Calculation of the molecular weight distribution of polymers from experimental data

Different methods of calculating the molecular weight distribution (MWD) of polymers from experimental data are discussed. The procedure without fractionation, making use of series expansions in orthogonal polynomials (method of moments), is of limited value. A reasonable approximation of the MWD can be obtained after fractionation of the polymer. The shape of the MWD may be strongly influenced by the treatment given the experimental fractionation data. Conventional methods assuming fraction distributions which cannot be physically real must be rejected. Good results can be obtained when the fraction distributions are represented by functions satisfying certain conditions. It is then necessary to determine at least two average molecular weights of each fraction. This is demonstrated for different functions with the aid of literature data.