Highly Selective Separation of Isopropylbenzene and α-Methylstyrene by Nonporous Adaptive Crystals of Perbromoethylated Pillararene via Vapor- and Liquid-Phase Adsorptions

Isopropylbenzene (IPB) and α-methylstyrene (AMS), two members of C9
aromatics, are important in both industrial
production and laboratory research, but the separation of IPB/AMS mixtures is still a big challenge. Here, we provide
a new strategy to separate IPB and AMS using
nonporous adaptive crystals of four pillararenes, perethylated pillar[5]­arene,
perethylated pillar[6]­arene, perbromoethylated pillar[5]­arene, and
perbromoethylated pillar[6]­arene (BrP6). Among them, BrP6 selectively adsorbs IPB from an equal volume
mixture of IPB and AMS with >95% purity
for solid–vapor phase adsorption and >94% purity for solid–liquid
phase adsorption, while the selectivities for the other three pillararenes
are unsatisfactory. Single-crystal structural analyses combined with
powder X-ray diffraction and differential scanning calorimetry experiments
demonstrate that the selectivity arises from the different stabilities
of guest-loaded BrP6 crystals. Moreover, the reversible
transitions between guest-free and IPB-loaded structures
indicate the preeminent recycling performance of BrP6 crystals.