Multicomponent polymers, electron

The application of this technique as a morphological tool requites that there be a close coupling between polymer photophysics and polymer physics. In the photophysical studies described in this paper emphasis will be placed on the development of analytical models for electronic excitation transport (EET). The areas of polymer physics that we will consider involve the configurational statistics of Isolated chains and phase separation in multicomponent polymer systems. The polymer system of primary interest is the blend of polystyrene (PS) with poly(vinyl methyl ether) (PVME). 

A powerful method of examining the morphology of many multicomponent polymer materials utilizes transmission electron microscopy [Woodward, 1989]. If the two phases are nearly equal in electron density, staining with osmium tetroxide or other agents can be used. For more detailed discussion on the methods of morphology characterization, see Chapter 8. 

Yu. S. Lipatov, Role of Interfacial Phenomena in the Formation of Micro and Macro-Heterogeneities in Multicomponent Polymer Systems, PureAppl. Chem. 43,273 (1975). Review of blends and filled IPNs. Physical properties, electron microscopy. 

Michler [2] has nicely summarized and realized practical examples of some of the modern tools of microscopy used to study the morphology and microstructure of polymers and polymer-based materials. The most frequently employed microscopic tool remains the scanning electron microscope. It is the fastest and allows one to reach interesting dimensions in multicomponent polymer blends and composites. Transmission electron microscopy can be ranked in the second position, whereas the optical microscope is usually used as a "first-check tool" before deeper investigation. It is nevertheless the strategic tool employed in life science (biomedical, Wlogics, etc.). In all these cases the sample preparation step is crucial before investigating the material s microstructure. 

The method of differential radiation induced contrast depends on enhancement of contrast in multicomponent polymers where the components have different electron beam-polymer interactions [173]. Contrast has been observed in sections of styrene-acrylonitrile/poly(methyl methacrylate) (SAN/PMMA) polymers where the PMMA exhibits a high rate of mass loss compared to SAN, creating contrast between the phases. It is well known that electron irradiation results in chain scission and crosslinking, loss of mass and crystallinity [75]. Polystyrene, polyacrylonitrile and SAN crosslink and thus are stable in the electron beam whereas polymers exhibiting chain scission, PMMA and poly(vinyl methyl ether), degrade in the beam. It is suggested that experiments be conducted on the homopolymers to determine the expected irradiation damage mechanism in the multi-component system [173]. 

Most, but not aU, of the multicomponent polymer combinations exhibit some type of phase separation, as is discussed in Chapters 4 and 13. Where the polymers are stainable and observable under the electron microscope, characteristic morphologies are often manifest. The principal polymers that are... 

The method of differential radiation induced contrast depends on enhancement of contrast in multicomponent polymers where the components have different electron beam-pol5aner interactions [140]. Contrast has been observed in sections of styrene-acrylonitrile/poly(methyl... 

Electron Microscopic Analysis of Multicomponent Polymers and Blends... 

Multicomponent Polymer Systems Polymerization - Depolymerization Equilibria Copolymers of - Olefins Medical Applications of Plastics Scanning Electron Microscopy Kinetics and Mechanism of Stereoregular Polymerization Glass Transition Phenomena in Plastics and Coatings Properties of Polymers in Interfaces... 

Conducting Polymer Blends, Composites, and Colloids. Incorporation of conducting polymers into multicomponent systems allows the preparation of materials that are electroactive and also possess specific properties contributed by the other components. Dispersion of a conducting polymer into an insulating matrix can be accompHshed as either a miscible or phase-separated blend, a heterogeneous composite, or a coUoidaHy dispersed latex. When the conductor is present in sufftcientiy high composition, electron transport is possible. 

Radicals add to unsaturated bonds to form new radicals, which then undergo addition to other unsaturated bonds to generate further radicals. This reaction sequence, when it occurs iteratively, ultimately leads to the production of polymers. Yet the typical radical polymerization sequence also features the essence of radical-induced multicomponent assembling reactions, assuming, of course, that the individual steps occur in a controlled manner with respect to the sequence and the number of components. The key question then becomes how does one control radical addition reactions such that they can be useful multicomponent reactions Among the possibilities are kinetics, radical polar effects, quenching of the radicals by a one-electron transfer and an efficient radical chain system based on the judicious choice of a radical mediator. This chapter presents a variety of different answers to the question. Each example supports the view that a multicomponent coupling reaction is preferable to uncontrolled radical polymerization reactions, which can decrease the overall efficiency of the process. 

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