Study Of Thermo-initiated Cationic Polymerization Of Cycloaliphatic Epoxy Resins

Cycloaliphatic epoxy resins are widely used as adhesives, coatings, insulation encapsulation materials due to their high mechanical strength, low water absorption, excellent electrical insulation properties and high security. Compared to the traditional methods that used anhydrides as curing agents, cationic polymerization has many advantages such as high curing rates, low energy consumption, lack of initiation by oxygen, low shrinkage and good adhesion properties to various substrates. Cationic polymerization of epoxy resins can be initiated by UV light or heat. Compared to the photopolymerization, the the thermo-initiated polymerization is not limited by the shape and thickness of samples. In this paper, the bifunctional cycloaliphatic epoxide ERL-4221 and trifunctional cycloaliphatic epoxide Epoxide-Si5 were cured by the thermo-initiated cationic polymerization in the presence of different diols (1.2-ethanediols,1,4-butanediols and 1.6-hexanediols). The effects of different diols on the thermal properties, fracture toughness and water absorption properties were systematically discussed.The Cycloaliphatic epoxy resin ERL-4221 and Epoxide-Si5 were cured by thermo-initiated cationic polymerization using a triarylsolfonium (KWM-753) as the initiator and diols as the chain transfer agents. The curing program has been established by the curing kinetics and Kissinger models.The soft alkyl segment has been introduced to the epoxy resin network by chain transfer reaction, proved by FTIR and DSC analysis. The ERL-4221/diols system can be cured completely by thermo-initiated cationic polymerization and DSC analysis has confirmed this.The properties of the epoxy resin system were systematically studied and discussed. With the increasing molecular chain length of diols. the glass transition temperature, cross-linking density and the toughness increased gradually. Based on this discovery, we can regulate the properties of epoxy resin without losing the thermal stability by simply changing the molecular chain length and molar ratio of diols added to the cured system.