Main‐chain viologen polymers with organic counterions exhibiting thermotropic liquid‐crystalline and fluorescent properties*

A series of viologen polymers with bromide, tosylate, and triflimide as counterions were prepared by either the Menshutkin reaction or metathesis reaction in a common organic solvent. Their polyelectrolyte behavior in methanol was determined by solution viscosity measurements, and their chemical structures were determined by Fourier transform infrared and Fourier transform NMR spectroscopy. They were characterized for their thermotropic liquid‐crystalline properties with a number of experimental techniques. Each of the viologen polymers with organic counterions had a low melting transition or fusion temperature above which it formed either a high‐order smectic phase or a low‐order smectic phase. Each of them also exhibited a smectic‐to‐isotropic transition. The ranges of the liquid‐crystalline phase were 80–88 °C for viologen polymers with tosylate as a counterion and 120–146 °C for viologen polymers with triflimide as a counterion. They had excellent thermal stability. The ranges of thermal stability were 288–329 °C for viologen polymers with tosylate as a counterion and 343–350 °C for viologen polymers with triflimide as a counterion. The fluorescence property for all of the viologen polymers in either aqueous or methanol solution was also included in this study. For example, the viologen polymer containing the 4,4′‐bipyridinium and p‐xylyl units along the backbone of the polymer chain with triflimide as a counterion had an absorption spectrum (λ_max = 265 nm), an excitation spectrum (λ_ex values = 357, 443, and 454 with monitoring at 533 nm), and an emission spectrum (λ_em = 536 nm with excitation at 430 and 450 nm) in methanol. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 659–674, 2002; DOI 10.1002/pola.10134     

Double thermoresponsive block–random copolymers with adjustable phase transition temperatures: From block‐like to gradient‐like behavior

Stimuli‐responsive block–random copolymers are very useful “smart” materials as their switching behavior can be tuned by simply adjusting the composition of the random copolymer block. Because of that, we synthesized double thermoresponsive poly(N‐acryloylpyrrolidine)‐block‐poly(N‐acryloylpiperidine‐co‐N‐acryloylpyrrolidine) (PAPy‐b‐P(APi‐co‐APy)) copolymers via reversible addition fragmentation chain transfer (RAFT) polymerization and investigated their temperature‐induced self‐assembly in aqueous solution. By varying the APi/APy ratio in the random copolymer block, its phase transition temperature (PTT₁) can indeed be precisely adjusted while the temperature‐induced collapse upon heating leads to a fully reversible well‐defined micellization. By making the two blocks compositionally similar to more than 60%, the polymers' mechanistic thermoresponsiveness can furthermore be changed from block‐like to rather gradient‐like behavior. This means the micellization onset at PTT₁ and the corona collapse at the PTT of the more hydrophilic pure PAPy block (PTT₂) overlap resulting in one single broad transition. This work thus contributes to the detailed understanding of design, synthesis and mechanistic behavior of tailored “on‐demand” switchable materials. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 399–411     

Photoactive,liquid‐crystalline,hyperbranched benzylidene polyesters: Synthesis and characterization

A novel photoactive, liquid‐crystalline, hyperbranched benzylidene polyester (PAHBP) was synthesized from a dilute solution of an A₂ photoactive monomer [bis(4‐hydroxybenzylidene)‐4‐phenyl cyclohexanone] and a B₃ monomer (1,3,5‐benzene tricarboxylic acid chloride) by the solution polycondensation method in the presence of pyridine as a condensing agent. PAHBP was thoroughly characterized by Fourier transform infrared, ¹H and ¹³C NMR, ultraviolet–visible spectrometry, and gel permeation chromatography. The inherent viscosity of the polymer was 0.35 dL/g in tetrahydrofuran. The degree of branching was 0.53, which confirmed the branched architecture of the polymer. Furthermore, thermogravimetric analysis, differential scanning calorimetry, and polarized optical microscopy were used to examine the thermal stability and thermotropic liquid‐crystalline properties of the hyperbranched polyester. The polymer exhibited a nematic mesophase over a wide range of temperatures. The photoreactivity of PAHBP was studied by photolysis under ultraviolet light. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 53–61, 2006     

Solution processing of polymer semiconductor: Insulator blends—Tailored optical properties through liquid–liquid phase separation control

