Mega-supramolecules for safer, cleaner fuel by end-association of long telechelic polymers

Abstract

Liq. fuels, such as gasoline, diesel and kerosene, are the world's dominant power source, representing 34% of global energy consumption. Transportation relies on such liqs., presenting the risk of explosive combustion in the event of impact, such as the 1977 Tenerife airport disaster-an otherwise-survivable runway collision that claimed 583 lives in the post-crash fireball. The UK and the U.S. responded with a multi-agency effort to develop polymeric fuel additives for "mist control." Ultra-long, associative polymers (e.g., ICI's "FM-9," >3,000 kg/mol copolymer, 5 mol% carboxylic acid units) increased the drop diam. in post-impact mist, resulting in a relatively cool, short-lived mist fire. However, the polymers interfered with engine operation, and their ultra-long backbone-essential for mist control-degraded upon pumping. They were abandoned in 1986. 15 years later, the post-impact fuel fireball involved in the collapse of the World Trade Center motivated us to revisit polymers for mist control. Building on recent advances in supramol. assembly as a route to emergent functional materials, particularly assembly of complex polymer architectures, we discovered an unexplored class of polymers that is both effective and compatible with fuel systems. Here, we show that long (>400 lg/mol) end-associative polymers form "mega-supramols." that control post-impact mist without adversely affecting power, efficiency or emissions of unmodified diesel engines. They also reduce turbulent drag, hence, conserving energy used to distribute fuel. The length and end-assocn. strength of the present polymers were designed using statistical mech. considerations. In comparison with ultra-long polymers for mist control, the present polymers are an order of magnitude shorter; therefore, they are able to resist shear degrdn. In contrast to prior randomly-functionalized associative polymers, these end-associative polymers also avoid chain collapse. We find simple carboxylic-acid/tertiaryamine end-assocn. to be effective, and the unprecedented length of these telechelic polymers to be essential for their potent rheol. effects.