Ethylene–propylene–methyl methacrylate (MMA) and ethylene–hexene–MMA A‐B‐C block copolymers with high molecular weight (>100 000) are synthesized using fluorenylamide‐ligated titanium complex activated by modified methylaluminoxane and 2,6‐di‐tert‐butyl‐4‐methylphenol for the first time. After diblock copolymerization of olefin is conducted completely, MMA is added and activated by aluminum Lewis acid to promote anionic polymerization. The length of polyolefin and poly (methyl methacrylate) (PMMA) is controllable precisely by the change of the additive amount of olefin and polymerization time, respectively. A soft amorphous polypropylene or polyhexene segment is located between two hard segments of semicrystalline polyethylene and glassy PMMA blocks.
The synthesis of thiol‐functionalized long‐chain highly branched polymers (LCHBPs) has been accomplished in combination of ring‐opening metathesis polymerization (ROMP) and thiol‐Michael addition click reaction. A monotelechelic polymer with a terminal acrylate and many pendent thiol groups is first prepared through adding an internal cis‐olefin terminating agent to the reaction mixture immediately after the completion of the living ROMP, and then utilized as an ABn‐type macromonomer in subsequent thiol‐ene reaction between acrylate and thiol, yielding LCHBPs as the reaction time prolonged. Au nanoparticles are then covalently conjugated onto the surface of thiol‐functionalized LCHBP to fabricate novel hybrid nanostructures, which is shown as one interesting application of such functionalized metathesis polymers. This facile approach can be extended toward the fabrication of novel nanomaterials with sophisticated structures and tunable multifunctionalities.
This paper reports on the synthesis of well‐defined polyacrylamide‐based nanogels via reversible addition–fragmentation chain transfer (RAFT) dispersion polymerization, highlighting a templateless route for the efficient synthesis of nanogels based on water‐soluble polymers. RAFT dispersion polymerization of acrylamide in co‐nonsolvents of water–tert‐butanol mixtures by chain extension from poly(dimethylacrylamide) shows well‐controlled polymerization process, uniform nanogel size, and excellent colloidal stability. The versatility of this approach is further demonstrated by introducing a hydrophobic co‐monomer (butyl acrylate) without disturbing the dispersion polymerization process.
The synthesis of two 4,7,12,15‐tetrakisalkoxy‐substituted [2.2.2]‐paracyclophane‐1,9,17‐trienes and their polymerization employing ring opening metathesis polymerization (ROMP) using Ru‐carbenes (third‐generation Grubbs catalyst) is reported. Phenylene ethynylene trimers are reduced via a Grignard reagent, followed by an intramolecular McMurry cyclization to give the cyclophenes. The cyclophenes are polymerized into soluble poly(para‐phenylene vinylene)s (PPV), which are analyzed in solution by NMR, UV–vis, and fluorescence spectroscopy. They are spin coated into amorphous, fluorescent thin films, and investigated by optical spectroscopy and cyclic voltammetry.
The modulation of the cloud point of aqueous poly(N,N‐diethylacrylamide) solutions via the formation of supramolecular cyclodextrin complexes with hydrophobic end groups, namely adamantyl, tert‐butyl phenyl and azobenzene, synthesized via RAFT polymerization is described. The dependence of the apparent cloud points after cyclodextrin complexation is investigated with respect to the type and quantity of the guest end group, the polymer chain length and the cyclodextrin/end group ratio. Furthermore, the effect is reversed via the addition of guest molecules or via biocompatible enzymatic degradation of the cyclodextrins entire.
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.
Controlling the orientation and long‐range order of nanostructures is a key issue in the self‐assembly of block copolymer micelles. Herein, a versatile strategy is presented to transform one‐component oxime‐based block copolymer micelles into long‐range ordered dense nanopatterns. Photoisomerization provides a straightforward and versatile approach to convert the hydrogen‐bonding association from inward dimerization (E‐type oxime motifs, slightly desolvated in ethyl acetate) into outward interchain association (Z‐type ones, highly desolvated in ethyl acetate). This increases the glass transition temperature in bulk and converts swollen micelles into compact spherical micelles in solution. The reconstruction of these micelles on various substrates demonstrates that the phase transformation enables reconstruction of spherical micelles into mesoscopic sheets, nanorods, nanoworms, nanowires, networks, and eventually into long‐range ordered and densely packed textile‐like and lamellar nanopatterns on a macroscopic scale by adjusting E/Z‐oxime ratio and solvent‐evaporation rate.
