Polymerization Reactions and Modifications of Polymers by Ionizing Radiation (original) (raw)

Ionizing Radiation-Induced Polymerization

Ionizing Radiation Effects and Applications, 2018

Ionizing radiation can induce some kinds of reactions, other than polymerization, such as dimerization, oligomerization, curing, and grafting. These reactions occur through a regular radical chain causing growth of polymer by three steps, namely, initiation, propagation, and termination. To understand ionizing radiation-induced polymerization, the water radiolysis must be taken into consideration. This chapter explores the mechanism of water molecules radiolysis paying especial attention to the basic regularities of solvent radicals' interaction with the polymer molecules for forming the crosslinked polymer. Water radiolysis is the main engine of the polymerization processes, especially the "freeradical polymerization." The mechanisms of the free-radical polymerization and crosslinking will be discussed in detail later. Since different polymers respond differently to radiation, it is useful to quantify the response, namely in terms of crosslinking and chain scission. A parameter called the G-value is frequently used for this purpose. It represents the chemical yield of crosslinks, scissions and double bonds, etc. For the crosslinked polymer, the crosslinking density increases with increasing the radiation dose, this is reflected by the swelling degree of the polymer while being immersed in a compatible solvent. If crosslinking predominates, the crosslinking density increases and the extent of swelling decreases. If chain scission predominates, the opposite occurs. A further detailed discussion of these aspects is presented throughout this chapter.

Ionizing radiation: a versatile tool for nanostructuring of polymers

Pure and Applied Chemistry, 2016

Very high energies of particulate (accelerated electrons, swift heavy ions) or electromagnetic wave (γ-, X-rays) radiation can be used to initiate free radical based reactions in solids, liquids or gases. Because of non-selectivity of absorption of X-rays, γ rays and accelerated electrons in matter free radicals are generated homogeneously in the bulk material. These free radicals on the polymers or monomers are used extensively in the synthesis and modification of polymeric materials. The unique properties of ionizing radiation make it a very useful tool in the top-down and bottom-up synthesis of nanomaterials. In this article the utilization of ionizing radiation in the form of swift heavy ions, accelerated electrons, X- and γ rays will be described for development of advanced materials by radiation-induced grafting in nanoscale, synthesis of polymeric nanoparticles, radiation-assisted synthesis of nanogels and nanocomposites. The properties difficult to be attained by other techn...

Progress in radiation processing of polymers

Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms, 2005

Modification in polymeric structure of plastic material can be brought either by conventional chemical means or by exposure to ionization radiation from ether radioactive sources or highly accelerated electrons. The prominent drawbacks of chemical cross-linking typically involve the generation of noxious fumes and by products of peroxide degradation. Both the irradiation sources have their merits and limitations. Increased utilization of electron beams for modification and enhancement of polymer materials has been in particular witnessed over the past 40 years. The paper highlights several recent cases of EB utilization to improve key properties of selected plastic products. In paper is provided a survey of radiation processing methods of industrial interest, encompassing technologies which are already commercially well established, through developments in the active R&D stage which show pronounced promise for future commercial use. Radiation cross-linking technologies discussed include: application in cable and wire, application in rubber tyres, radiation vulcanization of rubber latex, development of radiation crosslinked SiC fiber, polymer recycling, development of gamma compatible pp, hydrogels etc. Over the years, remarkable advancement has been achieved in radiation processing of natural polymers. Role of radiation in improving the processing of temperature of PCL for use as biodegradable polymer, in accelerated breakdown of cellulose into viscose and enhancement in yields of chitin/chitosan from sea-food waste, is described.

Radiation Processing of Polymers for Medical and Pharmaceutical Applications

Macromolecular Symposia, 2015

The use of ionizing radiation for the preparation of polymeric biomaterials is one of the examples of the application of atomic energy for the benefit of humanity. Radiation processing is based on the use of high energy ionizing radiation to induce chemical and biological changes in irradiated systems. High energy electron (EB) under 10 keV and gamma irradiation are the most frequently used of ionizing radiation for synthesis, modification of polymers, and sterilization of medical devices. Potential biomedical and pharmaceutical applications of these polymers are implants, topical dressings, injectable formulations, drug delivery devices, diagnostic assays, and immobilized enzyme. Through radiation crosslinking or degradation processes, polymers with specific characteristics can be prepared. The advantages of radiation processing include the absent of any chemical residues (since no chemical additives are requires to initiate the reactions), can be used at all temperatures, can be limited to the surface only and in certain cases, the synthesis/modification of materials can be combined with sterilization.

