Interactions between polymer chains and nanoparticles can play a dominant role in composites mechanics, yet the control of such interfacial dynamics is still a significant challenge. This paper reports the effect of pH on cellulose nanofibrils (CNFs) transient hydrogels network mechanics via interfacial ionic cross‐linking bonds. For this purpose, carboxylated CNFs are incorporated with amine groups terminated 8‐arm poly(ethylene glycol) (PEG‐NH2) to assemble the first noncovalent network via reversible ionic interactions at the CNF surfaces, where the end‐group acrylate modified linear difunctional PEG forms the second lightly covalent cross‐linked network. The viscoelastic properties of the supramolecular gels are examined as a function of pH, and the unique transient mechanics resulting from CNF‐PEG complexation structures show that the processing from acidic‐to‐alkaline pH change leads to the gel cross‐links transition from covalent type to covalent–noncovalent hybrid one. This finding offers an alternative way to tune CNF gels mechanical reinforcement and sheds light on the pH dependence of network architectural changes.
Random copolymer gels of N‐isopropylacrylamide (NIPAM) and N‐ethylacrylamide (NEAM) are synthesized using different monomer compositions in 1:1 methanol–water mixtures. The samples are characterized by scanning electron microscopy, atomic force microscopy (AFM), and rheological studies. It is observed that with the variation of the monomer compositions in the reaction mixture, the thermoresponsive, morphological, AFM, and rheological properties varied significantly. Porosity and roughness of the gels gradually increase with the gradual increase in NIPAM loading in the gels, lower critical solution temperature, mechanical strength (Young's modulus, storage modulus) significantly decreases with the increase in poly(N‐isopropylacrylamide) loading in the gels. All results can be explained on the basis of the differences in thermoresponsive character of homo‐ and copolymer gels of NIPAM and NEAM in water, their composition in the reaction mixtures, and their different kind of interactions with solvents.
Copolymerization of carbon dioxide (CO2) and propylene oxide (PO) is employed to generate amphiphilic polycarbonate block copolymers with a hydrophilic poly(ethylene glycol) (PEG) block and a nonpolar poly(propylene carbonate) (PPC) block. A series of poly(propylene carbonate) (PPC) di‐ and triblock copolymers, PPC‐b‐PEG and PPC‐b‐PEG‐b‐PPC, respectively, with narrow molecular weight distributions (PDIs in the range of 1.05–1.12) and tailored molecular weights (1500–4500 g mol?1) is synthesized via an alternating CO2/propylene oxide copolymerization, using PEG or mPEG as an initiator. Critical micelle concentrations (CMCs) are determined, ranging from 3 to 30 mg L?1. Non‐ionic poly(propylene carbonate)‐based surfactants represent an alternative to established surfactants based on polyether structures.
A new synthetic strategy is developed for the synthesis of polyphosphazene bearing stable nitroxide radicals as a pendant group. The resulting material is investigated as a cathode‐active material for rechargeable lithium–ion batteries that performs 80 mAh g−1 capacities at a C/2 current density over 50 cycles. Thus, the inorganic–organic hybrid system can be proposed as an alternative cathode‐active material with improved performance.
Poly(ethylene glycol) (PEG) hydrogels are hydrophilic, high water content, polymeric networks that represent excellent candidates as engineering biomaterials for a broad range of applications. A key challenge for many biomedical applications is the control of transport properties within the resulting 3D crosslinked gels. The effects of the water content at synthesis and crosslinker molecular weights on gel chemical structure and equilibrium volumetric swelling ratio, Q , are studied for a series of PEG hydrogels. In addition, the translational diffusion coefficients of a model probe molecule, Rhodamine 110, are determined directly within the hydrogels by fluorescence correlation spectroscopy measurements. Increasing the water content at synthesis results in larger observed swelling behavior and faster particle transport within the formed PEG hydrogels for two different crosslinker molecular weights due to fewer physical crosslinks in the gels. Comparison of the particle translational diffusion coefficient to the swelling ratio shows a linear relationship for all crosslink densities examined.
