Self-Healing Supramolecular Materials Constructed by Copolymerization via Molecular Recognition of Cavitand-Based Coordination Capsules

The repeating guest units of poly-(R)- 2 were selectively encapsulated by the self-assembled capsule poly- 1 possessing eight polymer side chains to form the supramolecular graft polymer (poly- 1 )_n⋅poly-(R)- 2 . The encapsulation of the guest units was confirmed by ¹H NMR spectroscopy and the DOSY technique. The hydrodynamic radius of the graft polymer structure was greatly increased upon the complexation of poly- 1 . The supramolecular graft polymer (poly- 1 )_n⋅poly-(R)- 2 was stably formed in the 1:1 host–guest ratio, which increased the glass transition temperature by more than 10 °C compared to that of poly- 1 . AFM visualized that (poly- 1 )_n⋅poly-(R)- 2 formed the networked structure on mica. The (poly- 1 )_n⋅poly-(R)- 2 gelled in 1,1,2,2-tetrachloroethane, which led to fabrication of distinct viscoelastic materials that demonstrated self-healing behavior in a tensile test.     

Synthesis of Supramolecular A8Bn Miktoarm Star Copolymers by Host-Guest Complexation

We report a new synthetic method to construct supramolecular A₈B_n (n=1, 2, 4) miktoarm star copolymers by host-guest complexation between a resorcinarene-based coordination capsule possessing eight polystyrene chains and 4,4-diacetoxybiphenyl guest molecules that retain one, two or four polymethyl acrylate chains. The formation of the supramolecular A₈B_n (n=1, 2, 4) miktoarm star copolymers was confirmed by dynamic light scattering (DLS), size-exclusion chromatography (SEC), and diffusion-ordered NMR spectroscopy (DOSY). Differential scanning calorimetry (DSC) measurements revealed that the miktoarm copolymers were phase-separated in the bulk. The micro-Brownian motion of the A₈B₄ structure was markedly enhanced in the bulk due to a weak segregation interaction between the immiscible arms.     

Supramolecular Polymerization Engineered with Molecular Recognition

Supramolecular polymeric assemblies represent an emerging, promising class of molecular assemblies with enormous versatility compared with their covalent polymeric counterparts. Although a large number of host–guest motifs have been produced over the history of supramolecular chemistry, only a limited number of recognition motifs have been utilized as supramolecular connections in polymeric assemblies. This account describes the molecular recognition of host molecules based on calix[5]arene and bisporphyrin that demonstrate unique guest encapsulations; subsequently, these host–guest motifs are applied to the synthesis of supramolecular polymers that display polymer‐like properties in solution and solid states. In addition, new bisresorcinarenes are developed to form supramolecular polymers that are connected via a rim‐to‐rim hydrogen‐bonded dimeric structure, which is composed of two resorcinarene moieties.

     

Self‐Healing Supramolecular Materials Constructed by Copolymerization via Molecular Recognition of Cavitand‐Based Coordination Capsules

The repeating guest units of poly‐(R)‐ 2 were selectively encapsulated by the self‐assembled capsule poly‐ 1 possessing eight polymer side chains to form the supramolecular graft polymer (poly‐ 1 )_n?poly‐(R)‐ 2 . The encapsulation of the guest units was confirmed by ¹H NMR spectroscopy and the DOSY technique. The hydrodynamic radius of the graft polymer structure was greatly increased upon the complexation of poly‐ 1 . The supramolecular graft polymer (poly‐ 1 )_n?poly‐(R)‐ 2 was stably formed in the 1:1 host–guest ratio, which increased the glass transition temperature by more than 10 °C compared to that of poly‐ 1 . AFM visualized that (poly‐ 1 )_n?poly‐(R)‐ 2 formed the networked structure on mica. The (poly‐ 1 )_n?poly‐(R)‐ 2 gelled in 1,1,2,2‐tetrachloroethane, which led to fabrication of distinct viscoelastic materials that demonstrated self‐healing behavior in a tensile test.     

