Technology Spotlight: Episode 1
Reactive End Cappers and Co-monomers Balance Processing/Properties of Polyimide Resins
Curious about what type of polymers and applications can benefit from the use of reactive end-cappers and co-monomers? How about all of these! By introducing crosslinkers within or terminal to the polymer backbone, rheology, chemical/thermal resistance and mechanical properties can all be improved.
So who cooked up this idea? For that, let’s go back over 30 years to the 1990s, when both NASA Langley Research Center and the United States Air Force Research Laboratory developed alternatives to traditional polymerized monomeric reactant (PMR) resins, themselves dating back to the 1970s. The goal? Besides the removal of suspected carcinogenic raw materials, PETI and AFR-PE-4 resins delivered low melt viscosity, ideal for resin transfer molding. Higher service temperature capability, and in the case of RTM370, solvent-free processing, were added bonuses.
4-(Phenyl-ethynyl) phthalic anhydride (PEPA) became the foundational reactive end-capper for this new resin family. PEPA was even incorporated into the name: Phenyl ethynyl terminated imide (PETI) oligomeric resins!
As with other more conventional end-cappers, PEPA served to control molecular weight of the polyamic acid oligomers prior to imidization. The resultant lower melt viscosity resins could easily infuse woven carbon fiber fabrics. Thermal activation of the ethylinic groups in the range of 330-400 ºC led to densely crosslinked polymers.
Did this technology match that of legacy systems? Not only so, it excelled, with newfound levels of thermal resistance and themo-oxidative stability. Solvent-free, volatile-free, dialed-in processing freedom became the new paradigm, enabling the fabrication of advanced composites perfectly suited to replace metals in complex aerospace engines. Not a bad day’s work!
Whatever it is, the way you tell your story online can make all the difference. PEPA required commercialization, and several companies stepped up to join the polyimide value chain, including Nexam Chemical AB, with NEXIMID 100A, their high-purity version of PEPA. Nexam’s core competence in fine chemistry led to the introduction of several variants, both end-cappers
and dianhydrides, expanding the ethylinic activation temperature range, most interestingly, to 200 ºC and well below.
This technology unleashed new application areas including varnishes and other thin-mil coatings for electronics, specifically semiconductors, where precise dielectric properties are essential for sustained performance. You’d figure that the ability to balance processing and properties of polyimides with these heat-activated formulating tools would be ubiquitous by now, but they’re not.
Care to learn more about how to use ethynyl based end-cappers and co-monomers for your next project? Reach out for a free initial consultation today.