Hierarchical self-assembly of fluorine-containing diblock copolymer:From onion-like nanospheres to superstructured microspheres

Superstructured microspheres were prepared via a two-tier hierarchical assembly of a fluorine-containing diblock copolymer, poly(tert-butyl acrylate)-b-poly(2-[(perfluorononenyl)oxy]ethyl methacrylate) (PtBA-b-PFNEMA) with well controlled block lengths. At tier 1, water induced self-assembly of the diblock copolymer produced nanospheres of low dispersity with onion-like multilayer inside structures, which were the consequence of the gradual aggregation of the fluorinated segments by accessing the super-strong segregation regime. And both the size and inner structure could be tuned by changing the water addition rate. At tier 2, nanospheres with different sizes were chosen as the building blocks for the formation of closely packed superstructural microspheres through an evaporation assisted process. The packing rules were governed by the volatility distinction between THF and water, the dispersity of nanospheres, and other various forces, such as the capillary force.     

Self-assembly of amphiphilic liquid crystal block copolymers containing a cholesteryl mesogen: Effects of block ratio and solvent

We report on the self-assembly, in water and in bulk, of amphiphilic liquid crystal block copolymers consisting of a cholesterol-based smectic LC polymer block (PAChol) and poly(ethylene glycol) (PEG) block. Two series of block copolymers, PEG₄₅-b-PAChol and PEG₁₁₄-b-PAChol (45 and 114 are the degree of polymerization of PEG blocks) with different hydrophilic/hydrophobic weight ratios were synthesized and characterized in detail. Depending on the diblock composition, smectic polymer vesicles and/or nanofibers were formed by adding water into a dilute solution of copolymers in dioxane. If THF is used instead of dioxane as solvent, solid spherical aggregates were obtained upon water addition for PEG₄₅-b-PAChol series, while macroscopic precipitation occurred for PEG₁₁₄-b-PAChol series. The mesomorphic and microphase segregation structures of the block copolymers in bulk were studied by X-ray scattering, DSC and POM. The interdigital smectic A (SmA_d) phase with a lamellar period of 4.25 nm was detected in all block copolymers. For PEG₁₁₄-b-PAChol₅ (PEG/PAChol weight ratio = 66/34) and PEG₁₁₄-b-PAChol₁₂ (45/55), lamellar type of microphase segregation was observed.     

Formation of nanostructures in thermosets containing block copolymers: From self-assembly to reaction-induced microphase separation mechanism

In this work, we investigated the effect of formation mechanisms of nanophases on the morphologies and thermomechanical properties of the nanostructured thermosets containing block copolymers. Toward this end, the nanostructured thermosets involving epoxy and block copolymers were prepared via self-assembly and reaction-induced microphase separation approaches, respectively. Two structurally similar triblock copolymers, poly(ε-caprolactone)-block-poly(butadiene-co-styrene)-block-poly(ε-caprolactone) (PCL-b-PBS-b-PCL) and poly(ε-caprolactone)-block-poly(ethylene-co-ethylethylene-co-styrene)-block-poly(ε-caprolactone) (PCL-b-PEEES-b-PCL) were synthesized via the ring-opening polymerization of ε-caprolactone (CL) with α,ω-dihydroxyl-terminated poly(butadiene-co-styrene) (HO-PBS-OH) and α,ω-dihydroxyl-terminated poly(ethylene-co-ethylethylene-co-styrene) (i.e., HO-PEEES-OH) as the macromolecular initiators, respectively; the latter was obtained via the hydrogenation reduction of the former. Both the triblock copolymers had the same architecture, the identical composition and close molecular weights. In spite of the structural resemblance of both the triblock copolymers, the formation mechanisms of the nanophases in the thermosets were quite different. It was found that the formation of nanophases in the thermosets containing PCL-b-PBS-b-PCL followed a reaction-induced microphase separation mechanism whereas that in the thermosets containing PCL-b-PEEES-b-PCL was in a self-assembly manner. The different formation mechanisms of nanophases resulted in the quite different morphologies, glass transition temperatures (T_g's) and fracture toughness of the nanostructured thermosets.     

