Vinyl radiation polymerization

TABLE 5-8 Effect of Solvent on kp in Radiation Polymerization of Isopropyl Vinyl Ether at 30° C ... 

Because of acid-catalyzed hydrolysis of N-vinylpyrrolidone in water, polymerization was carried out in organic solvent - DMF. Three types of samples of poly(methacrylic acid) were used syndiotactic - obtained by radiation polymerization, atactic - obtained by radical polymerization, and isotactic - obtained by hydrolysis of isotactic poly(methyl methacrylate). It was found that in all cases the rate enhancement appeared in comparison with the blank polymerization (without template). The rate enhancement became more pronounced with increasing chain length and syndiotacticity of the template. According to the authors, the rate enhancement is connected with the stronger complex formation between poly(vinyl pyrrolidone) and syndiotactic poly(methacrylic acid) then with isotactic template. This conclusion was supported by turbimetric titration in DMF/DMSO system and by model considerations. It is worth noting, however, that... 

Panchromatic sensitization of vinyl addition polymerization requires the presence of suitable dyes as primary absorbers of radiation. In 1949 Bamford and Dewar (5) reported that styrene could be polymerized by irradiation of a variety of dyes. It was later shown by Koizumi, Watanabe, and Kuroda (6) that these reactions, and others uncovered by the Japanese group, were the result of photoinduced decomposition of the dyes rather than a true sensitization process. 

Because the reactivities of ions and ion pairs are similar and only weakly affected by the structure of the counteranions, kp + or kp determined by either stopped-flow studies or y-radiated systems (cf., Section IV. 13) can be used in Eq. (75). The equilibrium constant of ionization can then be estimated from the apparent rate constant of propagation and the rate constant of propagation by carbenium ions [Eq. (77)]. For example, Kf 10-s mol-,L in styrene polymerizations initiated by R-Cl/SnCl4 [148]. Kt for vinyl ether polymerization catalyzed by Lewis acids can also be estimated by using the available rate constant of ionic propagation (kp- = 104 mol Lsec-1 at 0° C) [217], The kinetic data in Ref. 258 yields Kj == 10 3 mol - l L in IBVE polymerizations initiated by HI/I2 in toluene at 0° C and Kf 10-1 mol- -L initiated by HI/ZnI2/acetone can be calculated from Eq. (76). 

The radiation polymerization of vinyl chloride is also described by this limiting case. The radiation polymerization of vinyl chloride, however, is somewhat different in character from chemically initiated systems. These differences are specifically... 

Under irradiation, the energy is transferred to the monomer causing the ionization, i.e., an electron is ejected from the monomer, which leads to a cation of the monomer. The monomers for radiation polymerization are vinyl-type double-bond-containing compounds that are recognized as monomers of conventional polymerization. The ionization occurs by ejecting an electron from n bond of olefinic double bond of a monomer molecule, which has the lowest bond energy within the molecule. Consequently, the ionization of monomer by the irradiation leads to a cation radical, in which one end of molecule has a free radical (unpaired electron) and the other end has an excess positive charge (cation). 

Moreover, high conversions of monomer to polymer can be attained with no apparent diminution In rate, yields of 80Z being obtained by suitably extending the Irradiation dose. While the average (-M) values of 2500 for llmonene oxide and ca. 400 for the epoxides of o-and B-plnene are somewhat lower than those reported for the cationic polymerization of some vinyl monomers ( - ) > they are only about an order of magnitude lower than the value of 10,000 often quoted as the benchmark for an economically viable radiation polymerization process (6). 

El-Hadi AA (2003) Eactors affecting the production of prednisolone by immobilization of Bacillus pumilus E601 cells in poly(vinyl alcohol) cryogels produced by radiation polymerization. Proc Biochem 38 1659-1664... 

VinyUdene fluoride can be polymerized in saturated fluorinated or fluorochlorinated solvents. These solvents dissolve fluoroalkenes like vinylidene fluoride and organic peroxide catalysts. Polymerization thus takes place in a homogeneous phase and the resulting poly-vinylidene fluoride is insoluble in the solvent, making the product readily separable from the solvent. In addition to organic peroxides, the reaction can be initiated or induced by radiation. This is helpful in avoiding contamination of the product with other reaction components such as the initiator, surfactant, and the others. Alkyl boron activated by oxygen has also been reported to catalyze vinylidene fluoride and vinyl fluoride polymerization in water and solvents. ... 

The rate data in radiation-induced bulk polymerization of vinyl fluoride revealed a heterophase process.Polymerization was conducted aty-ray dosage rates of 13-100 rad/s using Co. The rate of polymerization at 3 8°C was proportional to the dosage rate to the power 0.42. Gas-phase polymerization of VF with y-rays has been studied in the range of 10-100 rad/s. Polymerization rate increased sharply with the increase in dosage, leading to generation of active sites in the polymer chain and branches. Radiation polymerization of vinyl fluoride dissolved in solvents such as tetrachloromethane lead to chain transfer and incorporation of solvent in the polymer. Vinyl fluoride can also be polymerized in plasma. 

The most effective method for graft polymerization of vinyl fluoride has been radiation polymerization.fi l Vinyl fluoride has been grafted to low density polyethylene, polyisobutylene andpolyamides.t frfi l The density of the graft copolymers was higher than that of... 

Vinyl monomers polymerize by y-ray and electron beams that are higher in energy than visible radiation [12, 13]. Although it is possible to observe ionic polymerization, the majority of cases are by a free radical mechanism. It is possible to obtain homogeneous gels because (1) it is unnecessary to use a free radical initiator or catalyst (2) the reaction... 

The radiation polymerization, induced by an intense Co ° radiation, was used for emulsion polymerization of vinyl acetate in experiments and on industrial scale. 

ETHYLENE We discussed ethylene production in an earlier boxed essay (Section 5 1) where it was pointed out that the output of the U S petrochemi cal industry exceeds 5 x 10 ° Ib/year Approximately 90% of this material is used for the preparation of four compounds (polyethylene ethylene oxide vinyl chloride and styrene) with polymerization to poly ethylene accounting for half the total Both vinyl chloride and styrene are polymerized to give poly(vinyl chloride) and polystyrene respectively (see Table 6 5) Ethylene oxide is a starting material for the preparation of ethylene glycol for use as an an tifreeze in automobile radiators and in the produc tion of polyester fibers (see the boxed essay Condensation Polymers Polyamides and Polyesters in Chapter 20)... 

In tbe first attempt to prepare a two-dimensional crystalline polymer (45), Co y-radiation was used to initiate polymerization in monolayers of vinyl stearate (7). Polymerization at the air—water interface was possible but gave a rigid film. The monomeric monolayer was deposited to give X-type layers that could be polymerized in situ This polymerization reaction, quenched by oxygen, proceeds via a free-radical mechanism. 

Complexation of the initiator and/or modification with cocatalysts or activators affords greater polymerization activity (11). Many of the patented processes for commercially available polymers such as poly(MVE) employ BE etherate (12), although vinyl ethers can be polymerized with a variety of acidic compounds, even those unable to initiate other cationic polymerizations of less reactive monomers such as isobutene. Examples are protonic acids (13), Ziegler-Natta catalysts (14), and actinic radiation (15,16). 

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