Progress in Polymer Science最新文献

Radical polymerization of monomers with functional groups such as carboxylic acid and amide moieties yields materials of significant technical importance. The reactions are mostly carried out in aqueous phase, which provides the additional advantage of using a cheap and benign solvent. In addition to varying monomer concentration, temperature and pressure, the kinetics and thus the polymer properties may be tuned by varying the degree of monomer ionization, by changing pH and ionic strength of the aqueous solution, and by addition of an organic cosolvent. These systems exhibit strong interactions via hydrogen bonds resulting in large effects on rate coefficients, even for propagation, which for long have been considered as almost insensitive towards solvent environment. The determination of rate coefficients in aqueous solution largely assists the understanding of the impact of intermolecular interactions on polymerization rate. Despite the enormous importance of polymers produced by radical polymerization in aqueous solution, the associated mechanism and the availability of accurate rate coefficients have been very limited. This situation has improved by applying pulsed-laser techniques, which enable the precise measurement of individual rate coefficients in aqueous solution as required for the simulation of radical polymerization processes.

This review primarily addresses the two most important rate coefficients, i.e., those for propagation and termination, with the diffusion-controlled termination step depending on radical chain length. Both rate coefficients have been studied over a wide range of reaction conditions. The enormous improvement in data quality reached by using methods such as pulsed-laser polymerization (PLP) – size-exclusion chromatography (SEC) and single pulse (SP) – PLP – electron paramagnetic resonance (EPR) spectroscopy is illustrated. Outlined are results for homopolymerizations of non-ionized monomers, subdivided into monomers which may or may not undergo backbiting. This reaction adds considerable complexity, as backbiting results in the formation of midchain radicals with reactivity differing largely from the one of chain-end radicals. The kinetic investigations have been extended to partially and fully ionized monomers. Examples are given of how the rate coefficients from PLP experiments are used to simulate polymerization kinetics and polymer properties of continuously-initiated systems. The review demonstrates that the basic kinetic concepts for conventional radical polymerization in organic media also apply towards polymerization of monomers in aqueous solution.

The encapsulation of biologically active ingredients (e.g., peptides, proteins, enzymes, drugs) into polymer particles is extensively used for drug delivery purposes. However, this strategy relies mainly on emulsification processes from preformed polymers, which leads to strong limitations such as low particle concentrations (typically a few wt%), poor active ingredient loadings, as well as a rather limited structural diversity of the polymers usually used. Conversely, polymerizations in dispersed media, which allow for the formation of scalable suspensions of (nano)particles during the polymerization process, have been advantageously used for the in situ encapsulation of active ingredients. In this review, the in situ encapsulation of active ingredients, such as peptides, proteins, enzymes or drugs, in polymer particles obtained by polymerization in dispersed media for potential biomedical applications, is covered. Their physical and chemical encapsulations were both considered as function of the polymerization technique used. Several polymerization and encapsulation parameters will be discussed in view of adjusting the drug loading and the encapsulation efficiency of the active agent considered.

The adsorption and transport of molecules or ions in the confined space of microporous materials often reveal properties not seen in either dense bulk or microporous materials. The unexpected behavior of confined polymers motivates their application in advanced technologies. While the majority of microporous materials consist of network/framework-type strong intermolecular connections, making the processing and roll-to-roll fabrication of these materials particularly challenging, there exists a special category of microporous polymers that are amorphous and can be solution-processed. They feature relatively weak intermolecular bond strength, low long-range order, and large free-volume elements due to frustrated polymer chain motion. However, it remains elusive to design and synthesize solution-processable amorphous microporous organic polymers for those working in the field of membrane separations and electrochemistry. The application of membranes derived from these polymers in processes beyond gas separations is also overlooked. Thus, we review the synthetic strategies toward solution-processable amorphous microporous organic polymers (SAMOPs), with a particular focus on the characteristics and the monomer/polymer structural features of each reaction. Computation-based materials design, including computational tools are introduced that can reveal the monomer/polymer rigidity, polymer chain packing, thereby the generation of free volume elements, and the pore architecture, to facilitate the design and identification of desirable polymers. On-polymer modification methodology that can afford standing-alone membranes with functional groups for applications beyond gas separation, especially targeting membrane-based electrochemical devices are subsequently covered. The molecular transport/ion in the sub-1-nm space provided by solution-processable amorphous microporous organic polymers are presented and the wide range application of membranes derived from these polymers is demonstrated. Finally, challenges, perspectives, and future research directions are discussed.