Binary blends of linear ethylene copolymers over a wide crystallinity range: Rheology, crystallization, melting and structure properties

This study deals with the physical properties of melt-compounded blends of three linear ethylene copolymers covering a large crystallinity range, namely 77% - 46% - 16% for the high density - linear low density - ultra low density copolymers, respectively. The melt behavior assessed from the zero-shear viscosity (η_o) reveals immiscibility of the three binary systems over the whole composition range. However, the change from positive to negative deviation of η_o with respect to the log-additivity mixing law as a function of composition suggests a structural transition from partial miscibility at the interface of the phase-separated domains to incompatibility. Crystallization and melting behaviors of the blends corroborate the occurrence of phase separation in the three systems. For most blends, the temperature shift of the crystallization (T_c) and melting (T_m) peaks as compared to the ones of the pure copolymers yet indicates partial miscibility in the crystalline and/or in the amorphous regions. It is pointed out that miscibility in the amorphous phase resulting from partial miscibility in the melt may, on its own, entail T_m depression of the crystals via surface free energy effect without necessarily implying cocrystallization and crystal thickness reduction. In several cases, the presence of intermediate endotherm and exotherm between the two main peaks of the melting and crystallization traces, respectively, discloses hybrid crystals assigned to a composition gradient at the interface of the phase-separated domains. A marked positive deviation of the upper T_c from the linear mixing rule is observed for the three systems. A nucleating effect from the interface of the phase-separated domains is suggested to promote early crystallization in the upper T_c phase. The SAXS data reveal electron density fluctuations at a much larger scale than that of the semi-crystalline structure demonstrating the occurrence of micro-phase separation in the melt prior to crystallization. Solubility of low T_m chain species in the amorphous layers of the high T_m phase is also evidenced. AFM and DMTA support micro-phase separation in the three systems and provide complementary information on the crystalline habits in the phase-separated domains of the blends.     

Preparation of a new polymer‐dispersed liquid crystal film by using phthalocyanine‐functional photocurable copolymer

A new, asymmetrical zinc phthalocyanine (aZnPc)‐functional photocurable copolymer was prepared by the combination of atom transfer radical polymerization and copper (I)‐catalyzed azide‐alkyne cyclo‐addition (CuAAC) click reaction and used as polymer matrix of polymer dispersed liquid crystal (PDLC) film. For this purpose, aZnPc was prepared through statistical condensation of 4‐tert‐butylphthalonitrile and 4‐pent‐4‐ynyloxyphthalonitrile. Double CuAAC click reaction between azido‐functional poly(methyl methacrylate‐co‐2‐(2‐bromoisobutyryloxy)‐ethyl methacrylate), terminal alkynyl‐substituted aZnPc, and 4‐ethynyl‐N,N‐dimethyl aniline yielded photocurable aZnPc‐functional copolymer. Thereby, synthesized copolymer was crosslinked in the presence of liquid crystalline mesogen 4′‐(octyloxy)‐4‐biphenylcarbonitrile by ultraviolet irradiation using benzophenone as initiator and ethylene glycol dimethacrylate as difunctional crosslinker. Thermal and optical properties of PDLC film were investigated by using differential scanning calorimetry and polarized optical microscopy. Smectic A liquid crystal mesophases were observed in both PDLC film and its mesogenic component 4′‐(octyloxy)‐4‐biphenylcarbonitrile. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41574.     

Oxidative Desulfurization‐Fluorination: A Facile Entry to a Wide Variety of Organofluorine Compounds Leading to Novel Liquid‐Crystalline Materials

The oxidative desulfurization‐fluorination reaction of organosulfur compounds using an N‐haloimide and a fluoride source is demonstrated to be an effective and mild fluorinaton method that allows us to synthesize in high yields with high chemoselectivity various types of gem‐difluoro compounds, trifluoromethyl‐substituted (hetero)aromatics, trifluoromethyl ethers, and N‐trifluoromethylanilines. Herein briefly summarized are the synthetic procedures as well as the scope and limitations of the reaction. The applicability of the reaction is demonstrated by the synthesis of a difluorinated glutamic acid and novel liquid‐crystalline materials having an N‐trifluoromethylamino, trifluoromethoxy, or 1,2‐difluoroethylene group. The fluorine‐containing liquid‐crystalline materials are compared with the corresponding non‐fluorinated materials in respect to phase transition behaviors and electro‐optical properties and shown to be suitable for not only super twisted nematic (STN) but also for thin film transistor (TFT)‐addressed liquid crystals displays. 1. Introduction 2. Fluorination Reactions 2.1 Fluorination of Sulfides and Thiols 2.2 Fluorination of Dithioacetals 2.3 Oxidative Desulfurization‐Fluorination of Dithioester and Orthothioester 2.4 Synthesis of Trifluoromethyl Ethers from Dithiocarbonates 2.5 Oxidative Desulfurization‐Fluorination of Thionesters and Thioncarbonates 2.6 Synthesis of Trifluoromethylamines from Dithiocarbamates 3. Synthesis and Electro‐Optical Properties of Novel Fluorine‐Containing Liquid Crystals 3.1 Synthesis and Electro‐Optical Properties of N‐Trifluoromethylamino‐Substituted Liquid Crystals 3.2 Syntheses and Electro‐Optical Properties of Liquid Crystals having Trifluoromethoxy Polar Functional Group 3.3 Synthesis and Properties of 3‐Substituted Phenyl Trifluoromethyl Ethers 3.4 Synthesis and Electro‐Optical Properties of Liquid Crystals with a vic‐Difluoro‐Olefinic Moiety     

