The preparation of multifunctional polymers and block copolymers by a straightforward one‐pot reaction process that combines enzymatic transacylation with light‐controlled polymerization is described. Functional methacrylate monomers are synthesized by enzymatic transacylation and used in situ for light‐controlled polymerization, leading to multifunctional methacrylate‐based polymers with well‐defined microstructure.
A supramolecular block copolymer is prepared by the molecular recognition of nucleobases between poly(2‐(2‐methoxyethoxy)ethyl methacrylate‐co‐oligo(ethylene glycol) methacrylate)‐SS‐poly(ε‐caprolactone)‐adenine (P(MEO2MA‐co‐OEGMA)‐SS‐PCL‐A) and uracil‐terminated poly(ethylene glycol) (PEG‐U). Because the block copolymer is linked by the combination of covalent (disulfide bond) and noncovalent (A U) bonds, it not only has similar properties to conventional covalently linked block copolymers but also possesses a dynamic and tunable nature. The copolymer can self‐assemble into micelles with a PCL core and P(MEO2MA‐co‐OEGMA)/PEG shell. The size and morphologies of the micelles/aggregates can be adjusted by altering the temperature, pH, salt concentration, or adding dithiothreitol (DTT) to the solution. The controlled release of Nile red is achieved at different environmental conditions.
In this study, the group transfer polymerization (GTP) of the functional monomer 3‐(trimethoxysilyl)propyl methacrylate (TMSPMA) is reported to produce polymers of different architectures and topologies. TMSPMA is successfully polymerized and copolymerized with GTP to produce well‐defined (co)polymers that can be used to fabricate functional hybrid materials like hydrogels and films.
A new method for fabricating hydrogels with intricate control over hierarchical 3D porosity using microfiber porogens is presented. Melt electrospinning writing of poly(ε‐caprolactone) is used to create the sacrificial template leading to hierarchical structuring consisting of pores inside the denser poly(2‐oxazoline) hydrogel mesh. This versatile approach provides new opportunities to create well‐defined multilevel control over interconnected pores with diameters in the lower micrometer range inside hydrogels with potential applications as cell scaffolds with tunable diffusion and transport of, e.g., nutrients, growth factors or therapeutics.
Hypoxia plays a critical role in the development and wound healing process, as well as a number of pathological conditions. Here, dextran‐based hypoxia‐inducible (Dex‐HI) hydrogels formed with in situ oxygen consumption via a laccase−medicated reaction are reported. Oxygen levels and gradients were accurately predicted by mathematical simulation. It is demonstrated that Dex‐HI hydrogels provide prolonged hypoxic conditions up to 12 h. The Dex‐HI hydrogel offers an innovative approach to delineate not only the mechanism by which hypoxia regulates cellular responses, but may facilitate the discovery of new pathways involved in the generation of hypoxic and oxygen gradient environments.
Pulsed‐laser polymerization combined with polymer analysis by NMR and size‐exclusion chromatography is used to study the radical copolymerization kinetics of isoprene (IP) with glycidyl methacrylate (GMA). The copolymer is characterized by a close‐to‐alternating microstructure, with the addition of IP leading to a significant decrease in the composition‐averaged propagation rate coefficient. A rigorous fitting strategy is developed to fit a mixed penultimate model to the data, with the selectivity of the IP, but not the GMA, macroradical dependent on the penultimate unit.
High‐porosity interconnected, thermoresponsive macroporous hydrogels are prepared from oil‐in‐water high internal phase emulsions (HIPEs) stabilized by gelatin‐graft‐poly(N‐isopropylacrylamide). PolyHIPEs are obtained by gelling HIPEs utilizing the thermoresponsiveness of the copolymer components. PolyHIPEs properties can be controlled by varying the aqueous phase composition, internal phase volume ratio, and gelation temperature. PolyHIPEs respond to temperature changes experienced during cell seeding, allowing fibroblasts to spread, proliferate, and penetrate into the scaffold. Encapsulated cells survive ejection of cell‐laden hydrogels through a hypodermic needle. This system provides a new strategy for the fabrication of safe injectable biocompatible tissue engineering scaffolds.
(1‐Adamantyl)methyl glycidyl ether (AdaGE) is introduced as a versatile monomer for oxyanionic polymerization, enabling controlled incorporation of adamantyl moieties in aliphatic polyethers. Via copolymerization with ethoxyethyl glycidyl ether (EEGE) and subsequent cleavage of the acetal protection groups of EEGE, hydrophilic linear polyglycerols with an adjustable amount of pendant adamantyl moieties are obtained. The adamantyl unit permits control over thermal properties and solubility profile of these polymers (LCST). Additionally, AdaGE is utilized as a termination agent in carbanionic polymerization, affording adamantyl‐terminated polymers. Using these structures as macroinitiators for the polymerization of ethylene oxide affords amphiphilic, in‐chain adamantyl‐functionalized block copolymers.
