Abstract
Laser light scattering (LLS) and small-angle x-ray scattering (SAXS) studies have been made of the curing of epoxy resins from 1,4-butanediol diglycidyl ether with cis-1,2-cyclohexanedicarboxylic anhydride. The epoxy resin before its gelation threshold is soluble in methyl ethyl ketone, and scattering techniques can be used to determine the weight-average molecular weight (Mw), the fractal dimension (df), and the molecular weight distribution (MWD) of the branched epoxy polymer during each stage of the initial polymerization process. The MWDs obtained from LLS were compared with those determined by conventional size exclusion chromatography (SEC). From the comparison, we were able to develop a new absolute calibration procedure for SEC of specific branched polymers. By investigating the LLS envelope of the three-dimensional crosslinking process near and pass the gelation threshold and by applying the Debye-Bueche theory of light scattering for inhomogeneous solids, the structural changes of the branched epoxy polymer during the curing process could be evaluated. The change in the correlation length (a) and the mean squared average of local dielectric constant fluctuations (η −2) could be divided into four main stages. Finally, The branching kinetics of the copolymerization reaction could be approximated by using Smoluchowski’s coagulation equation.
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