Based on their rigid‐rod structure all‐conjugated, rod‐rod block copolymers show a preferred tendency to self‐assemble into low‐curvature vesicular or lamellar nanostructures independent from their specific chemical structure and composition. This unique and attractive behaviour is clearly illustrated in a few examples of such all‐conjugated block copolymers. The resulting nanostructured heteromaterials may find applications in electronic devices or artificial membranes.
Metallo‐supramolecular core cross‐linked (CCL) micelles are fabricated from terpyridine‐functionalized double hydrophilic block copolymers, poly(2‐(2‐methoxyethoxy)ethyl methacrylate)‐b‐poly(2‐(diethylamino)ethyl methacrylate‐co‐4′‐(6‐methacryloxyhexyloxy)‐2,2′:6′,2″‐terpyridine) [PMEO2MA‐b‐P(DEA‐co‐TPHMA)] via the formation of bis(terpyridine)ruthenium(II) complexes. These metallo‐supramolecular CCL micelles exhibit not only high structural integrity under different pH values and temperatures in aqueous solution, but multistimuli responsiveness including pH‐responsive cores, thermo‐responsive shells, and reversible dissociation of bis(terpyridine)ruthenium(II) complexes upon addition of competitive metal ion chelator, which allows for precisely controlled release of the encapsulated hydrophobic guest molecules via the combination of different stimuli.
Summary: Copolymers of poly(ethylene oxide) (PEO) and 5,5′‐azodisalicylic acid (Olsalazine, OLZ) were synthesized and evaluated by hydrolysis and in‐vitro biodegradation with azoreductase. It was found that changing the molecular weight of the PEO blocks affected the loading ratio of OLZ, and resulted in significant differences in the hydration and degradability of the copolymers. These novel azo‐containing copolymers can be used in colon‐specific drug delivery.
Release of 5‐ASA from OLZ and PEO‐OLZ copolymers incubated with rat cecum content in the presence of benzyl viologen and α‐D ‐glucose. 相似文献
Alternating copolymers comprised of (meth)acrylates and vinyl ethers with controlled molecular weights and polydispersities were synthesized for the first time by living radical polymerization using organotellurium, stibine, and bismuthine chain transfer agents. Combining living alternating copolymerization and living radical or living cationic polymerization afforded hitherto unavailable block copolymers with controlled macromolecular structures.
Summary: PE‐block‐PS and P(E‐co‐P)‐block‐PS block copolymers were synthesised via sequential monomer addition during homogeneous polymerisation on various phenoxyimine catalysts. One phenoxyimine catalyst was tailored to produce high molecular weight block copolymers containing both, polyolefin and polystyrene segments. According to chromatographic analysis and TEM morphology studies, blends of block copolymers and PE homopolymers [or P(E‐co‐P), respectively] were formed. The direct olefin/styrene block copolymer synthesis on phenoxyimine catalysts represents an attractive, new one‐pot route to styrenic block copolymers which are commercially prepared by anionic styrene/diene block copolymerisation followed by hydrogenation.
Stimuli‐responsive polymers are the subject of intense research because they are able to show responses to various environmental changes. Among those stimuli, light has attracted much attention since it can be localized in time and space and it can also be triggered from outside of the system. In this paper, we review light‐responsive block copolymers (LRBCs) that combine characteristic features of block copolymers, e.g., self‐assembly behavior, and light‐responsive systems. The different photo‐responsive moieties that have been incorporated so far in block copolymers as well as the proposed applications are discussed.
Summary: Fabrication of honeycomb‐patterned films from amphiphilic dendronized block copolymer (PEO113‐b‐PDMA82) by ‘on‐solid surface spreading’ and ‘on‐water spreading’ method is reported. Highly ordered honeycomb films with quasi‐horizontally paralleled double‐layered structure can be fabricated by the on‐solid surface spreading method. This work raises the possibility that such structures can be formed in amphiphilic dendronized block copolymers and extends the family of source materials.
