Styrene Purification by Guest-Induced Restructuring of Pillar[6]arene

The separation of
styrene (St) and ethylbenzene (EB) mixtures
is important in the chemical industry. Here,
we explore the St and EB adsorption selectivity
of two pillar-shaped macrocyclic pillar­[n]­arenes
(EtP5 and EtP6; n = 5 and
6). Both crystalline and amorphous EtP6 can capture St from a St-EB mixture with remarkably
high selectivity. We show that EtP6 can be used to separate St from a 50:50 v/v St:EB mixture,
yielding in a single adsorption cycle St with a purity
of >99%. Single-crystal structures, powder X-ray diffraction patterns,
and molecular simulations all suggest that this selectivity is due
to a guest-induced structural change in EtP6 rather than
a simple cavity/pore size effect. This restructuring means that the
material “self-heals” upon each recrystallization, and St separation can be carried out over multiple cycles with
no loss of performance.