Epoxy resins based upon 1,4-anhydroerythritol: Kinetics and determination of branching

Epoxy resins (polyhydroxyethers) based upon 1,4-anhydroerythritol and bisphenol-A diglycidyl ether have been prepared by step-growth reaction in the melt. A kinetic scheme taking into account branching and a substitution effect has been worked out. In addition, the molecular weight averages M w and M n have been calculated using the rate constants for step growth and branching obtained from the fit of the conversion curve, where the substitution effect has been taken into account. The conversion of epoxide as a function of time can be described by the present theory adequately up to a conversion of about 90%. Beyond this point diffusion control becomes effective. A reasonable description of M w as a function of β is possible, where β is the extent of reaction of the epoxy groups. However, predicted polydispersity is consistently lower than that found experimentally.