It has been demonstrated that the 0‐0 absorption transition of poly(3‐hexylthiophene) (P3HT) in blends with poly(ethylene oxide) (PEO) could be rationally tuned through the control of the liquid–liquid phase separation process during solution deposition. Pronounced J‐like aggregation behavior, characteristic for systems of a low exciton band width, was found for blends where the most pronounced liquid–liquid phase separation occurred in solution, leading to domains of P3HT and PEO of high phase purity. Since liquid–liquid phase separation could be readily manipulated either by the solution temperature, solute concentration, or deposition temperature, to name a few parameters, our findings promise the design from the out‐set of semiconductor:insulator architectures of pre‐defined properties by manipulation of the interaction parameter between the solutes as well as the respective solute:solvent system using classical polymer science principles. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 304–310     

Preparation of liquid–crystal thermosets: In situ photopolymerization of oriented liquid–crystal diacrylates

The photoinitiated polymerization of 2-chloro-1,4-phenylene bis[4-[6-(acryloyloxy)hexyloxy]benzoate] (1M) was studied. The monomer 1M exhibited a broad nematic phase between 24.9 and 113.7 °C on a DSC cooling scan. It was oriented in its nematic phase at a substrate coated with polyimide and unidirectionally rubbed with a nylon cloth. During polymerization, the ordering of the liquid–crystal molecules was fixed, yielding a uniaxially crosslinked network. The clear liquid–crystal networks (LCNs) exhibited a birefringence between 0.14 and 0.19, depending on the polymerization temperature. Finally, a nonmesogenic diluent, tetra(ethylene glycol)diacrylate, was mixed with 1M, subsequently decreasing the birefringence of the obtained LCNs. The LCNs containing nonmesogenic diluent exhibited not only a smaller birefringence but also a weaker birefringence dispersion in the visible region. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3929–3935, 1999     

Ferrocene‐based organophosphorus liquid–crystalline polymers: Synthesis and characterization

Ferrocene‐containing polyphosphate and phosphonate esters were synthesized by the solution polycondensation method. The structure of the polymers was confirmed using various spectroscopic techniques. The formation of two types of chain blocks was confirmed by ³¹P NMR spectroscopy. Hot stage optical polarized microscope (HOPM) analysis revealed that all the polymers have a liquid–crystalline property. The char yields of the synthesized similar polymers were much higher than those of nonphosphorus polymers already reported in the literature. DSC analysis confirmed our predictions over the liquid–crystalline property, glass‐transition temperature, isotropization temperature, and thermal stability of the polymers. The effects of substitution on the side chain, structure of the liquid‐–crystalline phase, and thermal stability of the polymers have also been discussed. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2396–2403, 2001     

Phase behavior study of poly(N‐tertbutylacrylamide‐co‐acrylamide) in the mixture of water–methanol: The role of polymer–nonsolvent second‐order interactions

The phase behavior of poly(N‐tertbutylacrylamide‐co‐acrylamide) (PNTBAM) in pure water and mixture of water–methanol is studied at different temperatures. The different compositions of PNTBAM are prepared by free‐radical polymerization technique and their phase behavior is studied by turbidimetry. The effects of copolymer and solvent composition on the phase behavior of the copolymers are discussed. It has been suggested that the inhomogenities in polymer chains are responsible for lowering the rate of phase transition by increasing the N‐tertbutylacrylamide (NTBAM) and methanol contents in copolymer and mixture, respectively. For the first time we have revealed that there are second‐order binary interactions in the water–methanol which are dominant in the special range of copolymer composition. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 455–462, 2009     

Phase equilibria in polymer–liquid–liquid systems

The phase equilibria in polymer–liquid 1–liquid 2 ternary systems have been calculated on the basis of the Flory-Huggins theory of polymer solutions. A new approximation method based on the “cluster” concept has been introduced for mixed solvents comprising a solvent and a nonsolvent. This concept has been verified with polystyrene–solvent–methanol systems.     

