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.
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 series of acrylate‐based shape‐memory materials are synthesized from bisphenol A diacrylate monomers as crosslinking agents. Networks are synthesized by keeping constant the content of bisphenol A‐based crosslinking agent and systematically varying the content ratio of different monofunctional chain builder monomers. The implications of the structure of bisphenol A‐based monomers and the chemical structure and content of monofunctional monomers on thermomechanical properties are discussed. Thermomechanical properties are analyzed using dynamic mechanical analyses and mechanical properties are studied at room temperature and at the onset of the glass transition temperature. Shape‐memory performances under isothermal and transient temperature conditions are also carried out. Tensile tests show excellent values of stress at break up to 45 and 15 MPa at room and high temperature, respectively. The measurements show excellent shape recovery and shape fixity ratios, ≈95% and 97%, respectively. These materials also show very high recovery velocities under transient temperature conditions, up to 24% min?1, and very short recovery times, up to 1.5 s, under isothermal conditions in a water bath. The results confirm that networks synthesized from bisphenol A crosslinkers are promising shape‐memory materials.
An atomistic molecular dynamics simulation approach is applied to model the influence of urethane linker units as well as the addition of water molecules on the simulated shape‐memory properties of poly[(rac‐lactide)‐co‐glycolide] (PLGA) and PLGA‐based copolyester urethanes comprising different urethane linkers. The shape‐memory performance of these amorphous packing models is explored in a simulated heating–deformation–cooling–heating procedure. Depending on the type of incorporated urethane linker, the mechanical properties of the dry copolyester urethanes are found to be significantly improved compared with PLGA, which can be attributed to the number of intermolecular hydrogen bonds between the urethane units. Good shape‐memory properties are observed for all the modeled systems. In the dry state, the shape fixation is found to be improved by implementation of urethane units. After swelling of the copolymer models with water, which results in a reduction of their glass transition temperatures, the relaxation kinetics during unloading and shape recovery are found to be substantially accelerated.
Multifunctional and multiresponsive hydrogels demonstrate excellent promise for multifarious applications but often suffer from high synthesis complexity and poor resource availability. Herein, based on the boronate–catechol interactions between a disulfide‐containing, boronic acid‐based crosslinker, and a catechol‐functionalized poly(N‐isopropyl acrylamide), a multitasking hydrogel with double dynamic network is developed. By integrating the inherent heat‐responsive property of poly(N‐isopropyl acrylamide) and bioadhesion of catechol moieties with the reversibility and dynamic features of boronate ester and disulfide bonds, the final hydrogel is endowed with not only temperature, pH, glucose, and redox quadruple‐stimuli sensitiveness, but also autonomic self‐healing property and biomimetic adhesion ability. Moreover, the rheological and adhesive properties can be readily tuned by adjusting the amount of crosslinker or the catechol in polymer precursor. Considering the readily prepared starting materials, easy preparation, high flexibility in tuning hydrogel properties, the procedure provided here opens up a promising avenue to develop multifunctional hydrogels for multifarious applications.
Molecular‐recognition‐responsive characteristics of a novel poly(N‐isopropylacrylamide‐co‐benzo‐12‐crown‐4‐acrylamide) (PNB12C4) hydrogel have been investigated. In the prepared PNB12C4 hydrogel, benzo‐12‐crown‐4 (B12C4) groups act as guest molecules and γ‐cyclodextrin (γ‐CD)‐receptors, and poly(N‐isopropylacrylamide) (PNIPAM) networks act as phase‐transition actuators. The formation of stable γ‐CD/B12C4 complexes enhances the hydrophilicity of the PNB12C4 hydrogel networks, and induces positive shift of the volume phase transition temperature (VPTT) of PNB12C4 hydrogel. Moreover, the PNB12C4 hydrogel also shows thermoresponsive adsorption property selectively towards γ‐CD. The γ‐CD‐recognition sensitivity of PNB12C4 hydrogel can be dramatically improved by increasing γ‐CD concentration in solution or B12C4 content in PNB12C4 copolymer networks. The results in this study provide valuable information for developing crown ether‐based smart materials in various applications.
