Radiation polymerization

Polymerization in aqueous solution of acrylamide can also be fulfilled in thin layers (up to 20 mm) applied on a steel plate or a traveling steel band. Polymerization is initiated by persulfates, redox system, UV or y radiation. Polymerization proceeds in isothermal conditions as the heat of polymerization is dissipated in the environment and, additionally, absorbed by the steel carrier. Nonadhesion of the polymer to the carrier is ensured by the addition of glycerol to isopropyl alcohol or by precoating the steel band with a film based on fluor-containing polymers. This makes polymerization possible at a high concentration of the monomer (20-45%) and in a wider process temperature range. This film of polyacrylamide is removed from the band, crushed, dried, and packed. 

Besides, polymerization processes were used to obtain PCSs with alternating C=N-bonds in the main chain. Thus, radiation polymerization of methacrylonitrile54 gives rise to a ladder polymer of the following type ... 

The polymerization of /3-(2-furyl) acrolein and some of its homologues by acids141 gave a similar phenomenology and thus, presumably, the mechanism is similar to that of the corresponding ketones. Their 7-radiation polymerization only proceeded in solution, probably because acidic substances were formed from the solvent142. ... 

The chemistry involved in LfV-curable resin systems has been extensively investigated and thoroughly surveyed [88-94]. LfV-radiation polymerization, is in principle, completely analogous to the conventional addition polymerization. A photoinitiator is used in UV polymerization. Its function is the same as the free-radical initiator. A conventional initiator possesses a thermally labile bond which is cleaved to form free-radical species, but the photoinitiator has a bond which breaks upon absorption of radiant energy. Benzoin ethers, benzyldialkyl ketals, benzophenone, and acetophenone derivatives are the important LfV-photoinitiators [95-99]. 

It is the author s hope that the foregoing detailed discussion has helped to clarify some features of cationic polymerizations. Many other aspects, such as co-polymerization and radiation polymerization, which I have not been able to discuss here, deserve equal attention. But perhaps the most urgent task, and one which is much more widely relevant, is the elucidation of details of reaction mechanism, and in particular the identification of the chain-carriers in many widely differing systems. The next problem then is to measure their concentration, its variation throughout the reaction, and, hence, the absolute rate constants. It is essential that the factors which decide whether a polymerization is ionic or pseudo-ionic be determined as soon as possible. 

The radiolysis of olefinic monomers results in the formation of cations, anions, and free radicals as described above. It is then possible for these species to initiate chain polymerizations. Whether a polymerization is initiated by the radicals, cations, or anions depends on the monomer and reaction conditions. Most radiation polymerizations are radical polymerizations, especially at higher temperatures where ionic species are not stable and dissociate to yield radicals. Radiolytic initiation can also be achieved using initiators, like those used in thermally initiated and photoinitiated polymerizations, which undergo decomposition on irradiation. 

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

Later, Tieke reported the UV- and y-irradiation polymerization of butadiene derivatives crystallized in perovskite-type layer structures [21,22]. He reported the solid-state polymerization of butadienes containing aminomethyl groups as pendant substituents that form layered perovskite halide salts to yield erythro-diisotactic 1,4-trans polymers. Interestingly, Tieke and his coworker determined the crystal structure of the polymerized compounds of some derivatives by X-ray diffraction [23,24]. From comparative X-ray studies of monomeric and polymeric crystals, a contraction of the lattice constant parallel to the polymer chain direction by approximately 8% is evident. Both the carboxylic acid and aminomethyl substituent groups are in an isotactic arrangement, resulting in diisotactic polymer chains. He also referred to the y-radiation polymerization of molecular crystals of the sorbic acid derivatives with a long alkyl chain as the N-substituent [25]. More recently, Schlitter and Beck reported the solid-state polymerization of lithium sorbate [26]. However, the details of topochemical polymerization of 1,3-diene monomers were not revealed until very recently. 

Fig. 4 Photographs of the crystals of a 2 and b poly(2). The polymer crystal was obtained by y-radiation polymerization...

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... 

In 1957 Davison, Pinner, and Worrall (8) published data on the radiation polymerization of isobutene, which could best be explained as an ionic process. These initial findings were further confirmed by subsequent investigations (7, 9, 26, 27), Needless to say, these disclosures prompted reinvestigation of the question of radiation-induced ionic polymerizations in other systems. 

