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.
The grafting of well‐defined polystyrene to graphene oxide (GO) using nitroxide‐mediated polymerization (NMP) is demonstrated by a two‐step reaction. In the first step, GO is functionalized with glycidyl methacrylate (GMA) to yield GO‐GMA. Polystyrene (PS), previously synthesized via SG1‐based NMP, is then grafted to GO‐GMA by a simple reaction between the SG1 end group and the GMA double bond to yield GO‐GMA‐g‐PS. 1H, heteronuclear single‐quantum correlation (HSQC), nuclear magnetic resonance (NMR), X‐ray photoelectron spectroscopy (XPS), Raman, Fourier transform infrared spectroscopy (FTIR), gel permeation chromatography (GPC), and thermogravimetric analysis (TGA) are consistent with attachment of the GMA group to the GO surface and with polystyrene being grafted to the GO surface to form the GO‐GMA‐g‐PS nanocomposite (NC). GPC analysis shows a number‐average molecular weight of 3330 g mol?1 for the PS with molecular weight dispersity (Ð) of 1.13. Up to 28 mass% of PS has been introduced into the GO NC. The present “grafting‐to” methodology holds promise for the facile and clean synthesis of graphene oxide polymer NCs.
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.
Improving fragility is important for the practical application of gels. In this study, the mechanical strength of gels composed of poly(N‐vinyl acetamide) (PNVA) and glycols is investigated focusing on the retained solvent in the gels. The solvent for the PNVA hydrogel is adequately replaced by various glycols. Using poly(ethylene glycol) (PEG) with molecular weights of 400 or 600 g mol?1, the compressive strength of the gel is dramatically enhanced to approximately 10 MPa while that of hydrogel is 0.2 MPa. This is because of solvent viscosity, interaction between PEG and PNVA, and the favorable aggregation of the PNVA. From FTIR spectroscopy investigations, the absorption bands of the carbonyl and amino groups of PNVA gels with PEG400 are shifted as compared with PNVA gels in water, suggesting hydrogen bond formation.
Hydrophilic naphthalene diimide based acceptor polymers are prepared by the incorporation of triethylene glycol or poly(ethylene glycol) side chains in the monomers and subsequent nitroxide‐mediated polymerization (NMP). The kinetic investigation of the polymerization reveals a controlled chain growth as well as a narrow molar mass distribution. Due to the utilization of a functional NMP initiator, a single Ru(II) photosensitizer unit is readily attached at the polymers chain terminus by a modular approach to construct water soluble photoredox‐active acceptor–photosensitizer dyads. The analysis of the optical properties by steady‐state absorption and emission spectroscopy reveals preserved optical absorption properties of the individual building blocks, and, more importantly, an efficient quenching of the Ru(II) emission assigned to intramolecular charge transfer from the complex to the acceptor polymer. The results demonstrate the versatility of side chain modifications to prepare water‐processible photoredox‐active architectures under preservation of the modular character known from hydrophobic systems.
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.
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.
Poly(N‐isopropylacrylamide‐co‐N‐isopropylmethacrylamide) (poly(NIPAAm‐co‐NIPMAAm)) is synthesized as an attractive thermo‐responsive copolymer by an original procedure. Due to the similar structure of the two co‐monomers, the poly(NIPAAm‐co‐NIPMAAm) copolymer displays a very sharp phase transition, under physiological conditions (phosphate buffer solution at pH = 7.4). The copolymer, showing the 51/49 co‐monomer NIPAAm/NIPMAAm molar ratio, displays a lower critical solution temperature (LCST) close to that of the human body temperature (36.8 °C). The poly(NIPAAm‐co‐NIPMAAm) microgels obtained at the 51:49 co‐monomer ratio displays a volume phase transition temperature (VPTT) slightly smaller than LCST. The deswelling rate of the microgels is very high (k = 0.019 s?1), the shrinkage occurring almost instantaneously, whereas the swelling rate is slightly lower (k = 0.0077 s?1). The microgels are loaded with the model drug dexamethasone and the drug release is investigated at different temperatures, below and above the VPTT. Under thermal cycling operation between 32 and 38 °C, the pulsatile release of dexamethasone is observed.
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.
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.
Novel nitrogen‐doped graphene nanoribbons (GNR‐Ns) are synthesized by the coupling reaction between a pyrazine (or benzene) derivative and naphthalene followed by cyclodehydrogenation. The amount of nitrogen doping in the GNR‐Ns is controlled by changing the monomer feed ratio of pyrazine to benzene for polymerization. The electron mobility of the GNR‐Ns increases while the hole mobility decreases, as the amount of nitrogen doping in the GNR increases, indicating that the charge‐transport behavior of GNRs is changed from ambipolar to an n‐type semiconductor. The threshold voltage of the GNR‐Ns also shifts from 20 to ?6 V as the amount of nitrogen doping increases.
