Polyhedral Oligomeric Silsesquioxane (POSS) Dianiline as a Replacement for Toxic Methylenedianiline in PMR-15: Chemistry and Properties
Technical Report,01 Aug 2016,31 Aug 2016
Air Force Research Laboratory (AFMC) AFRL/RQRP Edwards AFB United States
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With the goal of replacing methylene dianiline MDA in PMR-15 polymerizable monomeric reactant, which is a known toxin to humans, a thermally stable, polyhedral oligomeric silsequioxane POSS dianiline, which features an aromatic periphery, was copolymerized as a drop-in replacement. The chain length of the experimental oligomers was varied to study effects of cross-link density and nadic endcap concentration. The resultant oligomers were characterized for various neat resin and composite properties. The POSS dianiline has shown previously in 6-FDA-ODA-PEPA type polyimides to improve moisture resistance and processability. It was shown that the bulky monomer addition improved moisture resistance 80 decrease in ultimate moisture absorption and processability uncured Tg and rheology were improved. Uncured Tg values decreased by as much as 85C and complex viscosity decreased by 3 orders of magnitude. Viscosity is low enough that resintransfer molding RTM is possible. However, thermal properties such as glass transition temperature Tg and long-term thermal oxidative stability TOS along with composite strengths were hindered. Shortening the chain length, which increases cross-link density is shown to improve cured Tg and can be manipulated. The decreased chain length causes increased nadic endcap concentration which has been shown to lower the thermal stability of the polyimide.
- Polymer Chemistry