In step-growth polymerization, in order to achieve a high degree of polymerization (and hence molecular weight), , a high fractional monomer conversion, p, is required, according to Carothers equation  For example, a monomer conversion of p' = 99% would be required to achieve .
For chain-growth free radical polymerization, however, Carothers' equation does not apply. Instead long chains are formed from the beginning of the reaction. Long reaction times increase the polymer yield, but have little effect on the average molecular weight. The degree of polymerization is related to the kinetic chain length, which is the average number of monomer molecules polymerized per chain initiated. However it often differs from the kinetic chain length for several reasons:
* chain termination may occur wholly or partly by recombination of two chain radicals, which doubles the degree of polymerization  
* chain transfer to monomer starts a new macromolecule for the same kinetic chain (of reaction steps), corresponding to a decrease of the degree of polymerization
* chain transfer to solvent or to another solute (a modifier or regulator also decreases the degree of polymerization