CARIVERSETM resin: a thermally reversible network polymer for electronic applications

A series of network polymers derived from the reaction of 2,5-disubstituted furan resins and 2,4-bismaleimidotoluene were prepared and characterized. These polymers contain thermally reversible covalent crosslinks derived from the Diels-Alder addition of maleimide to furan. At elevated temperature, the crosslinks dissociate via a retro-Diels-Alder reaction to yield a low viscosity melt that readily polymerizes upon cooling to regenerate the network polymer. Consequently, these new materials are not only reworkable but also reusable and repairable. All samples were shown to be reversible by repeated melting and gelling. A broad range of material properties may be obtained by varying the structure, molecular weight and functionality of the furan resins as well as by adjusting the stoichiometric ratio of furan to maleimide. Softening temperature greater than 125°C as measured by thermomechanical analysis (TMA) has been achieved and many samples have melt viscosity less than 5 poise at processing temperatures of 160-180°C. Other important properties such as coefficient of thermal expansion, adhesion to printed circuit board, and modulus were also measured and found to be comparable to epoxy systems. At temperature >200°C, the irreversible thermal homopolymerization of bismaleimide becomes competitive thus offering the possibility of rendering these materials permanently crosslinked by a postbaking process if desirable