A facile and versatile method for the synthesis of Janus graphene oxide (GO) nanosheets with different structures is reported. Based on electrostatic assembly, Janus GO nanosheets can be easily functionalized with a template polymer or be defunctionalized by altering the ionic strength. By using this approach, Janus GO nanosheets are prepared successfully with hydrophobic polystyrene chains on one side and hydrophilic poly(2‐(dimethylamino)ethyl methacrylate) chains on the other side.
Poly(N‐isopropylacrylamide‐co‐3‐(trimethoxysilyl)propyl methacrylate), P(NIPAAm‐co‐TMSPMA), copolymers with relatively high TMSPMA contents without insoluble fraction are successfully synthesized. Subsequent sol–gel reactions in both the absence and presence of tetraethyl orthosilicate lead to gels with high gel fractions. The resulting gels undergo gel collapse at 28.6–28.7 °C, i.e., below that of poly(N‐isopropylacrylamide) homopolymer of 34.3 °C. Unexpectedly, the theophylline‐loaded hybrid gels release the drug not only below but also above the gel collapse temperature (GCT) with considerable rates and released amounts of drug. Surprisingly, evaluation of the sustained release profiles by the Korsmeyer–Peppas equation indicates that the release occurs by Fickian diffusion above GCT, which can be attributed to the lack of significant drug–polymer interaction at such temperatures. These results can be widely applied for the design and utilization of TMSPMA‐based sol–gel polymer hybrids with desired release profiles of solutes below and above GCT for a variety of applications.
Redox‐cleavable mikto‐arm star polymers are prepared by an “arm‐first” approach involving copolymerization of a dimethacrylate mediated by a mixture of macroRAFT agents. Thus, RAFT copolymerization of the monomers BMA, DMAEMA, and OEGMA, with the disulfide dimethacrylate cross‐linker (DSDMA), bis(2‐methacryloyl)oxyethyl disulfide, mediated by a 1:1:1 mixture of three macroRAFT agents with markedly different properties [hydrophilic, poly[oligo(ethylene glycol) methacrylate]—P(OEGMA)8–9; cationizable, poly[2‐(dimethylamino)ethyl methacrylate]—P(DMAEMA); hydrophobic, poly(n‐butyl methacrylate)—P(BMA)] provides low dispersity mikto‐arm star polymers. Good control (Đ < 1.3) is observed for the target P(DMAEMA)/P(OEGMA)/P(BMA) (3:3:1) mikto‐arm star, a double hydrophilic P(DMAEMA)/P(OEGMA) (3:3) mikto‐arm star and a hydrophobic P(BMA) homo‐arm star. However, Đ for the target mikto‐arm stars increases with an increase in either the ratio [DSDMA]:[total macroRAFT] or the fraction of hydrophobic P(BMA) macroRAFT agent. The quaternized mikto‐arm star in dilute aqueous solution shows a monomodal particle size distribution and an average size of ≈145 nm.
Wide‐angle X‐ray scattering (WAXS) and temperature‐dependent Fourier transform infrared spectroscopy (FTIR) spectroscopy are used to study hydrogen bonding interactions of a hydroxyl‐functionalized polyethylene (PE) prepared by acyclic diene metathesis (ADMET) chemistry. The hydroxyl polymer exhibits an orthorhombic unit cell structure with characteristic reflection planes at (110) and (200), comparable to pure crystalline PE. These data unequivocally demonstrate that the OH branch is excluded from the PE lamellae. Furthermore, the polymer melts 100 °C higher than all previous analogous polymers possessing precision placed long aliphatic branches that also are excluded from PE lamellae. Temperature‐dependent FTIR spectroscopy from ambient to 150 °C, followed by cooling to 125 °C supports exclusion of the hydroxyl group from the crystalline lattice. It is concluded that these hydroxyl groups form stable physical networks in the amorphous region via hydrogen bonding and are important for the overall morphology of such polymers.
The synthesis of a novel photoreactive poly(ethylene glycol) (PEG)‐based polymer with caged carbonyl groups is reported. We further demonstrate its use for the on‐demand fabrication of hydrogels. For rapid gelation, a hydrazide‐functionalized PEG is used as the second component for the hydrogel preparation. The photoreactive PEG‐based polymer is designed for controlled cleavage of the protecting groups upon exposure to UV light releases free aldehyde moieties, which readily react with hydrazide groups in situ. This hydrogel system may find applications in controlled release drug delivery applications, when combined with in situ gelation. Furthermore, the possibility of forming gels specifically upon UV irradiation gives an opportunity for 3D fabrication of degradable scaffolds.
