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Modeling of Chain Length and Long‐Chain Branching Distributions in Free‐Radical Polymerization
Author(s) -
Hutchinson Robin A.
Publication year - 2001
Publication title -
macromolecular theory and simulations
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.37
H-Index - 56
eISSN - 1521-3919
pISSN - 1022-1344
DOI - 10.1002/1521-3919(20010301)10:3<144::aid-mats144>3.0.co;2-a
Subject(s) - branching (polymer chemistry) , dispersity , polymer , molar mass distribution , chemistry , polymerization , bond cleavage , chain transfer , degree of polymerization , radical polymerization , polymer chemistry , thermodynamics , materials science , chemical physics , physics , organic chemistry , catalysis
The effect of long‐chain branching and β‐scission reactions on the complete molecular weight (MW) and branching density distributions of polymer produced in a well‐mixed continuous reactor has been systematically studied. An improved statistical description of how 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 indication of average branching in the system; appropriate averaging across the chain 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 mechanism. Furthermore, a uniform branching density distribution is obtained, provided that a sufficient number of scission 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.