Effect of Solubility Parameter of Polymer-Solvent Pair on Turbulent Drag Reduction

Polymer-induced turbulent drag reduction by adding a minute amount of high-molecular weight polyisobutylene (PIB) into two different organic solvents of n-heptane and xylene was examined using a rotating disk system. The dependence of drag reduction (DR) efficiency on various factors such as polymer molecular weight, polymer concentration (C), and solvent quality was examined. Based on the linear relationship between C and C/DR for different molecular weights of PIB, a universal curve was able to characterize a particular polymer/solvent family, independent of the molecular weight of polymer.     

Thermomechanical investigation of a thick film of aniline-formaldehyde copolymer and poly(methyl methacrylate)

A thick film of aniline-formaldehyde copolymer and PMMA is synthesized via dispersion of aniline-formaldehyde copolymer powder as filler particles in PMMA with two different concentrations. Variation of the complex elastic modulus and mechanical loss factor (tanδ) with temperature is studied. It is observed that the complex elastic modulus decreases with temperature owing to thermal expansion of films. On the other hand, tanδ increases up to a characteristic temperature beyond which it shows a decreasing trend toward melting. Transition temperature T _g of sample S₁ (pure PMMA) is found to be 80°C. In sample S₂ (1 wt % aniline formaldehyde copolymer), the peak of tanδ at a lower temperature (66°C) corresponds to glass transition temperature T _g of the PMMA matrix, while the peak of tanδ at a higher temperature (107.8°C) corresponds to T _g of a polymer chain restricted by filler particles of aniline-formaldehyde copolymer. A further increase (10 wt % aniline-formaldehyde copolymer) in the concentration of filler particles of aniline-formaldehyde copolymer results in a more compact structure and a shift of T _g to a higher temperature, 122.2°C. This shift in the glass transition temperature of thick films of aniline-formaldehyde copolymer and PMMA is dependent upon the concentration of filler particles in the sample.     

Poly[(N-isopropylacrylamide-co-acrylamide-co-(hydroxyethylmethacrylate))] thermoresponsive microspheres: An accurate method based on solute exclusion technique to determine the volume phase transition temperature

Poly[(N-isopropylacrylamide-co-acrylamide-co-(hydroxyethylmethacrylate))] [poly(NIPAAm-co-AAm-co-HEMA)] copolymer was synthesized as a new thermoresponsive material possessing a lower critical solution temperature (LCST) around 37 °C in phosphate buffer, pH 7.4, at a solution concentration of 1%, w/v. The influence of polymer concentration on LCST was determined by cloud point measurements and by microcalorimetric analysis. The copolymer was transformed in hydrogel microspheres by suspension reticulation of OH groups with glutaraldehyde. The volume phase transition temperature (VPTT) of microspheres was determined by a new approach, which involves measurement of the increase in concentration of a blue dextran (BD) solution at different temperatures in the presence of dry microspheres. The minimum BD concentration that gives reliable and reproducible results was determined to be 1 mg/ml. However, the higher is the concentration of BD in solution the smaller is the error. Contrary to solution of the linear polymer which displays a sharp phase transition temperature, the dependence of water regain of the hydrogel with temperature lasts from 4 °C to 50 °C.     

Polymers incorporating backbone thiophene,furan, and alcohol functionalities formed through chemical modifications of alternating olefin–carbon monoxide copolymers

The reaction of the alternating ethylene–carbon monoxide copolymer with Lawesson's reagent resulted in the conversion of 75% of the carbonyl groups to thiophene units. A few thioketone groups were also present in the derived polymer. A polymer with furan units in the backbone was formed upon treatment of the alternating propylene–carbon monoxide copolymer with P₂O₅. Depending on the reaction conditions, up to 90% of the carbonyl groups were converted. Finally, 1,4-polyalcohols were prepared from the alternating propylene-carbon monoxide copolymer by reduction. Hydrogenation using Raney nickel as catalyst resulted in the reduction of 60% of the carbonyl groups, whereas reaction with LiAlH₄ at room temperature caused the reduction of 85% of the carbonyl groups. The glass transition temperature was found to increase monotonically with increasing concentration of hydroxyl groups in the polymer backbone. © 1994 John Wiley & Sons, Inc.     

