Acid catalyzedepoxy–methylolphenolthermosets: Astructure–propertystudy

Abstract

We have explored the structure–property relationships of a series epoxy–methylolphenol based thermoset films. Ortho‐, meta‐, and para‐isomers of methylolphenol, that is, ortho‐methylolphenol, meta‐methylolphenol and para‐methylolphenol, respectively, were reacted with the diglycidyl ether of bisphenol A (DGEBA) in the presence of an acid catalyst (CYCAT® XK 406 N). Thermogravimetric analyses showed that irrespective of the methylolphenol structure used, all crosslinked films exhibit 5% weight loss at 343–360°C under nitrogen. The glass transition temperature (Tg) decreases in the order of ortho‐ (Tg = 117°C) > para‐ (Tg = 102°C) > meta‐methylolphenol (Tg = 82°C) as measured by differential scanning calorimetry. Uniaxial tensile testing of thin films shows good stress–strain behavior, with ultimate tensile strength values of 75 MPa and 6% strain‐at‐break. Homo‐crosslinking of methylolphenol moieties can occur under the reaction conditions used but in the presence of DGEBA, the methylolphenols prefer to undergo epoxy ring‐opening reactions. This was confirmed by the uniform networks that were formed, that is, no block‐formation was observed. The results of this study confirm that simple methylolphenol hardeners can be used to prepare crosslinked epoxy‐based films with excellent thermomechanical properties.