Supramolecular polymers are, in broad brushstrokes, self-assembled structures built up from small building blocks via the use of noncovalent interactions. In favorable cases, supramolecular polymers embody the best features of covalent polymers while displaying unique reversibility, responsiveness, adaptiveness, and stability. This has made them of interest across a wide variety of fields, from molecular devices to sensors, drug delivery, cell recognition, and environmentally friendly materials systems. This review is concerned with the determinants that underlie supramolecular polymer construction, specifically the driving forces that have been exploited to create them. To date, nearly the full range of known noncovalent interactions (e.g., hydrogen-bonding, electrostatic interactions, charge transfer effects, and metal coordination, among others) has been exploited to create supramolecular polymers. Typically, one or more types of interactions is used to link appropriately designed monomers. The choice of noncovalent interaction can have a significant influence on the structure and function of the resulting supramolecular polymers. Understanding the connections between the forces responsible for the assembly of supramolecular polymers and their properties provides the foundation for further advances in this fast-moving field. Given the above, this review will discuss recent progress in the rapidly advancing field of supramolecular polymers organized by the types of underlying interactions. An overview of future challenges and opportunities for supramolecular polymers, including their formation, characterization, and applications, is also provided.

The macroscopic functions and properties of conjugated polymers depend on their microcosmic morphology and microstructure in the solid state. However, such morphology and microstructure from molecules to solid states are complicated. Therefore, it is a significant challenge to reveal the relationship among molecular structures to the complex microstructure and finally to device functions. This review focuses on the formation, behavior, and evolution of solution-state aggregation of conjugated polymers, which can influence and even determine the solid-state morphology and microstructure, ultimately clarifying the relationship between the microstructure and the properties of conjugated polymers. The critical role of solution-state aggregation is highlighted from a theoretical understanding of molecular interactions between polymer chains (conjugated backbones and/or flexible side chains) and solvent molecules. We highlight the recent progress on high-performance polymer-based devices through the solution-state aggregation strategy. Furthermore, we summarize the challenges and essential research direction on the solution-state aggregation, which will be addressed and established in the future. Therefore, an in-depth understanding of polymer aggregation will advance the development of high-performance conjugated polymers in various functional devices.

Poly(amino ester)s (PAEs) refer to a class of synthetic polymers characterized by repeating units in the backbone having tertiary amines and ester bonds, and bringing together the inherent biodegradability of polyesters and the rich tunable functionalities provided by tertiary amines. The presence of tertiary amines allows the introduction of various pendant groups, leading to diverse PAE material and properties, such as biodegradability, biocompatibility, water-solubility, stimulus-responsiveness (pH or temperature), etc. To date, PAEs are evolving into a new class of biodegradable polymer materials independent of aliphatic polyesters and have been widely used in various biomedical fields, such as gene delivery, drug delivery, bioimaging agents, etc. In addition, a new family of PAEs, namely N-acylated PAEs, with the same pendant carbonyl groups as poly(2-oxazoline)s, is expected to develop into new biopolymer platforms similar to polypeptoids and polyoxazolines. This review comprehensively summarizes the synthesis methods of PAEs, including polycondensation (PCD), Michael addition polymerization (MAP), spontaneous zwitterionic copolymerization (SZWIP), and ring-opening polymerization (ROP).

