Synthesis of azobenzene‐functionalized two‐arm,three‐arm and four‐arm telomers using polyfunctional chain transfer agents

BACKGROUND: Star‐shaped polymers are very attractive because of their interesting properties such as reduced viscosity, good solubility, low glass transition temperature and fast response to external stimuli. The incorporation of azobenzene moieties in star‐shaped polymers could significantly widen their potential applications in various optical devices. One of the most important properties of the azobenzene chromophore is its reversible trans–cis photoisomerization induced by UV or visible light. Photoisomerization induces conformational changes in azopolymer chains, which in turn lead to macroscopic variations in chemical and physical properties of the surroundings and media. RESULTS: This study reports the synthesis of azobenzene‐functionalized two‐, three‐ and four‐arm telomers via free radical telomerization using the di‐, tri‐ and tetrafunctional chain transfer agents 1,2‐ and 1,4‐benzenedimethanethiol, trimethylolpropane‐tris(2‐mercaptoacetate) and pentaerythritol‐tetrakis(3‐mercaptopropionate), respectively, in the presence of azobisisobutyronitrile. Azotelomers were characterized using gel permeation chromatography and ¹H NMR and Fourier transform infrared spectroscopy. Thermal phase transition behaviors were investigated using differential scanning calorimetry and polarized optical microscopy. Azotelomers synthesized in this study showed reversible photoisomerization and a fast generation of birefringence. CONCLUSION: Considering the photoisomerization behavior and birefringence of the two‐, three‐ and four‐arm azotelomers, it can be concluded that they could be potential candidates for use in various optical devices. Copyright © 2009 Society of Chemical Industry     

Synthesis of azobenzene‐containing side chain liquid crystalline diblock copolymers using RAFT polymerization and photo‐responsive behavior

Well‐defined azobenzene‐containing side chain liquid crystalline diblock copolymers composed of poly[6‐[4‐(4‐methoxyphenylazo)phenoxy]hexyl methacrylate] (PAzoMA) and poly(glycidyl methacrylate) (PGMA) were synthesized by a two‐step reversible addition–fragmentation chain transfer polymerization (RAFT). The thermal liquid‐crystalline phase behavior of the PGMA‐b‐PAzoMA diblock copolymers in bulk were measured by differential scanning calorimetry (DSC) and polarized light microscopy (POM). The synthesized diblock copolymers exhibited a smectic and nematic liquid crystalline phase over a relatively wide temperature range. With increasing the weight fraction of the PAzoMA block, the phase transition temperatures, and corresponding enthalpy changes increased. Atomic force microscope (AFM) measurements confirmed the formation of the microphase separation in PGMA‐b‐PAzoMA diblock copolymer thin films and the microphase separation became more obvious after cross‐linking the PGMA block. The photochemical transition behavior of the PGMA‐b‐PAzoMA diblock copolymers in solution and in thin films were investigated by UV–vis spectrometry. It was found that the trans–cis isomerization of diblock copolymers was slower than that of the corresponding PAzoMA homopolymer and the photoisomerization rates decreased with increasing either the length of PAzoMA block or PGMA block. The photo‐induced isomerization in solid films was quite different with that in CHCl₃ solution due to the aggregation of the azobenzene chromophore. The cross‐linking structures severely suppressed the photoisomerization of azobenzene chromophore. These results may provide guidelines for the design of effective photo‐responsive anisotropic materials. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 2165–2175, 2013     

Substituent effects on thermal and photo‐alignment behavior of poly(ethylene imine)s carrying azobenzene side groups

