Hydroxyl-Free Epoxy Thermoplastics from Active Esters with Low Dielectric Constant and Water Sorption
Fabricating epoxy resins low in both dielectric properties and moisture absorption is of emerging need but challenging, especially in the application of microelectronic packaging materials that are intensively exposed to harsh environments. In this work, a series of diphenols of different substituent positions and groups blocked with ester groups were copolymerized with diglycidyl ether of bisphenol A (DGEBA)-based epoxy resin to synthesize high-molecular-weight hydroxyl-free epoxy thermoplastics (phenoxy resins). Remarkably low dielectric constants down to 2.26 at 1 MHz and low dielectric losses were found in these hydroxyl-free epoxy thermoplastics, which also showed excellent hydrophobicity compared with those of epoxy thermosets and commercialized epoxy thermoplastic. The migration of ester groups in the polymerization process was studied by a series of model reactions, indicating that the reaction mainly undergoes an associative mechanism under catalysis of the imidazole derivative. In addition, the polymers demonstrated good thermal stability, while thermal properties can be easily modulated by changing the substituent group of phenolic ester monomers. In short, these hydroxyl-free epoxy thermoplastics could be a promising candidate for antimoisture microelectronic packing materials and have versatile applications.
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