Abstract
The significant contributions of Stepto to the development and understanding of gelation in non-linear random polymerizations are briefly reviewed. As an example, the recent Ahmad–Rolfes–Stepto theory is used to interpret experimental gel points in stoichiometric polyurethane network-forming systems based on hexamethylene diisocyanate and 4,4′-diphenylmethane diisocyanate reacting with polyoxypropylene triols. The results confirm more exactly the dependence of intramolecular reaction on dilution, reactant structure and molar mass. Significantly less intramolecular reaction occurs in the aromatic-based system because of the presence of stiffer network-forming chains. Values of the effective bond lengths are consistent with reactant structure and show excellent correlation with those expected from solution properties. A comparative analysis of the reaction kinetics of the aliphatic- and aromatic-based polymerizations is also presented. ©1997 SCI
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