A new class of liquid‐crystalline poly(ethylene imine)s (PEIs) having four differently substituted (? CN,? C₄H₉,? OCH₃ and? NO₂) azobenzene side‐chain groups attached through alkyl spacer groups were successfully synthesized using a solution polycondensation reaction. The synthesized polymers were characterized using differential scanning calorimetry, polarized optical microscopy and X‐ray diffraction. The photochemical, thermo‐optical and photo‐orientational behavior of the polymers were investigated in detail. Spin‐coated films of PEIs with azobenzene groups having? C₄H₉,? OCH₃ and? NO₂ substituents showed out‐of‐plane molecular orientation on annealing. Except for the PEI with an azobenzene group having ? NO₂ substituent, all polymers exhibited good photoresponsive properties upon irradiation with UV and visible light. Films of PEIs with azobenzene side groups having? CN,? C₄H₉ and? OCH₃ substituents showed reversible alignment behavior from random state to out‐of‐plane and from out‐of‐plane to random state on annealing and on irradiation with UV and non‐polarized visible light. The reversibility of the molecular orientation of PEIs from random state to out‐of‐plane and from out‐of‐plane to random state greatly depended on the substituent attached to the azobenzene side‐chain group. Copyright © 2010 Society of Chemical Industry     

Preparation and self‐assembly of poly(diglycidyl maleate‐co‐stearyl methacrylate)

Poly(diglycidyl maleate‐co‐stearyl methacrylate) (P(DGMA‐co‐SMA)) with reactive epoxy groups was synthesized by reaction of poly(maleic anhydride‐co‐stearyl methacrylate) (P(MA‐co‐SMA)) and epichlorohydrin. The effect of precipitant on self‐assembly behaviors of the resultant copolymer was investigated. It was found that vesicles and nanotubule liked aggregates can be obtained through self‐assembly of P(DGMA‐co‐SMA) in THF solution using CH₃CH₂OH (EtOH) as precipitant while spheral aggregates can be obtained using H₂O as precipitant. The mechanism of the self‐assembly behavior was discussed. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Construction of a Artificial Glutathione Peroxidase with Temperature‐Dependent Activity Based on a Supramolecular Graft Copolymer

A supramolecular artificial glutathione peroxidase (PNIPAM‐CD‐g‐Te) was prepared based on a supramolecular graft copolymer. PNIPAM‐CD‐g‐Te was constructed by supramolecular host–guest self‐assembly. Significantly, PNIPAM‐CD‐g‐Te displayed noticeable temperature‐dependent catalytic activity and typical saturation kinetics behavior. It was also proved that the change in the self‐assembled structure of PNIPAM‐CD‐g‐Te during the temperature‐dependent process played a significant role in the temperature‐dependent catalytic behavior. The construction of PNIPAM‐CD‐g‐Te based on supramolecular graft copolymer endows artificial GPx with temperature‐dependent catalytic ability, enriched catalytic centers, and homogeneously distributed catalytic centers. This work bodes well for the development of other biologically related host–guest supramolecular biomaterials.     

Light‐triggered reversible solubility of α‐cyclodextrin and azobenzene moiety complexes in PDMAA‐co‐PAPA via molecular recognition

Photoresponsive polymer with azobenzene pendant group (PDMAA‐co‐PAPA) was synthesized by radical polymerization of N,N‐dimethylacrylamide (DMAA) and N‐4‐phenylazophenyl acrylamide (PAPA), and the characterization of the inclusion complexes of the PDMAA‐co‐PAPA with α‐cyclodextrin (α‐CD) were performed by FTIR, GPC, ¹H NMR, 2D NOESY, and UV–vis spectroscopy. It was found that the solubility of PDMAA‐co‐PAPA and α‐CD inclusion complexes in aqueous solution showed tunable property, which could be triggered by alternating UV–vis light irradiation at a certain temperature due to the effect of molecular recognition of α‐CD with azobenzene moiety in the polymer. After UV irradiation, the lower critical solution temperature (LCST) of the polymer aqueous solution increased slightly without α‐CD while the LCST decreased sharply at presence of α‐CD. Furthermore, UV spectroscopy showed that the photoisomerization of the polymer solution went on rapidly and reversibly, and 2D NOESY data suggested that the inclusion complexation of α‐CD with trans azobenzene moiety and the decomplexation with cis azobenzene resulted in reversible solubility behavior when objected to UV and Vis light irradiation alternately. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Syntheses and properties of polyurethanes containing side‐chain azobenzene groups

