Polycation radius of gyration in a polymeric ionic liquid (PIL): the PIL melt is not a theta solvent

Lucas N. Wong; Seamus D. Jones; Kathleen Wood; Liliana de Campo; Tamim Darwish; Michael Moir; Hua Li; Rachel A. Segalman; Gregory G. Warr; Rob Atkin

doi:10.1039/D1CP05354J

Polycation radius of gyration in a polymeric ionic liquid (PIL): the PIL melt is not a theta solvent†

Lucas N. Wong,

^a Seamus D. Jones,^b Kathleen Wood,^c Liliana de Campo,^c Tamim Darwish,^d Michael Moir,^d Hua Li,^a Rachel A. Segalman,^b Gregory G. Warr

^e and Rob Atkin

*^a

Author affiliations

* Corresponding authors

^a School of Molecular Sciences, The University of Western Australia, Crawley, Perth 6009, Australia
E-mail: rob.atkin@uwa.edu.au

^b Chemical Engineering Department and Materials Department, University of California, Santa Barbara, California 93106, USA

^c Australian Centre for Neutron Scattering, Australian Nuclear Science and Technology Organisation, New Illawarra Road, Lucas Heights, NSW 2234, Australia

^d National Deuteration Facility (NDF), ANSTO, Lucas Heights, NSW 2234, Australia

^e School of Chemistry and University of Sydney Nano Institute, The University of Sydney, Sydney, NSW 2006, Australia

Abstract

The conformation of the polycation in the prototypical polymeric ionic liquid (PIL) poly(3-methyl-1-aminopropylimidazolylacrylamide) bis(trifluoromethylsulfonyl)imide (poly(3MAPIm)TFSI) was probed using small-angle neutron scattering (SANS) and ultra-small-angle neutron scattering (USANS) at 25 °C and 80 °C. Poly(3MAPIm)TFSI contains microvoids which lead to intense low q scattering that can be mitigated using mixtures of hydrogen- and deuterium-rich materials, allowing determination of the polycation conformation and radius of gyration (R_g). In the pure PIL, the polycation adopts a random coil conformation with R_g = 52 ± 0.5 Å. In contrast to conventional polymer melts, the pure PIL is not a theta solvent for the polycation. The TFSI⁻ anions, which comprise 48% v/v of the PIL, are strongly attracted to the polycation and act like small solvent molecules which leads to chain swelling analogous to an entangled, semi-dilute, or concentrated polymer solution in a good solvent.

Physical Chemistry Chemical Physics

Polycation radius of gyration in a polymeric ionic liquid (PIL): the PIL melt is not a theta solvent†

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Polycation radius of gyration in a polymeric ionic liquid (PIL): the PIL melt is not a theta solvent

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