A great extent of past work has focused on the development of stimuli‐responsive hydrogels that can primarily achieve a two‐state transition, such as sol‐gel translation. In the current work, a reversible hydrogel with three‐state transition is designed. The three transformations between original, oxidized, and reduced states are achieved via controlling the external stimuli conditions. Hydrogels in their original state possess a weak self‐healing property and negligible fluidity. The oxidized state hydrogel can keep molding, however, losing the self‐healing property. In contrast, the reduced state hydrogels exhibit strong self‐healing property. Moreover, the hydrogel becomes injectable subsequent to dithiothreitol addition. Thereafter, under UV‐light irradiation or NaClO immersion, the hydrogels can be remolded to any desired shapes. These properties provide novel designing strategies and potential applications for smart and reusable materials.
A new polymeric material utilizing a highly efficient as well as reversible thiol‐ene click reaction is presented. For this purpose, a trithiol is reacted with a bisbenzylcyanoacetamide derivative resulting in the formation of a dynamic polymer network. The self‐healing ability of this novel material is tested by scratch healing experiments. Healing is found to take place from 60 °C onward. The underlying healing mechanism is studied in detail using temperature‐dependent Raman spectroscopy confirming the reversible opening of the thiol‐ene adducts. Additionally, the thermal and mechanical properties are investigated by differential scanning calorimetry, thermogravimetric analysis, and rheological measurements proving the network formation as well as its reversibility during the thermal treatment.
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.
Amphiphilic polymers are synthesized from various biobased compounds involving telomerization of glycerin‐derived acrylate monomers with mercaptan‐modified fatty acids. The effects of the chemical structure of the saturated or unsaturated hydrophobic block are investigated. Dynamic and static light scattering measurements, transmission electronic microscopy, and atomic force microscopy observations show that these copolymers are capable of self‐assembling into nanosized spherical particles in aqueous solution, made from compound micelles. The critical micellar concentration of these polymers is in the range of 10–60 mg L?1 determined by fluorescence. These biobased polymers could have applications in various industrial fields, such as cosmetics and agrochemicals.
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.
A new block‐co‐polymer based on poly(arylene ether sulfone) and nitrile‐functionalized poly(phenylene oxide) is prepared via polycondensation. Upon swelling with Li triflate dispersed in succinonitrile, a polymer electrolyte suitable for application in secondary Li ion batteries is obtained, which at temperatures above 313 K exhibits conductivities of 10?4–10?3 S cm?1. The presence of distinct coordination modes of the Li ions (not discernible from inspection of 7Li chemical shifts) is revealed based on a dynamic contrast identified from a distribution of transverse relaxation times. Three relaxation components reflecting polymer‐bound, partially and fully solvated Li ion species are identified on the basis of Carr–Purcell–Meiboom–Gill NMR data after inverse Laplace transformation and multiexponential relaxation analysis toolkit analysis thus highlighting the versatility of the applied methods.
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.
Cyclodextrin (CD)‐based host–guest interactions are one of the important supramolecular interactions and have been playing significant role in the design of self‐healing materials due to high selectivity and dynamic equilibrium. However, a deeper understanding of the self‐healing mechanism is still rare, although self‐healing materials based on CD–guest interactions have many advantages. This study provides a first step for the fundamental understanding of the influence factors on self‐healing behavior of materials containing CD–guest complexes. It is found that the healing motifs are CD–guest interactions. Sufficient polymer chains mobility, a small amount of water, and high inclusion constant (K ) of host–guest interactions are also essential to the self‐healing process. The threshold of K value is around 102 M−1.
Histidine–zinc interactions are believed to play a key role in the self‐healing behavior of mussel byssal threads due to their reversible character. Taking this as inspiration, the authors synthesize here histidine‐rich copolymers, as well as model histidine compounds and characterize them using isothermal titration calorimetry (ITC). With this approach, the influence of two different zinc(II) salts and the role in the complex formation of the amine function of the imidazole ring are investigated in detail. The extracted metal–ligand ratios are utilized to design novel self‐healing metallopolymers. For this purpose, n‐lauryl methacrylate is copolymerized with the histidine monomer via reversible addition‐fragmentation chain transfer polymerization. The copolymers are crosslinked using different zinc salts, and the resulting coatings are characterized with Raman spectroscopy to investigate the metal coordination behavior and with scratch healing tests to investigate the self‐healing capacity. Finally, the self‐healing behavior of the different materials is correlated with the metal–ligand binding affinity measured by ITC.
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.
A fluorine‐containing difunctional benzoxazine is synthesized by hydrosilylation of a monofunctional benzoxazine based on o‐allylphenol and p‐fluoroaniline. Besides the intramolecular and intermolecular hydrogen bonding associated with the nitrogen and oxygen atoms in the oxazine ring, specific self‐complementary intermolecular Ar F···HO hydrogen bonding is formed in the polymerization of the benzoxazine, which leads to the resultant polybenzoxazine possessing a broad glass transition temperature range and showing two not well‐separated transitions. Based on the two glass transition temperatures, the polybenzoxazine exhibits triple‐shape‐memory behaviors by manipulating temperature and strain in the shape fixing process under tensile and bending modes. The dynamic mechanical and shape‐memory properties of the polybenzoxazine are influenced by the combined effect of the cross‐linking density and the Ar F···HO hydrogen bonding.