In this study, an effective way is presented to synthesize a mussel‐inspired adhesive from two inexpensive commercially available materials: polyvinyl alcohol (PVA) and 3,4‐dihydroxybenzoic acid via the esterification reaction and deprotection technology. This bioinspired adhesive exhibits good bonding ability on metal, glass, plastic, and wood, and the maximum bonding strength can be up to 4.0 MPa at dry conditions on glass substrate. Meanwhile, this adhesive can also be used as a wet/underwater adhesive. Such a PVA‐based bioinspired adhesive may be used as a potential candidate for applications in industrial field.
The application of selenol‐X chemistry in nucleophilic substitution and Se‐Michael addition reactions for polymer chain end modification is presented. Selenol‐labeled polystyrene can easily react with alkyl halides, methyl methacrylate, methyl acrylate, pentafluorostyrene, etc. The mild conditions make it attractive for the synthesis of macromonomers. The resulting polymers are analyzed and characterized by UV, size‐exclusion chromatography (SEC), NMR, and matrix assisted laser desorption/ionization time of flight mass spectroscopy.
Comb‐like polyethylene glycol (PEG)‐based copolymer electrolytes with given crosslinking density are synthesized using PEG as the main chain segments (denoted as MC‐PEG), methoxy polyethylene glycol (MPEG) as side chain segments (denoted as SC‐PEG), and hexamethylene‐1,6‐diisocyanate homopolymer (HDI trimer) as bridging and/or crosslinking agent. In this study, the effects of molecular weight of MC‐PEG and SC‐PEG on Li ion conductivities of the copolymer have been examined. If MC‐PEG and/or SC‐PEG do not crystallize, the ion conductivities of graft copolymer electrolyte increase with either decreasing MC‐PEG or increasing SC‐PEG segment length. The highest ion conductivity of the copolymer electrolyte at room temperature reaches up to 7.7 × 10?4 S cm?1 when the molecular weight of MC‐PEG is 400 g mol?1 and SC‐PEG is 1000 g mol?1 (denoted as GC400‐1000). However, when the MC‐PEG and/or SC‐PEG segments begin to crystallize (i.e., GC400‐2000), where the flexibility of the related PEG molecular chains is largely reduced, the ion conductivity drops by almost two orders comparing to that of GC400‐1000 copolymer electrolyte. Meanwhile, crosslinked GC400‐1000 electrolyte has good thermal and electrochemical stability as well as high mechanical properties, making it suitable for commercial applications in Li ion secondary batteries.
Thermoresponsive polypeptoids are promising candidates for medical applications due to their biomimetic properties. When such polymers are grafted on magnetic nanoparticles, materials can be obtained that combine a temperature‐triggered solubility transition with magnetic extraction. The synthesis of monodisperse, superparamagnetic iron oxide nanoparticles is described with densely surface‐grafted polypeptoid shells that have tunable thermoresponsive colloidal stability. The synthesis combines ligand exchange with controlled surface‐initiated polymerization of N‐substituted N‐carboxyanhydrides for the preparation of well‐defined core–shell nanoparticles.
In the context of novel sustainable and structurally significant building blocks for polymer science, the synthetic routes are described to new oligoamide structures based on the terpenoid ketone (?)‐menthone. The basic concept is an oxime formation of this cyclic ketone followed by the Beckmann rearrangement, resulting in the corresponding lactams. These lactams are polymerized under anionic or acid‐catalyzed conditions (ring‐opening polymerization (ROP)) to give alkyl‐substituted and stereocenter containing oligoamide scaffolds that are assumed to be suitable for further copolymerizations and modifications and thus for a wide range of different applications. The regio‐ and the stereochemistry of the formed oximes and lactams as well as their impact on the polymerization behavior is discussed.
