(Supercritical) Ammonia for Recycling of Thermoset Polymers

Chemical recycling of thermosetting bisphenol‐A‐polycyanurate, triphenylisocyanurate and of N‐phenylmaleimide (pPMI) as well as 4,4′‐methylenbis‐ (4‐N‐phenylmaleimide) (pBMI) has been studied. Polycyanurate thermosets undergo ammonolytic degradation to the level of oligomeric soluble products already at room temperature, complete degradation to bisphenol‐A and melamine, however requires supercritical conditions (160 °C) and longer reaction times. Polyimides prepared by free radical polymerisation after ammonolysis at 160 °C give the corresponding amines and linear polymers with unsubstituted imide and diamide units. SEC of the polymer analogous (with respect to the carbon chain) reaction products and of linear pPMI shows that the polymers have a polymodal molar mass distribution with a high molar mass and an oligomeric fraction.