Thermo-initiated cationic polymerization of phosphorus-containing cycloaliphatic epoxides with tunable degradable temperature

The present work is to investigate thermally reworkable cycloaliphatic epoxy resins containing two or three phosphate groups per molecule for electronic and LED encapsulations. Different form the conventional reworkable epoxy resins, the epoxides here were cured via thermo-initiated cationic polymerization at a moderately low temperature. The experimental results showed that the incorporation of thermally-labile phosphate groups made the cured products start to degrade at around 220 °C, and lose over 50% weight after thermal treatment at 250 °C for only 3 min. The residue could be conveniently removed, exhibiting excellent reworkable properties of thermosetting epoxy resins. More importantly, through the copolymerization of phosphate-containing epoxide with commercial ERL-4221, the degradation temperatures could be readily tuned within the desirable reworking temperature range from 200 °C to 300 °C by adjusting the ratio of two monomers. The comparison of degradation behaviors and mechanism as well as the physical properties between the cationic and anhydride curing methods were studied by means of thermogravimetry, infrared spectroscopy and dynamic mechanical analysis in detail.