The swelling, viscoelastic, and mechanical behavior of phase‐segregated poly(ester urethane) (PEU) block copolymers, composed of 4,4′‐methylenediphenyl diisocyanate, 1,4‐butanediol as a chain extender, and crystallizable poly(1,4‐butylene adipate) (PBA) with molecular weights between 1330 and 4120 g mol?1, are investigated. Wide‐angle X‐ray scattering (WAXS) is employed to study the overall PEU crystallinity, which increases from 8.6 to 13.6% at higher PBA contents. The existence of two crystalline, polymorphic PBA phases, a thermodynamically stable α phase and a metastable β phase, is confirmed by further WAXS measurements. Calorimetric and thermomechanical investigations give evidence for controllable PBA polymorphic behavior. The crystallization conditions, like the cooling rate, affect the emerging polymorphic mixture, whereas the storage conditions either promote or inhibit the polymorphic (β to α) transition. The introduced concepts represent a new approach for gaining control over programmable thermoresponsiveness, which may be transferable to other shape‐memory polymers with polymorphic switching segments.
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 .
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 this study, the bifunctional hydroxyketone based photoinitiator (PI) 1,1′‐{[(2,3‐dihydroxybutane‐1,4‐diyl)bis(oxy)]bis(4,1‐phenylene)}bis(2‐hydroxy‐2‐methylpropan‐1‐one) (Di‐PI) is synthesized with the aim to facilitate a highly photoactive water‐soluble PI which offers high migration stability. Di‐PI provides a five times higher water‐solubility than the state of the art water soluble PI 2‐hydroxy‐1‐[3‐(hydroxymethyl)phenyl]‐2‐methyl‐1‐propanone (I2959). Photo differential scanning calorimetry (Photo‐DSC) measurements reveal that the curing speed and conversion of N‐acroylmorpholine (NAM) in aqueous solution containing 0.5 mol% of Di‐PI are only slightly lower than formulations containing the reference PI I2959 in a concentration of 1 mol%. Most importantly, Di‐PI offers almost identical activity in dipropylene glycol diacrylate (DPDA) as I2959, although its migration from cured DPDA is significantly reduced by a factor of 7.6 compared to I2959.
Three medium‐bandgap polymers based on a 4,5‐ethylene‐2,7‐dithienyl carbazole as the electron‐donating unit and different 5,6‐dialkoxy‐2,1,3‐benzothiadiazoles as the electron‐accepting units, are synthesized as polymer donors for photovoltaic applications. The three copolymers possess highest occupied molecular oribital (HOMO) levels around ?5.47 eV and medium bandgaps of about 1.94 eV. The solar cells with polymer:[6,6]‐phenyl C71‐butyric acid methyl ester (PC71BM) = 1:4 as the active layer, show an especially high open‐circuit voltage (Voc) of 0.95 V and attain good power conversion efficiency up to 5.91%. The hole mobilities of the active layer films, measured by space‐charge‐limited current (SCLC), are up to 3.5 × 10?4 cm2 V?1 s?1. Given the favorable medium bandgaps, low‐lying HOMO levels, and good hole mobilities, these copolymers are promising candidates for the construction of a highly efficient front cell to harvest the shorter wavelength band of the solar radiation in a tandem solar cell with high Voc.
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.
In this study, the self‐assembly of ionic porphyrins and polyelectrolytes in dependence on the polyelectrolyte architecture and molecular mass is investigated systematically. The systems consist of tetravalent anionic meso‐tetrakis(4‐sulfonatophenyl)‐porphyrin (TPPS), which is combined with different positively charged macroions: poly(amidoamine) dendrimer of generation 4, linear polylysine of different molecular masses, poly(diallyldimethylammonium chloride), and a cylindrical poly‐l ‐lysine brush. Light scattering reveals defined supramolecular assemblies with hydrodynamic radii between R H = 30 nm and R H = 180 nm. Further, size and shape of TPPS–polyelectrolyte assemblies are substantially affected by the polyelectrolyte architecture but less by the molecular mass of the polyelectrolyte. ζ‐potential measurements detect an assembly charge corresponding to the excess component that is responsible for the aggregate being stable in solution.
In this study, the authors report a novel class of super tough nanocomposite hydrogels with physically dual‐crosslinking effects (DC hydrogels) through introducing strong ionic coordination interactions. Herein, graphene oxide (GO) nanosheets and iron (Fe3+) ions act as physical cross‐linkers. GO nanosheets trigger the formation of the first cross‐linking points through hydrogen bonding with poly(acrylamide‐co‐acrylic acid) (p(AAm‐co‐AAc)) chains, while the second cross‐linking points are formed by strong ionic coordination interactions between Fe3+ ions and ? COO? groups of p(AAm‐co‐AAc) chains. The optimal tough DC hydrogel displays superstretchability (≈20.8 times), remarkable tensile strength (≈3.7 MPa), high toughness (≈48.71 MJ m?3), good self‐recovery property (≈84.1% toughness recovery within 4 h without any external stimuli) and fatigue resistance. In summary, this study opens up a new avenue to design and fabricate highly tough hydrogels with outstanding comprehensive properties by the synergistic effects of nanocomposite and dual‐crosslinked hydrogels.