Polymers containing azobenzene groups have the characteristic reaction of photo‐induced cis–trans isomerism. The study of new materials for optical information storage has prompted making use of these photo‐isomerizations. In this study, we report the syntheses and properties of four different polyurethanes (DR‐PUns) containing azobenzene groups in the side‐chains. The structurally similar polyurethanes (DR‐PUns) were synthesized by the polycondensation reaction of Disperse Red 19 (DR 19) and four different diisocyanates in dimethylformamide. By introducing of DR 19 into the polymer, we obtained polymers containing a photochromic group in the side‐chain. The weight‐average molecular weights of the DR‐PUns were in the range 5500–12 900. The T_gs of the DR‐PUns range from 119.5 °C to 157.0 °C, depending on the structure of the diisocyanate. Optical properties and solubilities of the polyurethanes were compared. The diffraction efficiencies of films were measured as a function of the reaction time. Typically, the diffraction efficiencies of the DR‐PU1 film prepared from toluene 2,4‐diisocyanate were observed up to a level of 0.25%. For the DR‐PU1 film, the effect of the intensity of the induced laser beam on the diffraction efficiency is also discussed. © 2003 Society of Chemical Industry     

Coordination‐Driven Self‐Assembly of Functionalized Supramolecular Metallacycles: Highlighted Research during 2010–2018

During the past few decades, the construction of macrocyclic molecules/complexes has attracted considerable attention because of their wide applications in sensing, catalysis, molecular machine, drug delivery, etc. Coordination‐driven self‐assembly has proven to be a simple yet highly efficient approach for the preparation of various supramolecular metallacycles with the predetermined shapes and sizes as well as the distribution and total number of functional groups. Since the significant progress has been made during the last few years in the field of coordination‐driven self‐assembly, it is time to summarize the recent development in coordination‐driven self‐assembly of functionalized supramolecular metallacycles. In this review, we will highlight some recent advances concerning the preparation of functionalized supramolecular metallacycles via coordination‐driven self‐assembly between the year 2010–2018. In addition, the properties and the applications of these metallacycles in the areas of photo‐ and electrochemistry, sensing, supramolecular gel, biological applications, etc. will be also discussed.     

Preparation and morphology of amphiphilic polystyrene–poly (2‐vinylpyridine) heteroarm star copolymers prepared by ATRP

BACKGROUND: The self‐assembly of amphiphilic copolymers has been demonstrated to be a powerful route towards supramolecular objects with novel architectures, functions and physical properties. In this study, the synthesis and morphology of amphiphilic linear polystyrene (PS)‐block‐poly(2‐vinylpyridine) (P2VP) and heteroarm star PS‐star‐P2VP copolymers are studied. The dispersion of silver nanoparticles with the prepared PS‐block‐P2VP and PS‐star‐P2VP copolymers is also discussed. RESULTS: Amphiphilic copolymers with different P2VP chain lengths were successfully synthesized using atom transfer radical polymerization (ATRP). The copolymers prepared had low polydispersity indices. Various aggregate morphologies, including spheres, vesicles, rods, large compound micelles, two‐dimensional ring‐like and three‐dimensional hollow structures, were formed by varying the hydrophilic coil length and the selective solvent content. Silver nanoparticles showed good dispersion behavior in both types of copolymers. CONCLUSION: Based on this study, it will be possible to prepare metal/copolymer nanocomposites by direct mixing. Further, the PS‐block‐P2VP and PS‐star‐P2VP copolymers prepared can be used in the preparation of nanoporous films as templates and nanoparticles as nanoreactors. They can also be applied in terms of oil recovery, paints and cosmetics formulations, as well as in pharmaceutical and medical applications as rheological agents. Copyright © 2008 Society of Chemical Industry     

Thermal‐ and Photo‐Induced Isomerization of All‐E‐ and Z‐Isomer‐Rich Xanthophylls: Astaxanthin and Its Structurally‐Related Xanthophylls,Adonirubin, and Adonixanthin

