PMR-15, regarded as the technological foundation of "Polymerizable Monomeric Reactants", is nearing half a century since its inception. Although it has persisted within the aerospace industry as a mid-tier performance matrix resin for organic matrix composite (OMC) structures, its continued legacy is being challenged domestically. Methylene dianiline (MDA), a principal constituent monomer in PMR-15, is recognized as biologically toxic. Attempts at identifying a suitable replacement for MDA, spanning three decades, have resulted in awareness that the balance of properties afforded by this monomer is unique. In the past two years, DoD laboratories within the Air Force, Army, and Navy have participated in a coalition, along with Drexel University, seeking to develop new monomers for PMR technologies that target high performance yet are sustainable. At the core of this effort is the spiral development of novel aniline monomers through a harmonization of chemical structure design, synthesis, resin screening, composite fabrication and testing, and monomer toxicology assessments. Notable achievements thus far are the genesis of aniline monomers derived from bio-renewable sources and a solution to the time tested problem of themo-oxidative aging induced micro-cracking in OMCs. An overview of these results is presented.