Support surface pore structures matter: Effects of support surface pore structures on the TFC gas separation membrane performance over a wide pressure range

In this work, the effects of support surface pore structures(including surface pore size, surface pore density and surface porosity) on the performance of thin film composite(TFC) gas separation membrane over a wide pressure range(from 0.3 to 2.0 MPa) were studied. To fulfill it, the polysulfone(PSf) supports with different surface pore structures were prepared. Two kinds of wide-accepted polymeric membrane materials, i.e., polyvinylamine(PVAm) and Pebax 1657 copolymer, were used as skin layer materials. We pointed out for the first time that the support surface average pore size and pore density could affect the chain mobility of polymer of skin layer at the support surface pore entrance, then, can affect the TFC membrane performance. Besides, we also discussed the effects of support on the TFC membrane performance when the feed pressure changes for the first time. This work can provide guidance for choosing a suitable support for TFC gas separation membrane.     

Synthesis and Photobehavior of a New Dehydrobenzoannulene-Based HOF with Fluorine Atoms: From Solution to Single Crystals Observation

Hydrogen-bonded organic frameworks (HOFs) are the focus of intense scientific research due their potential applications in science and technology. Here, we report on the synthesis, characterization, and photobehavior of a new HOF (T12F-1(124TCB)) based on a dehydrobenzoannulene derivative containing fluorine atoms (T12F-COOH). This HOF exhibits a 2D porous sheet, which is hexagonally networked via H-bonds between the carboxylic groups, and has an interlayers distance (4.3 Å) that is longer than that of a typical π–π interaction. The presence of the fluorine atoms in the DBA molecular units largely increases the emission quantum yield in DMF (0.33, T12F-COOH) when compared to the parent compound (0.02, T12-COOH). The time-resolved dynamics of T12F-COOH in DMF is governed by the emission from a locally excited state (S1, ~0.4 ns), a charge-transfer state (S1(CT), ~2 ns), and a room temperature emissive triplet state (T1, ~20 ns), in addition to a non-emissive triplet structure with a charge-transfer character (T1(CT), τ = 0.75 µs). We also report on the results using T12F-ester. Interestingly, FLIM experiments on single crystals unravel that the emission lifetimes of the crystalline HOF are almost twice those of the amorphous ones or the solid T12F-ester sample. This shows the relevance of the H-bonds in the photodynamics of the HOF and provides a strong basis for further development and study of HOFs based on DBAs for potential applications in photonics.     

Measurement of Consumed Energy Due to the Two-Phase Pressure Drop in a Pulsed Semi-Industrial Column: Effect of Geometry

This article deals with the evaluation of pressure drop and consumption of energy for a steady-state solvent extraction in a horizontal pulsed sieve-plate column, which are important for the design and optimization of the periodic-flow processes for industrial applications. In this study, the pressure drop and the position of loading points are investigated. Moreover, a mathematical evaluation on the energy consumption in the case of a pulsed flow is conducted, and besides the influence of pulsation intensity, the effect of geometrical parameters including the plate spacing and plate-free area is investigated as well. The results of this study are helpful for optimization of column geometry targeted to higher performance and lower energy consumption.     

High molecular weight hydrophilic functional copolymers by free‐radical copolymerization of acrylamide and of N‐acryloylmorpholine with N‐acryloxysuccinimide: Application to the synthesis of a graft copolymer

Free‐radical solution copolymerization of acrylamide (AAm) and of a disubstituted acrylamide derivative, N‐acryloylmorpholine (NAM), with N‐acryloxysuccinimide (NAS) was investigated with the aim to obtain a copolymer of at least 100,000 g mol^?1. Different polymerization conditions likely to increase the molecular weight were studied such as monomer and initiator concentrations, temperature, and nature of the solvent. The molecular weights were determined by SEC using a light‐scattering detector. The grafting of end‐functionalized polysaccharide chains onto such high molecular weight poly(NAM‐co‐NAS) was performed and a graft copolymer bearing a high number of saccharidic branches was obtained. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1808–1816, 2003