Chemically Recyclable Dithioacetal Polymers via Reversible Entropy-Driven Ring-Opening Polymerization**

In a sustainable circular economy, polymers capable of chemical recycling to monomers are highly desirable. We report an efficient monomer-polymer recycling of polydithioacetal (PDTA). Pristine PDTAs were readily synthesized from 3,4,5-trimethoxybenzaldehyde and alkyl dithiols. They then exhibited depolymerizability via ring-closing depolymerization into macrocycles, followed by entropy-driven ring-opening polymerization (ED-ROP) to reform the virgin polymers. High conversions were obtained for both the forward and reverse reactions. Once crosslinked, the network exhibited thermal reprocessability enabled by acid-catalyzed dithioacetal exchange. The network retained the recyclability into macrocyclic monomers in solvent which can repolymerize to regenerate the crosslinked network. These results demonstrated PDTA as a new molecular platform for the design of recyclable polymers and the advantages of ED-ROP for which polymerization is favored at higher temperatures.     

Consequences of Amide Connectivity in the Supramolecular Polymerization of Porphyrins: Spectroscopic Observations Rationalized by Theoretical Modelling

The correlation between molecular structure and mechanism of supramolecular polymerizations is a topic of great interest, with a special focus on the pathway complexity of porphyrin assemblies. Their cooperative polymerization typically yields highly ordered, long 1D polymers and is driven by a combination of π-stacking due to solvophobic effects and hydrogen bonding interactions. Subtle changes in molecular structure, however, have significant influence on the cooperativity factor and yield different aggregate types (J- versus H-aggregates) of different lengths. In this study, the influence of amide connectivity on the self-assembly behavior of porphyrin-based supramolecular monomers was investigated. While in nonpolar solvents, C=O centered monomers readily assemble into helical supramolecular polymers via a cooperative mechanism, their NH centered counterparts form short, non-helical J-type aggregates via an isodesmic pathway. A combination of spectroscopy and density functional theory modelling sheds light on the molecular origins causing this stunning difference in assembly properties and demonstrates the importance of molecular connectivity in the design of supramolecular systems. Finally, their mutual interference in copolymerization experiments is presented.     

Self-Complementary Quadruple Hydrogen-Bonding Motifs as a Functional Principle: From Dimeric Supramolecules to Supramolecular Polymers

The self-association of individual molecules can lead to the formation of highly complex and fascinating supramolecular aggregates. However, for binding motifs which rely only on hydrogen bonds, a combination of several such weak interactions is necessary to observe self-association in solution. Systems based on four hydrogen bonds in a linear array can be obtained which efficiently aggregate at least in chloroform. Besides the physical-organic characterization of these aggregates and the factors influencing their stability, such quadruple hydrogen-bonding motifs can also be used in the field of materials science to synthesize, for the first time, supramolecular polymers through the self-association of self-complementary monomers. As the formation of noncovalent interactions is reversible and their strength depends significantly on the chemical environment (for example, solvent, temperature), the macroscopic properties of such polymers can be controlled by variation of these parameters; hence a first step towards intelligent materials with tailor-made properties is made.     

Progress in controlled polymerization and design of novel polymer architectures

Recent developments of new synthetic methods are stimulating the design of new polymers. Modern generations of highly active and selective transition metal catalysts give excellent control on molecular weight, regio- and stereoregularities, long- and short-chain-branching, polymer crystallization, and morphology of olefin, diene, cyclolefin, and styrene polymers. Ethene is copolymerized with polar comonomers such as carbon monoxide and acrylates in new low pressure processes. Catalytic coupling reactions of aromatic halogen compounds and bisphenols afford rigid polyarylenes. „Living” radical polymerization (“TEMPO” and “ATRP”) produce a wide range of telechelics, block copolymers and cascade macromolecules. In reactive processing oxazoline-mediated coupling reactions are the key to melt diversification of well-known polymers. Supramolecular concepts are being applied to tailor hybrid polymers and nanocomposites. Precision in polymer synthesis is the key to new materials with wide application range.     

