text: On occasion, the polymer chain is disengaged from the active centers in the chain termination reaction.  Several pathways exist for termination:
  :Cp−(CH−CHR)−CH + CH=CHR → Cp−CH−CHR + CH=CR–polymer
  Another type of chain termination reaction called a β-hydride elimination reaction also occurs periodically: 
  :Cp−(CH−CHR)−CH → Cp−H + CH=CR–polymer
  Polymerization reactions of alkenes with solid titanium-based catalysts occur at special titanium centers located on the exterior of the catalyst crystallites. Some titanium atoms in these crystallites react with organoaluminum cocatalysts with the formation of Ti–C bonds. The polymerization reaction of alkenes occurs similarly to the reactions in metallocene catalysts:
  :LTi–CH−CHR–polymer + CH=CHR → LTi–CH-CHR–CH−CHR–polymer
  The two chain termination reactions occur quite rarely in Ziegler–Natta catalysis and the formed polymers have a too high molecular weight to be of commercial use. To reduce the molecular weight, hydrogen is added to the polymerization reaction:
  :LTi–CH−CHR–polymer + H → LTi−H + CH−CHR–polymer
  Another termination process involves the action of protic (acidic) reagents, which can be intentionally added or adventitious.