title: Guest-responsive covalent frameworks by the cross-linking of liquid-crystalline salts: tuning of lattice flexibility by the design of polymerizable units.
abstract: Cross-linked polymers prepared by the in-situ polymerization of liquid-crystalline salts were found to work as solid-state hosts with a flexible framework. As a component of such hosts, four kinds of polymerizable amphiphilic carboxylic acids bearing alkyl chains with acryloyloxy (A), dienyl (D), and/or nonreactive (N) chain ends (monomeric carboxylic acids; M(AAA), M(ANA), M(DDD), and M(DND)) were used. The carboxylic acids were mixed with an equimolar amount of a template unit, (1R,2S)-norephedrine (guest amine; G(RS)), to form the corresponding salts. Every salt exhibited a rectangular columnar LC phase at room temperature, which was successfully polymerized by (60)Co γ-ray-induced polymerization without serious structural disordering to afford the salt of cross-linked carboxylic acid (polymeric carboxylic acid; P(AAA), P(ANA), P(DDD), and P(DND)) with G(RS) . Owing to the noncovalency of the interactions between the polymer framework P and the template G(RS), the cross-linked polymers could reversibly release and capture a meaningful amount of G(RS). In response to the desorption and adsorption of G(RS), the cross-linked polymers dramatically switched their nanoscale structural order. A systematic comparison of the polymers revealed that the choice of polymerizable groups has a significant influence on the properties of the resultant polymer frameworks as solid-state hosts. Among these polymers, P(DDD) was found to be an excellent solid-state host, in terms of guest-releasing/capturing ability, guest-recognition ability, durability to repetitive usage, and unique structural switching mode.
authors.affiliation: RIKEN Advanced Science Institute, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan. y-ishida@riken.jp
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Ishida
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Sakata
authors.forename: Ammathnadu S
authors.initials: AS
authors.lastname: Achalkumar
authors.forename: Kuniyo
authors.initials: K
authors.lastname: Yamada
authors.forename: Yuki
authors.initials: Y
authors.lastname: Matsuoka
authors.forename: Nobutaka
authors.initials: N
authors.lastname: Iwahashi
authors.forename: Sayaka
authors.initials: S
authors.lastname: Amano
authors.forename: Kazuhiko
authors.initials: K
authors.lastname: Saigo