CW occurs after the polymer chain has grown somewhat on the metal catalyst.  The precursor is a 16 e complex with the general formula [ML(CH)(chain)].  The ethylene ligand (the monomer) dissociates to produce a highly unsaturated 14 e cation.  This cation is stabilized by an agostic interaction. β-Hydride elimination then occurs to give a hydride-alkene complex. Subsequent reinsertion of the M-H into the C=C bond, but in the opposite sense gives a metal-alkyl complex.  
This process, a step in the chain walk, moves the metal from the end of a chain to a secondary carbon center.  At this stage, two options are available: (1) chain walking can continue or (2) a molecule of ethylene can bind to reform the 16e complex.  At this second resting state, the ethylene molecule can insert to grow the polymer or dissociate inducing further chain walking. If many branches can form, a hyperbranched topology results. Therefore, ethene only homopolymerization can provide branched polymer whereas the same mechanism leads to chain straightening in α-olefin polymerization. The variation of CW by changing T, monomer concentration, or catalyst switch can be used to produce block copolymer with amorphous and semi-crystalline blocks or with blocks of different topology.