| Abstract
| - The sol−gel transition, or gelation, in a polymer network-forming system is defined as thecritical point in the polymerization at which an infinite macromolecule is formed. There are many studiesin the literature concerning the exact and accurate determination of the gel point and its interpretationin terms of the critical conversions of reactant functional groups. However, these have mainly involvedstep-growth polymerizations with few studies of chain-growth polymerizations such as that described inthis study. Chemorheological studies on a cationically polymerized epoxy network-forming system areused to determine accurate gel times and critical conversions, which are interpreted in terms of classicalbranching and chemical bond percolation models for nonlinear polymerizations. Rheological studies duringthe polymerization of a trifunctional epoxide monomer, using BF3 as the Lewis acid initiator, yielded agel conversion of 0.17 ± 0.02 and a power law dependence for the development of shear modulus, with acritical exponent n = 0.64 ± 0.03, which is shown to be independent of temperature and BF3 concentration.The viscosity at conversions close to the gel point was shown to vary according to a power law with acritical exponent k = 1.33 ± 0.03 in the pregel region. The critical behavior of this complex network-forming system is shown to be closely predicted by percolation theory.
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