Number and weight mass average degrees of polymerization

1 NUMBER AND WEIGHT (MASS) AVERAGE DEGREES OF POLYMERIZATION 

The quantity h of eqns. (166) or (167) is identical with the number average degree of polymerization P. The expression for P is usually written in the form 

Various average quantities are related as F Pw Pz Pz + y The equality sign is only valid for strictly monodisperse polymers. The number average values F or M are very sensitive to the presence of low molecular components, even when these are present in very small amounts. The higher averages, Fz or Mz, are strongly affected by the presence of high molecular components, even in trace concentrations. 

The width of the distribution function can be roughly characterized by the polydispersity coefficient, v, which is equal to the ratio of the weight and number averages 

The values of v are only slightly higher than 1 for products of living polymerizations with rapid initiation. They are around 2 for radical polymers, and in extreme cases values of several tens for sets of macromolecules generated by some coordination polymerizations. 

The mass average degree of polymerization, P, is defined as the first moment with respect to zero of the differential mass distribution 

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