STUDIES OF THE MICROHETEROGENEITY OF POLYBUTADIENE AND GR-S: I. THE PROPAGATION MECHANISM IN THE POLYMERIZATION OF BUTADIENE

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Abstract
When n-butyl mercaptan is reacted in a one to one ratio with butadiene in an emulsion system containing persulphate, crotyl n-butyl thioether is exclusively formed as the product of the initiation step. That is, no 1, 2 or 3, 4 addition was found for this step but only the 1, 4. Crotyl n-butyl thioether and methylvinylcarbinyl n-butyl thioether have both been synthesized and certain physical properties determined. It is concluded that in all free radical attacks upon butadiene, the terminal carbon is attacked. The resulting radical may or may not resonate between structures which yield 1, 4 addition and 1, 2 addition; for example, when a mercaptan radical attacks, the resonance is suppressed, but, when styryl or butadienyl radical attacks, the resonance results in the observed ratios of 1, 2, 1, 4 addition in polybutadiene and copolymers of butadiene and styrene. The nature of the products and the yield indicates that the overwhelming number of initiations are made by butyl mercaptan radicals and termination is almost exclusively made by mercaptan.

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