Cascading retro-Diels-Alder cycloreversion and sydnone-maleimide based double 1,3-dipolar cycloaddition for quantitative thermal cross-linking of an amorphous polymer solid

A new approach to polymer cross-linking is investigated using a cascading cycloreversion of a maleimide-furan adduct and a double 1,3-dipolar cycloaddition between a sydnone and maleimide. The cross-linking proceeds quantitatively above 63°C, despite the polymer possessing no observable glass transition temperature. The resulting polymer network possesses a high thermal stability (>300°C) due to the irreversibility of the sydnone-maleimide cycloaddition, which releases CO₂ during the cross-linking, driving the reaction. The rigid three-dimensional structure of the bis-maleimide-sydnone cycloadduct produced local free volumes in films, decreasing the dielectric constant of the material.