A series of novel segmented linear and crosslinked polyurethanes (PUs) are synthesized from poly(ε‐caprolactone) (PCL) (25 kg mol?1), methylene diphenyl diisocyanate (MDI), and various polyether diols (Pluronic (PLU) and polyethylene glycol (PEG)). The basic structures of the highly deformable PUs are PLU/PEG–MDI–PCL–MDI–PLU/PEG and PLU–MDI–PCL–MDI–PLU, respectively. The linear and crosslinked PUs are characterized. Changes in the tensile behavior are attributed to the effects of compositional variables and alterations in the crosslink density. Additional information on the morphology of the segmented PUs is deduced from differential scanning calorimetry, as well as transmission and scanning electron microscopy investigations. Both the linear and the crosslinked PUs exhibit a broad rubbery plateau above the melting temperature of the crystalline PCL phase, which is highly beneficial for shape memory function. This work highlights that the chemical build‐up of soft segments containing high‐molecular‐weight crystallizable chain units is a proper tool to tailor the morphology and mechanical properties of PUs, and thus also their shape memory properties.
Novel self‐healing silicone rubbers are prepared by a two‐step procedure: aminopropyl methyl phenyl polysiloxanes is first reacted with salicylaldehyde and then with copper acetate. The reversible nature of the metal–ligand coordination interaction between polysiloxanes with pendent Schiff‐base groups and Cu2+ has endowed silicone rubbers with superior self‐healing properties. As compared with other self‐healing silicone rubbers based on hydrogen bonds or Diels–Alder reaction, this cross‐linked system shows high healing power. The materials are cut into two parts and put together in a mold for 1 h at 30 °C, observing a macroscopic healing and a strength recovery up to 87.0%.
Ion‐mobility mass spectrometry of doubly charged polyethylene glycol (PEG) is performed after electrospray‐ionization time‐of‐flight mass spectrometry and the dependency of the effective collision cross‐section, CCSeff, on the number of monomer units, n , is evaluated with the help of molecular dynamics simulations. Assuming a balance between elastic and Coulomb forces inside short and asymmetric doubly charged chains, a method is developed for evaluating the dielectric constant, ε, which is found to be 7.87 for PEG for n = 14–28. From the same experiment at higher chain lengths, the characteristic ratio Cn of 4.30 for PEG (n ≥ 63) can be evaluated according to an earlier reported method, which is demonstrated here to also work with doubly charged species. The proposed method enables an extremely swift and precise measurement both of ε and Cn of polymer that is free of solvent or impurities from one single experiment.
High‐performance carbon‐nanotube‐based thermoplastic composites are synthesized through in situ polymerization of cyclic butylene terephthalate (pCBT) on aligned carbon nanotube buckypaper. The initial results show that the buckypaper/pCBT composites have a tensile strength of approximately 600 MPa and a modulus of 96 GPa due to the aligned nanotubes in the composite acting as a framework and the in situ polymerization resulting in increased interfacial interactions between the pCBT chains and nanotubes. The buckypaper/pCBT composites also demonstrate significantly improved thermal (70 W m?1 °C?1) and electric conductivities (526 S cm?1), as well as thermoelectric power (Seebeck coefficient of 64 μV °C?1). With low mass density, these combined excellent multi‐properties indicate that the composites can act as multifunctional materials in numerous applications.
The self‐assembly and structure formation in binary blends of asymmetric polystyrene‐block‐poly(4‐vinylpyridine) diblock copolymers in different solvent systems and the bulk morphology of the blend films are studied by using dynamic light scattering, small‐angle X‐ray scattering, and transmission electron microscopy. In dilute solutions, the chains of pure diblock copolymers or binary blends of diblock copolymers having similar or different molecular weights remain as unimers, form common micelles in selective solvents or form unimers in coexistence with micelles in slightly selective solvents or solvent mixtures. The blends show mixing of the chemically similar blocks in the blend films and solutions at high concentrations. A single‐phase with common spherical morphology is formed in the blend films similar with the morphology of the individual components in the pure state. The characteristic length scale of the blends depends on the number average molecular weight following the typical scaling behavior of a strongly segregated block copolymer.
