Acid catalyzed epoxy-methylolphenol thermosets: A structure-property study (vol 139, e51944, 2022)

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 (R) XK 406 N). Thermogravimetric analyses showed that irrespective of the methylolphenol structure used, all crosslinked films exhibit 5% weight loss at 343-360 degrees C under nitrogen. The glass transition temperature (T-g) decreases in the order of ortho- (T-g = 117 degrees C) > para- (T-g = 102 degrees C) > meta-methylolphenol (T-g = 82 degrees 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.