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.
Flame‐retardant polypropylene (PP)/carbon nanotubes (CNTs) nanocomposites influenced by surface functionalization and surfactant molecular weights are studied. 3‐Aminopropyl‐triethoxysilane (APTES) is utilized to modify the CNTs (f‐CNTs), and maleic‐anhydride‐grafted PP (MAPP) with two molecular weights ( of 800 and 8000 g mol?1) is used to further improve the dispersion of f‐CNTs in the PP matrix. Thermal gravimetric analysis (TGA) and microscale combustion calorimetry (MCC) reveal that the molecular weight of MAPP directly affects the thermal stability and flammability of PP/f‐CNTs PNCs: both MAPP polymers ( of 800 and 8000 g mol?1) increase the thermal stability of PP; however, the heat release rate of PP/f‐CNTs is reduced in the presence of MAPP ( of 800 g mol?1) and increased in the presence of MAPP ( of 8000 g mol?1). MAPP ( of 800 g mol?1) also results in a lower viscosity of the PP/f‐CNTs PNCs compared with pure PP.
Biobased polymers have gathered a lot of interest and are currently attracting ever‐increasing attention. However, polymeric microspheres especially those derived from biomasses of small molecules, have not been extensively explored yet. This contribution reports recent exciting success in designing and preparing methyl isoeugenol (MeIE)‐derived renewable microspheres. Owing to the difficulty in homopolymerizing MeIE, it undergoes precipitation copolymerization with maleic anhydride to form the anticipated copolymeric microspheres in a high yield (both cross‐linked and non‐cross‐linked). The copolymers show high heat resistance, and the microspheres can be easily functionalized by taking advantage of the highly reactive anhydride groups. A novel type of cation exchange microspheres is further prepared by transforming the anhydride groups into carboxyl groups through hydrolyzation. The hydrolyzed microspheres demonstrate remarkable adsorption toward Cu2+ (maximum, 300 mg g?1). Accordingly, the microspheres may find practical applications, e.g., as green adsorbents. The established preparing methodology can also be taken for other bio‐phenylpropenes.
A convenient one‐pot method for the controlled synthesis of polystyrene‐block‐polycaprolactone (PS‐b‐PCL) copolymers by simultaneous reversible addition–fragmentation chain transfer (RAFT) and ring‐opening polymerization (ROP) processes is reported. The strategy involves the use of 2‐(benzylsulfanylthiocarbonylsulfanyl)ethanol (1) for the dual roles of chain transfer agent (CTA) in the RAFT polymerization of styrene and co‐initiator in the ROP of ε‐caprolactone. One‐pot polymerizations using the electrochemically stable ROP catalyst diphenyl phosphate (DPP) yield well‐defined PS‐b‐PCL in a relatively short reaction time (≈4 h; = 9600?43 600 g mol?1; / = 1.21?1.57). Because the hydroxyl group is strategically located on the Z substituent of the CTA, segments of these diblock copolymers are connected through a trithiocarbonate group, thus offering an easy way for subsequent growth of a third segment between PS and PCL. In contrast, an oxidatively unstable Sn(Oct)2 ROP catalyst reacts with (1) leading to multimodal distributions of polymer chains with variable composition.
Dynamic covalent bonds placed within a polymer chain result in stimulus‐responsive materials where the breaking/making and/or exchange of the dynamic bonds controls the response. A key attribute to access such properties is the molecular mobility of the dynamic bonds. The focus of this work is to understand how incorporating a dynamic bond, in the form of disulfide bonds, into the hard phase of a polyurethane will impact the properties of the materials. Thus, uncross‐linked polyurethanes with aliphatic disulfide‐containing hard segments are synthesized via a two‐step protocol, using 2,2′‐dithiodiethanol and/or 1,4‐butanediol in the second step as the chain extenders. Thermomechanical studies show that, if the dynamic bonds are selectively placed in the hard phase of the polyurethane, the dynamic nature of the disulfide bond can be effectively “switched‐off” below the melting temperature of the hard phase. As such the dynamic and mechanical properties of the materials can be controlled by tailoring the nature of the hard phase.