分子印迹技术用于模拟酶及分子反应器的研究进展

分子印迹技术是制备特异性分子识别材料的新技术. 分子印迹聚合物(Molecularly-imprinted polymer, MIP)具有可同酶相媲美的选择性识别能力, 能够催化手性及区域选择性的反应, 是一种新型的分子反应器; 同时MIP具有良好的化学和物理稳定性, 因而在替代酶用于某些苛刻条件下的催化反应方面有良好的应用前景. 就近年来利用MIP模拟酶催化有机合成反应, 以及利用MIP作为分子反应器反面的研究进展进行了综述.     

Dendrimer effects on peptide and protein fibrillation

Dendrimers are synthetic, symmetrically branched polymers that can be manufactured to a high degree of definition and therefore present themselves as monodisperse entities. Flexible and globular in shape and compartementalized into a partly inaccessible interior and a highly exposed surface, they offer numerous possibilities for interactions with and responses to biological macromolecules and biostructures including cell membranes and proteins. By way of their multiple functional surface groups, they allow the design of surfaces carrying a multitude of biological motifs and/or charges giving rise to quite significant biological and physico-chemical effects. Here we describe the surprising ability of dendrimers to interact with and perturb polypeptide conformations, particularly efficiently towards amyloid structures; that is, the structures of highly insoluble polypeptide aggregates involved in a range of serious and irreversibly progressive pathological conditions (protein-misfolding diseases). Interesting as this may be, the interaction of dendrimers with such generic peptidic aggregates also offers a new perspective on the molecular mechanisms governing assembly and disassembly of amyloid structures and thereby on determinants of protein and peptide folding. Despite the potent disaggregative nature of various dendrimers, they have variable effects on the stability of different proteins, suggesting that they do not act as generic denaturants, but rather exert their effects via specific interactions with individual parts of each protein.     

Methods for the synthesis of uniform polymers

The difficulties encountered in the preparation of polymers that are uniform chemically, structurally, and in their molecular weight are due mainly to the wide variety of possible polymers. This arcticle gives a review of attempts to synthesize homogeneous polymers by chain reactions and by stepwise synthesis. Syntheses on templates are extremely important in living cells; methods have recently been found for syntheses of this type that are independent of natural processes. Uniform polymers can also be obtained by reactions on existing polymers. In replicating polymers, this in principle requires the modification of only one polymer molecule.     

The effect of inhomogeneous stickiness on polymer aggregation

The aggregation of polymers is important in the formation of marine aggregates and the vertical transport of material in the ocean. A polymer may be inhomogeneous along its length, with associating groups at some points along its length where bonds are more likely to form. In this paper we investigate the effects of inhomogeneous 'stickiness' along the polymer length. We describe the results of three-dimensional off-lattice simulations of polymer-polymer aggregation for four different types of polymer: polymers which are sticky along their entire length, polymers which are sticky at the ends only and two types of polymer which are slightly sticky along their entire length. We examine the mean radius of gyration and the fractal dimension of the resulting aggregates and the dynamics of aggregation. The slightly sticky polymers and the polymers which are sticky only at the ends form aggregates with a higher fractal dimension than the polymers which are sticky along their entire length. However, the mean radius of gyration of the aggregates formed by polymers which are sticky only at the ends is significantly larger than that of the aggregates formed from slightly sticky polymers. The aggregation dynamics are also different for the polymers which are sticky only at the ends compared to the slightly sticky polymers. A single 'stickiness value' is therefore likely to be inadequate to describe a polymer. We also examine the effect of polymer rigidity; it seems that the effect of inhomogeneous stickiness is greater for almost-straight polymers than for coiled chains.     

