Megasupramolecules for safer, cleaner fuel by end association of long telechelic polymers
We used statistical mechanics to design polymers that defy conventional wisdom by self-assembling into "megasupramolecules" (≥5000 kg/mol) at low concentration (≤0.3 weight percent). Theoretical treatment of the distribution of individual subunits—end-functional polymers—among cyclic and linear supramolecules (ring-chain equilibrium) predicts that megasupramolecules can form at low total polymer concentration if, and only if, the backbones are long (>400 kg/mol) and end-association strength is optimal. Viscometry and scattering measurements of long telechelic polymers having polycyclooctadiene backbones and acid or amine end groups verify the formation of megasupramolecules. They control misting and reduce drag in the same manner as ultralong covalent polymers. With individual building blocks short enough to avoid hydrodynamic chain scission (weight-average molecular weights of 400 to 1000 kg/mol) and reversible linkages that protect covalent bonds, these megasupramolecules overcome the obstacles of shear degradation and engine incompatibility.
Additional Information© 2015 American Association for the Advancement of Science. Received for publication 30 March 2015. Accepted for publication 30 July 2015. Funding for this research was provided from U.S. Army TARDEC, FAA, and NASA (NAS7-03001) and the Gates Grubstake Fund. B.L. is grateful for support from the Schlumberger Foundation Faculty for the Future Program. We thank P. Arakelian (GALCIT) and T. Wynne (JPL) for assistance with the fuel impact tests; B. Hammouda (NIST) and L. He (ORNL) for assistance with SANS; T. Durbin, R. Russell, D. Pacocha, and K. Bumiller at UCR CE-CERT for assistance with engine tests; A. Meyer at Wyatt Technology and Caltech graduate student J. Kim for assistance with MALLS; and Caltech undergraduates S. Li and A. Guo for assistance with shear degradation tests and rheological measurements. A patent application (WO/2014/145920) based on some results reported here has been submitted.
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