The effects of heating and photo‐irradiation on the stability of all‐E‐isomer‐rich and Z‐isomer‐rich xanthophylls, astaxanthin and its structurally related xanthophylls, adonirubin, and adonixanthin, are investigated. The xanthophylls with high Z‐isomer content are prepared from their high‐purity all‐E‐isomers by thermal isomerization and filtering techniques, that is, total Z‐isomer ratios of adonirubin, astaxanthin, and adonixanthin are 80.9%, 89.5%, and 72.5%, respectively. The all‐E‐ and Z‐isomer‐rich xanthophylls dissolved in ethanol are stored at 4, 30, and 50 °C in the dark and at 30 °C under photo‐irradiation using a fluorescent light for 21 days. In the all‐E‐isomer‐rich xanthophylls, as the storage temperature increases, the total Z‐isomer ratio becomes higher, whereas in the Z‐isomer‐rich xanthophylls, the all‐E‐isomer ratio becomes higher. Photo‐irradiation slightly promotes Z‐isomerization in (all‐E)‐xanthophylls, but highly promotes all‐E‐isomerization in Z‐isomer‐rich xanthophylls. In addition, photo‐irradiation prevents thermal Z‐isomerization of (all‐E)‐xanthophylls. Moreover, it is found that some xanthophyll Z‐isomers such as (9Z)‐astaxanthin are more stable than that of the other Z‐isomers against heating and photo‐irradiation. These findings can contribute not only to establishing suitable storage conditions for Z‐isomer‐rich xanthophylls, but also to developing control techniques for the E/Z‐isomer ratio of the xanthophylls. Practical Applications: The fundamental data on the stability of xanthophyll isomers against heating and photo‐irradiation and finding stable xanthophyll Z‐isomers are very important to develop xanthophyll materials rich in the Z‐isomers. Moreover, this study clearly shows that the heat treatment enhances the Z‐isomerization of xanthophylls, whereas the photo‐irradiation enhances the all‐E‐isomerization and prevents thermal Z‐isomerization of them. This information can be utilized in technology for arbitrarily controlling E/Z‐isomerization of xanthophylls.     

Perspectives on main‐chain hydrogen bonded supramolecular polymers

Supramolecular polymers are assembled from monomeric units held together by reversible non‐covalent interactions. These supramolecular materials display polymeric properties and may soon have important industrial applications. This mini review focuses on the advances in main‐chain supramolecular polymers whose assembly is guided primarily by hydrogen bonding interactions. The design constraints of these new systems discussed include assembly motifs, the strength and directionality of the non‐covalent interactions, association versus reversibility, and environmental effects on the degree of polymerization. Selected literature examples including Meijer's ureidopyrimidinone system are used to highlight the challenges and potential of these supramolecular polymeric materials. Copyright © 2007 Society of Chemical Industry     

Synthesis,characterization, and photo‐responsive properties of Y‐shaped amphiphilic azo triblock copolymer

In this study, we report the synthesis, characterization, and photo‐responsive properties of a new Y‐shaped amphiphilic azo triblock copolymer composed of two isotropic polyethylene glycol (PEG) blocks and an azobenzene liquid crystalline block. The azo block, with two ending groups suitable for the azo coupling reaction, is polymerized by atom transfer radical polymerization with a synthesized initiator containing two functional terminal groups. The macromolecular diazonium salts are prepared by the diazotization of PEG terminated with an amino group. The triblock copolymer is obtained by the azo coupling reaction between the azo block and macromolecular diazonium salts in DMF under mild condition. The intermediates and the obtained triblock copolymer are characterized by ¹H NMR, FT‐IR, GPC, POM, DSC, TEM, and UV‐vis. The photoinduced isomerization behavior of the azo copolymer is investigated by UV‐vis. With the addition of water into the solution of the triblock copolymer, spherical aggregates with an average diameter of about 400 nm can be easily obtained. The aggregates are elongated when irradiated with polarized 365 nm UV light. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43695.     

