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A treatment is given of the effect of network flaws due to the finite chain length of the primary elastomer molecules on the elastic properties of rubber vulcanizates. In this treatment full allowance is made for the elastically inactive material which exists either as sol or as loose ends of the network. The cases of linear primary molecules with either a random distribution of lengths or with uniform lengths are considered, and the results are compared with those of earlier theoretical treatments.

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An experimental and theoretical study of the introduction of crosslinks into stretched peroxide-vulcanized rubber by heating it with di-cumyl peroxide in vacuo is described. The observed permanent set and swelling behaviour is in fair agreement with theoretical predictions.An important property of vulcanized rubber is an increase in the unstrained length after stretching, the so-called permanent set. When stretching is for short duration at ordinary temperatures the set is in fact not permanent but decreases with time and largely disappears after swelling. This reversible set has been attributed to secondary forces of the rubber network.l.2 In contrast, stretching at higher temperatures in oxygen produces an irreversible set, which can be attributed very plausibly to the formation of chemical cross-links.3Cross-link formation in stretched networks has been considered as a factor in oxidative ageing, during which a second factor, network degradation, is also operative. Neither process has been investigated separately, and consequently quantitative tests of any theory could not be readily applied.Andrews, Tobolsky, and Hanson 3 have visualized a process of rupture of the GO were made on each strip in this series and the decane removed in wacuo at 60" C over