High temperature triggered shape memory polymers are currently attracting considerable attention due to their potential applications in the context of harsh environments. Herein, tunable dual‐ and triple‐shape memory binary mixture polyimides with high transition temperatures that may meet some of these requirements are presented. The binary mixtures are prepared by blending two poly (amic acid)s of rodlike poly(benzoxazole‐imide) (PIB) and flexible polyetherimide (PIO), followed by solvent evaporation and thermal imidization. The aggregation structures, thermal mechanical properties, and shape memory behaviors are systematically studied. It is found that dual‐shape memory cycles give excellent shape fixity and recovery of up to 98 and 97%. Moreover, binary mixtures with broad glass transition temperatures endow good triple‐shape memory effects and the shape memory at each step crucially depends on the content of the PIB due to the enhancement of physical crosslinks. Additionally, their thermally tough and mechanically strong properties would suggest wide potential applications of the mixtures.
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.
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.
Reduction‐responsive biodegradable polymeric micelles based on functional 2‐methylene‐1,3‐dioxepane (MDO) copolymers are developed and investigated for triggered doxorubicin (DOX) release. The MDO‐based copolymers P(MDO‐co‐PEGMA‐co‐PDSMA) are synthesized via the simple one‐step radical ring‐opening copolymerization of MDO, poly(ethylene glycol) methyl ether methacrylate (PEGMA), and pyridyldisulfide ethylmethacrylate (PDSMA). The copolymers can self‐assemble to form micelles in aqueous solution. DOX, a model anticancer drug, is loaded into the micelles with the drug loading content (DLC) of 11.3%. The micelles can be disassembled under a reductive environment (10 × 10?3m glutathione), which results in a triggered drug release behavior. The glutathione‐mediated intracellular drug release of DOX‐loaded micelles is investigated against A549 cells. Confocal laser scanning microscopy (CLSM) results demonstrated that DOX‐loaded micelles exhibits faster drug release in glutathione monoester (GSH‐OEt)‐pretreated A549 cells, compared with untreated and buthionine sulfoximine (BSO)‐pretreated A549 cells. Based on the facile synthetic strategy, the reduction‐sensitive biodegradable micelles with triggered intracellular drug release are promising for anticancer drug delivery.
The bio‐based diamine and epoxy monomer derived from isosorbide are synthesized. Especially, the diamine is obtained using microwave assistant thiol‐ene coupling reaction in the aqueous media and the influence of reaction parameters, such as initiator content and reaction time, are investigated. After curing the synthesized epoxy monomer together with the diamine, properties of the cured resins are studied by differential sscanning calorimetry, dynamic mechanical analysis, and thermogravimetric analyzer. Results demonstrate that the cured resin has good shape fixity, good shape recovery, and satisfied thermal stability despite the presence of heteroatoms. This bio‐based epoxy resin shows great potential to be used as a candidate for shape memory material. Considering the bio‐based feedstock and environmental friendly synthetic process, a “green + green” strategy to prepare thermosetting resins with advanced properties is provided in this paper.
Supramolecular hydrogels composed of poly(ethylene glycol) (PEG) containing polymer and α‐cyclodextrins (α‐CDs) show great potential in drug delivery. Herein, PEGylated magnetic nanoparticles (MNPs) and gold nanoparticles (AuNPs) of ≈10 nm are synthesized in the presence of poly(poly(ethylene glycol) methyl ether acrylate) (PPEGMA) grafted poly(acrylic acid) copolymers (PPEGMA‐co‐PAA, P1) and PPEGMA grafted poly(2‐(dimethylamino)ethyl methacrylate) copolymers (PPEGMA‐co‐PDMAEMA, P2), respectively. The produced PEGylated NPs are hybridized into supramolecular hydrogels by mixing them with α‐CDs through inclusion complexation between PEG branches and α‐CDs. As a result, supramolecular hydrogels hybridized with inorganic MNPs and AuNPs are prepared and characterized by rheological measurements, X‐ray diffraction, and scanning electron microscopy. Both MNP and AuNP hybrid hydrogels show reversible sol–gel transition, which is stimulated by changes in temperature and pH. The nanoparticles hybridized in the hydrogels can be released gradually in the process of hydrogel disruption. These hydrogels may have potential applications in biomaterials and drug delivery.
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