Self‐assemblies Based on Poly(4‐diazonium styrene)

Summary: A series of self‐assembled photosensitive ultra‐thin films have been fabricated from poly(4‐diazonium styrene) (PDS) via different driving forces, mainly by electrostatic and H‐bonding interaction. Under exposure of UV light, the weak ionic and H‐bonds between the layers of the film will be converted to covalent bonds through a photoreaction. Thus, the stability of the film towards polar solvents is reinforced greatly.

UV‐vis spectra of the PDS‐MPR film with different bilayers.     

Effect of Imidazolium Monomer Structure on Properties of Imidazolium‐Functionalized Self‐Healing UV‐Cured Polymers for Flexible Electronic Devices

Self‐healing UV‐cured polymeric materials based on ionic interactions possess many distinct advantages such as reliability, long lifetime, and green preparation process, and thus obtain great potential development. In this work, a series of UV‐curable imidazolium monomers with different structures are designed and synthesized, and then imidazolium ionic interaction‐based self‐healing materials are prepared through fast and eco‐friendly UV‐curing technology. Also, the structures of imidazolium monomers on properties of self‐healing UV‐cured polymers are investigated. The results show that the structures of imidazolium monomers have no obvious influences on photopolymerization properties of the polymers. The hydroxyl group and polar ether chains in imidazolium monomers can increase the glass transition temperature (T_g) of the polymers. The large substituent at 1‐position of the imidazole ring enhances tensile strain of the polymers due to the reduction of the intermolecular force. The intermolecular forces and content of imidazole ionic groups all affect self‐healing efficiency of the polymers. The polymer containing HD‐IM‐E with a long and nonpolar pendent side chains exhibits an excellent self‐healing efficiency (>90%) and can be healed repeatedly. Importantly, the self‐healing polymer can also be used as a flexible electronic substrate to fabricate a flexible electronic device with good self‐healing function.     

A Comparative Study of Self‐Assembled Superstructures from Cellulose Stearoyl Ester and Poly(Vinyl Stearate)

Comb‐like cellulose stearoyl ester (CSE₃) and poly(vinyl stearate) (PVS) with distinct skeletons are successfully synthesized. Their self‐assembled superstructures are described and discussed comparatively herein. Differential scanning calorimetry investigation indicates that both comb‐like polymers with various molecular weights show the feasibility to form self‐assembled crystalline structures. The self‐assembled superstructures are obtained from both the evaporation‐induced and temperature‐induced phase separation processes. Due to the interference of different skeletons, self‐assembled superstructures of both comb‐like polymers demonstrate totally different morphologies. CSE₃ with semi‐flexible skeleton forms robust petals, which further grows into well‐organized flower‐like particles. In contrast, PVS with more flexible skeleton only form non‐ordered porous structures through stacking of the wrinkled and folded nanofilms.     

Universal Bioinert Control of Polystyrene Interfaces via Hydrophobic‐Driven Self‐Assembled Surface PEGylation with a Well‐Defined Block Sequence

This work proposes a new molecular insight of interfacial design in the control of antifouling performance for the versatile biofoulants, including proteins, blood cells, tissue cells, and bacteria. A self‐assembled bioinert interface with universal fouling resistance to general biofoulants via hydrophobic‐driven surface PEGylation is presented. The study systematically discriminates the optimum PEGylated block polymer configuration and hydrophobic/hydrophilic segmental ratio enabling to optimize the surface coverage by the bioinert moieties, thus ensuring the best resistance to biofouling. For similar copolymer molecular weights and similar polystyrene (PS)/poly(ethylene glycol) methacrylate (PEGMA), the coating density obtainable is the highest if a random copolymer is used, while it is the lowest with a triblock copolymer. That measured with a diblock copolymer lies in between. Random copolymers offer more numerous anchoring possibilities than diblock copolymers, while they are importantly fewer if triblock copolymers are used. For similar total number of hydrophilic blocks, the diblock copolymer is more efficient to resist larger cells (leukocytes, fibroblasts) while the triblock is better to promote mitigate biofouling by smaller molecules or cells (proteins, platelets, red blood cells). The length of the hydrophilic PEGylated block seems to dominate fouling resistance of large biofoulants.     