Micro ATR‐FTIR study of the hydration state of poly(N‐tert‐butylacrylamide‐co‐acrylamide) copolymers during phase transition in aqueous media and in the mixture of water–methanol

Coil‐globule transition of poly(N‐tert‐butylacrylamide‐co‐acrylamide) P(NTBAM‐co‐AM) copolymers is investigated in the aqueous solution and in the mixture of water–methanol by micro ATR‐FTIR spectroscopy technique. In this study the microstructure and its changes in the hydration states of the distinct groups of these copolymers are investigated by micro ATR/FTIR technique. The results showed that by heating the solution above the LCST hydrogen bonding between C?O and water was decreased but the hydrogen bonding between polymeric chains increased, which prove the aggregation of polymer chain during phase separation. The chemical shifts of IR bands are also studied in the mixture of water–methanol. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 356–363, 2010     

Development of new extraction method based on liquid–liquid–liquid extraction followed by dispersive liquid–liquid microextraction for extraction of three tricyclic antidepressants in plasma samples

In the present study, a new extraction method based on a three–phase system, liquid–liquid–liquid extraction, followed by dispersive liquid–liquid microextraction has been developed and validated for the extraction and preconcentration of three commonly prescribed tricyclic antidepressant drugs – amitriptyline, imipramine, and clomipramine – in human plasma prior to their analysis by gas chromatography–flame ionization detection. The three phases were an aqueous phase (plasma), acetonitrile and n–hexane. The extraction mechanism was based on the different affinities of components of the biological sample (lipids, fatty acids, pharmaceuticals, inorganic ions, etc.) toward each of the phases. This provided high selectivity toward the analytes since most interferences were transferred into n–hexane. In this procedure, a homogeneous solution of the aqueous phase (plasma) and acetonitrile (water–soluble extraction solvent) was broken by adding sodium sulfate (as a phase separating agent) and the analytes were extracted into the fine droplets of the formed acetonitrile. Next, acetonitrile phase was mixed with 1,2–dibromoethane (as a preconcentration solvent at microliter level) and then the microextraction procedure mentioned above was performed for further enrichment of the analytes. Under the optimum extraction conditions, limits of detection and lower limits of quantification for the analytes were obtained in the ranges of 0.001–0.003 and 0.003–0.010 μg mL⁻¹, respectively. The obtained extraction recoveries were in the range of 79–98%. Intra– and inter–day precisions were < 7.5%. The validated method was successfully applied for determination of the selected drugs in human plasma samples obtained from the patients who received them.     

Upper liquid–liquid transition in unsaturated polyesters

The upper liquid–liquid transition (T_lρ) was detected and investigated in unsaturated polyesters. This less known transition is caused by a stepwise decrease of intramolecular short‐range local order that remains above the glass and lower liquid–liquid transitions. The local order is based on secondary valent interactions and is enhanced by hydrogen bonding, if possible, as in the polyesters under consideration. The T_lρ was detected as a change in the temperature dependence of the viscosity and electrical conductivity and differential scanning calorimetry thermograms revealed an endothermic change, above which the activation energy of crosslinking decreased. The T_lρ temperature was lower in a polyester containing a diole with more flexible structure. The changes in electrical conductivity and ¹H NMR spectra indicated that the breaking of hydrogen bonding caused the T_lρ. Its intramolecular nature resulted in low sensitivity to crosslinking and addition of solvents. Near‐IR spectroscopy was chosen for further investigation because of its greater sensitivity to structural changes in polymers than mid‐IR. The spectra were recorded at selected temperatures. Significant intensity changes and wavelength shifts of hydroxyl and carbonyl absorptions at 1430 and between 1900 and 2100 nm, respectively, occurred at the T_lρ, while carbon–hydrogen absorptions showed only minor changes. This confirmed that breaking of the hydrogen bonding was responsible for disruption of the short‐range local order. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 129–145, 2001     

Synthesis and characterization of star graft copolymers with asymmetric mixed “V‐shaped” side chains via “click” chemistry on a hyperbranched polyglycerol core

The star graft copolymers composed of hyperbranched polyglycerol (HPG) as core and well defined asymmetric mixed “V‐shaped” identical polystyrene (PS) and poly(tert‐butyl acrylate) as side chains were synthesized via the “click” chemistry. The V‐shaped side chain bearing a “clickable” alkyne group at the conjunction point of two blocks was first prepared through the combination of anionic polymerization of styrene (St) and atom transfer radical polymerization of tert‐butyl acrylate (tBA) monomer, and then “click” chemistry was conducted between the alkyne groups on the side chains and azide groups on HPG core. The obtained star graft copolymers and intermediates were characterized by gel permeation chromatography (GPC), GPC equipped with a multiangle laser‐light scattering detector (GPC‐MALLS), nuclear magnetic resonance spectroscopy and fourier transform infrared. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1308–1316, 2009     

Metastable liquid–liquid and solid–liquid phase boundaries in polymer–solvent–nonsolvent systems

