  Poly(ionic liquid)s (PILs), similar to their ionic liquid (IL) analogues,
present a nanostructure arising from local interactions. The influence of this
nanostructure on the macromolecular conformation of polymer chains is
investigated for the first time by means of an extensive use of small angle
neutron scattering on a series of poly(1-vinyl-3-alkylimidazolium)s with
varying alkyl side-chain length and counter-anion both in bulk and in dilute
solutions. Radii of gyration are found to increase with the side-chain length
in solution as a consequence of crowding interactions between neighboring
monomers. In bulk, however, a non monotonic evolution of the radius of gyration
reflects a change in chain flexibility and a potential screening of
electrostatic interactions. Additionally at smaller scale, SANS provides an
experimental estimation of both the chain diameter and the correlation length
between neighboring chains, comparison of which unveils clear evidence of
interdigitation of the alkyl side-chains. These structural features bring
precious insights in the understanding of the dynamic properties of PILs.
