Rubber elasticity polymer molecules

In suspension processes the fate of the continuous liquid phase and the associated control of the stabilisation and destabilisation of the system are the most important considerations. Many polymers occur in latex form, i.e. as polymer particles of diameter of the order of 1 p.m suspended in a liquid, usually aqueous, medium. Such latices are widely used to produce latex foams, elastic thread, dipped latex rubber goods, emulsion paints and paper additives. In the manufacture and use of such products it is important that premature destabilisation of the latex does not occur but that such destabilisation occurs in a controlled and appropriate manner at the relevant stage in processing. Such control of stability is based on the general precepts of colloid science. As with products from solvent processes diffusion distances for the liquid phase must be kept short furthermore, care has to be taken that the drying rates are not such that a skin of very low permeability is formed whilst there remains undesirable liquid in the mass of the polymer. For most applications it is desirable that destabilisation leads to a coherent film (or spongy mass in the case of foams) of polymers. To achieve this the of the latex compound should not be above ambient temperature so that at such temperatures intermolecular diffusion of the polymer molecules can occur. 

Finkelmann et al. 256 274,2781 have also investigated the synthesis and the characteristics of siloxane based, crosslinked, liquid crystalline polymers. This new type of materials displays both liquid crystallinity and rubber elasticity. The synthesis of these networks is achieved by the hydrosilation of dimethylsiloxane-(hydrogen, methyl)siloxane copolymers and vinyl terminated mesogenic molecules in the presence of low molecular weight a,co-vinyl terminated dimethylsiloxane crosslinking agents156 ... 

It may be shown that when the polymer concentration is large, the perturbation tends to be less. In particular, in a bulk polymer containing no diluent a = l for the molecules of the polymer. Thus the distortion of the molecular configuration by intramolecular interactions is a problem which is of concern primarily in dilute solutions. In the treatment of rubber elasticity—predominantly a bulk polymer problem—given in the following chapter, therefore, the subscripts may be omitted without ambiguity. 

Prior to a discussion of the theory of rubber elasticity, it is important to review how isolated polymer chains behave as this will provide a picture of the size and shape of a polymer. Clearly a polymer chain in a vacuum will collapse into a dense unit, but when in a solution the molecule will take on a conformation which is a function of the interaction with the surrounding molecules and the balance between the entropically driven tendency to maximise the spatial configuration and the connectivity of the monomer units. This is the case whether the chain is surrounded by small molecules (solvent) or other macromolecules that may or may not act like a solvent. 

Viscoelastic properties of molten polymers conditioning the major regularities of polymer extension are usually explained within the framework of the network concept according to which the interaction of polymer molecules is localized in individual, spaced rather far apart, engagement nodes. The early network theories were developed by Green and Tobolsky 49) and stemmed from successful network theories of rubber elasticity. These theories were elaborated more fully in works by Lodge50) and Yamamoto S1). The major elasticity. These theories is their simplicity. However, they have a serious drawback the absence of molecular weight in the theory. 

First study of co-polymerisation by Wagner-Jauregg Early theories of rubber-elasticity (Mark, Meyer, Guth, Kuhn and others) Carothers famous work proves by means of organic synthesis that polymers are giant, stable molecules. He first proves it by the discovery of neoprene (polychloro-butadiene), then by the condensation polymerisation of amino acids and esters. As a consequence the first fully synthetic textile fibre, nylon, is developed. In Carothers group Flory elucidates the mechanisms of radical and condensation polymerisation... 

If the polymer is in its pseudo-rubber-elastic state, the surface layer will contain 8 and 82. Solvent molecules are able to penetrate faster into the polymer matrix than the macromolecules can be disentangled and transported into the solution. 

Rigid rodcrystallisation, 706 Rod climbing effect, 526 Rod-like molecules, 252 Rod-like polymer molecules, 274 Rod-shaped particle, 276 Rubber elasticity, 401 Rubbery plateau, 400 Rudin equations, 272 Rudin-Strathdee equation, 602 Rules of thumb for substituting an H-atom by a group X, 182... 

A similar approach has also been developed by Susteric [108], who compares the behavior during low-amplitude deformation of rubbers, loaded with aggregated carbon black, with the visco-elastic behavior of macromolecules undergoing high-frequency deformation. The specific features of the breaking of carbon black aggregates defined by the deformation amplitude of loaded rubbers are described by the above author by a mathematical model developed for the description of the dynamic, visco-elastic behavior of polymer molecules. This approach revealed... 

Elastomers are necessarily characterized by weak intermolecular forces. Elastic recovery from high strains requires that polymer molecules be able to assume coiled shapes rapidly when the forces holding them extended are released. This rules out chemical species in which intermolecular forces are strong at the usage temperature or which crystallize readily. The same polymeric types are thus not so readily interchangeable between rubber applications and uses as fibers or plastics. 

Polymers differ from small molecules in that the space-filling dimensions of macromolecules are not fixed. This has some important consequences, one of which is that certain polymers behave elastically when they are deformed. The nature of this rubber elasticity and its connection with changes in the dimensions of elastomeric polymers are explored in this and the subsequent section of this chapter. 

Portions of polymer molecules which are in crystalline regions have overall dimensions and space-filling characteristics that arc determined by the particular crystal habit which the macromoleculc adopts. Here, however, we are concerned with the sizes and shapes of flexible polymers in the amorphous (uncrystallized) condition. It will be seen that the computation of such quantities provides valuable insights into the molecular nature of rubber elasticity. 

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