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synopsisThe published data on molecular weight distribution in polysulfide are rather contradictory and cannot be correlated with the concept of the existence of thiol-disulfide interchange in these polymers. In the present work the viscosity and molecular weights of liquid thiokols have been investigated (the number-average molecular weight by iodometric titration and by ebulliometry and the weight-average molecular weight by the light-scattering method). When measuring the light scattering in Thiokol solutions a considerable depolarisation of the scattered light was observed. This fact must be taken into account in the molecular weight determination. It has been established that in polydisulfides with thiol endgroups thiol-disulfide interchange reactions take place not only during the synthesis, but also in the polymer itself (in bulk). These reactions lead to the formation of polymers with an equilibrium molecular weight distribution. A relation of log 7 = f ( has been found that can be used in determining the weightaverage molecular weight of liquid Thiokols.It is known that organic compounds containing sulfhydryl groups and disulfide bonds (for example cystine, cysteine, etc.) are capable of reactions of thiol-disulfide and disulfide-disulfide interchange. 1--3 A linear disulfide polymer undergoing these reactions should have a random molecular weight distribution;4 in this case the ratio of the weightaverage molecular weight ( nw) to the number-average molecular weight (nn) equals 2.However the data published on molecular weight distribution of disulfide polymers containing terminal sulfhydryl groups are not consistent w ith this concept and are highly contradictory.Polymers of narrow molecular weight distributions ( g w / f l m = 1 .l-1.2) have been obtained by fractionation the low molecular VI eight Thiokols by eluent chr~matography.~ On the other hand, Fettes and Mark6 determined (by light-scattering and endgroup analysis) molecular weights for liquid Thiokols over the range of g n = 60G4000 and obtained values of flw/nn ratio in the range of 3-6.The authors came to the conclusion that in the synthesis of liquid Thiokols the thiol-disulfide interchange reactions did not take place. Their attempt to reach equilibrium molecular weight distribution by heating polymers for a long period at 100°C., by ultraviolet irradiation, and by introducing certain catalysts did not lead to an appreciable narrowing of molecula r weight distribution. 567

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