Polyhydroxyethers synthesis, analysis and crosslinking

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Virginia Polytechnic Institute and State University


Epoxy resins are used throughout the commercial field as coatings and adhesives. Commercially, these polymers are generally synthesized via the "Taffy Process" which involves the reaction of 4,4′ isopropylidene diphenol (Bis-A) with epichlorohydrin under basic conditions. They may also synthesized from the base catalyzed reaction of diglycidylether of Bis-A and Bis-A, which is referred to as the "Advancement Process". Both processes are complicated by a branching side reaction which consumes epoxy groups and upsets the stiochiometric control and hence influences the materials final molecular weight.

A possible method to eliminate the side reaction and obtain high molecular weight polymers was investigated which involved the use of sterically hindered basic catalysts in a non-polar solvent to promote the reaction between the diglycidylether of Bis-A and Bis-A. Reactions conducted using quaternary ammonium hydroxides in diglyme solutions produced high molecular weight polymers. In contrast, trialkylamine catalyzed systems run under similar conditions only produced polymers of moderate molecular weights at best.

A quantitative ¹H-NMR analysis for measuring the degree of branching in polyhydroxyethers has been developed. The ¹H-NMR analysis involved the derivatization of the polymers using trichloroacetyl isocyanate. This was performed in order to separate the methine proton into a branched and non-branched signal. Analysis of both polymers and oligomers synthesized by this method indicate that the degree of branching is less than 10% for all materials. However the low precision of the technique limited the analysis and the conclusion as to the best reaction conditions required to obtain the lowest amount of branching.

The kinetics of crosslinking oligomeric epoxy resins with multifunctional isocyanates was also studied using Fourier transform infrared spectroscopy (FT-IR). The reaction was modeled by using phenyl isocyanate and a low molecular weight epoxy resin synthesized from para t-butyl phenol and diglycidylether of Bis-A. Tin octoate proved to be the most effective catalyst for this reaction.