The cover image by Dongwu Li shows how Guangtao Qian and colleagues synthesized new poly (benzimidazole imide)s containing a biamide structure. The crank-shaft-like amide groups effectively increase the linearity and stiffness of polymer segments, providing colorless polyimide films with low CTE. (DOI: 10.1002/pol.20230055)
Blend films of poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b']dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl]] (PTB7) in combination with 6,6-phenyl-C61-butyric-acid-methyl-ester (PCBM) are a model system for low bandgap organic photovoltaics. Typically, solvent additives are used to improve the power conversion efficiencies of the resulting devices but possibly also decrease the device stability. In this study, we use the binary solvent additive 1,8-diiodooctane:diphenylether (DIO:DPE) for PTB7:PCBM blend films and study how different film drying procedures influence the physical and chemical stability of the polymer blend. The strong influence of the drying procedure on the stability against photoinduced degradation of the PTB7:PCBM films, produced with solvent additives, is shown with data from UV–visible (UV–vis), Fourier transform infrared (FTIR) and Raman spectroscopy. The addition of solvent additive molecules DIO:DPE to the PTB7:PCBM blend accelerates the degradation compared with the pristine blend. At higher annealing temperature a removal of the additives is bringing degradation back to the level of the pristine blend films, which is promising for photovoltaic applications.
Polylactic acid (PLA) packaging materials are useful, safe, and degradable in the natural environment, and hence, have attracted considerable interest. In particular, the barrier properties of PLA are the focus of current research. In this study, organic montmorillonite (OMMT) modified with an epoxy chain extender (CE) was prepared as a barrier functional additive for PLA and PLA alloy materials. The effects of the CE-OMMT on the properties of PLA and PLA/PHA (polyhydroxyalkanoates) composites were investigated. The CE-OMMT was characterized using Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), and thermogravimetry (TG). The results showed that the CE-OMMT was successfully synthesized, and that the addition of the CE did not change the crystal structure of OMMT. The morphology and microstructure of the PLA/CE-OMMT and PLA/PHA/CE-OMMT composites were characterized using XRD and transmission electron microscopy (TEM). The dispersion of the CE-OMMT in the PLA and PLA/PHA composite films was significantly enhanced. XRD analysis showed that OMMT intercalated well into the matrix. The rheological, barrier, and mechanical properties of the PLA nanocomposite films were systematically studied. The results showed that the CE-OMMT enhanced the mechanical and barrier properties of the composite films. Compared with neat PLA, the elongation at break of the PLA/CE-OMMT and PLA/PHA/CE-OMMT composite films with the addition of 3% CE-OMMT increased by 449% and 788.4%, the oxygen permeability decreased by 57.74% and 59%, and the water vapor permeability decreased by 44.79% and 53.25%, respectively. Therefore, the modified PLA composite film is a promising substitute for packaging applications.
Microgels are soft particles that offer excellent colloidal stability, large surface area, and fluid-like transport characteristics, making them ideal for enzyme immobilization and reaction regulation. In recent years, the use of microgels in enzyme processes has rapidly increased and reviewed. Here in this review, we have provided a comprehensive overview of the strategies involved in microgel synthesis, practical aspects of microgel–enzyme conjugate formation, and the effects of microgel on enzyme stabilization and activities. In the end, we have discussed important biocatalytic applications of microgel and enzyme. The aim of this review is to provide a detailed understanding of enzyme–microgel conjugates and their potential applications, which can aid in the design of new microgels, responsive platforms, and biochemical applications.
We investigate the effect of alcohol fraction (isopropanol, IPA) in a binary water-alcohol solvent mixture on the shear and extensional rheological properties, as well as the role of viscoelasticity on fiber formation of poly(acrylic acid) (PAA) in electrospinning. Comparison of the scaling of both specific viscosities ηsp and extensional relaxation times λE of PAA in water–IPA mixtures, showed stronger scaling compared to salt-free aqueous polyelectrolyte solutions, except for the ηsp in the unentangled regime displaying a polyelectrolyte-like scaling ηsp ~ c0.5 for all IPA%. Such deviation suggested IPA induces association/aggregation of PAA. However, the trends between ηsp and λE magnitudes as a function of IPA% differ for concentrations compared in the entangled regime. The ηsp as well as their elastic moduli exhibit a maximum, whereas λE increases monotonically with IPA%, suggesting a complex interplay of various interactions are dictating their structure in water-IPA mixtures, affecting their shear and extensional response differently. Electrospinning experiments showed increasing IPA% reduces the onset of both beaded and uniform fibers. Analysis using dimensionless numbers indicated the enhancement of their elasticity by IPA, and the consequent stabilizing effect on their jets/filaments against break-up during electrospinning, plays a role in the improvement of their fiber formation.
Double-network hydrogels have outstanding mechanical characteristics but mostly suffer from poor self-healing performance since most hydrogels are chemically crosslinked via covalent links for each network. In this work, a tough and self-healing double network hydrogel with multiple dynamic non-covalent bonds is developed by combining the hydrophobically modified polyacrylamide (HPAM) with a thermally reversible potassium ion crosslinked κ-carrageenan (K+C) network through a dual physical crosslinked network strategy. Being the multiple dynamic non-covalent bond interactions and dual physical crosslink networks, the K+C/HPAM DN hydrogel exhibits excellent mechanical characteristics (tensile strength: 1.86 MPa, tensile strain: 1637%) and good self-healing ability (maximum stress self-healing efficiency: 87%, maximum tensile strength after self-healing: 0.95 MPa). Due to the three-dimensional pore structure and the conductive ions in the system, the K+C/HPAM DN hydrogel also achieves good strain sensing capabilities with a strain sensitivity of 2.98 (gauge factor, GF) in the 100% strain range. Even after being cut and self-healed, the gel still exhibits good strain sensing capabilities (GF = 2.79), which is still better than the most similar DN hydrogel strain sensors in sensitivity. We believe this work offers a new material for self-healing flexible strain sensors.
