Hydrogels that can form spontaneously via covalent bond formation upon injection in vivo have recently attracted significant attention for their potential to address a variety of biomedical challenges. This review discusses the design rules for the effective engineering of such materials, and the major chemistries used to form injectable, in situ gelling hydrogels in the context of these design guidelines are outlined (with examples). Directions for future research in the area are addressed, noting the outstanding challenges associated with the use of this class of hydrogels in vivo.
A general method for very fast and efficient optical healing of crystalline polymers is reported. By loading a very small amount of gold nanoparticles (AuNPs) in either poly(ethylene oxide) (Tm ≈ 63 °C) or low‐density polyethylene (Tm ≈ 103 °C), the heat released upon surface plasmon resonance (SPR) absorption of 532 nm light by AuNPs can melt crystallites in the interfacial region of two polymer pieces brought into contact; and the subsequent recrystallization of polymer chains on cooling merges the two pieces into one. The fracture strength of such repaired sample can reach the level of the undamaged polymer after 10 s laser exposure. Moreover, in addition to an ability of long‐distance remote and spatially selective healing, the optical method also works for polymer samples immersed in water.
Supramolecular polyfluorenol enable assembly into conjugated polymer nanoparticles (CPNs). Poly{9‐[4‐(octyloxy)phenyl]fluoren‐9‐ol‐2,7‐diyl} (PPFOH)‐based supramolecular nanoparticles are prepared via reprecipitation. PPFOH nanoparticles with diameters ranging from 40 to 200 nm are obtained by adding different amounts of water into DMF solution. Size‐dependent luminescence is observed in PPFOH‐based hydrogen‐bonded nanoparticles that is different from that of poly(9,9‐dioctylfluorenes). Finally, white light‐emitting devices using CPNs with a size of 80 nm exhibit white emission with the CIE coordinates (0.31, 0.34). Amphiphilic conjugated polymer nanoparticles are potential organic nano‐inks for the fabrication of organic devices in printed electronics.
Various bicolored fluorescent micropatterns are fabricated on a single polymer film by concurrent photobleaching and a photobase generation process. A polymer, bearing anthracene and oxime–urethane groups, is dyed with rhodamine B isothiocyanate after irradiation with 310‐nm UV light. The photochemical reaction of the polymer is monitored by UV, IR absorption, and fluorescence emission spectroscopy. Differently colored fluorescent micropatterns are obtained by selectively exciting each dye moiety. Various bicolored fluorescent micropatterns are observed through varying the excitation wavelength and observation wavelength ranges using a confocal microscope. This bicolored fluorescence patterning method will be useful to apply in photonic/electronic devices.
Two soluble poly(phenyltriazolylcarboxylate)s (PPTCs) with high molecular weights (M w up to 26 800) are synthesized by the metal‐free 1,3‐dipolar polycycloadditions of 4,4′‐isopropylidenediphenyl diphenylpropiolate ( 1 ) and tetraphenylethene‐containing diazides ( 2 ) in dimethylformamide at 150 °C for 12 h in high yields (up to 93%). The resultant polymers are soluble in common organic solvents and are thermally stable with 5% weight loss temperatures higher than 375 °C. The PPTCs are nonemissive in solutions, but become highly luminescent upon aggregation, showing a phenomenon of aggregation‐induced emission. Their aggregates can be used as fluorescent chemosensors for high‐sensitivity detection of explosives.
The different mechanisms contributing to adhesion between two polymer surfaces are summarized and described in individual examples, which represent either seminal works in the field of adhesion science or novel approaches to achieve polymer–polymer adhesion. A further objective of this article is the development of new methodologies to achieve strong adhesion between low surface energy polymers.
Using the third‐generation Grubbs catalyst, the living ring‐opening metathesis polymerization of ferrocene/cobalticenium copolymers is conducted with theoretical numbers of 25 monomer units for each block, and their redox and electrochemical properties allow using the Bard–Anson electrochemical method to determine the number of metallocenyl units in each block.
A novel strategy for the incorporation of carbon dioxide into polymers is introduced. For this purpose, the Ugi five‐component condensation (Ugi‐5CC) of an alcohol, CO2, an amine, an aldehyde, and an isocyanide is used to obtain step‐growth monomers. Polymerization via thiol‐ene reaction or polycondensation with diphenyl carbonate gives diversely substituted polyurethanes or alternating polyurethane‐polycarbonates, respectively. Furthermore, the application of 1,12‐diaminododecane and 1,6‐diisocyanohexane as bifunctional components in the Ugi‐5CC directly results in the corresponding polyamide bearing methyl carbamate side chains ( = 19 850 g mol−1). The latter polymer is further converted into the corresponding polyhydantoin in a highly straightforward fashion.
Hierarchical self‐assembly of transient composite hydrogels is demonstrated through a two‐step, orthogonal strategy using nanoparticle tectons interconnected through metal–ligand coordination complexes. The resulting materials are highly tunable with moduli and viscosities spanning many orders of magnitude, and show promising self‐healing properties, while maintaining complete optical transparency.
A novel one‐component type II polymeric photoinitiator, poly(vinyl alcohol)–thioxanthone (PVA–TX), is synthesized by a simple acetalization process and characterized. PVA–TX enables photopolymerization of methyl methacrylate and acrylamide in both organic and aqueous media. Photopolymerization proceeds even in the absence of a co‐initiator since PVA–TX possesses both chromophoric and hydrogen donating sites in the structure.
