General properties of polymerizations

A chain polymerization can be radicalar, anionic, cationic, or stereospecific according to the type of initiator used. The reaction may occur in bulk, in suspension, in emulsion, as in solution. It is necessary to choose adequate temperatures for a good control of the processes. 

This last method, being more costly, is principally used in laboratories where by this means, better defined polymers can be prepared and the kinetics of the reaction can be studied. 

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If a weight is suspended from a polymeric filament the strain will not be constant but will increase slowly with time. The effect is due to a molecular rearrangement in the solid induced by the stress. On release of the stress, the molecules slowly recover their former spatial arrangement and the strain simultaneously returns to zero. This effect is termed creep and is a manifestation of a general property of polymeric solids known as viscoelasticity the solid is elastic in that it recovers, but is viscous in that it creeps. 

A typical balance of processability and end use performance is the general requirement of polymeric resins. The studies on the different polymer fractions have provided a great support in tailoring the MW and MWD in order to achieve the required properties and eliminating the unwanted molecular species. The increase in low-... 

When we consider the mechanical properties of polymeric materials, and in particular when we design methods of testing them, the parameters most generally considered are stress, strain, and Young s modulus. Stress is defined as the force applied per unit cross sectional area, and has the basic dimensions of N m in SI units. These units are alternatively combined into the derived unit of Pascals (abbreviated Pa). In practice they are extremely small, so that real materials need to be tested with a very large number of Pa... 

This chapter intends to discuss the fundamental role played by carbons, taking particularly into account their nanotexture and surface functionality. The general properties of supercapacitors are reviewed, and the correlation between the double-layer capacitance and the nanoporous texture of carbons is shown. The contribution of pseudocapacitance through pseudofaradaic charge transfer reactions is introduced and developed for carbons with heteroatoms involved in functionalities able to participate to redox couples, e.g., the quinone/hydroquinone pair. Especially, we present carbons obtained by direct carbonization (without any further activation) of appropriate polymeric precursors containing a high amount of heteroatoms. 

First, in order to understand the processing, structure, and properties of polymeric fibers, the main focus of Chapters 3 and 4, it will be useful to review some general and basic concepts regarding the structure of polymeric materials, and... 

There are an enormous variety of commercial emulsifiers that are employed in emulsion polymerization. Emulsifiers are generally categorized into four major classes anionic, cationic, nonionic and zwitterionic (amphoteric). The anionic and nonionic emulsifiers are the most widely used. In addition, mixtures of emulsifiers are also often used. Since the effects of the molecular structme and chemical and physical properties of an emulsifier on particle formation are still far from being well understood, numerous experimental investigations on particle formation have been carried out to date with various nonionic emulsifiers [99-102], mixed emulsifiers (ionic and nonionic emulsifiers) [18,103-106] and reactive surfactants [33, 107-110]. Recently, polymeric surfactants have become widely used and studied in emulsion polymerizations [111-116]. A general review of polymeric surfactants was published in 1992 by Piirma [117]. Recently, emulsion polymerization stabilized by nonionic and mixed (ionic and nonionic) emulsifiers was reviewed by Capek [118]. 

General properties of polymer 8.6 Some applications of polymeric systems... 

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