Rubber rubbery state

Finally, we turn from solutions to the bulk state of amorphous polymers, specifically the thermoelastic properties of the rubbery state. The contrasting behavior of rubber, as compared with other solids, such as the temperature decrease upon adiabatic extension, the contraction upon heating under load, and the positive temperature coefficient of stress under constant elongation, had been observed in the nineteenth century by Gough and Joule. The latter was able to interpret these experiments in terms of the second law of thermodynamics, which revealed the connection between the different phenomena observed. One could conclude the primary effect to be a reduction of entropy... 

Note If a perfect network is in the rubbery state then, on macroscopic deformation of the network, all of its chains are elastically active and display rubber elasticity. 

In a sense, it is much simpler to consider swelling and deswelling phenomena when a gel is initially in the swollen state. In this case the polymer is already in the rubbery state and glass-to-rubber relaxation ceases to be a rate determining factor. 

I11 addition to the primary effect of the great length of the molecule, the details of the distribution of functional groups along tlie polymer chain modify the behavior of these materials. This leads to differences in their applications. For example, natural rubber exists in the rubbery state at... 

The mechanical degradation and production of macroradicals can also be performed by mastication of polymers brought into a rubbery state by admixture with monomer several monomer-polymer systems were examined (10, 11). This technique was for instance studied for the cold mastication of natural rubber or butadiene copolymers in the presence of a vinyl monomer (13, 31, 52). The polymerization of methyl methacrylate or styrene during the mastication of natural rubber has yielded copolymers which remain soluble up to complete polymerization vinyl acetate, which could not produce graft copolymers by the chain transfer technique, failed also in this mastication procedure. Block and graft copolymers were also prepared by cross-addition of the macroradicals generated by the cold milling and mastication of mixtures of various elastomers and polymers, such as natural rubber/polymethyl methacrylate (74), natural rubber/butadiene-styrene rubbers (76) and even phenol-formaldehyde resin/nitrile rubber (125). 

Polymers are sometimes wholly amorphous and non-crystallizable they then follow the line ABDE. However, when such a polymer is heated up to above its Tg it is not immediately transferred into a liquid state, but first into a rubbery state, which, upon further heating, gradually passes into a fluid. Tg is, therefore, called the glass-rubber... 

In Ref. 26 34) the mechanical behaviour of several epoxy-aromatic amine networks was analyzed in the rubbery state at temperatures of about T + 40 °C. Figure 14 gives some experimental results. If the rubber elasticity theory is obeyed, the following relation holds for uniaxial deformation ... 

An excellent review of the various theoretical expressions of this physical fact has been offered by Kumins and Kwei At a fixed temperature, many investigators have found that gas diffusion coefficients in rubbers can be correlated with the Lennard-Jones gas collision diameter. Michaels and Bixler have shown, however, that even in the rubbery state, some orientation of anisotropic molecules such as CO2 may occur during a diffusion step. 

Because of its elastic texture and tendency to harden, marshmallow was assumed to exist in a rubber state. Molecules in the rubbery state of marshmallow can be mobile and lead to sugar crystallization, loss of moisture from the matrix, cross-linking of proteins in gelatin, and collapse of foam. In order to stabilize the product, it is necessary to identify the factors limiting the shelf life of the marshmallow under a specific storage condition. 

The rubber particles must be in the rubbery state to initiate the toughening mechanism (i.e., cavitation)... 

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