Aggregation behavior of rodlike ionogenic polymers in chloroform

The rodlike ionogenic polymers poly(p-pyridylene-phenylene) and poly(p-pyridylene/phenylene-ethynylene) form polyelectrolytes when protonated with toluene sulfonic acid or ethane sulfonic acid in chloroform solution. This molecular modification, clearly indicated by a marked red shift of the UV absorption band, induces the formation of prolate, bundlelike aggregates, whose size and shape are obtained from their rotational dynamics as revealed by electric birefringence relaxation and their translational dynamics as measured by dynamic light scattering. The aggregates have a length of 400-600 nm and a high aspect ratio >15. In general, the polyelectrolyte molecules are arranged with their long axes parallel to the long axis of the aggregates. They probably attract each other through the electrostatic interaction with counterions. The counterions are not bound to specific sites but may be shifted under the action of an external electric field to account for the highly anisotropic electric polarizability. When inert salt or excess sulfonic acid is added, these compounds seem to accumulate within the aggregates and influence the attractive forces. This is generally leading to an elongation of the aggregates and, in the case of added salts, even to a marked reduction of birefringence.     

FI catalysts: new olefin polymerization catalysts for the creation of value-added polymers

This contribution reports the discovery and application of phenoxy-imine-based catalysts for olefin polymerization. Ligand-oriented catalyst design research has led to the discovery of remarkably active ethylene polymerization catalysts (FI Catalysts), which are based on electronically flexible phenoxy-imine chelate ligands combined with early transition metals. Upon activation with appropriate cocatalysts, FI Catalysts can exhibit unique polymerization catalysis (e.g., precise control of product molecular weights, highly isospecific and syndiospecific propylene polymerization, regio-irregular polymerization of higher alpha-olefins, highly controlled living polymerization of both ethylene and propylene at elevated temperatures, and precise control over polymer morphology) and thus provide extraordinary opportunities for the syntheses of value-added polymers with distinctive architectural characteristics. Many of the polymers that are available via the use of FI Catalysts were previously inaccessible through other means of polymerization. For example, FI Catalysts can form vinyl-terminated low molecular weight polyethylenes, ultra-high molecular weight amorphous ethylene-propylene copolymers and atactic polypropylenes, highly isotactic and syndiotactic polypropylenes with exceptionally high peak melting temperatures, well-defined and controlled multimodal polyethylenes, and high molecular weight regio-irregular poly(higher alpha-olefin)s. In addition, FI Catalysts combined with MgCl(2)-based compounds can produce polymers that exhibit desirable morphological features (e.g., very high bulk density polyethylenes and highly controlled particle-size polyethylenes) that are difficult to obtain with conventionally supported catalysts. In addition, FI Catalysts are capable of creating a large variety of living-polymerization-based polymers, including terminally functionalized polymers and block copolymers from ethylene, propylene, and higher alpha-olefins. Furthermore, some of the FI Catalysts can furnish living-polymerization-based polymers catalytically by combination with appropriate chain transfer agents. Therefore, the development of FI Catalysts has enabled some crucial advances in the fields of polymerization catalysis and polymer syntheses.     

Metal-Catalyzed Coupling Reactions In The Synthesis Of New Conducting Polymers

The use of transition metal-catalyzed coupling reactions in the synthesis of conducting polymers is discussed. These reactions are of growing importance in polymer synthesis and are particularly important in the synthesis of highly functionalized conjugated (conducting) polymers. In this report we discuss applications of this methodology for the synthesis of conducting polymer sensory materials and polymers with reactive functional groups. In the sensory polymers we have incorporated crown ether groups which induce perturbations to the polymer's electronic structure when exposed to an alkali metal ion. Our interest in polymers with reactive functional groups is for the development of polymers which can be transformed into novel all-carbon ladder polymers.     

Synthesis and properties of amphiphilic star polysulfides

We here present the synthesis and characterisation of linear and star-shaped amphiphilic block copolymers based on hydrophobic polysulfides (poly(propylene sulfide), PPS) and hydrophilic polyethers (poly(ethylene glycol), PEG). We also discuss the proof of the principle of their responsiveness to oxidising conditions. In a water environment, these polymers aggregate in the form of sub-micron carriers that, due to the sensitivity to oxidation reactions typical of PPS, can be used for responsive drug delivery. In this first study we have focused on the study of large aggregates, which do not apparently show dramatic differences in behaviour when polymer chains with different degrees of branching are studied.     

