Polymerization by radiation

Acrylamide polymerization by radiation proceeds via free radical addition mechanism [37,38,40,45,50]. This involves three major processes, namely, initiation, propagation, and termination. Apart from the many subprocesses involved in each step at the stationary state the rates of formation and destruction of radicals are equal. The overall rate of polymerization (/ p) is so expressed by Chapiro [51] as ... 

Methyl methacrylate can also be polymerized by radiation using either a cobalt-60 source or accelerated electrons at dose rates up to 3 megarads/sec. The activation energy for the electron beam polymerization is about 7.0kcal/ mole (Ref 12). Radical polymerization can also occur using diisocyanates or hydroperoxides as the initiating species (Ref 15)... 

Cationic polymerization by radiation Polymerization of both wet and dry monomers by exposure to °Co 7-ray radiation (4)... 

DiaHyl esters find Htde appHcation in lenses. However, DAP and DAIP can be polymerized by high energy radiation in lens molds (74). Coatings of sihca and alumina by vaporization give antiglare, scratch-resistant lenses. 

The bismaleimide can then be polymerized by reaction with additional amine to form polyaininobismaleknide or by radiation-induced homopolymerization to form polybismaleimide (4). 

Fig. 3. Polymerization initiation and propagation by radiation-generated free radicals. A is the initiating radical produced by irradiating the Hquid coating. (1) represents the Hquid monomer—unsaturated polymer reactive coating system. R is functional. (2) is the growing polymer chain (free radical). The cured...

Acrylamide readily undergoes polymerization by conventional free radical methods, ionizing radiation, ultrasonic waves, and ultraviolet radiation. The base-cata-lized hydrogen transfer polymerization of acrylamide yields poly-/3-alanine (Nylon 3) a water insoluble polymer that is soluble in certain hot organics. All current industrial production is believed to be by free radical polymerization. 

Addition of metallic oxides to isobutene polymerized by high energy radiation leads to a spectacular increase in the yield.313. It seems that some ions are stabilized by complexing with the surface of the oxide and such an interaction prevents their recombination with the gegen-ions. These observations confirm therefore the suggested cause of inefficient ionic polymerization in systems exposed to ionizing radiation. 

The creation of active sites as well as the graft polymerization of monomers may be carried out by using radiation procedures or free-radical initiators. This review is not devoted to the consideration of polymerization mechanisms on the surfaces of porous solids. Such information is presented in a number of excellent reviews [66-68]. However, it is necessary to focus attention on those peculiarities of polymerization that result in the formation of chromatographic sorbents. In spite of numerous publications devoted to problems of composite materials produced by means of polymerization techniques, articles concerning chromatographic sorbents are scarce. As mentioned above, there are two principle processes of sorbent preparation by graft polymerization radiation-induced polymerization or polymerization by radical initiators. We will also pay attention to advantages and deficiencies of the methods. 

Nakase, Y., Kurijama, I. and Odajima, A. Analysis of the Fine Structure of Poly(Oxyme-thylene) Prepared by Radiation-Induced Polymerization in the Solid State. Vol. 65, pp. 79-134. 

Cross-linking of polymers is done routinely by radiation technology. The factors influencing the cross-linking or the efficiency of cross-linking of polymeric materials are ... 

In this brief section, we have not touched the vast field of radiation-induced polymerization and radiation effects on polymers. Fortunately, the field has been surveyed very well in international conference proceedings published in Radiation Chemistry and Physics referred in the beginning of this section. The earlier books by Charlesby (1960) and by Dole (1973) provide adequate background information. 

Kumakura, M., and Kaetsu, I. (1984) Polymeric microspheres by radiation copolymerization of acrolein and various monomers at low temperatures. Colloid Poly. Sci. 262, 450-454. 

The theory of polymerizations by ionizing radiations gives the rate of initiation Rt (ions cm"3 s 1) as... 

In polymerizations by ionizing radiations in the presence of strong electron acceptors which reduce the reactivity of the electrons, the termination reaction is inhibited, the concentration of ions grows and under these conditions the participation of paired cations becomes relevant (Hayashi et al. 1977 Yamamoto et al. 1977). 

These ideas are new, since traditionally non-propagating cations have not been considered and the polymerizations by ionizing radiations have been thought of as monoeidic, the sole propagator being the cation P+K, solvated of course, but otherwise unencumbered. 

When considering the polymerizations by ionizing radiations in solution, I adopt a point of view opposite to that customary in conventional reaction kinetics. In these it is normal practice to progress from dilute to more concentrated solutions, usually up to no more than ca. 2 mol dm"3. In the present context, the actual experimental practice determines that we think in terms of a gradual dilution of the bulk monomer this also happens to be heuristically fruitful. 

According to my view, the polymerizations by ionizing radiations at the lowest m are bimolecular reactions, propagated by the species P+ Sv. For these reactions there are no ambiguities, and [P+ Sv] = c, so that k+p is defined by (4.1) and (4.15). The available values, including those calculated in this Section and in Section 5, are collected in Table 5. 

The irradiation of polymers is widespread in many industries. For example, microlithography is an essential process in the fabrication of integrated circuits that involves the modification of the solubility or volatility of thin polymer resist films by radiation. The sterilization by radiation of medical and pharmaceutical items, many of which are manufactured from polymeric materials, is increasing. This trend arises from both the convenience of the process and the concern about the toxicity of chemical sterilants. Information about the radiolysis products of natural and synthetic polymers used in the medical industry is required for the evaluation of the safety of the process. 

There is sometimes a question as to whether a particular initiator or initiator system initiates polymerization by radical, cationic, or anionic means. Such a question can easily arise, for example, in polymerizations initiated by ionizing radiation. The mode of initiation of a particular initiator can be distinguished by a consideration of its characteristics compared to those of known radical, cationic, and anionic initiators ... 

Stannett, V. T., J. Silverman, and J. L. Garnett, Polymerization by High-Energy Radiation, pp. 317-336 in Comprehensive Polymer Science, Vol. 4, G. C. Eastmond, A. Ledwith, S. Russo, and P. Sigwalt, eds., Pergamon Press, London, 1989. 

For initiation of polymerizations by light or high energy radiation, the initiator concentration [/] is replaced by the radiation intensity in the above kinetic equations. 

Cationic polymerizations can be initiated with protic acids (e.g., sulfuric, perchloric, trifluoroacetic acid), with Lewis acids (see Sect. 3.2.1.1), and with compounds that form suitable cations (e.g., iodine, acetyl perchlorate). Some monomers are also polymerized by high-energy radiation according to a cationic mechanism. 

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