Endowing unimolecular soft nanoobjects with biomimetic functions is attracting significant interest in the emerging field of single‐chain technology. Inspired by the compartmentalized structure and polymerase activity of metalloenzymes, copper‐containing compact nanoglobules have been designed, synthesized, and characterized endowed with metalloenzyme mimicking characteristics toward controlled synthesis of water‐soluble polymers and thermoresponsive hydrogels. When compared to metalloenzymes, artificial nanoobjects endowed with metalloenzyme mimicking characteristics offer increased stability against thermal changes and reduced degradability by hydrolytic enzymes.
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.
A straightforward and expeditious monotopic approach for the preparation of 1,2,3‐triazolium‐based poly(ionic liquids) (TPILs) is reported. It is based on the solvent‐ and catalyst‐free polyaddition of an α‐azide‐ω‐alkyne monomer in the presence of methyl iodide or N‐methyl bis[(trifluoromethyl)sulfonyl]imide alkylating agents. Poly(1,2,3‐triazole)s generated in bulk or by thermal azide–alkyne cycloaddition (AAC) are quaternized in‐situ to afford TPILs composed of 1,3,4‐ and 1,3,5‐trisubstituted 1,2,3‐triazolium units. The physical and ion‐conducting properties of the prepared samples are compared with the TPILs composed solely of 1,3,4‐trisubstituted 1,2,3‐triazolium units obtained through a multistep approach involving copper(I)‐catalyzed AAC polyaddition, quaternization of the 1,2,3‐triazole groups, and anion metathesis. TPILs obtained through the monotopic approach display thermal stabilities and ionic conductivities comparable to their pure regioisomeric analogues.
This communication describes photoresponsive gels, prepared using ring‐opening metathesis polymerization (ROMP), that dissolve upon irradiation with ultraviolet light. Exposure of mixtures of norbornene‐type ROMP monomers and new photoreactive cross‐linkers comprising two norbornene units bound through a chain containing o‐nitrobenzyl esters (NBEs) to well‐known ruthenium carbene catalysts gave cross‐linked polymer networks that swelled in organic solvents or water depending on the structure of the monomer. These gels became homogeneous upon irradiation with UV light, consistent with breaking of the cross‐links through photolysis of the NBE groups. The irradiation time required for homogenization of the gels depended on the cross‐link density and the structure of the photoresponsive cross‐linker.
The synthesis of tetracene‐ and pentacene‐annulated norbornadienes, formed through the Diels–Alder reaction of a dehydroacene with cyclopentadiene is reported. Ring‐opening metathesis polymerization (ROMP) leads to polymers that are investigated with respect to their physical, optical, and electronic properties by gel permeation chromatography (GPC), UV–vis spectroscopy, and cyclic voltammetry. The pentacene‐containing polymer P1 is successfully integrated into an organic field‐effect transistor (OFET); the tetracene‐containing polymer P2 is integrated into an organic light‐emitting diode (OLED).
Novel photoresponsive linear, graft, and comb‐like copolymers with azobenzene chromophores in the main‐chain and/or side‐chain are prepared via a sequential ring‐opening metathesis polymerization (ROMP) and head‐to‐tail acyclic diene metathesis (ADMET) polymerization in a one‐pot procedure using Grubbs ruthenium‐based catalysts. The diluted solutions of these as‐prepared copolymers containing azobenzene chromophores exhibit photochemical trans–cis isomerization under the irradiation of UV light, followed by their cis–trans back‐isomerization in visible light. The rates of photoisomerization are found to be slower than those of back‐isomerization, and the rate for the comb‐like copolymer is found to be from 3 to 7 times slower than that obtained for the linear or graft copolymer. This is ascribed to the differences in structure of the copolymers and the specific location of azobenzene chromophores in the copolymer, which favor a side‐chain graft structure.
The β‐scission rate coefficient of tert‐butyl radicals fragmenting off the intermediate resulting from their addition to tert‐butyl dithiobenzoate—a reversible addition–fragmentation chain transfer (RAFT) agent—is estimated via the recently introduced electron spin resonance (ESR)‐trapping methodology as a function of temperature. The newly introduced ESR‐trapping methodology is critically evaluated and found to be reliable. At 20 °C, a fragmentation rate coefficient of close to 0.042 s−1 is observed, whereas the activation parameters for the fragmentation reaction—determined for the first time—read EA = 82 ± 13.3 kJ mol−1 and A = (1.4 ± 0.25) × 1013 s−1. The ESR spin‐trapping methodology thus efficiently probes the stability of the RAFT adduct radical under conditions relevant for the pre‐equilibrium of the RAFT process. It particularly indicates that stable RAFT adduct radicals are indeed formed in early stages of the RAFT polymerization, at least when dithiobenzoates are employed as controlling agents as stipulated by the so‐called slow fragmentation theory. By design of the methodology, the obtained fragmentation rate coefficients represent an upper limit. The ESR spin‐trapping methodology is thus seen as a suitable tool for evaluating the fragmentation rate coefficients of a wide range of RAFT adduct radicals.