In general liquid–liquid demixing processes are responsible for the porous morphology of membranes obtained by immersion precipitation. For rapidly crystallizing polymers, solid–liquid demixing processes also generate porous morphologies. In this study, the interference of both phase transitions has been analyzed theoretically using the Flory–Huggins theory for ternary polymer solutions. It is demonstrated that four main thermodynamic and kinetic parameters are important for the structure formation in solution: the thermodynamic driving force for crystallization, the ratio of the molar volumes of the solvent and the nonsolvent, the polymer–solvent interaction parameter, and the rate of crystallization of the polymer compared to the rate of solvent-nonsolvent exchange. An analysis of the relevance of each of these parameters for the membrane morphology is presented. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 763–770, 1997     

Synthesis,photochemical and phase behavior of linear and hyperbranched photoactive benzylidene liquid‐crystalline polyesters

Photoactive hyperbranched benzylidene liquid‐crystalline polyester (PAHBP) and photoactive linear benzylidene liquid‐crystalline polyester (PALBP) were synthesized by solution polycondensation with pyridine as an acid acceptor. PAHBP and PALBP were thoroughly characterized with Fourier transform infrared, ¹H and ¹³C NMR, ultraviolet–visible spectrophotometry, fluorescent spectrophotometry, gel permeation chromatography, thermogravimetric analysis, differential scanning calorimetry, and polarized optical microscopy. Both polymers exhibited nematic mesophase. The glass‐transition temperature and liquid‐crystalline isotropic temperature of PAHBP were higher than those of PALBP. During photolysis under ultraviolet light, both polymers underwent an intermolecular photocycloaddition reaction, and the photoactivity of PAHBP was faster than that of PALBP; this was further confirmed by photoviscosity studies. PALBP and PAHBP were fluorescent in nature. An increase in the fluorescence intensity with the time of ultraviolet‐light irradiation was observed for both PAHBP and PALBP. The rate of increase in the fluorescence intensity of the linear analogue (PALBP) was higher than that of the hyperbranched polymer (PAHBP). This behavior could be attributed to the attainment of better planarity in the case of the linear one but not in the case of PAHBP because of the rapid crosslinking of PAHBP leading to an irregular architecture. This behavior was further confirmed by the calculation of the steric energy from corresponding model compounds. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3986–3994, 2006     

Synthesis of a new type of core–shell particle from hyperbranched polyglycerol

Based on hyperbranched polyglycerol (PG), a route to prepare particles with a novel topology was developed. The hydroxyls of PG were converted to trithiocarbonates, and the latter were used to mediate the surface graft polymerization of N,N‐dimethylaminoethyl acrylate. The poly(N,N‐dimethylaminoethyl acrylate) shell was crosslinked by 1,6‐dibromohexane and then parted from the core by the cleavage of trithiocarbonates with sodium borohydride. Novel particles with thiol groups located on the interface between the PG core and poly(N,N‐dimethylaminoethyl acrylate) shell were thus formed. The shell crosslinking could be performed at very high solid contents (2–4%). These polymer particles showed pH‐ and temperature‐dependent solubility. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5458–5464, 2005     

Ultrapreconcentration and determination of organophosphorus pesticides in water by solid‐phase extraction combined with dispersive liquid–liquid microextraction and high‐performance liquid chromatography

Solid‐phase extraction coupled with dispersive liquid–liquid microextraction was developed as an ultra‐preconcentration method for the determination of four organophosphorus pesticides (isocarbophos, parathion‐methyl, triazophos and fenitrothion) in water samples. The analytes considered in this study were rapidly extracted and concentrated from large volumes of aqueous solutions (100 mL) by solid‐phase extraction coupled with dispersive liquid–liquid microextraction and then analyzed using high performance liquid chromatography. Experimental variables including type and volume of elution solvent, volume and flow rate of sample solution, salt concentration, type and volume of extraction solvent and sample solution pH were investigated for the solid‐phase extraction coupled with dispersive liquid–liquid microextraction with these analytes, and the best results were obtained using methanol as eluent and ethylene chloride as extraction solvent. Under the optimal conditions, an exhaustive extraction for four analytes (recoveries >86.9%) and high enrichment factors were attained. The limits of detection were between 0.021 and 0.15 μg/L. The relative standard deviations for 0.5 μg/L of the pesticides in water were in the range of 1.9–6.8% (n = 5). The proposed strategy offered the advantages of simple operation, high enrichment factor and sensitivity and was successfully applied to the determination of four organophosphorus pesticides in water samples.     

