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.

Functional Liquid Crystals towards the Next Generation of Materials

“…Polymer materials with LC nanopores can be also used as adsorbents at the molecular level as well as in filtration membranes.Inaddition, the size of pores in LC polymer films can be tuned by post-modification procedures.P olymerizable host molecules and non-polymerizable content were combined using non-covalent bonding [153][154][155][156] and dynamic covalent bonding. [157] Formation of the LC state and subsequent in situ polymerization for example by photopolymerization [153][154][155] or acyclicd iene metathesis (ADMET) polymerization [156,157] gives polymer films with nanochannels filled with non-polymerized small compounds.T he LC nanopores were obtained by removal of the non-polymerized small molecules in the nanochannels (Figure 6b). TheL Cn anopores selectively adsorb molecules and ions which are of as uitable size and charge.T he adsorption properties of the pores can be tuned by modifying the wall surfaces of the pores by chemical reaction with chemically active groups.…”

Funktionelle organische Materialien auf der Basis polymerisierter flüssigkristalliner Monomere: supramolekulare wasserstoffverbrückte Systeme

“…[35,36] Der Vorteil einer hexagonalen kolumnaren Struktur ist, dass nach dem Entfernen des Templatmoleküls dank der Starrheit der polymerisierten, lateral verknüpften Wabenstrukturen die Porengrçße behalten wird. Jüngste detaillierte Studien haben gezeigt, dass durch Modifizieren des polymeren porçsen Materials Eigenschaften wie strukturelle Ordnung, Erkennung und Freisetzung von Gastmolekülen stark verändert werden kçnnen.…”

“…Jüngste detaillierte Studien haben gezeigt, dass durch Modifizieren des polymeren porçsen Materials Eigenschaften wie strukturelle Ordnung, Erkennung und Freisetzung von Gastmolekülen stark verändert werden kçnnen. [35,36] Der Vorteil einer hexagonalen kolumnaren Struktur ist, dass nach dem Entfernen des Templatmoleküls dank der Starrheit der polymerisierten, lateral verknüpften Wabenstrukturen die Porengrçße behalten wird. Eine ähnliche Prozedur kann für smektische LC-Materialien nicht verwendet werden; in diesem Fall wird die molekulare Organisation nach dem Entfernen des Templats zerstçrt, weil die polymerisierten Regionen als nicht miteinander verbundene Schichten existieren.…”

Hydrogen Bonding in Supramolecular Nanoporous Materials

“…More recent studies have demonstrated that the polymer porous material also readily incorporates other guest molecules with sizes that fit in the chiral nanochannels [67]. Detailed studies indicate that modification of the polymer porous material has large effects on properties such as structural order, guest recognition and release, and its repetitive switching [64,68].…”