Three‐ and four‐arm star shaped polymers, as well as diblock copolymers, are synthesized via acyclic diene metathesis (ADMET) polymerization. This is accomplished by using an asymmetric α,ω‐diene containing a terminal double bond and an acrylate, which is polymerized in the presence of multifunctional acrylates as selective and irreversible chain transfer agents using Hoveyda‐Grubbs second generation catalyst. High cross‐metathesis selectivities are achieved at low temperatures enabling good control over molecular weights. Furthermore, additional polyethyleneglycol (PEG) blocks are attached to these polymers via Heck coupling of the acrylate end‐groups of these polymers with aryl iodide functionalized PEG, obtaining three‐ and four‐arm star shaped di‐ and triblock copolymers with molecular weights up to 31 kDa.
Well‐defined poly(2,5‐dihexyloxyphenylene‐1,4‐diyl) (PPP) is successfully synthesized by the Negishi catalyst‐transfer polycondensation (NCTP) using dilithium tetra(tert‐butyl)zincate (tBu4ZnLi2). The obtained PPP possesses the number‐averaged molecular weight (M n) values in the range of 2100–22 000 and the molar‐mass dispersity (Ð M) values in the range of 1.09–1.23. In addition, block copolymers containing PPP and poly(3‐hexylthiophene) (P3HT) segments (PPP‐b‐P3HT) are synthesized to confirm the feasibility of chain extension between the different monomers based on NCTP.
Moisture or water has the advantages of being green, inexpensive, and moderate. However, it is challenging to endow water‐induced shape memory property and self‐healing capability to one single polymer because of the conflicting structural requirement of the two types of materials. In this study, this problem is solved through introducing two kinds of supramolecular interactions into semi‐interpenetrating polymer networks (semi‐IPNs). The hydrogen bonds function as water‐sensitive switches, making the materials show moisture‐induced shape memory effect. The host–guest interactions (β‐cyclodextrin‐adamantane) serve as both permanent phases and self‐healing motifs, enabling further increased chain mobility at the cracks and self‐healing function. In addition, these polyvinylpyrrolidone/poly(hydroxyethyl methacrylate‐co‐butyl acrylate) semi‐IPNs also show thermosensitive triple‐shape memory effect.
Today's olefin metathesis catalysts show high reactivity, selectivity, and functional group tolerance and allow the design of new syntheses of precisely functionalized polymers. Here the synthesis of a new end‐capping reagent is investigated allowing the introduction of a highly reactive activated ester end‐group at the polymer chain end as well as its prefunctionalization to directly introduce functional moieties. The versatility of this new end‐capping reagent is demonstrated by utilizing it to synthesize a so‐called termimer (a monomer with termination capabilities). Copolymerization of a norbornene derivative with the termimer leads to hyperbranched ring‐opening metathesis polymerization polymers as proven by gel permeation chromatography and MALDI‐ToF‐(matrix‐assisted laser desorption/ionization time of flight) mass spectrometry.
Organometallic‐mediated radical polymerization (OMRP) has given access to well‐defined poly(vinyl acetate‐alt‐tert‐butyl‐2‐trifluoromethacrylate)‐b‐poly(vinyl acetate) and poly(VAc‐alt‐MAF‐TBE) copolymers composed of two electronically distinct monomers: vinyl acetate (VAc, donor, D) and tert‐butyl‐2‐trifluoromethacrylate (MAF‐TBE, acceptor, A), with low dispersity (≤1.24) and molar masses up to 57 000 g mol−1. These copolymers have a precise 1:1 alternating structure over a wide range of comonomer feed compositions. The reactivity ratios are determined as r VAc = 0.01 ± 0.01 and r MAF‐TBE = 0 at 40 °C. Remarkably, from a feed containing >50% molar VAc content, poly(VAc‐alt‐MAF‐TBE)‐b‐PVAc block copolymers are produced via a one‐pot synthesis. Such diblock copolymers exhibit two glass transition temperatures attributed to the alternating and homopolymer sequences. The OMRP of this fluorine‐containing alternating monomer system may provide access to a wide range of new polymer materials.
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.