Computer Simulations of Natural and Synthetic Polymers in Confined Systems

Nanotechnology is the ability to work at the molecular and supramolecular levels in order to create and use devices, structures and systems with the desired properties and functions. This is what Nature already does in living systems. In this work we investigated the consequences of confinement in the ordering of natural (namely proteins) and synthetic polymers by means of computational techniques. The focus is put on the possibility to design new materials in a Nature-like fashion. In the first part of the paper, the possibility to select/design different folding of the same peptide is investigated by means of full atoms molecular dynamics. In the second part of the paper dynamic mean-field density functional method is applied to the dynamics of block copolymer melts in three-dimensional lattice model. The analysis of the aggregates and their temporal evolution in free space and in confined space are compared.     

Through-space delocalized water-soluble paracyclophane bichromophores: new fluorescent optical reporters

Conjugated polymers and oligomers can serve as highly responsive fluorescent reporters for biosensor applications. However, their optical properties in aqueous media are highly dependent upon environmental conditions. The structure of the paracyclophane framework provides a platform for designing optical reporters that show little sensitivity to surfactants, and thus is well-suited for fluorescent assays. The permanent intramolecular delocalization through the paracyclophane core dominates intermolecular perturbations in spontaneously formed aggregates.     

Enzyme-responsive polymeric assemblies, nanoparticles and hydrogels

Being responsive and adaptive to external stimuli is an intrinsic feature characteristic of all living organisms and soft matter. Specifically, responsive polymers can exhibit reversible or irreversible changes in chemical structures and/or physical properties in response to a specific signal input such as pH, temperature, ionic strength, light irradiation, mechanical force, electric and magnetic fields, and analyte of interest (e.g., ions, bioactive molecules, etc.) or an integration of them. The past decade has evidenced tremendous growth in the fundamental research of responsive polymers, and accordingly, diverse applications in fields ranging from drug or gene nanocarriers, imaging, diagnostics, smart actuators, adaptive coatings, to self-healing materials have been explored and suggested. Among a variety of external stimuli that have been utilized for the design of novel responsive polymers, enzymes have recently emerged to be a promising triggering motif. Enzyme-catalyzed reactions are highly selective and efficient toward specific substrates under mild conditions. They are involved in all biological and metabolic processes, serving as the prime protagonists in the chemistry of living organisms at a molecular level. The integration of enzyme-catalyzed reactions with responsive polymers can further broaden the design flexibility and scope of applications by endowing the latter with enhanced triggering specificity and selectivity. In this tutorial review, we describe recent developments concerning enzyme-responsive polymeric assemblies, nanoparticles, and hydrogels by highlighting this research area with selected literature reports. Three different types of systems, namely, enzyme-triggered self-assembly and aggregation of synthetic polymers, enzyme-driven disintegration and structural reorganization of polymeric assemblies and nanoparticles, and enzyme-triggered sol-to-gel and gel-to-sol transitions, are described. Their promising applications in drug controlled release, biocatalysis, imaging, sensing, and diagnostics are also discussed.     

Influence of intermolecular orientation on the photoinduced charge transfer kinetics in self-assembled aggregates of donor-acceptor arrays

The kinetics of photoinduced charge transfer reactions in covalently linked donor-acceptor molecules often undergoes dramatic changes when these molecules self-assemble from a molecular dissolved state into a nanoaggregate. Frequently, the origin of these changes is only partially understood. In this paper, we describe the intermolecular spatial organization of three homologous arrays, consisting of a central perylene bisimide (PERY) acceptor moiety and two oligo(p-phenylene vinylene) (OPV) donor units, in nanoaggregates and identify both face-to-face (H-type) and slipped (J-type) stacking of the OPV and PERY chromophores. For the J-type aggregates, short intermolecular OPV-PERY distances are created that give rise to a charge-transfer absorption band. The proximity of the donor and acceptor groups in the J-type aggregates enables a highly efficient photoinduced charge separation with a rate (k(cs) > 10(12) s(-1)) that significantly exceeds the rate of the intramolecular charge transfer of the same compounds when molecularly dissolved, even in the most polar media. In the H-type aggregates, on the other hand, the intermolecular OPV-PERY distance is not reduced compared to the intramolecular separation, and hence, the rates of the electron transfer reactions are not significantly affected compared to the molecular dissolved state. Similar to the forward electron transfer, the kinetics of the charge recombination in the aggregated state can be understood by considering the different interchromophoric distances that occur in the H- and J-type aggregates. These results provide the first consistent rationalization of the remarkable differences that are observed for photoinduced charge-transfer reactions of donor-acceptor compounds in molecularly dissolved versus aggregated states.     

