Interpenetrating polymer networks (IPN’s) are a unique type of polyblend, synthesized by swelling a crosslinked polymer (I) with a second monomer (II), together with crosslinking and activating agents, and polymerizing monomer II in situ (Sperling, 1974–1975 ; Sperling and Friedman, 1969). The term IPN was adopted because, in the limiting case of high compatibility between crosslinked polymers I and II, both networks could be visualized as being interpenetrating and continuous throughout the entire macroscopic sample.* As with other types of polyblends, if components I and II consist of chemically distinct polymers, incompatibility and some degree of phase separation usually result (Sperling, 1974–1975; Sperling and Friedman, 1969; Sperling et al., 1970a,b,c; 1971). Even under these conditions, the two components remain intimately mixed, the phase domain dimensions being on the order of hundreds of angstroms. If one polymer is elastomeric and one polymer is plastic at the use temperature, the combination tends to behave synergistically, and either reinforced rubber or impact-resistant plastics result, depending upon which phase predominates (Curtius et al., 1972; Sperling and Mihalakis, 1973; Sperling et al., 1971; Huelck et al., 1972). Among the other kinds of polymer blends discussed in this monograph, the graft-type copolymers are the ones most closely related to the IPN’s.

Interpenetrating Polymer Networks

A condensed description is given of the fundamental processes involved in radiation damage and the effects of radiation on the physical and chemical properties of organic materials, particularly polymers It is shown that the radiation doses received by specimens in the electron microscope are extremely high, very much greater than those used in radiation chemistry experiments Because of this, only qualitative predictions of behaviour in the electron microscope can be made A number of authors have described the changes in the image or diffraction pattern of particular specimen types during observation in the electron microscope and their work is reviewed here In general, contrast features in the image may disappear, due to loss of mass or crystallinity, or new features may appear due to distortion of ordered regions The effects of radiation damage on attainable resolution, and possible methods of improving the resolution are then discussed

Radiation damage and electron microscopy of organic polymers

A condensed description is given of the fundamental processes involved in radiation damage and the effects of radiation on the physical and chemical properties of organic materials, particularly polymers. It is shown that the radiation doses received by specimens in the electron microscope are extremely high, very much greater than those used in radiation chemistry experiments. Because of this, only qualitative predictions of behaviour in the electron microscope can be made. A number of authors have described the changes in the image or diffraction pattern of particular specimen types during observation in the electron microscope and their work is reviewed here. In general, contrast features in the image may disappear, due to loss of mass or crystallinity, or new features may appear due to distortion of ordered regions. The effects of radiation damage on attainable resolution, and possible methods of improving the resolution are then discussed. I. Introduction Specimens in the electron microscope are inevitably exposed to irradiation by electrons. A certain fraction of these electrons will interact with orbital electrons in the specimen and transfer energy to them. At normal accelerating voltages the excited states formed in metals and most other inorganic substances dissipate their energy as heat, and no permanent change occurs. In some inorganic salts and all organic substances, however, some fraction of the excited states decay to altered structures, giving permanent changes in the chemical and physical properties of the specimen. In general, some fraction of the mass is lost, the chemical composition changes and any long range order originally present is destroyed. When organic material provides the image contrast, the appearance of the specimen changes considerably during observation in the electron microscope, because of radiation damage. The impermanence of the original appearance limits the possible resolution. After considerable irradiation - which may only take a short time in the microscope - the specimen stabilizes in a new form, resistant to further radiation. All of the initial structure of interest may have been

http://rd.springer.com/content/pdf/10.1007%2FBF00540772.pdf

Koichi Kato

Papers

Osmium tetroxide fixation of rubber latices

Osmium Tetroxide Fixation of Rubber Latices