A novel hydrogel with super stability and toughness is obtained by polymerizing acrylamide and maleic acid in the presence of poly(vinyl alcohol) chains. Then the hydrogel is processed with dry‐anneal and loading with cation solution method in order to construct a polymer network containing covalent, crystalline, and ionic cross‐links. Various hydrogels are measured via tensile and compressive tests to determine the optimal preparation and mechanical properties of hydrogels. The hydrogels show high tensile stress of ≈ 8 MPa and toughness of ≈ 25.4 MJ m?3. The hydrogel exhibits good chemical stability that remained up to 93% of original strength after 12 h soaking in phosphate buffered saline. Finally, an energy dissipation mechanism is discussed.
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.
A new fluoro‐containing four‐arm organosiloxane has been successfully synthesized, which can be easily converted to a cross‐linked network, showing water uptake of below 0.12 wt% (maintained in boiling water for 72 h) and dielectric constant of below 2.56 with dissipation factor of near 1.8 × 10−3 at 30 MHz, as well as showing high transparency and good thermostability. These data indicate that this new organosiloxane is suitable as an adhesive or sealant for the applications in microelectronic industry.
The thermally induced spontaneously initiated autopolymerization of methyl methacrylate (MMA) upon air exposure in amide‐type polar solvents at 75–90 °C is unexpectedly observed and then investigated. By using iodometric analysis, it is confirmed that oligo(MMA peroxide)s in situ form at a moderate rate via thermally induced interpolymerization of MMA with O2 diffusing from air above 70 °C and give rise to an equivalent concentration above 10?4 mol L?1 in 2–4 h in N,N‐dimethylacetamide, N,N‐dimethylformamide, and N‐methyl‐2‐pyrrolidinone (in a descending order of the formation rate). Simultaneously, oligo(MMA peroxide) undergoes thermally induced homolytic decomposition into alkyloxyl radicals to initiate polymerization of MMA in the above solvents at a rate comparable to those initiated by chemical initiators. Thus, the thermally induced in situ O2 activation into peroxides via interpolymerization accounts for the spontaneous initiation of the autopolymerization of MMA in these solvents at moderate temperature.
This paper presents a microfluidic approach for fabricating stereocomplexed hollow microcapsules that uses water‐in‐oil‐in‐water double‐emulsion droplets as templates. The polylactides functionalized with 2‐ureido‐4[1H]‐pyrimidinone (UPy) end groups are intermolecularly stereocomplexed by polylactides with opposite configurations to promote their self‐assembly at a water‐chloroform interface. This intermolecular interaction can significantly enhance the stability of resulting hollow microcapsules so that they preserve their shape and size after drying. Moreover, because these stimuli‐responsive polylactides can assemble and disassemble into superstructures, they can be made to release their cargo by varying the pH values. The interfacially assembled supramolecular microcapsules, which possess stimuli‐responsiveness and long‐term stability, are potentially useful for encapsulation and delivery of drugs.
Alternating copolymers of an oligopeptide (N3‐GVGV‐N3, where G: glycine; V: valine) and an oligothiophene (5,5′‐bis(ethynyl)‐3,3'‐dioctyltetrathiophene) are prepared by click chemistry. The experimental results discover that these copolymers exhibit strong molecular‐weight‐dependent self‐assembly behaviors. The copolymer P1 with the lowest weight‐average molecular weight ( = 7400 g mol?1), assembles into well‐ordered fibrous nanostructures. P3 ( = 16 980 g mol?1) assembles into nanoballs. P2, which has the medium between P1 and P3, ( = 14 800 g mol?1), exhibits more‐complicated self‐assembly behaviors, more like a transition state between the other two. All of the results suggest the self‐assembly ability of these oligopeptide segments might be the major reason for the nano‐structure evolution.
