Zinc Oxide Crosslinking Reaction of Polychloroprene Rubber
Abstract There was some ambiguity on the reality of the formation of ether crosslinks in the ZnO crosslinking of CR. This report clearly indicates the absence of the ether crosslinks. The main reaction pathway of the ZnO crosslinking of CR is the addition of the carbonium ion formed from the isomerized 1,2 unit to the double bond in the neighboring 1,4 unit, catalyzed by ZnCl2. The isomerized 1,2 unit is formed by the rearrangement of allylic chlorine in the 1,2 unit. The crosslinking reaction takes place between one curing site and one main chain component, not between two curing sites. The intramolecular cyclization predominantly occurs as compared with the intermolecular reaction (crosslinking) in Scheme 2. Therefore, the efficiency of the ZnO crosslinking of CR is quite small as expected from the concentration of the curing sites (1,2 units). Model polymer of low molecular weight and NMR spectroscopy have led to a better understanding of the chemistry of this process.