Porous organic frameworks (POFs) have been synthesized by Yamamoto‐type Ullmann cross‐coupling reaction using tetrakis (4‐bromophenyl) methane (TBPM) and poly‐4‐bromostyrene (PBS) as monomers. Among these POFs, JUC‐Z13 synthesized solely from PBS is found to be microporous (1.27 nm) and SBET = 372 m2 g?1, and copolymerization with TBPM results in POFs with apparent surface areas up to 3137 m2 g?1 and pore size up to 1.41 nm. Interestingly, JUC‐Z14 and JUC‐Z15 show hierarchical porosity. Low pressure gas uptake experiments on activated JUC‐Z13‐JUC‐Z19 show enhanced gas storage capacities and isosteric heats of sorption (Qst) among porous materials.
Cationic polyelectrolytes find potential applications in electronic device fabrication, biosensing as well as in biological fields. Herein, a series of cationic main‐chain polyelectrolytes with pyridinium‐based p ‐phenylenevinylene units that are connected via alkylene spacers of varying lengths are synthesized by a base‐catalyzed aldol‐type coupling reaction. Their mean average molecular weights range from 15 000 to 32 000 g mol‐1, corresponding to about 16–33 repeat units. Due to the presence of alkyl side‐chains and alkylene spacers as well as cationic hard‐charges the polymers are endowed with amphiphilic character and hence, aggregation of these polyelectrolytes at high concentration leads to thermoreversible physical gel formation in dimethyl sulfoxide accompanied by interchain interactions. Morphological analysis shows spherical aggregates in case of C16‐Poly‐S12 in dimethyl sulfoxide. Dependence of gelation behavior on the length of alkyl side‐chains and alkylene spacers of the polyelectrolytes are addressed.
Shape memory polymers (SMPs) are an important class of smart materials. Usually, these polymers can be switched between two shapes. Recently, the possibility of switching more than two shapes was introduced for SMPs with relatively low strain storage capability. In this work, a lightly cross‐linked polyethylene blend comprising 80 wt% EOC, 15 wt% LDPE, and 5 wt% HDPE is prepared in order to obtain a tunable multiple‐shape memory polymer with high strain storage capacity. It is found that depending on the programming procedure, this SMP obtains a dual‐, triple‐, or quadruple‐shape memory effect, with well‐defined intermediate temporary shapes (retraction < 0.5% K?1) over a significantly broad temperature range (up to 30 K), large storable strains (up to 1700%), and nearly full recovery of all shapes (>98.9%).
A two‐step synthesis of high‐molecular‐weight and bio‐based poly(butylene succinate) (PBS) from succinic anhydride and butane‐1,4‐diol is established, in which the first step is a 12 h atmospheric polycondensation at 95 °C in the presence of succinic acid. The subsequent polymerization, catalyzed by Novozym 435 suspended in toluene, yields PBS with a molecular weight above 73 000 g mol?1. The recovered lipase catalyst appears to give similar performance after six cycles. The versatility of this atmospheric synthetic route to PBS copolymers is validated through the syntheses of poly(butylene succinate‐co‐butylene malate) (PBSM), poly(butylene succinate‐co‐butylene fumarate) (PBSF), and poly(butylene succinate‐co‐butylene terephthalate) (PBST), in which succinic acid is replaced by corresponding di‐acids as monomers.
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.
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.
A set of copolyesters (PHTxGluxy) with compositions ranging between 90/10 and 50/50 in addition to the parent homopolyesters poly(hexamethylene terephthalate) (PHT) and PHGlux, are prepared by the melt polycondensation of 1,6‐hexanediol (HD) with mixtures of dimethyl terephthalate (DMT) and dimethyl 2,4:3,5‐di‐O‐methylene‐d ‐glucarate (Glux). The copolyesters have in the 35 000–45 000 g mol?1 range, their microstructure is random, and they start to decompose at a temperature well above 300 °C. Crystallinity of PHT is repressed by copolymerization so that copolyesters containing more than 20% of sugar‐based units are essentially amorphous. On the contrary, PHTxGluxy displays a Tg that increases monotonically with composition from 16 °C in PHT up to 73 °C in PHGlux. Compared with PHT, the copolyesters show an accentuated susceptibility to hydrolysis and are sensitive to the action of lipases upon incubation under physiological conditions. The degradability of PHTxGluxy increases with the content in Glux units.
A family of novel (X‐TATAT)n‐type conjugated polymers based on the carbazole (X), thiophene (T), and benzoxadiazole (A) moieties is designed and explored as electron‐donor materials for organic bulk heterojunction solar cells. Incorporation of the branched side chains of different size and shape affects significantly the optoelectronic properties of the materials, particularly frontier energy levels of polymers translated to the open circuit voltages of the photovoltaic cells. The revealed unprecedented correlation between the parameters of the solar cells (V OC, fill factor (FF), J SC) and bulkiness of the alkyl side chains provides useful guidelines for rational design of novel materials for organic photovoltaics.
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 .
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