Beauty of Explicit Dispersity (D) Equations in Controlled Polymerizations.

Dispersity (D) as a critical parameter indicates the level of uniformity of the polymer molar mass or chain length. In the past several decades, the development of explicit equations for calculating D experiences a continual revolution. This viewpoint tracks the historical evolution of the explicit equations from living to reversible-deactivation polymerization systems. Emphasis is laid on displaying the charm of explicit D equations in batch reversible-deactivation radical polymerization (RDRP), with highlights of the relevant elegant mathematical manipulations. Some representative emerging applications enabled by the existing explicit equations are shown, involving nitroxide-mediated polymerization (NMP), atom transfer radical polymerization (ATRP), and reversible addition-fragmentation chain transfer (RAFT) polymerization systems. Stemming from the several outlined challenges and outlooks, sustained concerns about the explicit D equations are still highly deserved. It is expected that these equations will continue to play an important role not only in traditional polymerization kinetic simulation and design of experiments but also in modern intelligent manufacturing of precision polymers and classroom education.

Long-Term Stable Hydrogen Production from Water and Lactic Acid via Visible-Light-Driven Photocatalysis in a Porous Microreactor.

Photocatalytic hydrogen (H2 ) production is significant to overcome challenges like fossil fuel depletion and carbon dioxide emission, but its efficiency is still far below that which is needed for commercialization. Herein, we achieve long-term stable H2 bubbling production from water (H2 O) and lactic acid via visible-light-driven photocatalysis in a porous microreactor (PP12); the catalytic system benefits from photocatalyst dispersion, charge separation, mass transfer, and dissociation of O-H bonds associated with H2 O. With the widely used platinum/cadmium-sulfide (Pt/CdS) photocatalyst, PP12 leads to a H2 bubbling production rate of 602.5 mmol h-1 m-2 , which is 1000 times higher than that in a traditional reactor. Even when amplifying PP12 into a flat-plate reactor with an area as large as 1 m2 and extending the reaction time to 100 h, the H2 bubbling production rate still remains at around 600.0 mmol h-1 m-2 , offering great potential for commercialization.

Ring Repeating Unit: An Upgraded Structure Representation of Linear Condensation Polymers for Property Prediction.

Unique structure representation of polymers plays a crucial role in developing models for polymer property prediction and polymer design by data-centric approaches. Currently, monomer and repeating unit (RU) approximations are widely used to represent polymer structures for generating feature descriptors in the modeling of quantitative structure-property relationships (QSPR). However, such conventional structure representations may not uniquely approximate heterochain polymers due to the diversity of monomer combinations and the potential multi-RUs. In this study, the so-called ring repeating unit (RRU) method that can uniquely represent polymers with a broad range of structure diversity is proposed for the first time. As a proof of concept, an RRU-based QSPR model was developed to predict the associated glass transition temperature (Tg) of polyimides (PIs) with deterministic values. Comprehensive model validations including external, internal, and Y-random validations were performed. Also, an RU-based QSPR model developed based on the same large database of 1321 PIs provides nonunique prediction results, which further prove the necessity of RRU-based structure representation. Promising results obtained by the application of the RRU-based model confirm that the as-developed RRU method provides an effective representation that accurately captures the sequence of repeat units and thus realizes reliable polymer property prediction by data-driven approaches.

Role of External Field in Polymerization: Mechanism and Kinetics.

The past decades have witnessed an increasing interest in developing advanced polymerization techniques subjected to external fields. Various physical modulations, such as temperature, light, electricity, magnetic field, ultrasound, and microwave irradiation, are noninvasive means, having superb but distinct abilities to regulate polymerizations in terms of process intensification and spatial and temporal controls. Gas as an emerging regulator plays a distinctive role in controlling polymerization and resembles a physical regulator in some cases. This review provides a systematic overview of seven types of external-field-regulated polymerizations, ranging from chain-growth to step-growth polymerization. A detailed account of the relevant mechanism and kinetics is provided to better understand the role of each external field in polymerization. In addition, given the crucial role of modeling and simulation in mechanisms and kinetics investigation, an overview of model construction and typical numerical methods used in this field as well as highlights of the interaction between experiment and simulation toward kinetics in the existing systems are given. At the end, limitations and future perspectives for this field are critically discussed. This state-of-the-art research progress not only provides the fundamental principles underlying external-field-regulated polymerizations but also stimulates new development of advanced polymerization methods.

Electrospun Fibrous Mat with pH-Switchable Superwettability That Can Separate Layered Oil/Water Mixtures.