New chemoenzymatic‐facilitated synthesis of diblock copolymers and biomedically appropriate vesicles

BACKGROUND: Biocatalytic approaches in polymer science are expected to further increase the diversity of polymeric materials. And the full exploitation of biocatalysis in polymer science will require the development of compatible chemoenzyme‐catalyzed methods. RESULTS: The well‐defined diblock copolymer poly(2,2,2‐trichloroethanol 10‐hydroxydecanate)‐block‐poly(glycidyl methacrylate) (P(TCE‐10‐HD)‐b‐PGMA) was obtained by combining enzymatic condensation polymerization and atom transfer radical polymerization (ATRP). P(TCE‐10‐HD) was prepared by enzymatic condensation polymerization of 10‐hydroxydecanoic acid and 2,2,2‐trichloroethanol. This ? CCl₃‐terminated polyester permitted subsequent ATRP of glycidyl methacrylate. Kinetic studies indicated a ‘living’ controlled radical polymerization. The self‐assembly behavior of the amphiphilic diblock copolymer, in tetrahydrofuran/water, gave rise to aggregates with diameters ranging from 160 to 240 nm. The morphology of the assembly particles was studied using atomic force microscopy, transmission electron microscopy and scanning electron microscopy. CONCLUSION: To obtain the ATRP macromolecular initiator, this one‐step method is more convenient than other two‐step methods. The results of NMR, Fourier transform infrared and gel permeation chromatography analyses testified that this method is feasible. The formulated vesicles have great potential as biomedical materials. Copyright © 2008 Society of Chemical Industry     

Synthesis of photoisomeric azobenzene monomers and model compound effect on electric–optical properties in PDLC films

A series of azobenzene monomers and related model compounds with various side‐chain lengths were synthesized. The electrooptical properties of a polymer‐dispersed liquid crystal (PDLC) were verified by side‐chain methoxy azobenzene in various chain lengths (n = 3, 6, 11). The properties under various voltages were measured and the effect of extra voltage on the transmittance of PDLC was researched as well. The experiment demonstrated the validity of employing these side chain methoxy azobenzene materials in electrooptical devices. The azobenzene model compound showed better electric–optical and thermal–optical properties, having a higher contrast ratio (CR = 689) and a lower saturation voltage (4.7 V/μm). All the azobenzene molecules can be photoisomerized through UV light irradiation, following the mechanism of isomerization. The reversible photo and heat isomerization property was studied. The cis‐azobenzene that was transformed from the trans‐azobenzene irradiated by UV light can decrease the clearing point of the liquid crystal phase. We used this unique characteristic to record image patterns and it worked successfully. We synthesized the azobenzene monomers can stabilize the PDLC and their relative model compounds with various alkyl chain lengths even got better electric–optical effects. We found that azobenzene monomer shows different behaviors in the electric–optical property from its relative model compound. The difference between the systems were explained using a proposed model. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 721–732, 2005     

From Metal‐Metal Bonding to Supra‐Metal‐Metal Bonding Directed Self‐Assembly: Supramolecular Architectures of Group 10 and 11 Metals with Ligands from Mono‐ to Poly‐Pyrazoles

The supramolecular architectures of pyrazole ligands with polynuclear metal centers have established a wide variety of constructing motifs. This review focuses on the metal‐metal bonding and Supra‐Metal‐Metal Bonding directed self‐assembly of supramolecular architectures of pyrazole ligands ranging from simple mono‐pyrazoles and derivatives to bipyrazoles and polypyrazoles with group 10 and 11 elements. The utility of the constructing motifs (μ‐pyrazolato‐N,N′)₂ doubly‐bridged dimetal corners in the metal‐metal‐bonding directed self‐assembly approaches with spontaneous deprotonation from bipyrazole to tripyrazole and tetrapyrazolyl calix[4]arene ligands, metallomacrocyclic and cage‐like complexes have been synthesized. The proton switching programmable self‐assembly strategy using pyrazole‐based bifunctional ligands has been developed by Yu. They have obtained organic homo‐ or hetero‐metallic supramolecular complexes from macrocycles, cages, to one dimensional polymers.     