Metal‐containing polymer hydrogels have attracted increasing interest in recent years due to their outstanding properties such as biocompatibility, recoverability, self‐healing, and/or redox activity. In this short review, methods for the preparation of metal‐containing polymer hydrogels are introduced and an overview of these hydrogels with various functionalities is given. It is hoped that this short update can stimulate innovative ideas to promote the research of metal‐containing hydrogels in the communities.
A novel procedure has been developed for the Gilch reaction leading to poly(p‐phenylene vinylenes) (PPVs). In the first step, selective activation of the starting material is achieved at low temperature. Subsequently, controlled chain growth is induced by lighting the α‐halo‐p‐quinodimethane monomer. In contrast to the thermal Gilch polymerization, the photoinduced process allows adjusting crucial parameters such as intensity and energy of light. The progress of PPV formation can be followed visually or by in situ UV–vis spectroscopy. If the polymers are formed under appropriate conditions, they show very high molar masses, polydispersities in the common range, and higher constitutional homogeneity than thermally grown PPVs.
A series of fluorene‐based conjugated polymers containing the aggregation‐induced emissive (AIE)‐active tetraphenylethene and dicarboxylate pseudocrown as a receptor exhibits a unique dual‐mode sensing ability for selective detection of lead ion in water. Fluorescence turn‐off and turn‐on detections are realized in 80%–90% and 20% water in tetrahydrofuran (THF), respectively, for lead ion with a concentration as low as 10−8 m .
This work describes the synthesis of π‐conjugated polymers possessing arylene and 1,3‐butadiene alternating units in the main chain by the reaction of α,β‐unsaturated ester/nitrile containing γ‐H with aromatic/heteroaromatic aldehyde compound. By using 4‐(4‐formylphenyl)‐2‐butylene acid ethyl ester as a model monomer, the different polymerization conditions, including catalyst, catalyst amount, and solvent, are optimized. The polymerization of 4‐(4‐formylphenyl)‐2‐butylene acid ethyl ester is carried out by refluxing in ethanol for 72 h with 1,8‐diazabicyclo[5.4.0]undec‐7‐ene (DBU) as a catalyst to give a 1,3‐butadiene‐containing π‐conjugated polymer, poly(phenylene‐1,3‐butadiene), in 84.3% yield with and / (PDI) estimated as 6172 and 1.65, respectively. Based on this new methodology, a series of π‐conjugated polymers containing 1,3‐butadiene units with different substituents are obtained in high yields. A possible mechanism is proposed for the polymerization through a six‐membered ring transition state and then a 1,5‐H shift intermediate.
Nitroxide‐mediated polymerization (NMP) is one of the most powerful reversible deactivation radical polymerization techniques and has incredibly gained in maturity and robustness over the last decades. However, control of methacrylic esters is one of the different aspects of NMP that still requires improvement. This family of monomers always represented an important challenge for NMP, despite the many different nitroxide structures that have been designed over the course of time. This Review aims to present the most successful strategies directed toward the control of the NMP technique of methacrylic esters and especially methyl methacrylate. NMP‐derived materials comprising uncontrolled methacrylate segments will also be discussed.
Well‐defined ABC triblock copolymers based on two hydrophilic blocks, A and C, and a hydrophobic block B are synthesized and their self‐assembly behavior is investigated. Interestingly, at the same solvent, concentration, pH, and temperature, different shape micelles are observed, spherical and worm‐like micelles, depending on the preparation method. Specifically, spherical micelles are observed with bulk rehydration while both spherical and worm‐like micelles are observed with film rehydration.
A double hydrophilic block copolymer, poly(ethylene glycol)‐poly(3‐dimethyl (methacryloyloxyethyl) ammonium propane sulfonate) (PEG‐SB), is synthesized by reversible addition‐fragmentation transfer (RAFT) polymerization using PEG methyl ether (4‐cyano‐4‐pentanoate dodecyl trithiocarbonate) as a chain transfer agent. PEG‐SB forms multi‐layered microspheres with dipole‐dipole interactions of the SB side chains as the driving force. The PEG‐SB polymers show an upper critical solution temperature (UCST) and the UCST is controllable by the polymerization degree. The PEG‐SB microspheres are dissociated above the UCST and then monodispersed microspheres (∼1 μm) are obtained when the solution temperature is decreased below the UCST again. The disassociation/association of the microspheres is also controllable using the concentration of NaCl. These multi‐responsive microspheres could be a powerful tool in the field of nano‐biotechnology.
