Three-Component Multiblock 1D Supramolecular Copolymers of Ir(III) Complexes with Controllable Sequences

Multicomponent supramolecular block copolymers (BCPs) have attracted much attention due to their potential functionalities, but examples of three-component supramolecular BCPs are rare. Herein, we report the synthesis of three-component multiblock 1D supramolecular copolymers of Ir(III) complexes 1 – 3 by a sequential seeded supramolecular polymerization approach. Precise control over the kinetically trapped species via the pathway complexity of the monomers is the key to the successful synthesis of BCPs with up to 9 blocks. Furthermore, 5-block BCPs with different sequences could be synthesized by changing the addition order of the kinetic species during a sequentially seeded process. The corresponding heterogeneous nucleation-elongation process has been confirmed by the UV/Vis absorption spectra, and each segment of the multiblock copolymers could be characterized by both TEM and SEM. Interestingly, the energy transfer leads to weakened emission of 1 -terminated and enhanced emission of 3 -terminated BCPs. This study will be an important step in advancing the synthesis and properties of three-component BCPs.     

Highly Ordered Nanoporous Films from Supramolecular Diblock Copolymers with Hydrogen‐Bonding Junctions

We designed efficient precursors that combine complementary associative groups with exceptional binding affinities and thiocarbonylthio moieties enabling precise RAFT polymerization. Well defined PS and PMMA supramolecular polymers with molecular weights up to 30 kg mol^?1 are synthesized and shown to form highly stable supramolecular diblock copolymers (BCPs) when mixed, in non‐polar solvents or in the bulk. Hierarchical self‐assembly of such supramolecular BCPs by thermal annealing affords morphologies with excellent lateral order, comparable to features expected from covalent diblock copolymer analogues. Simple washing of the resulting materials with protic solvents disrupts the supramolecular association and selectively dissolves one polymer, affording a straightforward process for preparing well‐ordered nanoporous materials without resorting to crosslinking or invasive chemical degradations.     

Integrating DNA Photonic Wires into Light‐Harvesting Supramolecular Polymers

An approach combining DNA nanoscaffolds with supramolecular polymers for the efficient and directional propagation of light‐harvesting cascades has been developed. A series of photonic wires with different arrangements of fluorophores in DNA‐organized nanostructures were linked to light‐harvesting supramolecular phenanthrene polymers (SPs) in a self‐assembled fashion. Among them, a light‐harvesting complex (LHC) composed of SPs and a photonic wire of phenanthrene, Cy3, Cy5, and Cy5.5 chromophores reveals a remarkable energy transfer efficiency of 59 %. Stepwise transfer of the excitation energy collected by the light‐harvesting SPs via the intermediate Cy3 and Cy5 chromophores to the final Cy5.5 acceptor proceeds through a Förster resonance energy transfer mechanism. In addition, the light‐harvesting properties are documented by antenna effects ranging from 1.4 up to 23 for different LHCs.     

环糊精超分子聚合物在药物/基因递送载体领域的研究进展

超分子聚合物通常以非共价键作为构筑驱动力,其结构具有动态可逆的特点,在新型响应性聚合物材料中具有突出优势。环糊精可通过主客体识别作用与客体分子如二茂铁、偶氮苯、金刚烷、苯环等形成包合,以此构筑的超分子组装体展现出丰富的自组装-解组装特性、刺激响应性、较低的细胞毒性和较好的生物相容性,有望在药物/基因载体领域得到应用。本文从环糊精超分子聚合物的生物医用出发,着重对近年来环糊精超分子聚合物载体在药物控制释放、基因转染以及药物/基因共递送三方面的研究进展进行了总结和评述,并在此基础上展望了环糊精超分子聚合物的研究方向和发展趋势。     

Introduction of Ferrocene as a Facilitator for the Construction of Supramolecular Polymers

Proper monomer design is the key to enhancing the strength of noncovalent interactions between the molecules toward the efficient formation of supramolecular polymers (SPs). We have designed and synthesized 1,n′-disubstituted ferrocene-azobenzene-long alkyl chains, Fc(CONH-Azo-TDP)₂, to afford SPs with a high probability. The design exploits the ‘‘molecular ball-bearing’’ property of the ferrocene core, which allows two azobenzene arms to rotate in the planes of cyclopentadienyl rings, generating the most suitable molecular conformation required for SP formation. This ferrocene monomer formed a supergel consisting of SPs supported by strong intermolecular (H-bonding and π-π stacking) interactions and higher enthalpy gain than the reference molecules, where the central ferrocene core was replaced by flexible aliphatic as well as rigid benzene linkers. The molecular conformation involved in SPs, the strength of noncovalent interactions, and the process of supramolecular polymerization were investigated through NMR, UV-Vis, XRD and TEM studies. The results demonstrate that ferrocene may act as a good modulator for constructing efficient SPs.     