The coupling of hyperbranched polychloromethylstyrene (PCMS) radicals with nitrone is studied in this work. Hyperbranched PCMS radicals are generated by a redox reaction of terminal chloride groups with Cu(I)Cl. The molecular weight data show that nitrone mediated radical coupling of PCMS is a kind of step polymerization. The molecular weights of the coupled products in a fixed coupling reaction time increase as the contents of nitrone increase in a wide concentration range, whereas are less affected by the content of CuCl. FTIR and NMR spectra prove the formation of alkoxyamine in the mid‐chains arising from nitrone‐mediated coupling. The nitrone‐coupled hyperbranched polymers show the birefringent property if being watched in a crossed polarizing microscope. The intrinsic viscosity data imply that the nitrone‐coupled hyperbranched polymers in solution behave like rod‐like structures. These nitrone‐coupled hyperbranched polymers are thermodegradable. This kind of cylindrical polymers with highly branched substructures may find important application as anisotropic monomolecular gels or molecular reinforcement, catalyst hosts, etc.
The doping of a liquid crystalline (LC) photoemissive compound into a LC polymethacrylate with photoemissive side groups induces repeatable changes in the photoemission wavelength upon mechanical grinding and thermal annealing. The color changes observed in a handwritten pattern demonstrate the successful induction of anisotropic photoemission behavior in a LC composite polymeric film parallel to the grinding direction. The LC characteristics of the composite films play an important role in the directional selectivity of the polarized mechanoinduced color change.
Graft polymers with poly(2,6‐dimethyl‐1,4‐phenylene oxide) (PPO) as backbones are successfully prepared via two convenient steps. The utilization of semiflexible PPO as backbones offers unique properties for the graft polymers. Thermal, rheological, and phase behaviors of these new graft polymers are well controlled via the precise design of architectural parameters. The disordered microphase separation in melt state and the proper composition of side grafts provide the ease of thermal processing for these graft polymers. The graft density shows impact on the relaxation and mechanical properties of the thermoplastics. This work shows the possibility to use lots of semiflexible engineering polymers as backbones to construct new thermoplastics.
Iron‐mediated atom‐transfer radical polymerization (ATRP) of methyl methacrylate (MMA) in N‐methylpyrrolidin‐2‐one (NMP) solution is investigated via online VIS/NIR spectroscopy up to 2500 bar. The activation–deactivation equilibrium constant, KATRP, decreases towards higher NMP content due to the formation of catalytically less active FeII/NMP species. The reaction volume increases from 1 to 15 cm3 mol?1 in passing from 16 to 92 mol% NMP. The same effects are observed for monomer‐free model systems with poly(MMA)–Br as the initiator. Investigations into iron‐catalyzed ATRP of MMA in less polar solvents or even without an additional solvent (i.e., for bulk ATRP) yield KATRP values, which are by two to three orders of magnitude higher than in the presence of NMP.
This paper reports on the effect of a semifluorinated alkyl side chain for achieving a self‐organized nanostructure to facilitate the efficient charge carrier transport. So far, semifluorinated alkyl side chains have rarely been introduced into semiconducting polymers, despite their interesting properties such as hydrophobicity, thermal stability, and solvent resistance, as well as self‐organization. Herein, this study synthesizes the semifluorinated alkyl chain introduced poly(3‐dodecylthiophene), SFA‐P3DT, and demonstrates that self‐organization of SFA‐P3DT is intensely induced in nonfluorous solvent by the so‐called fluorophobic effect, resulting in the formation of nanofibrillar structure. In presence of the semifluorinated alkyl side chain, organic thin film transistor (OTFT) devices exhibit the improved charge carrier mobility than that of poly(3‐dodecylthiophene) with hydrocarbon alkyl chain. Moreover, higher charge carrier mobility can be obtained from the nonfluorous solvent, in comparison to the fluorous solvent, confirming the crucial role of fluorophobic effect. These observations suggest that the introduction of semifluorinated alkyl chains into a conjugated polymer may enhance the performance of OTFTs through the development of a well‐ordered nanostructure via self‐organization by fluorophobic effect, which, in turn, facilitates the efficient charge carrier transport.
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