Thermoreversible UCST-type phase behavior of comb-like poly(N-phenyl maleimide-co-n-octadecyl vinyl ether) in organic media

Comb-like copolymer of N-phenyl maleimide and n-octadecyl vinyl ether was synthesized by conventional free radical solution polymerization. The molecular weight and molecular weight distribution were measured by GPC. The chemical composition of copolymer was characterized by FT-IR, ¹H NMR and ¹³C NMR, and the results indicated that the obtained copolymer contained much more content of N-phenyl maleimide rather than equal molar ratio of monomer unit. The comb-like copolymer can exhibit upper critical solution temperature thermoresponsive phase behavior reversibly in N,N-dimethylformamide and some proper alcohols such as 1-butanol, 1-hexanol, etc. The effect of polymer concentration and co-solvent on thermoresponsive behavior of polymer solution was investigated, and the cloud point of polymer solution can be tuned conveniently. The high resolution ¹H NMR method was used to comprehend the reversible thermoresponsive behavior in molecular level, and the results revealed that as temperature decreased the pendent long alkyl side chain aggregated and phase separation occurred at cloud point temperature; however, the mobility of main polymer chain decreased at lower temperature.     

Copolymerization in N-vinylcaprolactam-N-vinylpyrrolidone and N,N-diethylacrylamide-N,N-dimethylacrylamide systems: The effect of composition and spatial structure of copolymers on their thermal sensitivity

Factors that affect the temperature-responsive properties of water-soluble polymers were revealed by studying the copolymerization of two pairs of monomers: N-vinylcaprolactam-N-vinylpyrrolidone and N,N-diethylacrylamide-N,N-dimethylacrylamide. In each pair, the first monomer forms a temperature-responsive polymer and the second gives a polymer soluble in water up to the boiling point. It was found that in all cases, the addition of the second (more hydrophilic) monomer resulted in a monotonous increase in the phase separation temperature in an aqueous copolymer solution, with the temperature rise being comparatively slow in the initial stage and sharply accelerating after the addition of more than 40–50 mol % second monomer. The phase-separation temperature versus copolymer composition curves for N,N-diethylacrylamide-N,N-dimethylacrylamide copolymers of iso-and heterotactic structure synthesized via anionic polymerization are rather similar. At the same time, the copolymers of both types prepared via radical polymerization are characterized by steeper curves, a pattern that may be due to a high content of the syndiotactic structure, however, changes in the copolymer spatial structure have a lesser effect on the phase separation temperature than the presence of units of a more hydrophilic monomer. The addition of a relatively low amount (20–25 mol %) of a less hydrophilic monomer imparts temperature sensitivity to polymers, such as polyvinylpyrrolidone or polydimethylacrylamide, which do not possess this property in the pure form.     

Thermoresponsive N-vinyl caprolactam grafted sodium alginate hydrogel beads for the controlled release of an anticancer drug

A series of thermoresponsive sodium alginate-g-poly(vinyl caprolactam) (NaAlg-g-PNVCL) beads were prepared as drug delivery matrices of 5-flurouracil (5-FU) crosslinked by glutaraldehyde (GA) in the hydrochloric acid catalyst. Graft copolymers of sodium alginate with vinyl caprolactam were synthesized using azobisisobutyronitrile as an initiator, and characterized by Fourier infrared spectroscopy, differential scanning calrimetry and X-ray diffraction for analysis of the amorphous nature drug in the beads, and by scanning electron microscopy for the spherical nature of the beads. Preparation condition of the beads was optimized by considering the percentage of encapsulation efficiency, swelling behavior of beads and their release data. Effects of variables such as GA concentration, drug/polymer ratio and catalyst concentration on the release of 5-FU were carried out at two different temperatures (25 and 37 °C) in simulated intestinal fluid for 12 h. It was observed that, drug release from the beads decreased with increasing drug/polymer (d/p) ratio, extent of crosslinking agent and catalyst concentration. The swelling degree of graft copolymer beads was found to be increased with decreasing of environmental temperature. In vitro release studies were performed at 25 and 37 °C for 12 h, and showed that thermoresponsive graft copolymer beads had higher drug release behavior at 25 °C than that at 37 °C, following Fickian diffusion transport mechanism with slight deviation.     

Hydrophobic modification of high molar mass polyglycidol to thermosensitive polymers

The results concerning a new class of thermosensitive polymers based on modified poly(2,3-epoxypropanol-1) - the polyglycidol are presented. Thermo-responsive water-soluble poly(glycidol-co-ethyl glycidyl carbamate)s were obtained by the hydrophobic modification of hydroxyl groups of the polyglycidol chain with ethyl isocyanate. The cloud points of the synthesized poly(glycidol-co-ethyl glycidyl carbamate)s were measured by UV-VIS and the hydrodynamic behaviour of the polymer chains near the transition temperature was characterized by dynamic light scattering. The influence of copolymer composition and polymer concentration on the cloud point was investigated. The cloud point was easy controlled in a range from 22 to 81 °C by change of the degree of modification. The effect of the surfactant sodium n-dodecylsulphate (SDS) and inorganic salt (NaCl) on the temperature response of synthesized copolymer was also examined.     

