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

Phys Chem Chem Phys. 2022 Feb 16;24(7):4526-4532. doi: 10.1039/d1cp05354j.

Authors

Affiliations

¹ School of Molecular Sciences, The University of Western Australia, Crawley, Perth 6009, Australia. rob.atkin@uwa.edu.au.
² Chemical Engineering Department and Materials Department, University of California, Santa Barbara, California 93106, USA.
³ Australian Centre for Neutron Scattering, Australian Nuclear Science and Technology Organisation, New Illawarra Road, Lucas Heights, NSW 2234, Australia.
⁴ National Deuteration Facility (NDF), ANSTO, Lucas Heights, NSW 2234, Australia.
⁵ School of Chemistry and University of Sydney Nano Institute, The University of Sydney, Sydney, NSW 2006, Australia.

PMID: 35119064
DOI: 10.1039/d1cp05354j

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.