Quasi‐Block Copolymers Based on a General Polymeric Chain Stopper

Quasi‐block copolymers (q‐BCPs) are block copolymers consisting of conventional and supramolecular blocks, in which the conventional block is end‐terminated by a functionality that interacts with the supramolecular monomer (a “chain stopper” functionality). A new design of q‐BCPs based on a general polymeric chain stopper, which consists of polystyrene end‐terminated with a sulfonate group (PS‐SO₃Li), is described. Through viscosity measurements and a detailed diffusion‐ordered NMR spectroscopy study, it is shown that PS‐SO₃Li can effectively cap two types of model supramolecular monomers to form q‐BCPs in solution. Furthermore, differential scanning calorimetry data and structural characterization of thin films by scanning force microscopy suggests the existence of the q‐BCP architecture in the melt. The new design considerably simplifies the synthesis of polymeric chain stoppers; thus promoting the utilization of q‐BCPs as smart, nanostructured materials.     

Utilizing the Hofmeister Effect to Induce Hydrogelation of Nonionic Supramolecular Polymers into a Therapeutic Depot

Nonionic hydrogels are of particular interest for long-term therapeutic implantation due to their minimal immunogenicity relative to their charged counterparts. However, in situ formation of nonionic supramolecular hydrogels under physiological conditions has been a challenging task. In this context, we report on our discovery of salt-triggered hydrogelation of nonionic supramolecular polymers (SPs) formed by self-assembling prodrug hydrogelators (SAPHs) through the Hofmeister effect. The designed SAPHs consist of two SN-38 units, which is an active metabolite of the anticancer drug irinotecan, and a short peptide grafted with two or four oligoethylene glycol (OEG) segments. Upon self-assembly in water, the resultant nonionic SPs can be triggered to gel upon addition of phosphate salts. Our ¹H NMR studies revealed that the added phosphates led to a change in the chemical shift of the methylene protons, suggestive of a disruption of the water-ether hydrogen bonds and consequent reorganization of the hydration shell surrounding the SPs. This deshielding effect, commensurate with the amount of salt added, likely promoted associative interactions among the SAPH filaments to percolate into a 3D network. The formed hydrogels exhibited a sustained release profile of SN-38 hydrogelator that acted potently against cancer cells.     

刺激响应性刚柔嵌段共聚物的自组装

刚柔嵌段共聚物是指刚性链段和柔性链段以共价键相连形成的共聚物。不仅由于刚性链段有序排列的特点使得其自组装行为更为丰富多样,而且刚性分子将优异的功能特性赋予到超分子组装体中,有望实现超分子材料的功能应用。这类嵌段共聚物在溶液中自组装形成的聚集体会对外界的刺激(例如pH、光、温度、化学添加剂等)敏感,产生聚集体形态的变化。本文选取了部分典型的具有刺激响应性的刚柔嵌段共聚物,介绍了其智能自组装行为,并对其良好的发展前景做了展望。     

Kinetic Control of Aggregation Shape in Micellar Self‐Assembly

The first steps towards top‐down morphology control in micellar self‐assembly are introduced. Kinetically stable micelles are formed from block copolymers (BCPs) using continuous flow techniques by turbulent mixing of water with a THF solution of polymers. In this way, particle shape and size can be altered from spheres to ellipsoids solely via tuning of mixing parameters from a single BCP.     

An Antitumor Dual-Responsive Host-Guest Supramolecular Polymer Based on Hypoxia-Cleavable Azocalix[4]arene

The exploitation of specific guests which can respond to external stimuli is the main approach for the construction of stimuli-responsive supramolecular polymers (SPs) based on host–guest interactions. Most functional guests, however, fail to manifest stimuli-responses. Herein, a hypoxia-responsive dimeric azocalixarene (D-SAC4A) with outstanding hosting properties was used as the macrocyclic building block for the preparation of host stimuli-responsive SPs. Since azocalixarenes can also be compatible with stimuli-responsive guests, an antitumor drug, camptothecin (CPT), was chosen and linked via a disulfide-containing linker to afford a glutathione (GSH)-responsive ditropic guest (D-CPT). A unique dual-responsive SP was obtained by 1 : 1 mixing of D-SAC4A and D-CPT in water, which further assembled into SP nanoparticles (DSPNs). DSPNs displayed outstanding stability against dilution and biological interferants, as well as precise CPT-release under GSH and hypoxia conditions. In vitro and in vivo experiments demonstrated the good biosafety and tumor-suppressive effects of DSPNs.     