A New Class of Organosoluble Rigid‐Rod,Fully Aromatic Poly(1,3,4‐oxadiazole)s and Their Solid‐State Properties, 2. Solid‐State Properties

New symmetrical and unsymmetrical dialkoxy‐substituted aromatic poly(1,3,4‐oxadiazole)s are investigated by cyclovoltammetric measurements. The electrochemical redox behaviour of these materials is compared with the chemical structure. The reduction behaviour allows the estimation of the electron affinity, and shows that these polymers are suitable candidates for electron‐transport materials in electronic devices. Surprisingly it is found from UV‐vis and fluorescence spectroscopic measurements that the polyoxadiazole with linear alkoxy side chains (C16) shows a reversible thermochromism in solution as well as in the solid state. The changes in this temperature range are ascribed to a phase transition between aggregated chains, in solution as well as in the film, at room temperature and molecularly dissolved polymer chains at higher temperature. The other poly(1,3,4‐oxadiazole)s with branched alkoxy side chains exhibit an improved solubility and they are completely soluble in o‐dichlorobenzene at room temperature. The absorption and emission behaviour does not change in the temperature range from 25°C to 100°C. The fluorescence excitation studies of these poly(1,3,4‐oxadiazole)s show a blue emission in solution and in the film. Due to these results the poly(1,3,4‐oxadiazole)s are used as electron transport and blue emitting layers in electronic devices like diodes or polymer light emitting diodes (PLED).     

Poly(2‐vinylnaphthalene)‐block‐poly(acrylic acid) Block Copolymer: Self‐Assembled Pattern Formation,Alignment, and Transfer into Silicon via Plasma Etching

P2VN‐b‐PAA is a novel diblock copolymer which has potential as a self‐assembled nanoscale patterning material. Thin spin cast P2VN‐b‐PAA films rapidly reorganize to vertical lamellar with exposure to acetone vapor. P2VN‐b‐PAA lamellar morphology was aligned by electric field under acetone vapor at a significantly faster rate and at lower electric field strengths than other polymer systems. Observed dry etching selectivity for P2VN to PAA were comparatively high for a variety of etch gases, consistent with estimations from Ohnishi and ring parameters. Block copolymer self assembled patterns were transferred to silicon via two‐step CF₄ and SF₆ etching.

     

Effect of Light Exposure on UV‐Vis Spectrum of [(nBuCp)2ZrCl2] Based Catalyst

UV‐vis spectroscopic study revealed that vinylcyclohexane interaction with zirconocene catalyst is enhanced on light exposure. If oxygen is present it interacts with the catalyst, hindering vinylcyclohexane interaction and consequently lowering the catalyst activity. The catalyst activity can be recovered with light exposure if low O₂ concentrations are used since in light the zirconocene‐vinylcyclohexane interaction is favoured over the zirconocene‐O₂ interaction. Moreover, ¹H NMR studies of the reaction products showed that the structures of the vinylcyclohexane‐based species produced with light irradiation were identical to the species produced in dark. This indicates that light exposure of the catalytic system does not change the reaction mechanism.

Absorption spectrum of [(nBuCp)₂ZrCl₂]/MAO/VCH. (a) reaction in dark, (b) reaction with irradiation, (c) reaction with O₂ treatment in dark and (d) reaction with O₂ treatment with irradiation.     

Self‐Assembly of a Hydrogen‐Bonded Association Chain Liquid Crystalline Polymer (LCP)

A hydrogen‐bonded association chain liquid crystalline polymer (LCP) based on tetraethyleneglycoxy‐bis(2,6‐dimethyl‐4‐benzoic acid) and 4,4′‐(p‐phenylenedi‐1,2‐ethenediyl)bipyridyl in a 1 : 1 stoichiometric ratio was synthesized using melting mixing method. X‐ray scattering from fiber drawn from its nematic phase exhibits preferred orientation, indicating that hydrogen bonding association chain polymer can also be strong enough to withstand the shear or tensile force and could be macroscopically oriented under shear or tensile force. Two complimentary components are likely to form a co‐crystallized structure to form a monoclinic crystal.     

Method of Preparation of Soluble PEDOT: Self‐Polymerization of EDOT without Oxidant at Room Temperature

The preparation of soluble conducting polymers proceeds by the chemical oxidation method in the presence of water‐soluble polyelectrolytes. Among conducting polymers, polyethylene‐(3,4‐dioxythiophene) (PEDOT) is the most investigated due to its intrinsic properties. In this work, for the first time a simple method of ethylene‐(3,4‐dioxythiophne) self‐polymerization without applying any oxidant and with the formation of PEDOT solution at room temperature with a yield of 100% is presented. This PEDOT solution could be deposited on many desirable surfaces (by simple evaporation of the solvent) for various applications from photovoltaic cell to pseudocapacitors. Moreover, it is discovered that the self‐polymerization method does not produce byproducts, which makes the method environmentally friendly. The effect of light and different acids is explored. Fourier transform infrared spectroscopy, X‐ray photoelectron spectroscopy (XPS), and Raman spectroscopy confirm the formation of PEDOT by the self‐polymerization method. Moreover, this method provides a way to obtain and study individual PEDOT chains. The self‐polymerization method may be applied for the preparation of other conducting polymers.     

