A Thermoresponsive Membrane for Chiral Resolution

• Published in: Advanced functional materials 2008-02, Vol.18 (4), p.652-663
• Main Authors: Yang, Mei, Chu, Liang-Yin, Wang, Hai-Dong, Xie, Rui, Song, Hang, Niu, Catherine Hui
• Format: Article
• Language: English
• Subjects: Chiral separation; Graft copolymers; Membranes:polymer; Molecular recognition; Phase transitions; Stimuli-responsive materials
• ISSN: 1616-301X; 1616-3028
• DOI: 10.1002/adfm.200700534

A novel thermoresponsive membrane for chiral resolution with high performance has been developed. The membrane exhibits chiral selectivity based on molecular recognition of beta‐cyclodextrin (β‐CD) and thermosensitivity based on the phase transition of poly(N‐isopropylacrylamide) (PNIPAM). Linear PNIPAM chains were grafted onto porous nylon‐6 membrane substrates by using a plasma‐graft pore‐filling polymerization method; the chains thus acted as microenvironmental adjustors for β‐CD molecules. β‐CD moieties were introduced into the linear PNIPAM chains by a chemical grafting polymerization method and acted as chiral selectors. The phase transition of grafted PNIPAM chains affects the microenvironment of β‐CD molecules and, thus, the association between β‐CD and guest molecules. The chiral selectivity of the prepared thermoresponsive membranes in chiral resolution operated at temperature below the lower critical solution temperature (LCST) of PNIPAM is higher than that of membranes with no thermosensitivity. Furthermore, the decomplexation ratio of enantiomer‐loaded thermoresponsive membranes in decomplexation at temperatures above the LCST is much higher than that of membranes with no thermosensitivity. Thus, by simply changing the operation temperature, high, selective chiral resolution and efficient membrane regeneration are achieved. The proposed membrane provides a new and efficient way to solve the difficult decomplexation problem of chiral solid membranes, which is highly attractive for chiral resolution. Thermoresponsive gating membranes composed of functional gates with grafted thermoresponsive poly(N‐isopropylacrylamide) (PNIPAM) chains and appended β‐cyclodextrin (β‐CD) moieties are a novel route to “smart”, efficient chiral resolution. With the cooperative function of β‐CD's chiral recognition and PNIPAM's thermoresponsiveness, high, selective chiral resolution and efficient membrane regeneration are achieved by simply controlling the temperature (see figure; LCST: lower critical solution temperature).