Kinetics and properties of diethyltoluenediamine type benzoxazine-cured diglycidyl ether of bisphenol-A

• Detailed curing kinetics of aromatic diamine benzoxazine/epoxy was first studied.
• Non-crosslinkable benzoxazine can be effective hardener for epoxy.
• The reaction between benzoxazine and epoxy was not affected by the steric hindrance.
• The resulting benzoxazine/epoxy copolymer exhibited favorable properties.

A novel diethyltoluenediamine type benzoxazine (PDETDA) was used as a hardener for diglycidyl ether of bisphenol-A (DGEBA), and the curing kinetics was investigated by non-isothermal differential scanning calorimetry (DSC). The results showed that PDETDA/DGEBA exhibited two curing processes, which were attributed to the ring-opening polymerization of benzoxazine (reaction 1) and the etherification between hydroxyl groups of polybenzoxazine and epoxide groups (reaction 2), respectively. Both reactions were autocatalytic in nature and can be well described by the proposed kinetic models. The average activation energies (Eas) of reaction 1 and reaction 2 were determined to be 104.9 kJ mol−1 and 125.0 kJ mol−1, respectively. It was concluded from Ea that the alkyl substituents in PDETDA significantly affected the reaction 1 due to the steric hindrance, but had no influence on the reaction 2. The PDETDA-cured DGEBA exhibited higher strength and modulus, higher char yield, and lower water absorption than diethyltoluenediamine (DETDA)-cured DGEBA.

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