Phosphorus-containing phthalonitrile thermosetting polymers are promising high-temperature materials for the next generation of polymeric composite materials used in extreme environments beyond Earth’s atmosphere. It is well established that phosphorus-containing polymers resist degradation by highly reactive atomic oxygen present in low-earth orbit through the formation of a passivating polyphosphate layer which forms on the surface of the substrate during oxidative degradation. Such moieties, when placed into the backbone of phthalonitrile polymers, have also been shown to dramatically increase monomer processability by reducing melt viscosity and monomer softening temperature.<br/><br/>Herein, we investigate the effects of phosphine oxide and phosphate backbone structures on the reactivity of bis-phthalonitrile monomers. Differential scanning calorimetry is used to characterize the kinetics of polymerization catalyzed by the aromatic diamine bis[4-(3-aminophenoxy)phenyl] sulfone (mBAPS). Starink method is applied to the thermograms of each system at varying heating rates to measure the activation energy of polymerization throughout cure. It was observed that the presence of an electron-withdrawing backbone linkage meta to the phthalonitrile end group increases the reactivity of the monomer towards nucleophilic attack from the diamine catalyst while also decreasing the activation energy of intramolecular ring formation and chain propagation.

Reaction kinetics of phthalonitrile thermosetting polymers containing meta-position phosphorus-oxide backbone structures

ACS Fall 2021

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