氢键识别超分子聚合物的新进展

近年来,由于氢键作用对聚合物的热力学性质、微观自组装、结晶及液晶行为的重要影响,氢键识别在超分子聚合物的分子设计与结构控制方面的应用受到广泛关注。本文系统介绍了氢键识别体系的类型与性质,以及分子结构、分子内氢键对氢键识别强度的影响,讨论了羧酸与吡啶间氢键识别体系、与核苷相关的氢键识别体系以及四重氢键识别体系在超分子聚合物中的最新应用,主要介绍了氢键识别超分子聚合物的合成、结构、性质及功能。     

pH‐Responsive Supramolecular Polymerization in Aqueous Media Driven by Electrostatic Attraction‐Enhanced Crown Ether‐Based Molecular Recognition

All the previously reported supramolecular polymers based on crown ether‐based molecular recognition have been prepared in anhydrous organic solvents. This is mainly due to the weakness of crown ether‐based molecular recognition in the presence of water. Here we report a linear supramolecular polymer constructed from a heteroditopic monomer in an aqueous medium driven by crown ether‐based molecular recognition through the introduction of electrostatic attraction. In addition, the reversible transition between the linear supramolecular polymer and oligomers is achieved by adding acid and base. This study realizes the breakthrough of the solvent for supramolecular polymerization driven by crown ether‐based molecular recognition from anhydrous organic solvents to aqueous media. It is helpful for achieving supramolecular polymerization driven by crown ether‐based molecular recognition in a completely aqueous medium.     

Synthesis and Characterization of Amphiphilic Poly(caprolactone) Star Block Copolymers

Summary: Novel, star‐shaped, amphiphilic block copolymers composed of fully degradable poly(caprolactone) were synthesized by sequential addition polymerization. In the first step, four‐arm macroinitiators were produced by ring‐opening polymerization of caprolactone by initiation with pentaerythritol. Then, block copolymers were synthesized by sequential addition of 4‐(2‐benzyloxyethyl)‐ε‐caprolactone to the four‐arm macroinitiators. Star‐shaped, amphiphilic block copolymers containing poly(caprolactone)‐block‐poly[4‐(2‐hydroxyethyl)caprolactone] segments were obtained by catalytic debenzylation.

Four‐arm amphiphilic polycaprolactone star block copolymer.     

Responsive Supramolecular Gels Constructed by Crown Ether Based Molecular Recognition

Responsive supramolecular gels were constructed from crown ether terminated four‐arm star poly(ε‐caprolactone) (PCL–DB24C8) and dibenzylammonium‐terminated two‐arm PCL–DBAS (see scheme), exploiting the formation of pseudorotaxane linkages between crown ether and ammonium moieties. The resultant supramolecular gels exhibit thermo‐ and pH‐induced reversible gel–sol transition.

     

超分子模糊识别

在超分子主-客体识别系统中,由专一作用如多重氢键、拓扑捕捉、金属-配体驱动的识别虽然具有高选择性,但要求主体具有严格的尺寸、形状和电子环境;同时识别通常限于那些具有拓扑特征和电子特征的分子,这类识别机制称为静态识别。另一方面,由超支化聚合物衍生的核-壳两亲大分子(CAM),方便易得且有广泛的客体亲合性,但客体选择性通常较低。近年的研究表明,CAM的核经过合适的电子性质改性后,竞争客体分子间的差异可被放大,从而实现高选择性包裹与分离,而CAM最大的特点是核内有大量随机分布的官能团,从而可以进行各种精细的改性。这一由复杂系统的非线性特征导致的识别不需要专一作用的推动,适合于复杂分子的识别,被称为超分子模糊识别。实验表明,超分子模糊识别主体可以用于各种离子客体的高效分离,还可以识别拓扑特征和电子特征非常相似的分子。本文就超分子模糊识别的机制、特点以及应用作了综述。     

Facile Determination of Molecular Structure Trends in Amphiphilic Core Corona Star Polymer Synthesis via Dielectric Property Measurement

The use of dielectric property measurements to define specific trends in the molecular structures of poly(caprolactone) containing star polymers and/or the interbatch repeatability of the synthetic procedures used to generate them is demonstrated. The magnitude of the dielectric property value is shown to accurately reflect: (a) the number of functional groups within a series of materials with similar molecular size when no additional intermolecular order is present in the medium, (b) the polymer molecular size for a series of materials containing a fixed core material and so functional group number, and/or (c) the batch to batch repeatability of the synthesis method. The dielectric measurements are validated by comparison to spectroscopic/chromatographic data.

     

Linear Supramolecular Polymers via Connecting Telechelic Polycaprolactone through Alkynylplatinum(II) Terpyridine Molecular Tweezer/Pyrene Recognition Motif

By anchoring alkynylplatinum(II) terpyridine molecular tweezer/pyrene recognition motif on the chain‐ends of telechelic polycaprolactone, high‐molecular‐weight supramolecular polymers have been successfully constructed via noncovalent chain extension, which demonstrate fascinating rheological and thermal properties. Moreover, the resulting assemblies exhibit interesting temperature‐ and solvent‐responsive behaviors, which are promising for the development of adaptive functional materials.