Self‐healing supramolecular elastomers based on the multi‐hydrogen bonding of low‐molecular polydimethylsiloxanes: Synthesis and characterization

Novel self‐healing supramolecular elastomers based on polydimethylsiloxanes (SESi) were synthesized from a mixture of polydimethylsiloxanes derivers with single, di‐, or tri‐carboxylic acid groups (PDMS–COOH_x, where x = 1, 2, and 3, respectively), diethylene triamine, and urea with a two‐stage procedure. The reactions and the final products were tracked, characterized, and confirmed by Fourier transform infrared spectroscopy, ¹H‐NMR, differential scanning calorimetry, dynamic mechanical analysis, and gel permeation chromatography. Compared with a supramolecular rubber based on dimer acid (reported previously) with a similar synthesis procedure, the SESi showed a lower glass‐transition temperature of about ?113°C for the softer chain of polydimethylsiloxane and showed real rubberlike elastic behavior and self‐healing properties at room temperature or even lower temperatures. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Controllable self‐assembly of polystyrene‐block‐poly(2‐vinylpyridine)

Block copolymers can form various ordered structures by self‐assembly, and their composites with inorganic materials may give surprising properties. This review summarizes recent developments in the preparation, mechanism and application of various types of self‐assembly of polystyrene‐block‐poly(2‐vinylpyridine) (PS‐b‐P2VP). The focus of the review is on how to control the self‐assembly of the dynamic and ordered structure of PS‐b‐P2VP based materials by applying effective factors such as thermal annealing, solvent annealing, block composition and blending. Moreover, the combination of the self‐assembly of PS‐b‐P2VP and various nanoparticles, with potentials in drug delivery, sensors and catalysis, is highlighted. © 2018 Society of Chemical Industry     

C3‐Symmetrical π‐Scaffolds: Useful Building Blocks to Construct Helical Supramolecular Polymers

In this review, we highlight some relevant examples of C₃‐symmetrical molecules that have been reported to form supramolecular polymers and helical aggregates. In particular, the number and type of non‐covalent forces are key to bias the supramolecular polymerization leading from a simple isodesmic or cooperative mechanism to a more complex self‐assembly process, i. e. pathway complexity. Furthermore, the attachment of stereogenic centres at the peripheral side chains of the C₃‐systems provokes efficient transfer and amplification of chirality phenomena when directional and specific non‐covalent interactions operate. Interestingly, the incorporation of hydrophilic side chains induces the formation of organized aggregates in aqueous media with potential biomedical applications. Overall, the examples shown in this review on C₃‐symmetrical scaffolds illustrate the relevance of this molecular shape in the development of functional supramolecular structures.     

Supramolecular composites of photo‐cured acrylated castor oil and fibers formed by the self‐assembly of low molecular weight organic gelators

A mixture of acrylated castor oil (ACO) with N‐carbobenzyloxy‐L ‐isoleucylaminooctadecane (CIA) or (R)‐12‐hydroxystrearic acid (HSA) containing photo‐initiators was heated to 130°C and gradually cooled to room temperature to give bio‐based gelatinous material. The photo‐curing of the gel generated a crosslinked ACO composite containing CIA or HSA. The optical micrographic and differential scanning calorimetry analyses revealed that a supramolecular fibrous network is formed for photo‐cured ACO (cACO)/CIA and that spherulitic crystals are formed for cACO/HSA. The tan δ peak temperatures measured by dynamic mechanical analysis for cACO/CIA and cACO/HSA composites were higher than that of cACO. The flexural strength and modulus of cACO/CIA composites increased with an increase of CIA content, and those values were higher than those of cACO/HSA composites. POLYM. COMPOS., 33:2001–2008, 2012. © 2012 Society of Plastics Engineers