Investigation of Templated Mesoporous Silicate Thin Films Using High Speed,Solid‐State 1H MAS and Double Quantum NMR Spectroscopy

Two‐dimensional DQ ¹H MAS NMR has been used the investigate the local structure of a surfactant‐templated silicate thin film prepared from adding 4% polyoxyethylene(10) cetyl ether to an acidic TEOS silica sol. A close spatial contact between the surfactant and the silicate present in these materials could be demonstrated, while the high sensitivity of the NMR experiments allowed systems with limited amounts of material to be investigated. The detected inorganic‐organic interactions in these materials provide additional information into the chemical processes occurring during the self‐assembly process and the formation of meso‐structured materials.

Graphical representation of the spatial interactions observed between the silanols, oxomethylene protons of the surfactant and water within the template silicate material.     

PLLA‐Grafted Gelatin Amphiphilic Copolymer and Its Self‐Assembled Nano Carrier for Anticancer Drug Delivery

A series of poly(l ‐lactide)‐grafted gelatin (Gel‐g‐PLLA) copolymers are synthesized by coupling the amino groups of gelatin with different molar masses and the carboxyl endgroup of poly(l ‐lactide) in the presence of 1‐ethyl‐3‐(3‐dimethylaminopropyl)carbodiimide hydrochloride and N‐hydroxysuccinimide. Fourier transform infrared and nuclear magnetic resonance (¹H NMR) data confirm the successful bonding between gelatin and PLLA. Self‐assembled micelles of copolymers are prepared by using the direct dissolution method. The size and micellar morphology are determined from dynamic light scattering as well as transmission electron microscopy measurements. Meanwhile, in vitro drug release reveals that Gel‐g‐PLLA micelles show excellent sustained‐release properties when used as the carrier of the anticancer drug paclitaxel. A burst release of about 70% is observed in the first 24 h. All these features, together with the outstanding biocompatibility, make Gel‐g‐PLLA micelles a promising drug carrier for cancer therapy.     

Electrochromic Response of Nanostructured Poly(3,4‐ethylenedioxythiophene) Films Grown in an Aqueous Micellar Solution

Poly(3,4‐ethylenedioxythiophene) (PEDOT) films have been electropolymerized from an aqueous micellar solution encompassing the monomer (EDOT) and the moieties sodium dodecyl sulfate (SDS) and lithium triflate. The presence of these anionic dopants in the polymer matrix and a doping level of 0.26 have been confirmed by X‐ray photoemission and electron paramagnetic resonance (EPR) spectroscopy. The hydrophobic micellar core encompassing the monomer orchestrates the growth of a uniform homogeneous polymer deposit as electron microscopy and atomic force microscopy studies reveal the film to be composed of a continuous interlinked network of quasi‐spherical grains (50–150 nm in dimensions) and pores alongwith a low surface roughness. The film exhibits a large coloration efficiency of 153 cm² · C^?1 and a transmission modulation of 62% (λ = 632.8 nm), which are manifestations of the open ion‐permeable morphology. The Q_{(inserted/extracted)} ratio ranges between 1.2 and 1.4 when cycled back and forth between the clear and blue states 2 500 times, thereby affirming the suitability of these films for practical electrochromic smart windows.

     

Synthesis of Polystyrene‐block‐Poly(methyl methacrylate) with Fluorene at the Junction: Sequential Anionic and Controlled Radical Polymerization from a Single Carbon

Polystyrene‐block‐poly(methyl methacrylate) (PS‐b‐PMMA) has been synthesized by sequential anionic and reverse atom transfer radical polymerization (ATRP) or a variation of nitroxide mediated polymerization (NMP) from a single initiating site, specifically the 9‐carbon on 2,7‐dibromofluorene or fluorene. The addition of the second arm (PS) relied on thermal decomposition of 2,2′‐azoisobutyronitrile (AIBN) to generate radicals, abstracting the 9‐H on the polymer‐bound fluorene species to form the initiating radical. Styrene was not present in the reaction mixture when AIBN was decomposed, preventing competition between addition across the monomeric alkene and hydrogen abstraction from the fluorene. After 1 h, styrene was introduced and mediation of the subsequent radical polymerization was achieved by the presence of CuCl₂/ligand or TEMPO. Characterization of the diblock copolymers by gel permeation chromatography (GPC) revealed substantial shifts in number average molecular weight ( ) values compared to the anionically prepared PMMA macroinitiator, while polydispersity indices (PDI's) remained relatively low (typically < 1.5). Characterization by UV detection with GPC (at 310 nm) verified that the diblock polymer is chromophore‐bound, which was further verified by UV‐vis spectroscopy of the isolated diblock.

