Polychloroprene and compounds of polychloroprene with ZnO and MgO were crosslinked by heating in a DSC at a programmed rate. The reaction was stopped at points along the thermogram and the crosslink density of the compound determined. The amount of chlorine evolved during reaction was measured as ZnCl2 and/or MgCl2. Two crosslinking processes were identified, both involving reaction of the 1,2 units in the polymer chain; the first comprising a rapid crosslinking reaction that occurs prior to the isomerization of 1,2 units and the second, a much slower reaction of isomerized 1,2 units. ZnCl2, which forms during compounding and on crosslinking, catalyzes the first reaction, while ZnO promotes the allylic rearrangment of 1,2 units. MgO increases the scorch time by trapping HCl evolved during compounding, thus limiting the amount of the crosslinking catalyst (ZnCl2) formed.