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.
This paper describes a method for fabricating protein‐based capsules with semipermeable and enzyme‐degradable surface barriers. It involves the use of a simple fluidic device to generate water‐in‐oil emulsion droplets, followed by cross‐linking of proteins at the water–oil interface to generate a semipermeable surface barrier. The capsules can be readily fabricated with uniform and controllable sizes and, more importantly, show selective permeability toward molecules with different molecular weights: small molecules like fluorescein sodium salt can freely diffuse through the surface barrier while macromolecules such as proteins can not. The proteins, however, can be released by digesting the surface barrier with an enzyme such as pepsin. Taken together, the capsules hold great potential for applications in controlled release, in particular, for the delivery of protein drugs.
An alkyne‐functionalized ruthenium(II) bis‐terpyridine complex is directly copolymerized with phenylacetylene by alkyne polymerization. The polymer is characterized by size‐exclusion chromatography (SEC), 1H NMR spectroscopy, cyclic voltammetry (CV) measurements, and thermal analysis. The photophysical properties of the polymer are studied by UV–vis absorption spectroscopy. In addition, spectro‐electrochemical measurements are carried out. Time‐resolved luminescence lifetime decay curves show an enhanced lifetime of the metal complex attached to the conjugated polymer backbone compared with the Ru(tpy)22+ model complex.
Synthesis of a cyclodextrin (CD) polyrotaxane is achieved for the first time by simultaneous free radical polymerization of isoprene, threading by CD, and stoppering by copolymerization of styrene. This reaction is performed in an eco‐friendly manner in an aqueous medium similar to classical emulsion polymerization. Threaded CD rings of the polyrotaxane are cross‐linked by hexamethylene diisocyanate, leading to highly elastic slide‐ring gels.
Polyfluorene‐bearing bromohexyl side chains are quaternized by 1‐vinylimidazole in order to attach dialkylimidazolium bromide ionic liquid (IL) species along the conjugated backbone. Subsequently, polyfluorene polyelectrolyte nanoparticles (NPs) of 40 nm in average size are created via radical cross‐linking of the pendant vinylimidazolium groups. Anion exchange from Br− to BF4−, PF6−, and bis(trifluoromethylsulfonyl)imide anion (TFSI−) renders NPs adjustable dispersability in various organic solvents. The hydrophobic‐conjugated backbone and the hydrophilic dialkylimidazolium bromide IL moieties depict an amphiphilic profile, which allows the NPs to be deployed as conductive stabilizer in the emulsion polymerization of styrene. The resultant latexes are fluorescent, tunable in size and can be transferred to organic solvents without forfeiting their colloidal stability.
Multiblock polystyrenes (PS) with trithiocarbonate groups as linkages are prepared via reversible addition‐fragmentation chain‐transfer polymerization using polytrithiocarbonate as a chain transfer agent. The photodegradability of the multiblock PS in the solid state is investigated under UV irradiation at room temperature in an air atmosphere. The experimental results demonstrate that the trithiocarbonate linkages in the multiblock PS can be broken under UV light irradiation at room temperature and the multiblock PS is degraded into separate PS blocks. Gel permeation chromatography measurement reveals that the molecular weight of multiblock PS is reduced from 27 900 to 7900 g mol−1 after UV light irradiation for 745 h. Moreover, the thermal stability of the multiblock PS is examined and the results indicate that the incorporation of trithiocarbonate shows little influence on the thermal stability of multiblock PS.
A one‐pot method is introduced for the successful synthesis of narrow‐distributed (Đ = 1.22) vinyl polymer with both ultrahigh molecular weight (UHMW) (Mw = 1.31 × 106 g mol−1) and micro‐/nanomorphology under mild conditions. The method involves the following four stages: homogeneous polymerization, polymerization‐induced self‐assembly (PISA), PISA and reorganization, and PISA and multiple reorganizations. The key points to the production of UHMW polystyrene are to minimize radical termination by segregating radicals in different nanoreactors and to ensure sufficient chain propagation by promoting further reorganizations of these reactors in situ. This method therefore endows polymeric materials with the outstanding properties of both UHMW and tunable micro‐/nanoparticles under mild conditions in one pot.
A facile and versatile approach to constructing colorless surface coatings based on green tea polyphenols is reported, which can further act as a photoinitiating layer to initiate radical polymerization. These colorless green tea polyphenol coatings are capable of successfully photografting polymer brushes, and the resulting polymer brush patterns show spatial shape adjustability by masked UV irradiation. Both surface modifications and photografted polymer brushes do not alter the original color of the substrates. This method could be promising for the development of surface modifications.
In this study, a material is designed which combines the properties of shape‐memory and electroactive polymers. This is achieved by covalent cross‐linking of polyvinylidene fluoride. The resulting polymer network exhibits excellent shape‐memory properties with a storable strain of 200%, and fixity as well as recovery values of 100%. Programming upon rolling induces the transformation from the nonelectroactive α‐phase to the piezoelectric β‐phase. The highest β‐phase content is found to be 83% for a programming strain of 200% affording a d33 value of −30 pm V−1. This is in good accordance with literature known values for piezoelectric properties. Thermal triggering this material does not only result in a shape change but also renders the material nonelectroactive.