Reduction of electroactive polymers via polyelectron transfer processes at solid electrodes

The reduction of an electroactive polymer at an electrode involves the transfer of a large number of electrons to a single molecule. A quantitative study of this process indicates whether the system behaves ideally. The electron transfer process in polyvinylbenzophenone and in polyvinylbenzophenone-co-styrene in N,N-dimethylformamide solution was investigated by voltammetry at a rotating disk electrode. It is concluded that benzophenone (BP) groups attached to the polymer backbone are noninteracting electroactive centers and that every BP group is reducible at the electrode. The relationship between limiting current and molecular weight was examined quantitatively for a series of polymers of low dispersity with molecular weights ranging up to 300,000, and with a controlled, varied content of electroactive groups. The diffusion coefficient was determined as a function of molecular weight from the electrochemical data, and was found to be in good agreement with the theoretical model based on transport properties. The dependence of the diffusion coefficient on concentration of polymer and on temperature were investigated and activation energies determined.     

Revisiting the thermosensitivity of poly(acrylamide-co-diacetone acrylamide)

The lower critical solution temperature （LCST） behavior of poly（acrylamide-co-diacetone acrylamide） （poly（AM-co-DAM）） copolymer in aqueous solutions was studied. The results demonstrate the LCST linearly decreases as the molar fraction of DAM （fDAM） increases. In the range of fDAM 〈 0.36, the transmittance increases as fDAM decreases because the more hydrophilic copolymer chains can form looser aggregates with a lower refractive index. The transmittance exhibits a minimum when fDAM is less than 0.28 as the chains form micelle-like structure with a size smaller than the wavelength. The LCST decreases with the initial polymer concentration, but it levels off when the polymer concentration is high enough. Moreover, no hysteresis can be observed in the change of transmittance during the heating-cooling process because no additional hydrogen bonds are formed in the collapsed state due to the steric hindrance of the large side groups in DAM units.     

Effect of composition and processing on the linear viscoelasticity of synthetic binders

The influence that composition and processing variables exert on the linear viscoelastic properties of model synthetic binders has been studied in a wide range of temperature and frequency. Model synthetic binders were prepared by blending a non-modified colophony resin (40-65%), a process aromatic oil and a styrene-butadiene-styrene (SBS) triblock copolymer (5-15%). At high SBS content (11% and 15%) and gentle processing conditions (i.e. 150 °C and 60 rpm), a plateau region in G′ is found in the mechanical spectrum. The microstructure of this binder is characterized by a continuous SBS-rich phase. On the contrary, a shoulder in G′ is found at low polymer content. The resulting microstructure consists of a continuous resin-rich phase and a dispersed polymer-rich phase. Under severe processing conditions (180 °C and 1200 rpm) and low polymer concentration, the polymer influence is dampened and the glassy region appears at higher temperatures or lower frequencies. At high polymer concentration, a phase inversion can be induced by processing (i.e. 180 °C and 1200 rpm.). Both resin oxidation and SBS degradation may explain such microstructural changes.     

Copolymer of poly(4-vinylpyridine)-g-poly(ethylene oxide) respond sharply to temperature, pH and ionic strength

The stimuli-responsive copolymers with poly(ethylene oxide) (PEO) as side chain were prepared by free-radical copolymerization of methacrylamide end-capped PEO macromonomer and 4-vinylpyridine (4VP). Phase transition behavior of these copolymers of poly(4-vinylpyridine)-g-poly(ethylene oxide) (P4VP-g-PEO) was investigated as a function of polymer concentration, temperature, pH and ionic strength by monitoring the turbidity of the polymer solutions. The copolymers displayed sharp response to temperature and pH. The LCST of P4VP-g-PEO copolymer increased with the increase of PEO content and decreased with increasing pH due to the deprotonation of the pyridine ring, indicating well-tunable LCST. In addition, the LCST of P4VP-g-PEO9 presented a unique phase transition behavior with varying salt concentration, showing a minimum with 1 M NaCl solution at pH 6.0.     

