THE PHOTOINITIATED ADDITION OF BUTYL MERCAPTAN TO CONJUGATED AND UNCONJUGATED DOUBLE BONDS

Abstract

This study elucidates the details of a typical initiation encountered in polymerization. A kinetic mechanism for the photoinitiated addition of normal butyl mercaptan to single and conjugated double bonds is proposed, and the corresponding velocity constants namely the attack kα, the transfer kct, and the termination kt have been measured employing a sector method. For the concentrations employed in this work the over-all rate of addition to the double bond is determined by the transfer rate of the composite mercapto monomer radical, while the capture of initiating radicals depends on the rate of attack of the mercaptyl radicals on the double bonds. The transfer rate is about 1000 times faster for a pentenyl than for a conjugated styryl radical, while the attack step is estimated to be several hundred times faster for the conjugated monomer. These conclusions are shown to be consistent with results observed when conjugated and unconjugated monomers are in competition, and are in agreement with the quantum mechanical structure of the radicals and molecules involved. This work reports a general survey of the field, and subsequent papers will extend the observations.