Modeling of Chain Length and Long-Chain Branching Distributions in Free-Radical Polymerization

Abstract

The effect of long-chain branching and β- scission reactions on the complete molecular weight (MW) and branching density distributions of polymer pro- duced in a well-mixed continuous reactor has been sys- ematically studied. An improved statistical description of ow branch points on a scissioning chain distribute between the two resulting polymer fragments has been developed and implemented in the PREDICI® software package, Simulations are used to illustrate that the branching density distribution does not provide a good visual ndication of average brarching in the system; appropriate averaging aeross the chair, length distribution must be performed, It is shown that chain lengths tend to the most probable distribution even in the presence of branching when scission is the principle MW-controlling mechanιsm. Furthemore, a uniform branchingdensity distribution is obtained, provided that a sufficient number of sciston events occur per chain relative to its average residence time in the reactor. Smaller amounts of scission, when combined with another MW-controlling mechanism such as transfer to solvent, can lead to the formation of chain length distributions with asymmetric or bimodal features as well as reducing the high-MW tail and polydispersity.