The Role Of Unsaturations In The Gamma Irradiation Of Crosslinkable Polymers

Radiation Physics and Chemistry, 2015

Nowadays, the understanding of the interaction of ionizing radiations with polymeric materials is becoming increasingly important. It is well known that many parameters regarding the synthesis of the polymers noticeably affect the irradiation process. In this work, an analysis of the effect of the type and the position of unsaturations in the molecular structure of crosslinkable polymers is performed. For such purpose, two solid semycristalline metallocenic ethylene 1-olefin copolymers (mEOC) which contain a low concentration of unsaturations from the synthesis, and their hydrogenated samples, were irradiated along with liquid poly(dimethylsiloxane) (PDMS) homo and copolymers containing different location and concentration of vinyl groups, which were structurally tailored through anionic synthesis. The source of irradiation was 60 Co, under vacuum at room temperature, in all the cases. The results indicated that terminal vinyls drastically accelerate the crosslinking to lower doses, even at much lower concentrations than other type and location of unsaturations for both, mEOC and PDMS, type of polymers.

Structural Modifications of Gamma Irradiated Polymers: An FT-IR Study

A comprehensive study of structural modifications of gamma irradiated polymers in the dose range of 10 1 Gy to 10 6 Gy, was conducted using FT-IR technique. The results were varied in nature, proving that all polymers do not undergo similar type of destruction under similar irradiation conditions. The IR spectrum of polypropylene polymer confirmed the total destruction of isotactic arrangements of the polymer. The destruction of the polypropylene polymer lead to the formation of alcoholic and ketonic groups. For polyacetate polymer, elimination of carbon dioxide took place due to destruction of the ester group. Interestingly, for polycarbonate polymer also, it was observed that at the dose of 10 6 Gy, phenolic group formed due to cleavage of ester bonds. For polyvinyl chloride, there was a clear spectral indication regarding the formation of C=C bond and simultaneous decrease in concentration of C-Cl bond which took place upon gamma irradiation.

Effects of Gamma Radiation on Polymer in Solution. II. Poly(Vinyl Methyl Ether)

Bulletin of the Institute for Chemical Research, Kyoto University, 1962

Dilute aqueous solutions of poly(acrylic acid) in acid form and in sodium-salt form have been irradiated with gamma-rays from a Co-60 source both in the presence and in the absence of air. Changes in gelation dose and viscosity have been measured. On irradiation in the absence of air, gel-formation was observed, and both the gelation dose and the critical concentration for gel-formation increased as the degree of neutralization of polymers increased. The critical concentrations were 0.25, 0.30, 0.56 and 1.0 wt. %, for polymers with degrees of neutralization of 0, 5, 10 and 20%, respectively. When NaC1 was added to the solution for irradiation so as to diminish the ionization of carboxyl groups, gelation occurred more readily with increasing NaC1 concentration, if the NaC1 concentration was relatively low. However, as the concentration of NaC1 became higher than O.O1N, gel-formation was increasingly suppressed with increasing NaC1 concentration. This fact demonstrates that there is an optimum expansion of polyion for crosslinking in aqueous solution. On irradiation in the presence of air, the polymer appeared to degrade exclusively. The higher the degree of neutralization, the higher the degree of degradation. If, however, NaCl was present sufficiently in the solution for irradiation, degradation did not occur practically.

Ion irradiation of polymers

Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms, 1991

The keV-MeV ion irradiation of polymers produces deep changes in their physical and chemical properties associated with the breaking and rearrangement of original bonds. The modification of chain structure occurs within a well defined ion fluence range which depends on the ion linear energy transfer as well as on the target parameters. At low ion fluences (≈1014 ions/cm2) crosslinks between chains and chain-scissions are detected with a chemical yield in the range 0.05–0.3, depending on the ion mass. With increasing ion fluence (1015 ions/cm 2) the original polymer structure is heavily modified and the irradiated films exhibit properties close to those of hydrogenated amorphous carbon. At very high fluences (≈1016 ions/cm 2) graphitization of the material occurs.

Radiation Effects on Polymers for Biological Use

Advances in Polymer Science, 2003

This series presents critical reviews of the present and future trends in polymer and biopolymer science including chemistry, physical chemistry, physics and materials science. It is addressed to all scientists at universities and in industry who wish to keep abreast of advances in the topics covered.

Properties of Selected Polymers after Radiation Cross-linking

2012

Radiation processing involves the use of natural or manmade sources of high energy radiation on an industrial scale. The principle of radiation processing is the ability of high energy radiation to produce reactive cations, anions and free radicals in materials. The industrial applications of the radiation processing of plastics and composites include polymerization, cross-linking, degradation and grafting. Radiation processing mainly involves the use of either electron beams from electron accelerators or gamma radiation from Cobalt-60 sources. The TPE-E thermoplastic elastomer, LDPE low density polyethylene and PA6 polyamide 6 tested showed significant changes of temperature stability and mechanical properties after irradiation. From this point-of-view, new applications could also be seen in areas with service temperatures higher than their former melting point. The comparison of the temperature stability and mechanical properties of irradiated and nonirradiated TPE-E, LDPE and PA6...