Technical Review - Polymers

NB Some technical reviews refer to polymer composites being used in film manufacture when it is not always obvious whether the reference is to the use of a physical blend of the component polymers or whether the polymers are separated in layers (as in coaxial extrusion) or in some combination. Clearly the effects can be quite different.]... 

I have been very fortunate in having access to the Smithers Rapra Polymer Library - a very comprehensive library which has a number of reports which I produced some years ago. Although some topics may read like a technical review, I have selected only sufficient information to make a point and not exhaustively included every reference. 

Technology Catalyst Inc., Liquid Crystal Polymer Technology Technical Review, 1988. 

Homogeneous GopolymeriZation. Nearly all acryhc fibers are made from acrylonitrile copolymers containing one or more additional monomers that modify the properties of the fiber. Thus copolymerization kinetics is a key technical area in the acryhc fiber industry. When carried out in a homogeneous solution, the copolymerization of acrylonitrile foUows the normal kinetic rate laws of copolymerization. Comprehensive treatments of this general subject have been pubhshed (35—39). The more specific subject of acrylonitrile copolymerization has been reviewed (40). The general subject of the reactivity of polymer radicals has been treated in depth (41). 

Photosensitized Reactions for Polymers. The economic and technical features for photocross-linking, photosolubilizafion, and photopolymerization reactions have been reviewed (55). The widely used poly(vinyl ciunamates) (PVCN) photocross-link by a photodimerization reaction. 

Section 1.2 gives a brief review of conjugated polymers in semiconducting and metallic phases. Section 1.3 discusses device architectures and their corresponding processes. Section 1.4 introduces some novel devices and their functions in thin-film polymer devices. Section 1.5 is devoted to technical merits of SMOLEDs and PLEDs used as emitter elements in flat-panel displays. 

Theoretical understanding of the properties of polymers has improved greatly in the last two decades or so. If attention is confined to linear polymers in solution or in the melt, it may be considered that most of their properties can be explained and even within limits predicted even for linear polymers, many properties of the technically important solid state are still rather intractable. However, as this review shows, when theories that appear to apply well to linear polymers are extended to branched ones, agreement with experiment is far less satisfactory. Thus a crucial test of a theory, though a severe one, is to apply it to branched polymers. 

This article reviews recent developments in polymer thermomechanics both in theory and experiment. The first section is concerned with theories of thermomechanics of polymers both in rubbery and solid (glassy and crystalline) states with special emphasis on relationships following from the thermomechanical equations of state. In the second section, some of the methods of thermomechanical measurements are briefly described. The third section deals with the thermomechanics of molecular networks and rubberlike materials including such technically important materials as filled rubbers and block and graft copolymers. Some recent data on thermomechanical behaviour of bioelastomers are also described. In the fourth section, thermomechanics of solid polymers both in undrawn and drawn states are discussed with a special focus on the molecular and structural interpretation of thermomechanical experiments. The concluding remarks stress the progress in the understanding of the thermomechanical properties of polymers. 

The broad landscape of chemical topology and topoisomerism has been summarized in comprehensive reviews [2-5], The accomplishments of Schill, Walba, Sauvage, Stoddart, and others are landmarks in organic synthesis. This chapter describes a personal odyssey in which the focus is on statistical approaches - tinged by polymer science in their continual reference to the flexibility of chains. Some early laboratory efforts, and the technical considerations which led to them, are discussed, as is more recent activity. 

We do not intend to discuss aspects of the use of cyclic strain conditions to obtain information on viscous, visco-elastic, and relaxation properties of polymers, although this, by itself, may present a significant interest for theoretical and experimental research. The aim of this publication is to review recent works which provide a basis for various technical applications, i.e., facilitate rearrangement of molding processes. 

Over the last decade, the poor economics of new polymer and copolymer production and the need for new materials whose performance/ cost ratios can be closely matched to specific applications have forced polymer researchers to seriously consider purely physical polymer blend systems. This approach has been comparatively slow to develop, however, because most physical blends of different high molecular weight polymers prove to be immiscible. That is, when mixed together, the blend components are likely to separate into phases containing predominantly their own kind. This characteristic, combined with the often low physical attraction forces across the immiscible phase boundaries, usually causes immiscible blend systems to have poorer mechanical properties than could be achieved by the copolymerization route. Despite this difficulty a number of physical blend systems have been commercialized, and some of these are discussed in a later section. Also, the level of technical activity in the physical blend area remains high, as indicated by the number of reviews published recently (1-10). 

Examples of Commercial Blends. In this subsection we will review some of the commercial activity in polymer blends. We find it interesting and informative to categorize examples into specific areas that relate to both technical issues associated with these mixtures, such as miscibility or crystallinity, and the intended commercial applications, such as rubbers or fibers. Other schemes of classification could be used, and the present one is not intended to be exhaustive. Likewise, there is no intent to mention all of the commercially interesting polymer blends, but rather, the present purpose is to illustrate some of the possibilities. Information about the examples used here was obtained from product literature supplied by the companies who sell these blends and from various literature references that have attempted to review commercial developments in polymer blends (70-76). 

The materials being reviewed in this book, as in the industry, are identified by different terms such as polymer, plastic, resin, elastomer, reinforced plastic (RP), and composite unreinforced or reinforced plastic. They are somewhat synonymous. Polymers, the basic ingredients in plastics, can be defined as high molecular weight organic chemical compounds, synthetic or natural substances consisting of molecules. Practically all of these polymers are compounded with other products (additives, fillers, reinforcements, etc.) to provide many different properties and/or processing capabilities. Thus plastics is the correct technical term to use except in very few applications where only the polymer is used to fabricate products. 

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