In 1979, Maciejewski et al. also explored Method 3 for the preparation of main-chain poly(vinylidene chloride-/ -CD rotaxane) 35 [74, 75]. Radiation polymerization and AIBN-initiated solution polymerization of the complex of vinyli-dene chloride with 21 gave products with min = 0.34 and 0.49, respectively. However, the polyrotaxane via Method 1 had a much lower min (0.087) with much lower CD/monomer feed ratio than for those via the polymerization of the complex (1 1 ratio). Therefore, the reported min values are not comparable, so the difference between the two methods in terms of threading efficiencies cannot be distinguished. Although the authors did not see any threading via Method 2 for the same polyrotaxanes, Ogino and coworkers prepared a true CD-based polyrotaxane of Type 5 using metal complexes as stoppers [76]. It was also found that... 

Acrylonitrile is reported to change properties of Nylons by grafting (14,18, 20,21,37,58,62). It is worthwhile to call the attention to Hargreaves work who studied extensively the subject. A 25% solution of acrylonitrile in a 15% solution of zinc chloride was used as immersion media. A flow diagram for radiation polymerization of liquid material is presented (27). 

R. Bird A.J. Power. Thermal Decomposition of Tetrazene at 90°C , MRL-R-710, Australia (1978) [The authors report that Tetrazene is converted into 5-aminotetrazole in less than three days at 90°, thus losing its stab sensy property. Spectroscopic evidence indicates that the 5-aminotetrazole is derived from both the side chain (via guanyl azide) and the Tetrazole ring] 24) G.B. Franklin C.F. Parrish, Radiation Polymerized Priming Compositions , USP 4056416 (1977) CA 88, 52661 (1978) [The inventors claim that extrudable primers with good percussion sensy are prepd from Tetrazene 3.9—4.1, n-Pb Styphnate 32—42,... 

Sb sulfide 14—16, Ba nitrate 30—33, powdered Al 6—8 and a binder 4.5-8%. The acrylate binder is radiation polymerized using a 60Co 7-ray source at approx 5 Mrad strength]... 

Radiation vs. Thermal Polymerization. Table IV compares the compressive strengths of several concrete-polymer systems for each of two polymerization methods. Generally, the radiation polymerized material gave higher strengths than the thermally polymerized material. 

A photoresist is used which is sensitive to radiation. The radiation polymerizes the spin-coated material locally (light can easily be focussed on a desired spot by masks) and stabilizes it against the following etching step. After radiation a washing step is included to remove the unpolymerized part (the hole in this case). Afterwards the gold and chromium layers are chemically etched and the polymer mask is removed completely, chemically. 

Perform optimization of a process of radiation polymerization on fibers. The system response is homopolymer yield. The aim of optimization is to define conditions that facilitate obtaining more than 50% of homopolymer (with respect to fiber mass) on radiation polymerization of styrene, on the surface of viscose fibers. The process is defined by two factors ... 

Figure 1. Plot of % conversion V5. time in bulk radiation polymerization for three...

Some new trends can be recognized in the points such as the interaction of short-lived active species in some spatial distributions measured by spin echo and pulse radiolysis methods. The application of polymers for drug-delivery systems is here discussed with reference to low temperature radiation polymerization techniques. Ion beam irradiation of polymers is also reviewed for which further research is becoming important and attractive for so-called LET effects and high density excitation problems. In the applied fields the durable polymers used in strong and dense irradiation environments at extremely low temperature are here surveyed in connection with their use in nuclear fusion facilities. 

In order to get further insight into the reaction mechanism for the degradation of PMMA, we have studied the nature and behavior of radical entities in irradiated PMMA by using the ESR and ESE techniques complementarily [37]. Two PMMA samples, a commerical PMMA and an initiator-free PMMA prepared by the radiation-polymerization of bulk monomer, were used, but no difference was found in the results. Residual monomer was carefully removed from the PMMA samples, because the monomer molecule readily modifies the radicals derived from the polymer. The samples were irradiated in vaccum. Figure 9 demonstrates the dose-yield curve we obtained by irradiating PMMA in vacuum at 273 K. The G value for the radical formation is determined to be 3.0 from the slope of the linear portion below 12 kGy. 

Fig. 5. Model scheme for the immobilization process by radiation polymerization in a supercooled state. (Adhesion method) c biofunctional component...

Fig. 6. Temperature dependency of activity yield in the immobilization of enzymes by radiation polymerization. Enzyme O ot-amylase in 50% HEMA A glucoamyla.se in 50% HEMA cellulase in 50% HEMA glucose oxidase in 50% HEMA A glucoamylase in 30% HEMA a-glucosidase in 50% HEMA. Monomer HEMA (2-hydroxyethyl methacrylate). Irradiation. 1 x 106 rad, in vacuo. % monomen in buffer solution...

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