The skin layer, i.e. the surface dense layer with relatively lower porosity, may significantly impede the permeability of porous polymer membranes. In this work, with the combination of experiment and finite element simulation, a facile strategy based on sandwich structure is proposed to eliminate the skin layer. The simulation results indicate that removing skin layers can increase the water flux of porous membranes by more than 4 times. In experiment, first the formation mechanism of skin layer is studied for the porous membranes fabricated from poly(ether-ether-ketone)/poly(ether-imide) (PEEK/PEI) blend based on crystallization template. It is found that the stronger interaction between PEI and the polyimide releasing film during hot-pressing is the cause of the PEEK skin layers of the obtained membranes. According to this mechanism, a skin-free PEEK membrane is prepared from the PEI/(PEEK/PEI blend)/PEI sandwich structure. The separation test indicates that the PEEK membrane fabricated following the new strategy has remained rejection ratio and enhanced flux by 3–5 times as the simulation result predicts. Furthermore, the universality of developed sandwich strategy has been validated in polyformaldehyde/poly(L-lactic acid) (POM/PLLA) blend (crystalline/crystalline system). Our results provide a novel solution to regulate the skin layer of porous membranes.
We synthesized a novel bivalent monomer 1 bearing 4-vinylbenzyl group and five-membered cyclic dithiocarbonate. This monomer 1 was polymerized orthogonally by free radical polymerization to afford polystyrene 1a bearing a five-membered cyclic dithiocarbonate moiety in the side chain. On the other hand, cationic ring-opening polymerization of five-membered cyclic dithiocarbonate in the monomer 1 successfully proceeded, resulting in a narrow molecular weight distribution of polydithiocarbonate 1b bearing a 4-vinylbenzyl group in the side chain. Furthermore, post-polymerizations of 1a and 1b maintaining the polymerizable functionality were carried out respectively by suitable polymerization methods. The five-membered cyclic dithiocarbonate of 1a underwent cationic ring-opening polymerization with a high molar ratio of methyl trifluoromethanesulfonate at a high temperature compared to the case of monomer 1, whereas radical polymerization of the 4-vinylbenzyl group of 1b successfully proceeded under the almost same conditions as the case of monomer 1. These post-polymerizations achieved the synthesis of corresponding networked polymers 2a and 2b.
In order to study the dispersion and compatibility of polysilsesquioxane (POSS) with different functional groups in benzoxazine resin, four different polysilsesquioxane/polybenzoxazine (POSS/PBZ) composites are prepared based on 3-phenyl-3,4-dihydro-2H-benzoxazine (PHa), unreactive Octaphenylsilsesquioxane (OPS), Mercaptopropyl-isobutyl silsesquioxane (SPOSS) containing one reactive sulfhydryl group, Aminopropyl-isobutylsilsesquioxane (NPOSS) containing one reactive amino group and Octa (aminophenyl) silsesquioxane (OAPS) containing eight reactive amino groups, respectively. Scanning electron microscope (SEM), transmission electron microscope (TEM), and transmission electron microscope with probe corrector (AC-TEM) are used to investigate compatibility. The results indicate that OAPS have very good compatibility and interaction with benzoxazine in the molecular level based on the microstructure. Besides, molecular and mesoscopic dynamic simulations (MesoDyn) also confirms OAPS and PHa have the best compatibility based on the micro and mesoscopic aspects. Then their properties of thermal stability and glass transition temperature (Tg) are identified by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC), respectively. While OAPS is beneficial to increase the initial decomposition temperature (T5%) of PBZ by 26 °C and the Tg by 16 °C, comparing with pure PHa. However, NPOSS and SPOSS aggregate into micron-sized silicon spheres, and OPS precipitates and deposits on the bottom of the resin, which could weaken the property of their thermal stability.
Two series of hybrid liquid crystalline (LC) diblock copolymers (DBCs) and triblock copolymers (TBCs) composed of hard and soft blocks with great control over their molecular masses, dispersities (Mw/Mn = Đ ≤ 1.38) and compositions were prepared via reversible addition-fragmentation chain transfer polymerization in anisole solvent using new p-dodecylphenyl-N-acrylamide monomer, azobisisobutyronitrile initiator, poly(2-[2-(4-cyano-azobenzene-4-oxy)ethylene-oxy]ethyl methacrylate) and poly(2-[2-(4-cyano-azobenzene-4-oxy)ethylene-oxy]ethyl methacrylate)-block-poly(n-butyl methacrylate) macroinitiators. Structures and properties of BCs were characterized by proton nuclear magnetic resonance, gel permeation chromatography, differential scanning calorimeter, optical polarizing microscope, atomic force microscope and grazing-incidence small angle X-ray scattering. Kinetic behavior indicated that block copolymerization proceeded with controlled/living characteristics. Every BCs revealed three endothermic transitions corresponding to glassy phase transition, smectic-to-nematic phase transition (TS-N) and melting phase transition. DBC-1, DBC-2, TBC-1 and TBC-2 with high-LC volume fractions exhibited strong TS-N contrasted to DBC-3, DBC-4, TBC-3 and TBC-4 having low-LC contents. DBC-1, DBC-2, DBC-3, TBC-1 and TBC-2 evidenced smectic C structure while TBC-3 containing low-LC segment (39 wt%) showed nematic structure. Morphologies of block copolymer thin films in mixed solvent (Tetrahydrofuran/cyclohexane) vapor annealing system varied significantly, depending on the volume fractions of building blocks and the interactions between the blocks and solvents.
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