Once the carbocation is formed, isomerization reactions become feasible. This is evident in the polymer hydrogenolysis chemistry described in Figure . Both iPP and HDPE react under these conditions to form extractable oils containing quite complex microstructures. Classic carbocation chemistry can explain these observations. The complete loss of tacticity in oils formed during iPP hydrogenolysis can be explained by fast 1,3-hydride shifts, a process known to occur with a barrier of 8.5 kcal mol -1 in the 2,4-dimethyl-2-pentyl cation, eq 1. The hyperbranched structure obtained from HDPE hydrogenolysis results from formation of a secondary carbocation followed by 1,2-migration that forms a tertiary carbocation and a branch, eq 2. 1,2-migrations also form regioirregular errors in iPP oils and chain-straightening in residual iPP.