Sensibility to environmental concerns and the actual demand for polymeric materials free of any metal contaminants in most applications have directed research towards significant breakthroughs in organocatalytic polymerizations. The overarching challenge is to develop new and efficient organocatalysts for extending the scope and to improve the performance of organocatalytic polymerizations. Since 2016 commercially available alkyl boranes, especially triethyl borane (TEB), have been discovered as exceptional Lewis acids that served to generate ate complexes by combination with chain ends on the one hand and to activate epoxides on the other. This double role of boranes has received widespread attention especially in oxygenated polymer synthesis. Lewis pairs consisting of alkyl boranes combined with an onium salt or organic base has indeed demonstrated unprecedented versatility for (co)polymerizations of oxygenated monomers such as epoxides, oxetanes, cyclic esters and with CO₂, COS, isocyanates, or cyclic anhydrides, producing a variety of oxygenated polymers. In this review, we take TEB-mediated polymerization systems as the main line of emerging area, summarize the progress comprehensively made to promote the rapid development of organocatalytic polymerizations of oxygenated polymers by these systems, and propose key challenges in organocatalytic synthesis in the future.

This review article discusses the origins of self-assembly behavior of linear and non-linear block co- and terpolymers and their application towards the fabrication of high-resolution patterns for nanolithography applications. Comparative analysis for the microphase separation in bulk and thin films is provided, to map the fundamentals of various types of block copolymers (BCPs) inherent properties prior to their use in advanced applications. The opportunities of high-χ/low-N and/or complex architecture co- and terpolymers to self-assemble into nanostructures that are beyond the limitations of current lithographic techniques will be presented. The role of molecular characteristics and immiscibility of the blocks on the formation of sub-10 nm or sub-5 nm structures will be discussed. Recent advances in directed self-assembly (or DSA) enable low defect density, extremely minimal dimensions, facile processability, etching selectivity, low-cost and ability to design various patterns. The opportunities of these strategies will be discussed in the context of technological standard requirements and their potential will be evaluated.

Hydrogels have been developed rapidly in recent years because of their great application prospects in biomedicine and intelligent devices. The excellent performance of hydrogels is very important for their applications. Introducing divalent metal ions (M²⁺) into hydrogels is an effective method to improve the performance of hydrogels. M²⁺ can interact with functional groups of polymers to affect the structures and properties of hydrogels. Here, we review the synthesis and theoretical simulation of M²⁺-hydrogels, the effect of M²⁺ on hydrogels and their applications in energy storage, sensing, biomedicine, resource utilization and environmental remediation. The challenges of M²⁺-hydrogels are also discussed. We hope that this review can provide ideas for the preparation of multifunctional hydrogels and point out the important role of M²⁺ in the development of hydrogels.

This article reviews the advances made over the past five decades of research in developing effective chemocatalytic pathways to synthesize polyhydroxyalkanoates (PHAs), a prominent class of biodegradable polyesters found in nature and considered as sustainable alternatives to petroleum-based non-degradable plastics. Focused in this review are recent efforts that seek to address the key challenges facing the biosynthetic routes by taking advantage of precision in synthesis, expedient tunability in polymer stereomicrostructures and structures of monomers and molecular catalysts, as well as scalability and speed in polymer production that chemical catalysis can offer. This article is organized by poly(3-hydroxybutyrate) (P3HB) stereomicrostructures (tacticities), from isotactic to syndiotactic to atactic P3HB materials, followed by other PHA homopolymers and copolymers. Under each type of stereochemically defined PHAs, monomers, catalysts, and polymerizations employed for the synthesis, as well as mechanistic aspects when possible, are described. Next, recent advances in expanding the PHA scope and developing functionalized, uncommon or unnatural PHAs, inaccessible by biological methods, especially block and stereoblock or stereosequenced PHAs, are highlighted in their synthetic methods and advanced materials properties. Lastly, four key remaining challenges, and thus corresponding future directions directed at addressing those challenges, are discussed.