Supramolecular self‐assembly of block copolymers in aqueous solution has received ever‐increasing interest over the past few decades due to diverse biological and technological applications in drug delivery, imaging, sensing and catalysis. In addition to relative block lengths, molecular weights and solution conditions, chain architectures of block copolymers can also dramatically affect their self‐assembling properties in selective solvents. This feature article mainly focuses on recent developments in the field of supramolecular self‐assembly of amphiphilic and double hydrophilic block copolymers (DHBCs) possessing nonlinear chain topologies, including miktoarm star polymers, dendritic–linear block copolymers, cyclic block copolymers and comb‐shaped copolymer brushes.
A novel approach is employed to produce core–corona nanospheres, which introduces a stereoregular hydrophilic part to an amphiphilic block copolymer. The resultant morphology is reported using isotactic‐poly(methacrylic acid)‐block‐poly(butyl acrylate). Infrared spectroscopy revealed a supramolecular interaction, and X ray diffraction revealed the crystallization of the outer isotactic‐poly(methacrylic acid) part. The nanostructure, which looks like a nanosized ‘grape’, was formed when nanospheres and nanofibers coexisted simultaneously and partially fused.
Blue‐light‐emitting 2,7‐carbazole‐based conjugated copolymers have been prepared by Yamamoto or Suzuki cross‐coupling reactions. By introducing highly substituted aromatic comonomers, fully soluble high‐molecular‐weight copolymers have been obtained. Moreover, these amorphous polymeric materials exhibit good thermal stability and interesting redox properties. All these features make these new conjugated polymers highly promising for the development of single‐polymer‐layer blue‐light‐emitting diodes.
Well‐defined amphiphilic PCL‐b‐PDMAEMA block copolymers were successfully synthesized by a combination of ATRP and “click” chemistry following either a commutative two‐step procedure or a straightforward one‐pot process using CuBr · 3Bpy as the sole catalyst. Compared to the traditional coupling method, combining ATRP and click chemistry even in a “one‐pot” process allows the preparation of PCL‐b‐PDMAEMA diblock copolymers characterized by a narrow molecular weight distribution and quantitative conversion of azides and alkynes into triazole functions. Moreover, the amphiphilic character of these copolymers was demonstrated by surface tension measurements and critical micellization concentration was calculated.
L,L ‐lactide (LA) and ε‐caprolactone (CL) block copolymers have been prepared by initiating the poly(ε‐caprolactone) (PCL) block growth with living poly(L,L ‐lactide) (PLA*). In the previous attempts to prepare block copolymers this way only random copolyesters were obtained because the PLA* + CL cross‐propagation rate was lower than that of the PLA–CL* + PLA transesterification. The present paper shows that application of Al‐alkoxide active centers that bear bulky diphenolate ligands results in efficient suppression of the transesterification. Thus, the corresponding well‐defined di‐ and triblock copolymers could be prepared.
The self‐assembly of two types of linear ABA triblock copolymers confined in cylindrical nanopores is studied using simulated annealing. The effects of pore size and block copolymer chain architecture on morphology, chain conformations and bridging fraction are investigated. For the bulk cylinder‐forming copolymers, novel structures such as helices and stacked toroids form, which depend sensitively on the pore size. Several significant differences between the two types of copolymers are predicted and explained based on the differences in their chain conformations and chain architectures. A simple model is proposed to explain the mean square radius of gyration for the bridge and loop chains.
ε‐Caprolactone (CL) was enzymatically polymerized with 2‐mercaptoethanol as the initiator, both in an oil bath and under microwave (MW) irradiation. The polymerization performed under MW irradiation maintaining equal conditions led to higher yields and less formation of side products, i.e., a higher chemoselectivity was observed. The resulting polyester with a terminal SH moiety had a of 3 600 g · mol−1, determined by size exclusion chromatography (SEC), and was used as a chain transfer reagent. Subsequent copolymerization with styrene in different ratios led to polycaprolactone‐block‐polystyrene. SEC analysis and polarization microscopy of crystallized samples with different styrene contents proved the formation of block copolymers.