New composite layer architecture of 3D hydrogel polymer network that is loaded with molecularly imprinted polymer nanoparticles (nanoMIP) is reported for direct optical detection of low‐molecular‐weight compounds. This composite layer is attached to the metallic surface of a surface plasmon resonance (SPR) sensor in order to simultaneously serve as an optical waveguide and large capacity binding‐matrix for imprinted target analyte. Optical waveguide spectroscopy (OWS) is used as a label‐free readout method allowing direct measurement of refractive index changes that are associated with molecular binding events inside the matrix. This approach is implemented by using a photo‐crosslinkable poly(N‐isopropylacrylamide)‐based hydrogel and poly[(ethylene glycol dimethylacrylate)‐(methacrylic acid)] nanoparticles that are imprinted with l ‐Boc‐phenylalanine‐anilide (l ‐BFA, molecular weight 353 g mol?1). Titration experiments with the specific target and other structurally similar reference compounds show good specificity and limit of detection for target l ‐BFA as low as 2 × 10?6 m .
Amphiphilic block copolymers based on sucrose methacrylate (SMA) and alkyl methacrylates (alkyl = ethyl, butyl, and hexyl) are synthesized by atom transfer radical polymerization, employing CuBr/CuBr2/2,2,2‐tribromoethanol/1,1,4,7,10,10‐hexamethyltriethylenetetramine as a catalyst/deactivator/initiator/ligand system. Poly(alkyl methacrylate)s with similar polymerization degrees are used as macroinitiators for SMA polymerization. The introduction of PSMA blocks with molar mass varying from 2000 to 12 000 g mol−1 results in changes in the solubility, thermal stability, and water swelling capacity. The copolymers are able to stabilize water/oil emulsion and also to self‐assemble in solution, as verified by gel permeation chromatography and dynamic light scattering, as well as in solid state, as verified by atomic force microscopy.
Three thioxanthone‐based hydrophilic visible photoinitiators (TX‐MPEG350, TX‐MPEG550, and TX‐MPEG750) are prepared and characterized. All of them exhibit excellent water dispersion properties. Real‐time FTIR investigation shows that they can be used as visible photoinitiators for radical polymerization in waterborne systems in the presence and absence of the hydrogen donors. Among them, TX‐MPEG550 has been illustrated as the best hydrophilic visible photoinitiator in the presence of hydrogen donors and would have great potential applications in waterborne visible photocuring systems after carefully investigating the photopolymerization behavior of TX‐MPEGs in different conditions.
Branched polymers with different branching densities and their cross‐linked analogues are synthesized by photoinduced self‐condensing vinyl polymerization via benzodioxinone photochemistry. Thus, methyl methacrylate is copolymerized with two different comonomers, namely, 2‐hydroxyethyl methacrylate (HEMA) and 2‐(dimethylamino)ethyl methacrylate in the presence of bisbenzodioxinone (BBNZ) under UV light. Upon irradiation, BBNZ undergoes irreversible decomposition leading to the formation of benzophenone photosensitizer and bisketene. The released benzophenone is further photoexcited at the same wavelength to give the initiating radicals through hydrogen abstraction from the inimer. In the case of HEMA, additional branching sites are formed by the reaction of bisketene with the hydroxyl functionalities of HEMA.
A new synthetic procedure is described for the preparation of dendritic polyethylene brushes with polysiloxane as the main chain, describing for the first time that it is possible to simply and efficiently prepare highly branched architectures for this type of polymer. Furthermore, as a result of the polymer brush architecture, polyethylene acts as the side chains and Si O Si as the backbone. The number average molecular weight (M n) of the polyethylene brushes, which is determined using a multiple angle laser light scattering detector, increases from 5946 to 27 684 g mol−1 while retaining relatively narrow polydispersities (1.5–2.4). The polymer brushes are characterized by solid 29Si NMR and high‐temperature 1H NMR spectra. In addition, X‐ray photoelectron spectroscopy and gel permeation chromatography were used to confirm the structure.