Here, the synthesis, characterization, and photovoltaic properties of four new donor–acceptor copolymers are reported. These copolymers are based on 4,4‐difluoro‐cyclopenta[2,1‐b:3,4‐b′] dithiophene as an acceptor unit and various donor moieties: 4,4‐dialkyl derivatives of 4H‐cyclopenta[2,1‐b:3,4‐b′]dithiophene and its silicon analog, dithieno[3,2‐b:2′,3′‐d]‐silol. These copolymers have an almost identical bandgap of 1.7 eV and have a HOMO energy level that varies from ?5.34 to ?5.73 eV. DSC and X‐ray diffraction (XRD) investigations reveal that linear octyl substituents promote the formation of ordered layered structures, while branched 2‐ethylhexyl substituents lead to amorphous materials. Polymer solar cells based on these copolymers as donor and PC61BM as acceptor components yield a power conversion efficiency of 2.4%.
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.
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.
A general route for the controlled functionalization of polyferrocenylsilane‐block‐polyvinylsiloxane copolymers, which should be transferable to other silicone‐based materials, is developed utilizing the photoinitiated thiol‐ene reaction. Poly(ferrocenyldimethylsilane)54‐block‐poly(methylvinylsiloxane)510 (PFDMS54‐b‐PMVS510) is synthesized via sequential living anionic polymerization and quantitatively functionalized with a range of thiols, with the aim of tuning the solubility of the resulting materials for self‐assembly studies or incorporating more complex functionality for subsequent applications. When functionalization is attempted using a deficit of thiol, the photoinitiator 2,2‐dimethoxy‐2‐phenylacetophenone, used to accelerate the radical reaction, is found to cause significant cross‐linking of the polysiloxane chain. Reproducible percentage thiol‐ene functionalization of the polysiloxane block can be achieved by the use of PFDMS53‐b‐PMVS58/PDMS444 (PDMS = polydimethylsiloxane), prepared by the copolymerization of cyclic siloxane monomers, [Me(CH?CH2)SiO]3 and [Me2SiO]3, to tune the vinyl group incorporation pre‐functionalization.
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.
Polyglycolide (PGA) is synthesized via ring‐opening polymerization (ROP) of diglycolide using the organocatalysts 1,8‐diazabicyclo[5.4.0]undec‐7‐ene (DBU), 1,5‐diazabicyclo[4.3.0]non‐5‐ene, or 1,5,7‐ triazabicyclo[4.4.0]dec‐5‐ene. ROP is carried out at low temperatures ranging from ?20 to 50 °C without adding any alcohol as initiator. All polymers are fully soluble in hexafluoroisopropanol. At ambient temperature number average molecular weights up to 27 000 g mol?1 are obtained. With DBU the highest molecular weights and conversions are accessible at ?20 °C. Melting temperature and glass transition temperature are independent of PGA molecular weight. Carrying out the reactions in the presence of polyethylene glycol serving as macroinitiator yields polymers with improved thermal stability and lowered melting temperatures.
Dendrigraft poly(l ‐lysine) (DGL) polyelectrolytes, obtained by iterative polycondensation of N‐trifluoroacetyl‐l ‐lysine‐N‐carboxyanhydride, constitute very promising candidates in many biomedical applications. In order to get a better understanding of their structure–property relationships in these applications, their absolute average molecular weights have to be accurately measured. Size‐exclusion chromatography coupled to a multi‐angle laser‐light‐scattering detector (SEC‐MALLS) is known to be the most appropriate analytical tool. These measurements require the determination of the refractive index increment, dn/dc, of these highly branched polycationic macromolecules in aqueous solution. This optical property has to be measured in the same aqueous conditions as SEC‐MALLS eluents. Consequently, data are determined and discussed as a function of different aqueous SEC‐MALLS eluents, as well as different counter‐ions of the many ammonium groups of DGL (generation 3, DGL‐3, used as a model herein). The resulting number‐average molecular weights, , are found to be very dissimilar when the measured dn/dc values are directly considered. In contrast, very close values are obtained (average = 18 700, standard error of 1110 g mol?1) with a low coefficient of variation for such data (ca. 6% for six analyses), when the dn/dc are corrected by the exact lysine amount (measured by the total Kjeldahl nitrogen method).
Inspired by the well‐known amphiphilic block copolymer platform known as Pluronics or poloxamers, a small library of ABA and BAB triblock copolymers comprising hydrophilic 2‐methyl‐2‐oxazoline (A) and thermoresponsive 2‐n‐propyl‐2‐oxazoline (B) is synthesized. These novel copolymers exhibit temperature‐induced self‐assembly in aqueous solution. The formation and size of aggregates depend on the polymer structure, temperature, and concentration. The BAB copolymers tend to agglomerate in water, with the cloud point temperature depending on the length of poly(2‐n‐propyl‐2‐oxazoline) chain. On the other hand, ABA copolymers form smaller aggregates with hydrodynamic radius from 25 to 150 nm. The dependence of viscosity and viscoelastic properties on the temperature is also studied. While several Pluronic block copolymers are known to form thermoreversible hydrogels in the concentration range 20–30 wt%, thermogelation is not observed for any of the investigated poly(2‐oxazoline)s at the investigated temperature range from 10 to 50 °C.
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.
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