Thermal field‐flow fractionation (ThFFF) is used as a novel fractionation technique to investigate the molecular heterogeneity of PB‐b‐PVP‐b‐PtBMA triblock copolymers. Such copolymers cause major problems in liquid chromatography due to very strong polar interactions with the stationary phase. ThFFF separates the copolymers with regard to size and/or chemical composition based on the normal and thermal diffusion coefficients. The separation mechanism in ThFFF and the chemical composition of the separated species is elucidated by online 1H NMR. Based on the compositional analysis and a calibration of the system with the respective homopolymers, the samples are quantified regarding their molar masses, chemical compositions, and microstructures providing comprehensive information on the complex structure of these block copolymers.
Amphiphilic H‐shaped block copolymers (PTMSPMA)2PEG(PTMSPMA)2 with 91 ethylene glycol (EG) units and four PTMSPMA chains have been synthesized by atom transfer radical polymerization of trimethoxylsilylpropyl methacrylate (TMSPMA) at room temperature in methanol. The structure, molecular weight, and molecular weight distribution have been characterized by 1H NMR spectroscopy and GPC traces. These H‐shaped block copolymers can self‐assemble in DMF/water, and multiple vesicle aggregates from large‐compound vesicles, to multilayer vesicles and unilamillar vesicles are formed. These morphologies can be simply controlled by variation of the chain length ratios.
Summary: In situ atom transfer radical polymerization techniques have been used to produce polymer‐grafted carbon spheres (CSs). The surfaces of as‐prepared CSs were functionalized in the presence of CS‐supported macroinitiators. The resulting materials were characterized by FTIR and NMR spectroscopy, TGA, SEM, TEM, and HRTEM. The amount of polymer grafted onto the surfaces of the spheres can be controlled by varying the monomer/initiator feed ratio. The wetting ability and dispersibility of the polymer‐grafted CSs were improved significantly, compared with crude CSs, enabling stable dispersions in organic solvents to be produced. SEM and TEM studies indicate that a uniform distribution of the carbon spheres in the continuous polymer phase can be produced.
SEM image (left) of poly(glycerol monomethacrylate) grafted carbon spheres, inset shows the structure. HRTEM image (right) of a polystyrene grafted carbon sphere, inset is the SAED pattern. 相似文献
This review deals with nanoporous materials made from the self‐assembly of block copolymers with a special interest in the chemical functions covering the surface of their nanopores. A detailed overview of the existing methods and strategies to generate well‐defined organic functional groups covering the surface of the pore walls is provided. This further enables to finely tune the affinity of the pore walls and to perform well‐defined chemical reactions onto them, which is essential for further dedicated applications.
This communication details the successful synthesis of low polydispersity core cross‐linked star (CCS) polymers via DPE‐mediated polymerisation. We demonstrate the ability to produce poly(methyl methacrylate) and poly(acrylonitrile) CCS polymers that are currently inaccessible via the two most common non‐metal‐based controlled radical polymerisation techniques (NMP and RAFT polymerisations).
Summary: A series of helix‐coil diblock copolymers based on poly(ethylene oxide) and optically active helical poly{(+)‐2,5‐bis[4′‐((S)‐2‐methylbutoxy)phenyl]styrene} (PMBPS) were synthesized via atom transfer radical polymerization (ATRP). The synthetic methodology permitted straightforward preparation of the diblock copolymers with relatively low polydispersities and a broad range of compositions and molecular weights. Depending on the composing block length and the initial concentration, the copolymers self‐assembled into different supramolecular structures in aqueous solution, including spherical micelles, vesicles, multilamellar vesicles, large compound vesicles, and tubules.
Schematic representation of the synthesis of PEO‐b‐PMBPS block copolymers and their aggregation in aqueous solution. 相似文献