     

Supramolecular Self‐Assembly of Nonlinear Amphiphilic and Double Hydrophilic Block Copolymers in Aqueous Solutions

Supramolecular self‐assembly of block copolymers in aqueous solution has received ever‐increasing interest over the past few decades due to diverse biological and technological applications in drug delivery, imaging, sensing and catalysis. In addition to relative block lengths, molecular weights and solution conditions, chain architectures of block copolymers can also dramatically affect their self‐assembling properties in selective solvents. This feature article mainly focuses on recent developments in the field of supramolecular self‐assembly of amphiphilic and double hydrophilic block copolymers (DHBCs) possessing nonlinear chain topologies, including miktoarm star polymers, dendritic–linear block copolymers, cyclic block copolymers and comb‐shaped copolymer brushes.

     

A Strategy for Synthesis of Ion‐Bonded Supramolecular Star Polymers by Reversible Addition‐Fragmentation Chain Transfer (RAFT) Polymerization

We have developed a novel strategy for the preparation of ion‐bonded supramolecular star polymers by RAFT polymerization. An ion‐bonded star supramolecule with six functional groups was prepared from a triphenylene derivative containing tertiary amino groups and trithiocarbonate carboxylic acid, and used as the RAFT agent in polymerizations of tert‐butyl acrylate (tBA) and styrene (St). Molecular weights and structures of the polymers were characterized by ¹H NMR and GPC. The results show that the polymerization possesses the character of living free‐radical polymerization and the ion‐bonded supramolecular star polymers PSt, PtBA, and PSt‐b‐PtBA, with six well‐defined arms, were successfully synthesized.

     

瓜环对氨基酸的分子识别研究

使用¹H NMR和UV-Vis光谱法研究了七、八元瓜环对九种天然氨基酸盐酸盐的分子识别作用. 结果表明, 瓜环对芳香侧基取代的L-酪氨酸、L-色氨酸、L-苯丙氨酸均能进行有效识别, 而侧链上不带芳香基团的氨基酸, 如L-组氨酸、L-谷氨酸、L-蛋氨酸、L-缬氨酸、L-白氨酸、L-丙氨酸, 与这些瓜环的作用相对较弱. 对于七元瓜环, 主客体间都以1∶1化学计量比形成包结物, 并得到它们相互作用的稳定常数; 八元瓜环与L-酪氨酸及L-色氨酸也以1∶1形成包结物, 而与L-苯丙氨酸以1∶2形成包结物. L-酪氨酸、L-色氨酸和L-苯丙氨酸荧光性质研究表明, 七、八元瓜环既可成为这些氨基酸荧光性质的增敏试剂, 也可成为它们荧光淬灭试剂, 这与氨基酸的结构有关.     

A Uniqueness Theorem of Molecular Recognition

Phrased in terms of electron density deformations due to molecular interactions, an optimality condition, and the fundamental holographic properties of molecular electron densities, it is shown that molecular recognition is necessarily unique. A simple proof is given and the connections of this result with the Duality Principle of Molecular Recognition and related Selectivity Measures for molecular recognition are discussed.     

Responsive Supramolecular Polymers Based on the Bis[alkynylplatinum(II)] Terpyridine Molecular Tweezer/Arene Recognition Motif

Supramolecular polymers are constructed based on the novel bis[alkynylplatinum(II)] terpyridine molecular tweezer/pyrene recognition motif. Successive addition of anthracene as the diene and cyano‐functionalized dienophile triggers the reversible supramolecular polymerization process, thus advancing the concept of utilizing Diels–Alder chemistry to access stimuli‐responsive materials in compartmentalized systems.     

Control over the Aspect Ratio of Supramolecular Nanosheets by Molecular Design

Recent developments in kinetically controlled supramolecular polymerization permit control of the size (i.e., length and area) of self-assembled nanostructures. However, control of molecular self-assembly at a level comparable with organic synthetic chemistry and the achievement of structural complexity at a hierarchy larger than the molecular level remain challenging. This study focuses on controlling the aspect ratio of supramolecular nanosheets. A systematic understanding of the relationship between the monomer structure and the self-assembly energy landscape has derived a new monomer capable of forming supramolecular nanosheets. With this monomer in hand, the aspect ratio of a supramolecular nanosheet is demonstrated that it can be controlled by modulating intermolecular interactions in two dimensions.