Functional porous organic polymers for heterogeneous catalysis

Porous organic polymers (POPs), a class of highly crosslinked amorphous polymers possessing nano-pores, have recently emerged as a versatile platform for the deployment of catalysts. The bottom-up approach for porous organic polymer synthesis provides the opportunity for the design of polymer frameworks with various functionalities, for their use as catalysts or ligands. This tutorial review focuses on the framework structures and functionalities of catalytic POPs. Their structural design, functional framework synthesis and catalytic reactions are discussed along with some of the challenges.     

Conjugated Microporous Polymers for Heterogeneous Catalysis

Conjugated microporous polymers (CMPs) are a class of crosslinked polymers that combine permanent micropores with π‐conjugated skeletons and possess three‐dimensional (3D) networks. Compared with conventional materials such as metal–organic frameworks (MOFs) and covalent organic frameworks (COFs), CMPs usually have superior chemical and thermal stability. CMPs have made significant progress in heterogeneous catalysis in the past seven years. With a bottom‐up strategy, catalytic moieties can be directly introduced into in the framework to produce heterogeneous CMP catalysts. Higher activity, stability, and selectivity can be obtained with heterogeneous CMP catalysts in comparison with their homogeneous analogs. In addition, CMP catalysts can be easily isolated and recycled. In this review, we focus on CMPs as an intriguing platform for developing various highly efficient and recyclable heterogeneous catalysts in organic reactions. The design, synthesis, and structure of these CMP catalysts are also discussed in this focus review.     

Detection and amplification of chirality by helical polymers

A unique feature of synthetic helical polymers for the detection and amplification of chirality is briefly described in this article. In sharp contrast to host-guest and supramolecular systems that use small synthetic receptor molecules, chirality can be significantly amplified in a helical polymer, such as poly(phenylacetylene)s with functional pendants, which enable the detection of a tiny imbalance in biologically important chiral molecules through a noncovalent bonding interaction with high cooperativity. The rational design of polymeric receptors can be possible by using chromophoric helical polymers combined with functional groups as the pendants, which target particular chiral guest molecules for developing a highly efficient chirality-sensing system. The chirality sensing of other small molecular and supramolecular systems is also briefly described for comparison.     

Parallel esterification of bio-based dicarboxylic acids in small scale film reactors: A high-throughput study

The applicability of polyesters across a wide range of fields creates a demand for novel polyester structures that can offer advanced product performance. Two critical factors to the development of unique polymer architectures are the speed at which new polymeric systems can be synthesized and the available selection of monomers from which polymers are designed. Herein, we successfully demonstrate the applicability of a high-throughput (HT) approach to polyesterification reaction between dicarboxylic acids and diols in reaction conditions similar to those used in industry. Furthermore, we apply our HT design to a series of bio-based monomers whose unique structures offer potential for enhanced properties in polyester-based systems. Using a custom-built array of small-scale film reactors, we conducted a parallel screening of 13 bio-based dicarboxylic acids as potential monomers in the synthesis of polyester polyols through copolymerization with 1,6-hexanediol. The polyester polyols were characterized for their molecular weight and thermal properties. Carrying out polyesterification reactions in small-scale film reactors is seen as a quick and powerful tool for screening the effectiveness of a series of potential monomers, as this method offers highly controllable and reproducible reaction conditions in every reactor coupled with the ability to use a minimum amount of reagents.