     

Polystyrene End‐Labeled with 2,7‐Dibromofluorene Synthesized Using an Adaptation of Reverse Atom Transfer Radical Polymerization

Summary: Polystyrene with high amounts of end‐labeling was synthesized using initiating systems comprised of conventional radical initiators and 2,7‐dibromofluorene or other fluorene derivatives in an adaptation of reverse atom transfer radical polymerization (RATRP). Benzoyl peroxide (BPO) or 2,2′‐azoisobutyronitrile (AIBN) were decomposed and allowed to react with 2,7‐dibromofluorene, 2‐bromofluorene, or fluorene in the presence of ligand‐bound CuX₂ allowing for abstraction of the 9‐H from the fluorenyl species and the establishment of an equilibrium between the subsequent active radical and the dormant alkyl halide. Gel permeation chromatography (GPC) traces indicated CuCl₂‐catalyzed reactions produced polymers possessing narrow polydispersity index (PDI) values <1.3 with AIBN and 2,7‐dibromofluorene systems, while analogous reactions catalyzed using CuBr₂ were less controlled (PDI > 1.7). Analysis of the polymers using UV‐vis spectroscopy and UV‐GPC demonstrated competition between initiation from both the conventional radical initiator and fluorenyl species generating polymers end‐labeled with both the 2,7‐dibromofluorene and isobutyronitrile groups. Fluorene or 2‐bromofluorene as co‐initiators led to lowered amounts of end‐labeling, but the polymers generally possessed lower PDI values compared to 2,7‐dibromofluorene systems.

     

The Swelling Behavior of Polyelectrolyte Multilayers in Air of Different Relative Humidity and in Water

The swelling properties of physisorbed polyelectrolyte multilayer self‐assemblies with alternating polyion charge in humid air and in aqueous environment were investigated via X‐ray and neutron reflectometry as well as optically, using surface plasmon spectroscopy. The sorption behavior was similar to that found for neutral polymers and was related to an internal screening of the charges of the adjacent layers owing to the high entanglement of the polyelectrolyte chains and the resulting low mobility of the polymer segments. The screening was found to be incomplete only in the top layer, resulting in a net charged surface.     

Poly(amine‐amide‐imide)s Bearing Pendent N‐Carbazolylphenyl Moieties: Synthesis and Electrochromic Properties

Summary: A series of novel poly(amine‐amide‐imide)s with pendent N‐carbazolylphenyl units that have inherent viscosities of 0.45–0.66 dL · g⁻¹ are prepared from various aromatic bis(trimellitimide)s and the new carbazole‐based aromatic diamine, 4,4′‐diamino‐4″‐N‐carbazolyltriphenylamine, by direct polycondensation. All the polymers are readily soluble in polar organic solvents. Flexible, amorphous, and deep reddish films of poly(amine‐amide‐imide)s can be obtained by solution casting, and have useful levels of thermal stability associated with high glass transition temperatures (307–343 °C), 10% weight‐loss temperatures in excess of 500 °C, and char yields at 800 °C in nitrogen higher than 65%. These polymers exhibit a maximum UV‐vis absorption at 300 nm with a fluorescence emission maxima around 449–454 nm in N‐methyl‐2‐pyrrolidinone solution. The hole‐transporting and electrochromic properties are examined by electrochemical and spectroelectrochemical methods. Cyclic voltammograms of the poly(amine‐amide‐imide) films cast onto an indium tin oxide‐coated glass substrate exhibit a reversible oxidation at 0.84 V and irreversible oxidation redox couples at 1.27 V versus Ag/AgCl in acetonitrile solution, and reveal good stability of electrochromic characteristics, with a color change from yellowish to green at applied potentials ranging from 0.00 to 0.95 V.

Structure and properties of PAI‐2M (bottom left: cyclic voltammetry; bottom right: potential‐step absorptometry).     

