonitrile (AN) polymerization by thiourea (TU) and H202, the following equation rate is valid 641... 

The trapped radicals stabilized by the gel effect can be used as post-polymerization initiators. During the post-polymerization of MMA in the presence of the residual MMA, enriched with MMA or acrylonitrile 1511 (Tables 3.6 to 3.8) a threshold in the polymer/solvent (alcohol — water — monomer) ratio has been observed, under which... 

Most of the peroxodisulfate produced (>65%) is used as a polymerization initiator in the production of poly(acrylonitrile), emulsion-polymerized PVC etc. The rest is utilized in numerous applications (etching of printed circuit boards, bleaching processes etc.). 

Cleavage of benzil to benzoyl radicals has also been suggested 32> to account for the observation that irradiation of a polystyrene film containing benzil produced a film which initiated polymerization of acrylonitrile. This initiation was observed even several hours after termination of irradiation. 

This reaction seems to be specific for monomers containing amide groups (acrylamide or methacrylamide), but once these monomers are present in the electrolytic medium, other monomers, e. g., acrylonitrile, can be polymerized. The authors attribute the polymerization initiation to the electrogenerated metal ions only, but it is possible that even the perchlorate ion plays a role in the formation of the initiating species. The polyacrylamide thus obtained has an electrical conductivity 3 to 4 times higher than that of polymers obtained by the usual methods. This is due to the presence of metallic cations coordinatively bound in the polymer bulk. The presence of these cations increases the thermal stability of the polymer by 20—40%. 

Anionic polymerization initiated by uncharged nucleophiles has been observed in several systems. The first example of such a reaction probably was furnished by the work of Horner et al.236), who initiated polymerization of nitroethylene and of acrylonitrile by trialkyl phosphines. The following mechanism was postulated ... 

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