The Force of Retraction in Relation to Network Structure

The equilibrium tension r at a = 2 for GR-S synthetic rubber vulcanized in this manner is plotted in Fig. 99 against the mole fraction (pXlOO) of units cross-linked. The straight line has been calculated 

Similar results have been obtained for natural rubber vulcanized in like manner. Here also the observed equilibrium stress tends 

Perhaps the most convincing test of the theoretical equation of state is provided by the work of Schaefgen on so-called multilinked polyamides, which would not ordinarily be classified as rubberlike. 

These were prepared by efficiently interhnking pairs of carboxyl end groups in fibers extruded from tetra-chain and from octachain poly- -caproamides (see p. 

using a diamine for this purpose. The products retain typical fiber properties below their melting points, ca. 225°C, but when heated above this temperature they melt to highly elastic rubbers. The strain (a—1) was measured at several temperatures in this range as a function of the stress. A typical set of results is compared in Fig. 101 with the theoreti- 

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