Oil/water separation has inspired much research interest because of the damages caused to our natural environment due to oily wastewater. As a leader of advanced separation materials, electrospun polymeric fibrous mats having the properties of special surface wettability, high specific surface area, and high porosity will be a good membrane material for the separation of oily wastewater. Herein, we first prepared pH-responsive polymer poly(dimethylsiloxane)-block-poly(4-vinylpyridine) (PDMS-b-P4VP) mat using electrospinning technology. The PDMS-b-P4VP fibrous mat with a thickness of around 250 µm exhibits good pH-switchable oil/water wettability and is able to effectively separate oil or water from layered oil/water mixtures by gravity driven through adjusting the pH value. Stemming from its porous structure and pH-switchable superwettability, the electrospun PDMS-b-P4VP fibrous mat achieved controllable separations with high fluxes of approximately 9000 L h-1 m-2 for oil (hexane) and 27 000 L h-1 m-2 for water. In addition, extended studies on the polymer/silica nanoparticulate (silica NP) composite fibrous mats show that the addition of an inorganic component improves the thermal stability, pH-switchable wettability, and separation performance of the fibrous mats (approximately 9000 L h-1 m-2 for hexane and 32 000 L h-1 m-2 for water). It can be concluded from the results that both polymer fibrous mats and silica-filled composite fibrous mats are good candidates for on-demand layered oil/water mixture separation.

Smart Fiber Membrane for pH-Induced Oil/Water Separation.

Wastewater contaminated with oil or organic compounds poses threats to the environment and humans. Efficient separation of oil and water are highly desired yet still challenging. This paper reports the fabrication of a smart fiber membrane by depositing pH-responsive copolymer fibers on a stainless steel mesh through electrospinning. The cost-effective precursor material poly(methyl methacrylate)-block-poly(4-vinylpyridine) (PMMA-b-P4VP) was synthesized using copper(0)-mediated reversible-deactivation radical polymerization. The pH-responsive P4VP and the underwater oleophilic/hydrophilic PMMA confer the as-prepared membrane with switchable surface wettability toward water and oil. The three-dimensional network structure of the fibers considerably strengthens the oil/water wetting property of the membrane, which is highly desirable in the separation of oil and water mixtures. The as-prepared fiber membrane accomplishes gravity-driven pH-controllable oil/water separations. Oil selectively passes through the membrane, whereas water remains at the initial state; after the membrane is wetted with acidic water (pH 3), a reverse separation is realized. Both separations are highly efficient, and the membrane also exhibits switchable wettability after numerous cycles of the separation process. This cost-effective and easily mass-produced smart fiber membrane with excellent oil-fouling repellency has significant potential in practical applications, such as water purification and oil recovery.

Light-responsive smart surface with controllable wettability and excellent stability.

Novel fluorinated gradient copolymer was designed for smart surface with light-responsive controllable wettability and excellent stability. The switchable mechanism and physicochemical characteristics of the as-prepared surface decorated by designed polymeric material were investigated by ultraviolet-visible (UV-vis) spectrum, scanning electron microscope (SEM), atomic force microscope (AFM), and X-ray photoelectron spectroscopy (XPS). Thanks to the functional film and surface roughening, etched silicon surface fabricated by copolymer involving spiropyran (Sp) moieties possesses a fairly large variation range of WCA (28.1°) and achieves the transformation between hydrophilicity (95.2° < 109.2°) and hydrophobicity (123.3° > 109.2°) relative to blank sample (109.2°). The synthetic strategy and developed smart surface offer a promising application in coating with controllable wettability, which bridge the gap between chemical structure and material properties.

A light and pH dual-stimuli-responsive block copolymer synthesized by copper(0)-mediated living radical polymerization: solvatochromic, isomerization, and "schizophrenic" behaviors.

A "schizophrenic" block copolymer (poly[1'-(2-methacryloxyethyl)-3',3'-dimethyl-6-nitrospiro-(2H-1-benzopyran-2,2'-indoline)]-b-poly(acrylic acid) (PSPMA-b-PAA)) was synthesized by sequential copper(0)-mediated living radical polymerization (Cu(0)-mediated LRP) at 30 °C in an oxygen-tolerant system followed by hydrolysis of the resulting polymer. The solvatechromic behaviors of the PSPMA10-b-poly(t-butyl acrylate)40 (PSPMA10-b-PtBA40) and PSPMA10-b-PAA40 block copolymers in organic solvents were investigated by UV-vis spectroscopy. The PSPMA10-b-PtBA40 stabilizes the nonpolar photoisomer and is not sensitive to the polarity of the solvent, while the PSPMA10-b-PAA40 stabilizes the planar zwitterionic form without irradiation. Furthermore, light-induced isomerization of spiropyran (Sp) moieties from Sp to merocyanine (Mc) was demonstrated. Finally, the "schizophrenic" micellization behavior of as-prepared copolymer in aqueous solution regulated by light and pH stimuli was vividly demonstrated, and the reversibility of micellization processes performed in this study was also examined. The large compound micelles can bring out a gradually extended and even transformed conformation with increasing deprotonation degree at pH > pKa.