Polymerization in catalyst particles: Calculation of molecular weight distribution

Factors which affect and broaden molecular weight distributions are investigated for polymerizations in catalyst particles which are accumulating polymer, such as Ziegler polymerizations of olefins. Expressions for the Q value, or ratio of weight‐average to number‐average molecular weight, are derived for simple, but important linear models. These expressions are of the form Q = FSX for a kinetic scheme in which polymer chains have an infinite growing lifetime, and Q = 2 FGSX for a kinetic scheme in which termination by hydrogen is dominant and each site produces many chains. The factors F , G , S , and X are equal to or greater than unity: F depends on particle geometry and the nature of diffusion and reaction; G depends on environmental history of the particle; S depends on the distribution of site activities; and X depends on the distribution of particle sizes. Effects of reactor type are also studied quantitatively.