Poly(ε‐caprolactone)–poly(isobutylene): A crystallizing,hydrogen‐bonded pseudo‐block copolymer

The crystallization of block copolymers (BCPs) under homogeneous and heterogeneous nucleation is currently well understood revealing the strong interplay of crystallization in competition to microphase separation. This article reports investigations on synthesis and crystallization processes in weakly interacting supramolecular pseudo‐BCPs, composed of poly(ε‐caprolactone) (PCL) and poly(isobutylene) (PIB) blocks, connected by a specifically interacting hydrogen bond (thymine/2,6‐diaminotriazine). Starting from ring opening polymerization of ε‐caprolactone, the use of “click”‐chemistry enabled the introduction of thymine endgroups onto PCL polymer, thus generating the fully thymine‐substituted pure PCLs ( 1a , 1b ) as judged via NMR and MALDI analysis. Physical mixing of 1a , 1b with a bivalent, bis(2,6‐diaminotriazine)‐containing molecule ( 2 ) generated the bivalent polymers BC1 and BC2 , whereas mixing of 1a or 1b with the 2,6‐diaminotriazine‐substituted PIB ( 3 ) generated the supramolecular pseudo‐BCPs BC3 and BC4 . Thermal investigations (DSC, Avrami analysis) revealed only minor changes in the crystallization behavior of BC1 – BC4 with Avrami exponents close to three, indicative of a confluence of the growing crystals during the crystallization process. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Fabrication of Supramolecular Semiconductor Block Copolymers by Ring‐Opening Metathesis Polymerization

ω‐Telechelic poly(p‐phenylene vinylene) species (PPVs) are prepared by living ring‐opening metathesis polymerization of a [2.2]paracyclophane‐1,9‐diene in the presence of Hoveyda–Grubbs 2nd generation initiator, with terminating agents based on N¹,N³‐bis(6‐butyramidopyridin‐2‐yl)‐5‐hydroxyisophthalamide (Hamilton wedge), cyanuric acid, Pd^II–SCS‐pincer, or pyridine moieties installing the supramolecular motifs. The resultant telechelic polymers are self‐assembled into supramolecular block copolymers (BCPs) via metal coordination or hydrogen bonding and analyzed by ¹H NMR spectroscopy. The optical properties are examined, whereby individual PPVs exhibit similar properties regardless of the nature of the end group. Upon self‐assembly, different behaviors emerge: the hydrogen‐bonding BCP behaves similarly to the parent PPVs whereas the metallosupramolecular BCP demonstrates a hypsochromic shift and a more intense emission owing to the suppression of aggregation. These results demonstrate that directional self‐assembly can be a facile method to construct BCPs with semiconducting networks, while combating solubility and aggregation.     

Crystallization-driven self-assembly of semicrystalline block copolymers and end-functionalized polymers: A minireview

Self-assembly has been a powerful method to fabricate the polymer materials with well-defined structures and morphologies. Such assembled materials have shown wide potential applications in many fields such as nanomaterial, nanomedicine, lithography, and microelectronic. Crystallization has been a general behavior of stereoregular polymers. Besides the various noncovalent interactions, crystallization of polymer blocks or end groups can be an efficient way to manipulate the self-assembly pathway and assembled structures of polymers in both solid and solution. Crystallization-driven self-assembly has been widely implemented for the semicrystalline block copolymers (BCPs) and end-functionalized polymers. This minireview briefly presents the recent progresses in the crystallization-driven self-assembly of BCPs and end-functionalized polymers in both solid and solution states. Formation process, mechanism, and hierarchical structure of the crystallization-induced assemblies for BCPs and end-functionalized polymers are highlighted.     

界面超分子聚合

超分子聚合物诞生于高分子化学与超分子化学的交叉融合,一般是指单体间通过非共价键作用连接形成的聚合物,并在溶液或体相中表现出类似聚合物的性质。目前超分子聚合物一般通过均相溶液聚合制备得到,但溶液中的超分子聚合是一个自发的组装过程,具有浓度依赖性,组装过程不易可控。为解决此问题,研究人员可以将超分子聚合从均相溶液转移到界面,在界面上可控地制备超分子聚合物。通过界面聚合制备超分子聚合物具有一些独特的优势,如可以制备得到分子量更高的超分子聚合物,易于制备一些缺陷少、面积大、有序的二维超分子聚合物等。本文基于在液-液、气-液和固-液三种界面上制备超分子聚合物的一些代表性工作,介绍了界面超分子聚合方法和应用,并展望其未来发展。     