Thermal transitions and dynamics in nanocomposite hydrogels

Hydrogels based on nanocomposites of statistical poly(hydroxyethyl acrylate-co-ethyl acrylate) and silica, prepared by simultaneous copolymerization and generation of silica nanoparticles by sol?Cgel process at various copolymer compositions and silica contents, characterized by a fine dispersion of filler, were investigated with respect to glass transition and polymer dynamics by dielectric techniques. These include thermally stimulated depolarization currents and dielectric relaxation spectroscopy, covering together broad ranges of frequency and temperature. In addition, equilibrium water sorption isotherms were recorded at room temperature (25?°C). Special attention was paid to the investigation of effects of silica on glass transition, polymer dynamics (secondary ?? and ?? _sw relaxations and segmental ?? relaxation), and electrical conductivity in the dry systems (xerogels) and in the hydrogels at various levels of relative humidity/water content. An overall reduction of molecular mobility is observed in the nanocomposite xerogels, in particular at high silica contents. Analysis of the results and comparison with previous work on similar systems enable to discuss this reduction of molecular mobility in terms of constraints to polymeric motion imposed by interfacial polymer?Cfiller interactions and by the formation of a continuous silica network interpenetrated with the polymer network at filler contents higher than about 15?wt%.     

Some properties of networks produced by the Diels-Alder reaction between poly(styrene-co-furfuryl methacrylate) and bismaleimide

Poly (styrene-co-furfuryl methacrylate) networks were prepared by the Diels-Alder (D-A) reaction in solution at 25 °C between the linear copolymer and bismaleimide (BM). The resultant crosslinked polymers were swollen to equilibrium in toluene at 25 °C and swelling properties were studied by gravimetric and dimensional measurements. The swelling behaviour of these organogels depended on the composition of the copolymer and the concentration of BM used. Shear and Young’s moduli and the effective crosslinking densities (ν_e) were determined by compression (stress)-strain measurements. The theoretical crosslinking density was higher than the ν_e for all the crosslinked copolymers. An endothermic peak without T_g was observed on the DSC curve on heating the dry crosslinked polymer. On reheating a T_g at ≈98 °C was found, which is attributed to presence of linear copolymer produced by the retro D-A reaction in the first heating. The thermal stability of a crosslinked copolymer under nitrogen and air showed differences with the stability of the linear copolymer. The increase in viscosity of the solution during the D-A reaction was followed with time, for initial linear copolymers of different molecular weights. It was found that onset of gelation increased to longer reaction times the lower the molecular weight of copolymer.     

Removal of strontium ions by a crosslinked copolymer containing methacrylic acid functional groups</p> </p>

Summary A tail-made polymer matrix is proposed to remove strontium ions from aqueous solutions. The removal behavior of strontium ions on a crosslinked copolymer containing methacrylic acid as functional groups was investigated as a function of sorptive concentration, time, temperature and pH. It was observed that an increase of these parameters enhanced the removal of Sr(II) ions from aqueous solution. It is found that a maximum adsorption of Sr(II) ions can be obtained on the crosslinked copolymer after 30 minutes and at pH 8. The increase of Sr(II) ion concentration in the solution resulted in an increase in the amount of Sr(II) ions adsorbed on the crosslinked copolymer containing methacrylic acid as functional groups. However, after a maximum of Sr(II) concentration in the solution, the percentage of adsorbed Sr(II) ions decreased. The adsorption data are well represented by the Freundlich, Langmuir and Dubinin-Radushkevich (D-R) isotherms. The adsorption capacity of the copolymer and the free energy change were calculated by using the D-R isotherm. For the adsorption of Sr(II) ions on the crosslinked copolymer the thermodynamic parameters (DH°,DS° andDG°) were calculated.</p> </p>     

P(VAc-MA)/PMMA为基体的聚合物电解质制备及其在电致变色器件中的应用

以醋酸乙烯酯(VAc)和丙烯酸甲酯(MA)为单体, 采用半连续种子乳液聚合法制备了无规共聚物P(VAc-MA), 以PMMA与P(VAc-MA)的共混物为基体制备了聚合物电解质. 用红外光谱(FTIR)、X射线衍射(XRD)、热重分析(TG)、紫外光谱(UV)、力学性能测试及电化学交流阻抗等方法研究了聚合物、聚合物膜和聚合物电解质的性质. 结果表明, VAc与MA通过打开各自的CC键聚合生成P(VAc-MA); P(VAc-MA)与PMMA共混后结晶状态发生了变化, 增加了无定形相区, 降低了链段运动的能量壁垒, 提高了热稳定性和拉伸强度. 以P(VAc-MA)/PMMA为基体的聚合物电解质膜具有很高的透明性, 最大室温电导率达到1.17×10-3 S/cm; 离子电导率随着温度的升高而迅速增加, 电导率-温度曲线符合Arrhenius方程; 将此电解质用于全固态电致变色显示器件显示出优良的性能.     