Synthesis of a novel hybrid liquid‐crystalline rod–coil diblock copolymer

A series of novel rod–coil diblock copolymers on the basis of mesogen‐jacketed liquid‐crystalline polymer were successfully prepared by atom transfer radical polymerization from the flexible polydimethylsiloxane (PDMS) macroinitiator. The hybrid diblock copolymers, poly{2,5‐bis[(4‐methoxyphenyl)oxycarbonyl]styrene}‐block‐polydimethylsiloxane, had number‐average molecular weights (M_n's) ranging from 9500 to 30,900 and relatively narrow polydispersities (≤1.34). The polymerization proceeded with first‐order kinetics. Data from differential scanning calorimetry validated the microphase separation of the diblock copolymers. All block copolymers exhibited thermotropic liquid‐crystalline behavior except for the one with M_n being 9500. Four liquid‐crystalline diblock copolymers with PDMS weight fractions of more than 18% had two distinctive glass‐transition temperatures. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1799–1806, 2003     

Application of ionic‐liquid‐supported magnetic dispersive solid‐phase microextraction for the determination of acaricides in fruit juice samples

In this study, ionic liquid (IL) supported magnetic dispersive solid‐phase microextraction was developed and a systematic investigation was conducted on imidazolium ILs for their extraction performance. This nano‐based pretreatment procedure was then applied for the determination of acaricides in fruit juice samples for the first time. A feature of this technique is that the commonly laborious chemical modification of magnetic nanoparticles (MNPs) was skillfully circumvented. Because of the combination of ILs, dispersive liquid–liquid microextraction, and dispersive MNP solid‐phase microextraction, the extraction efficiency can be significantly improved using commercial MNPs. Parameters of the extraction method were investigated by one‐factor‐at‐a‐time approach. The optimal experimental conditions were as follows: emulsification for 2 min by sonication with the addition of 50 μL [C₆MIM][NTf₂] in the dispersive liquid–liquid microextraction step and vortexing for 90 s after adding 40 mg spherical barium ferrite nanoparticles (20 nm). The desorption time was 2 min. Good linearity (0.5–500 ng/mL) and detection limits within the range of 0.05–0.53 ng/mL were achieved. The application of the proposed method was demonstrated by the analysis of real fruit juice samples, in which recoveries between 85.1 and 99.6% were obtained.     

Gel–sol transition for soluble polyimide solution

Copolyimides were synthesized in N‐methyl‐2‐pyrrolidone (NMP) to prepare polyimide (PI) solutions with various concentrations, and gels can form in PI/NMP solution with a suitable concentration or at a low temperature. Gel–sol transition in the PI/NMP solution has been investigated through a combination of polarized optical microscope, differential scanning calorimeter measurement, and rheological measurements. According to Winter–Chambon theory, the critical gel point is 12 wt %, and the loss tangent (tan δ) shows frequency independence. Gel–sol transition temperature (T_gel) for the 13 wt % solution is around 65 °C. Below the T_gel, the gel exhibits strong optical planar texture, indicating the formation of a fully anisotropic phase, which has a great importance for the fabrication of PI fibers by gel‐spinning. Dynamic temperature sweep measurements show that the formation of the gel from solution is thermoreversible and is significantly delayed in the cooling process. Under the favorable conditions, the tensile strength and modulus of the fibers derived from the solution are about 0.7 and 12.5 GPa using gel‐spinning method, which is believed to afford broad application potential in preparing high‐performance PI fibers. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 450–459     

Ring‐opening metathesis polymerization of functionalized cyclooctene by a ruthenium‐based catalyst in ionic liquid

This paper describes the synthesis of a novel monomer of 5‐substituted cyclooctene with the pendant of imidazolium salt (7) and the ring‐opening metathesis polymerization of the functionalized cyclooctenes ( 4 and 7 ) in CH₂Cl₂ and ionic liquid [bmim][PF₆] by a ruthenium‐based catalyst RuCl₂(PCy₃)(SIMes)(CHPh) (2). The polymerization, which was carried out in ionic liquid, afforded improved control over the molecular weight (M_n) and polydispersity of the resultant products (PDI <1.4). Furthermore, to facilitate the GPC measurement for molecular weight of polymers, the charged polymers (poly‐ 7 ) were hydrolyzed to give uncharged polymers (poly‐ 4 *) by removing the imidazolium pendant from the polymer chains. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3986–3993, 2007