Local electric dipole moments: A generalized approach

We present an approach for calculating local electric dipole moments for fragments of molecular or supramolecular systems. This is important for understanding chemical gating and solvent effects in nanoelectronics, atomic force microscopy, and intensities in infrared spectroscopy. Owing to the nonzero partial charge of most fragments, “naively” defined local dipole moments are origin‐dependent. Inspired by previous work based on Bader's atoms‐in‐molecules (AIM) partitioning, we derive a definition of fragment dipole moments which achieves origin‐independence by relying on internal reference points. Instead of bond critical points (BCPs) as in existing approaches, we use as few reference points as possible, which are located between the fragment and the remainder(s) of the system and may be chosen based on chemical intuition. This allows our approach to be used with AIM implementations that circumvent the calculation of critical points for reasons of computational efficiency, for cases where no BCPs are found due to large interfragment distances, and with local partitioning schemes other than AIM which do not provide BCPs. It is applicable to both covalently and noncovalently bound systems. © 2016 Wiley Periodicals, Inc.     

Controlling supramolecular polymerization through multicomponent self‐assembly

The self‐assembly into supramolecular polymers is a process driven by reversible non‐covalent interactions between monomers, and gives access to materials applications incorporating mechanical, biological, optical or electronic functionalities. Compared to the achievements in precision polymer synthesis via living and controlled covalent polymerization processes, supramolecular chemists have only just learned how to developed strategies that allow similar control over polymer length, (co)monomer sequence and morphology (random, alternating or blocked ordering). This highlight article discusses the unique opportunities that arise when coassembling multicomponent supramolecular polymers, and focusses on four strategies in order to control the polymer architecture, size, stability and its stimuli‐responsive properties: (1) end‐capping of supramolecular polymers, (2) biomimetic templated polymerization, (3) controlled selectivity and reactivity in supramolecular copolymerization, and (4) living supramolecular polymerization. In contrast to the traditional focus on equilibrium systems, our emphasis is also on the manipulation of self‐assembly kinetics of synthetic supramolecular systems. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 34–78     

Facile Synthesis of Supramolecular Ionic Polymers That Combine Unique Rheological,Ionic Conductivity,and Self‐Healing Properties

A new family of supramolecular ionic polymers is synthesized by a simple method using (di‐/tri‐)carboxylic acids and (di‐/tri‐)alkyl amines. These polymers are formed by carboxylate and ammonium molecules that are weakly bonded together by a combination of ionic and hydrogen bonds, becoming solid at room temperature. The supramolecular ionic polymers show a sharp rheological transition from a viscoelastic gel to a viscous liquid between 30 and 80 °C. This sharp viscosity decrease is responsible for an unprecedented jump in ionic conductivity of four orders of magnitude in that temperature range. As a potential application, this chemistry can be used to develop polymeric materials with self‐healing properties, since it combines properties from supramolecular polymers and ionomers into the same material.     

Controlling the Length of Cooperative Supramolecular Polymers with Chain Cappers

The design and the characterization of supramolecular additives to control the chain length of benzene-1,3,5-tricarboxamide (BTA) cooperative supramolecular polymers under thermodynamic equilibrium is unraveled. These additives act as chain cappers of supramolecular polymers and feature one face as reactive as the BTA discotic to interact strongly with the polymer end, whereas the other face is nonreactive and therefore impedes further polymerization. Such a design requires fine tuning of the conformational preorganization of the amides and the steric hindrance of the motif. The chain cappers studied are monotopic derivatives of BTA, modified by partial N-methylation of the amides or by positioning of a bulky cyclotriveratrylene cage on one face of the BTA unit. This study not only clarifies the interplay between structural variations and supramolecular interactions, but it also highlights the necessity to combine orthogonal characterization methods, spectroscopy and light scattering, to elucidate the structures and compositions of supramolecular systems.     

Supramolecular polymerization from polypeptide-grafted comb polymers

The helical and tubular structures self-assembled from proteins have inspired scientists to design synthetic building blocks that can be "polymerized" into supramolecular polymers through coordinated noncovalent interactions. However, cooperative supramolecular polymerization from large, synthetic macromolecules remains a challenge because of the difficulty of controlling the structure and interactions of macromolecular monomers. Herein we report the synthesis of polypeptide-grafted comb polymers and the use of their tunable secondary interactions in solution to achieve controlled supramolecular polymerization. The resulting tubular supramolecular structures, with external diameters of hundreds of nanometers and lengths of tens of micrometers, are stable and resemble to some extent biological superstructures assembled from proteins. This study shows that highly specific intermolecular interactions between macromolecular monomers can enable the cooperative growth of supramolecular polymers. The general applicability of this strategy was demonstrated by carrying out supramolecular polymerization from gold nanoparticles grafted with the same polypeptides on the surface.