Use of FT-IR Spectrometry for On-Line Detection in Temperature Rising Elution Fractionation

Summary: Temperature rising elution fractionation (TREF) has become a popular analytical technique that is able to determine the chemical composition distribution (CCD) of an ethylene/α-olefin copolymer. An infrared (IR) detector is commonly used in TREF detection to measure the concentration of the polymer solution exiting the column as a function of elution temperature. The chemical composition of the eluting polymer at a given elution temperature can be predicted from the relationship between comonomer content and TREF elution temperature pre-established through ¹³C nuclear magnetic resonance (NMR) analysis of TREF fractions. In this article, a Fourier transform infrared (FT-IR) spectrometer has been coupled with a TREF instrument to provide a more powerful tool for characterizing complex olefin copolymers. The Partial Least Squares (PLS) technique is used when analyzing the FT-IR spectra of the eluting polymer solutions. The power of on-line FT-IR detection in TREF is demonstrated using a few complex copolymer systems, such as ethylene-octene copolymer, polystyrene grafted ethylene-vinyl acetate copolymer and ethylene-methyl acrylate copolymer.     

The effect of nucleating agent on radiation stability of polypropylene

The radiation stability of polypropylene (PP) with and without nucleating agent (NA) is compared in relation to radiation sterilization of medical devices. In both cases high-and-low-molecular weight PP, the addition of NA increased the transparency and peak crystallization temperature of the PP. On the other hand, in poly(propylene-co-6%ethylene) copolymer, the addition of NA did not improve the transparency but crystallization occurred at higher temperature. Thus, adding NA to PP and copolymer give the advantage of shorter moulding time in the production of medical devices. It is found that both PP and copolymer with NA are less stable during irradiation and during storage after irradiation than without NA, this being the case especially for the lower molecular weight PP. The higher transparency and peak crystallization temperature in the PP and CP with NA were found to be due to smaller spherulites. As the effect of irradiation on polymer, addition of NA induce reduction of radiation stability of polymer owing to the change in morphology.     

A new temperature-sensitive polymer: Poly(ethoxypropylacrylamide)

In this study, a new temperature sensitive polymer was obtained by the solution polymerization of ethoxypropylacrylamide. The monomer, N-(3-ethoxypropyl)-acrylamide was synthesized by the nucleophilic substitution reaction of 3-ethoxy-propylamine and acryloyl chloride. The solution polymerization was performed in ethanol at 70 °C, by using azobisizobutyronitrile as the initiator. Poly(N-(3-ethoxypropyl)acrylamide), PEPA, exhibited a reversible phase transition by the temperature. The effects of polymer and salt concentrations on the lower critical solution temperature, (LCST) behaviour were investigated. LCST was found to be strongly dependent on the polymer concentration. The dynamic light scattering (DLS) measurements confirmed the formation of aggregates by the association of nucleated polymer chains at the temperatures higher than LCST. However an unusual behaviour, a marked decrease in the hydrodynamic diameter by the increasing PEPA concentration was observed below the LCST. The effect of salt concentration on the critical flocculation temperature of PEPA was reasonably similar to poly(isopropylacrylamide), PNIPA. In the ethanol-water media, the reversible phase transition behaviour was observed up the ethanol concentration of 30% v/v. This study indicated that PEPA was a new alternative thermally reversible material for PNIPA. With respect to the well-defined temperature-sensitive polymers like PNIPA, polymer concentration dependent LCST of PEPA can provide significant advantages in the applications like drug targeting, affinity separation and immobilization of bioactive agents.     

聚甲基丙烯酸甲酯接枝聚氧乙烯共聚物溶液性质的研究

采用核磁共振 (NMR)、动态激光光散射 (DLS)、透射电子显微镜 (TEM )等方法研究了规整性聚甲基丙烯酸甲酯接枝聚氧乙烯共聚物溶液性质 ,研究表明两亲接枝共聚物在选择性溶剂中可形成球状胶束 ,溶液的浓度、温度和聚合物结构等因素影响其胶束的大小、形态