Cross‐linked silicone elastomers constructed with dynamic‐covalent boronic esters are first synthesized by photoinitiated radical thiol−ene “click” chemistry. The resultant samples can be cut with a sharp knife into two pieces and then healed via the reversibility of the boronic ester cross‐linkages to restore the original silicone sample within 30 min. Regulation of luminescent properties is achieved by incorporating organic dye into the elastomers through a “one‐pot” thiol–ene reaction. The proposed synthesis procedure demonstrates a new strategy to produce boronic acid silicone materials capable of self‐healing without external forces.
Triptycene‐based micorporous polymer is functionalized with CO2‐philic tetrazole moieties via ZnCl2‐catalyzed post‐polymerization. Gas adsorption experiments indicate that it possesses high CO2 uptake capacity, reaching 134 cm3 g−1 (26.5 wt%) at 1.0 bar and 273 K, along with high selectivity towards CO2 over N2 and CH4. The porous polymeric networks present the promising potentials as efficient adsorbents in clean energy applications.
The synthesis of an ambipolar π‐conjugated copolymer consisting of alternating diketopyrrolopyrrole and tetrafluorobenzene via direct arylation polymerization (DAP) is reported. Two different combinations of monomers are investigated under various catalytic conditions for DAP. The target polymer obtained under an optimized catalytic condition shows minimal structural defects, a number‐average molecular weight of 33.2 kDa, and balanced electron and hole mobility of 1 × 10−2 cm2 V−1 S−1 in the organic field‐effect transistors fabricated and tested under ambient conditions.
Injectable hydrogels have been commonly used as drug‐delivery vehicles and tried in tissue engineering. Injectable self‐healing hydrogels have great advantage over traditional injectable hydrogels because they can be injected as a liquid and then rapidly form bulk gels in situ at the target site under physiological conditions. This study develops an injectable thermosensitive self‐healing hydrogel based on chain‐extended F127 (PEO90‐PPO65‐PEO90) multi‐block copolymer (m‐F127). The rapid sol–gel transition ability under body temperature allows it to be used as injectable hydrogel and the self‐healing property allows it to withstand repeated deformation and quickly recover its mechanical properties and structure through the dynamic covalent bonds. It is hoped that the novel strategy and the fascinating properties of the hydrogel as presented here will provide new opportunities with regard to the design and practical application of injectable self‐healing hydrogels.
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.
Polymeric scaffolds serve as valuable supports for biological cells since they offer essential features for guiding cellular organization and tissue development. The main challenges for scaffold fabrication are i) to tune an internal structure and ii) to load bio‐molecules such as growth factors and control their local concentration and distribution. Here, a new approach for the design of hollow polymeric scaffolds using porous CaCO3 particles (cores) as templates is presented. The cores packed into a microfluidic channel are coated with polymers employing the layer‐by‐layer (LbL) technique. Subsequent core elimination at mild conditions results in formation of the scaffold composed of interconnected hollow polymer microspheres. The size of the cores determines the feature dimensions and, as a consequence, governs cellular adhesion: for 3T3 fibroblasts an optimal microsphere size is 12 μm. By making use of the carrier properties of the porous CaCO3 cores, the microspheres are loaded with BSA as a model protein. The scaffolds developed here may also be well suited for the localized release of bio‐molecules using external triggers such as IR‐light.
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.
Poly (N‐isopropylacrylamide) (pNIPAm)‐based hydrogels and hydrogel particles (microgels) have been extensively studied since their discovery and “popularization” a few decades ago. While their uses seem to have no bounds, this Feature Article is focused on their development and application for sensing small molecules, macromolecules, and biomolecules. Hydrogel/microgel‐based photonic materials with order in one, two, or three dimensions are highlighted, which exhibit optical properties that depend on the presence and concentration of various analytes.
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.
The successful chain‐growth copper(I)‐catalyzed azide–alkyne cycloaddition (CuAAC) polymerization employing Cu(0)/pentamethyldiethylenetriamine (PMDETA) and alkyl halide as catalyst is first investigated by a combination of nuclear magnetic resonance, gel‐permeation chromatography, and matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry. In addition, the electron transfer mediated “click‐radical” concurrent polymerization utilizing Cu(0)/PMDETA as catalyst is successfully employed to generate well‐defined copolymers, where controlled CuAAC polymerization of clickable ester monomer is progressed in the main chain acting as the polymer backbone, the controlled radical polymerization (CRP) of acrylic monomer is carried out in the side chain. Furthermore, it is found that there is strong collaborative effect and compatibility between CRP and CuAAC polymerization to improve the controllability.
Electrohydrodynamic cojetting has been employed to synthesize compartmentalized microfibers from thermally responsive hydrogels. The synthesis of the hydrogels as well as their transformation into compartmentalized microcylinders is discussed. After programmable shape‐shifting, snail‐like particles are obtained that undergo functional and structural reconfiguration in response to a change in temperature.
