text: The termination steps of free radical polymerization steps are of two types: recombination and disproportionation. In a recombination step, two growing chain radicals (denoted by ) form a covalent bond in a single stable molecule. For the example of a vinyl polymer, 
  Termination by recombination increases the chain length and therefore the molecular weight of the final polymer.
  In a disproportionation step, one radical transfers a hydrogen atom to the other to form two stable molecules:
  Termination by disproportionation usually has a higher activation energy since it involves breaking of one bond, and therefore is more important at higher energy.