The Effect of NaCl on the Conformational Behavior of Acenaphthylene Labeled Poly(N,N‐diethylacrylamide) in Dilute Aqueous Solution

Summary: The effect of salts on the conformational behavior of acenaphthylene labeled poly(N,N‐diethylacrylamide) (PDEA/ACE) has been investigated in dilute aqueous solution using UV‐vis and fluorescence spectroscopy. It is demonstrated here that the effectiveness of various salts in changing the lower critical solution temperature (T_LCS) of the PDEA/ACE solution followed the Hoffmeister series. The addition of NaCl linearly lowered the T_LCS. In dilute aqueous solution, the PDEA/ACE adopted a loose coil conformation below its T_LCS. The PDEA/ACE adopted a compact globule conformation above the temperature at which the coil to globule transition (CGT) was completed. A fluorescence anisotropy investigation suggested that a molten globule conformation existed during the CGT of the PDEA/ACE solution. In all of the above three conformations, the PDEA/ACE was more compact in the presence of NaCl than in the absence of any salt.

Temperature and NaCl concentration dependence of fluorescence anisotropy of a PDEA/ACE solution. Inset: thermodynamically stable states of PDEA/ACE.     

Layer‐by‐Layer Formation of Polyamine‐Salt Aggregate/Polyelectrolyte Multilayers. Loading and Controlled Release of Probe Molecules from Self‐Assembled Supramolecular Networks

The use of soft materials as building blocks in layer‐by‐layer (LbL) assemblies represent a very appealing and useful approach to enhance the loading capacity of thin films. Here, the capacity of positively charged polyamine‐salt aggregates (PSAs) based on ionically crosslinked poly(allylamine hydrochloride) (PAH) with phosphate anions (Pi) is explored to act as building blocks in construction of multilayers by alternated deposition with poly(sodium 4‐styrenesulfonate). Hybrid thin films are successfully prepared by the LbL technique with a highly regular growth and a material deposition rate higher than the traditional full polyelectrolyte LbL. The loading of bromophenol blue (BPB) is evaluated by integration into PSAs followed by LbL deposition and monitored with UV–vis spectroscopy. Finally, the release of the dye molecules is carried out by exposing the film to different aqueous solutions. It is shown that a fully controlled release can be achieved by simply varying the media pH obtaining total BPB release over periods between minutes and months. The data obtained reveal that this new LbL construction strategy using ionically crosslinked PAH/Pi colloids allows to obtain nanoarchitectures with high loading capacity and remarkable properties for controlled release.     

Solvent‐Vapor‐Induced Rapid Assembly of Block‐Copolymer Film via Prevacuumizing

The undesired long time for the self‐assembly of block‐copolymer (BCP) thin films restricts their application as a template in lithography and other technologies. To shorten the assembly time, a facile but versatile strategy of solvent‐vapor‐induced rapid assembly into a uniform ordered morphology of polystyrene‐block‐poly(methyl methacrylate) (PS‐b‐PMMA) thin film via prevacuumizing is reported. Factors such as the prevacuum pressure and the temperature during the solvent‐vapor‐annealing process are investigated for their effects on the assembly time. The morphologies are observed by transmission electronic microscopy (TEM) and the results indicate that the time for the assembly of PS‐b‐PMMA with a PS‐cylinder‐forming composition into a morphology of hexagonally arranged PS spheres in the film, induced by the solvent vapor at a prevacuum pressure 0.02 atm, is only 4 min at 20 °C and shortens more to 1 min at 60 °C.

     

An Injectable ROS‐Responsive Self‐Healing Hydrogel Based on tetra‐poly(ethylene glycol)‐b‐oligo(l‐methionine)

Abnormal physiological conditions provide an ideal stimulus for the design of responsive hydrogels which function as controlled and site‐specific release of drugs. Here, an injectable reactive oxygen species (ROS) responsive self‐healing hydrogel based on tetra‐poly(ethylene glycol)‐b‐oligo (l ‐methionine) (t‐PEG₅₆‐b‐OMeth_n) synthesized by a novel and facile method is reported. The hydrophobic interactions between the side chains of l ‐methionine make the polymer chains crosslinked and lead to the formation of hydrogels which can be injected and self‐healed, meanwhile, the cross‐linker also provides a hydrophobic domain to encapsulate Dox. In presence of ROS, the side chain of l ‐methionine can be oxidized to methionine sulfoxide. The side chain of l ‐methionine is changed accordingly from hydrophobic to hydrophilic. As a result, both the hydrophobic domain and the hydrogel itself are destroyed. The controlled release of Dox by ROS at site‐specific is realized. The excellent biocompatibility of hydrogel based on t‐PEG₅₆‐b‐OMeth_n indicates the door of the potential application in controlled release of drug in a truly physiological environment.