Star‐shaped poly(2‐isopropyl‐2‐oxazolines) with dramatically hydrophobic dendrimer core are synthesized using carbosilane dendrimers of first to third generations as macroinitiators. It is observed that half of the initiator functional groups are incorporated in polymerization process. The polymerization degree of polyoxazoline arms is about 25. Strong arm folding results in small molecule dimensions in both aqueous and organic solutions. Thermosensitive properties are studied for second generation‐based star solution with the concentration of 0.00095 g cm−3. Model linear poly(2‐isopropyl‐2‐oxazolines) are investigated for comparison. Carbosilane dendrimer core interaction leads to the formation of different types of aggregates at low temperatures. The temperatures of the beginning (T 1 = 42–43 °C) and finishing (T 2 = 50 °C) of phase separation are determined. It is shown that macromolecule compactization and aggregation take place even far from the phase transition interval and alternately prevail on heating.
Novel vanadium‐oxide‐based catalysts supported on alumina, zirconia, or titania‐modified silica, which are able to synthesize ultrahigh molecular weight polyethylene (UHMWPE), are successfully developed. Compared with the unmodified silica supported catalyst, the activities of the modified catalysts are substantially enhanced. By changing the polymerization temperature (T p) from 90 to 60 °C, the molecular weight of the produced UHMWPE can be easily regulated from 2 × 106 to more than 6 × 106 g mol−1. It is the first time that chloride‐free nonsingle site catalysts have been developed to synthesize UHMWPE within such a broad range of T p. Catalyst characterization by NH3‐temperature‐programmed desorption and pyridine‐Fourier transform infrared spectroscopy reveals that the modified catalysts have increased acidity derived from both Lewis and Brønsted acid sites. The X‐ray photoelectron spectroscopy characterization indicates that the vanadium on the modified catalysts is more electron deficient. Thus, the acidity of the catalysts and the electronic state of the vanadium play a critical role in determining the activity of the vanadium active sites for ethylene polymerization.
In this paper, the preparation of nitrogen‐doped carbon fibers and thin films from mixtures of polyacrylonitrile (PAN) and a poly(ionic liquid) (PIL) by electrospinning and dip‐coating is presented, respectively, followed by carbonization at distinct temperatures. The poor processability of the PIL into sub‐micrometer fibers by electrospinning—originating from its high charge density and meanwhile low glass transition temperature—is successfully circumvented by using blends of PAN and PIL. The electrospun fiber mats exhibit a high surface‐to‐volume‐ratio with an intrinsically macroporous through‐pore structure and a uniform fiber diameter after carbonization. Physicochemical characterization of the N‐doped carbons by means of scanning electron microscopy, algorithmic X‐Ray diffraction analysis, nitrogen physisorption, thermogravimetry, elemental analysis, energy‐dispersive X‐ray, and X‐ray photoelectron spectroscopy gives insight into their physical and electrical structures. Impedance measurements on carbonized PIL/PAN‐blends reveal high electrical conductivities up to 320 S cm?1, which are attributed to the incorporation of predominantly quaternary‐graphitic nitrogen atoms into the carbon network during carbonization. The results indicate that the electrical conductance of the N‐doped carbons strongly depends on the chemical environment of the inserted nitrogen atoms, the microstructural evolution of π‐conjugated carbon network—which in turn correlate with the carbonization temperature—and the chemical composition.
The controlled radical polymerization of 2‐vinylpyridine is reported using commercial blue light‐emitting diodes as visible light source in the presence of S‐1‐dodecyl‐S′‐(α,α′‐dimethyl‐α″‐aceticacid) trithiocarbonate without exogenous initiators or photocatalysts. With this system, poly(2‐vinylpyridine) with well‐regulated molecular weight and narrow dispersity (?) (? = 1.13) and a conversion efficiency of 84.9% is obtained after 9 h irradiation. The polymerization can be instantly switch “on” or “off” in response to visible light while maintaining a linear increase in molecular weight with conversion and first order kinetics. These results demonstrate the simplicity and efficiency of the photocatalysts‐free, visible light mediated reversible addition fragmentation chain transfer polymerization as a platform to achieve well‐defined poly(2‐vinylpyridine) under mild conditions.
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