This report demonstrates the electroless deposition of Ni onto micropatterns of poly (acrylic acid) (PAA) photografted to phthalimide‐terminated self‐assembled monolayers (SAMs). PAA is spin‐coated onto phthalimide SAMs and covered with a photomask. UV irradiation selectively binds PAA to exposed regions of the surface, allowing PAA on unexposed regions to be rinsed off. A Pd catalyst is then selectively adsorbed to regions of the surface where PAA is bound. The adsorbed catalyst selectively initiates Ni plating upon immersion of the substrate into a Ni(SO4) bath.
Novel supramolecular phosphorescent polymers (SPPs) are synthesized as a new class of solution‐processable electroluminescent emitters. The formation of these SPPs takes advantage of the efficient non‐bonding assembly between bis(dibenzo‐24‐crown‐8)‐functionalized iridium complex monomer and bis(dibenzylammonium)‐tethered co‐monomer, which is monitored by 1H NMR spectroscopy and viscosity measurements. These SPPs show good film morphology and an intrinsic glass transition with a Tg of 94–116 °C. Noticeably, they are highly photoluminescent in solid state with quantum efficiency up to ca. 78%. The photophysical and electroluminescent properties are strongly dependent on the molecular structures of the iridium complex monomers.
1,5,7‐Triazabicyclo[4.4.0]dec‐5‐ene (TBD)‐catalyzed polycondensation reactions of fatty acid derived dimethyl dicarbamates and diols are introduced as a versatile, non‐isocyanate route to renewable polyurethanes. The key step for the synthesis of dimethyl carbamate monomers from plant‐oil‐derived dicarboxylic acids is based on a sustainable base‐catalyzed Lossen rearrangement. The formed polyurethanes with molecular weights up to 25 kDa are characterized by SEC, DSC, and NMR analysis.
A pH‐responsive core cross‐linked star (CCS) polymer containing poly(N,N‐dimethylaminoethyl methacrylate) (PDMAEMA) arms was used as an interfacial stabilizer for emulsions containing toluene (80 v%) and water (20 v%). In the pH range of 12.1‐9.3, ordinary water‐in‐oil emulsions were formed. Intermediate multiple emulsions of oil‐in‐water‐in‐oil and water‐in‐oil‐in‐water were formed at pH 8.6 and 7.5, respectively. Further lowering the pH resulted in the formation of gelled high internal phase emulsions of oil‐in‐water type in the pH range of 6.4‐0.6. The emulsion behavior was correlated with interfacial tension, conductivity and configuration of the CCS polymer at different pH.
Dispersions of short electrospun fibers are utilized for the preparation of nanofiber nonwovens with different weight area on filter substrates. The aerosol filtration efficiencies of suspension‐borne nanofiber nonwovens are compared to nanofiber nonwovens prepared directly by electrospinning with similar weight area. The filtration efficiencies are found to be similar for both types of nonwovens. With this, a large potential opens for processing, design, and application of new nanofiber nonwovens obtained by wet‐laying of short electrospun nanofiber suspensions.
Hybrid Pt(platinum)/carbon nanopatterns with an extremely low loading level of Pt catalysts derived from block copolymer templates as an alternative type of counter electrodes (CEs) in dye‐sensitized solar cells (DSSCs) are proposed. DSSCs employing hybrid Pt/carbon with tailored configuration as CEs exhibit higher short‐circuit current and conversion efficiencies as well as stability with a lapse of time compared with conventional cells on the basis of sputtered Pt thin films, evidencing that the new class of hybrid nanostructures possess high potential for cost‐effective electrodes in energy conversion devices.
Molecular bottle‐brush functionalized single‐walled carbon nanotubes (SWCNTs) with superior dispersibility in water are prepared by a one‐pot synthetic methodology. Elongating the main‐chain and side‐chain length of molecular bottle‐brushes can further increase SWCNT dispersibility. They show significant enhancement of SWCNT dispersibility up to four times higher than those of linear molecular functionalized SWCNTs.
Botryoid‐shaped reactive terpolymer nanoparticles, whose aldehyde‐functional living domains are miniaturized into small‐sized discrete “grapes” and attached onto the outwardly‐branched scaffolds of fluorinated segments, are reported. These nanostructures can be fabricated by spontaneous structural reorganization of core–shell terpolymer micelles simply by manipulating drying conditions. The miniaturized discrete living domains are stabilized by outwardly‐branched scaffolds and exhibit excellent accessibility to solution media, thus can effectively respond to solution media, which is desired in sensor‐related applications.
Via electron paramagnetic resonance (EPR) spectroscopy, the type of radicals occurring during acrylamide (AAm) homopolymerization in aqueous solution is investigated between −5 and +100 °C. The radicals are produced photochemically under stationary conditions. Midchain AAm radicals (MCRs) are clearly identified by EPR which demonstrates that secondary propagating AAm radicals (SPRs) undergo backbiting reactions. Above 50 °C, the fraction of MCRs even exceeds the one of SPRs. The extent of backbiting is however well below the one in butyl acrylate polymerization at identical temperature.
In this article, well‐defined cyclic amphiphilic random copolymers bearing azobenzene side chains and pendent carboxyl moieties, cyclic‐P(BHMEm‐co‐AAn)s, are synthesized by combining atom transfer radical polymerization (ATRP) with Cu(I)‐catalyzed azide/alkyne cycloaddition (CuAAC) “click” reaction and selective hydrolysis of tert‐butyl ester. Successful synthesis of the cyclic‐P(BHMEm‐co‐AAn)s is fully characterized and verified via conventional gel permeation chromatography, triple detection gel permeation chromatography, nuclear magnetic resonance, Fourier transform infrared, and matrix‐assisted laser desorption ionization–time‐of‐flight mass spectrometry. The cyclic topology induces profound effects on the glass transition temperatures, self‐assembly behavior, and photoresponsive performance of the copolymers compared with their linear counterparts.
