Micellization and Adsorption Parameters of Poly(Propylene Oxide)/Poly(Ethylene Glycol) Block and Graft Copolymers in Aqueous Medium

This work aims to measure the adsorption and micellization parameters of new water soluble nonionic amphiphilic block and graft copolymers based on hydrophilic poly (ethylene glycol) (PEG) and hydrophobic poly (propylene oxide) (PPO) at ambient temperature and normal atmospheric pressure. The chemical composition and molecular weights of the prepared copolymers were determined from ¹H NMR analyses. The surface properties of the prepared surfactants were determined by measuring the surface tension at different temperatures. The surface tension, critical micelle concentration, and surface activities were determined at different temperatures. Surface parameters such as surface excess concentration, the area per molecule at interface and the effectiveness of surface tension reduction were determined from the adsorption isotherms of the prepared surfactants. Some thermodynamic data for the adsorption and micellization process were calculated and are discussed.     

Surface and Thermodynamic Properties of Nonionic Surfactants Based on Rosin-Maleic Anhydride and Acrylic Acid Adducts

Ester-adduct derivatives of rosin were synthesized by reacting rosin maleic anhydride (RMA) or rosin acrylic acid (RAA) adducts with polyethylene glycol 600 (PEG600), 1000 (PEG1000) or 2000 (PEG2000) and at elevated temperature. These derivatives were evaluated for acid number, FTIR spectroscopy, molecular weight (Mw) and polydispersity. The surface properties of the prepared surfactants were determined by measuring the surface tension at different temperatures. The surface tension, critical micelle concentration, and surface activities were determined at different temperatures. Surface parameters such as surface excess concentration (Γmax), the area per molecule at interface (Amin) and the effectiveness of surface tension reduction (πCMC) were determined from the adsorption isotherms of the prepared surfactants. Some thermodynamic data for the adsorption process were calculated and are discussed.     

Novel thermolabile protecting groups with higher stability at ambient temperature

Novel thermolabile hydroxyl protecting groups of increased thermostability are proposed. The stability of these groups at different temperatures ranges has been determined. The 2-pyridyl-N-(2,4-difluorobenzyl)aminoethyl unit was selected as stable at ambient temperature and very labile at increased temperature. The half-life times for the best groups were established. Application of this chemistry to the protection of different hydroxyl groups of thymidine was also demonstrated.     

Synthesis and characterization of copolyesters of PET and substituted p-hydroxybenzoic acids

Random copolyesters of different compositions were synthesized by melt polycondensation of poly(ethylene terephthalate) and 3-bromo - and 3,5-dibromo-p-hydroxybenzoic acids. The copolymer compositions were determined by proton nuclear magnetic resonance spectroscopy. The thermal behavior of these copolyesters was investigated by differential scanning calorimetry. The glass transition temperature, crystallization temperature, and decomposition temperature were found to increase with increase in the paraoxybenzoate content of the copolyesters. The limiting viscosity number and the weight-average molecular weight were determined.     

Opto-thermal behavior of polypropylene fibres using a modified hot-stage attached to the interference microscope

The influence of temperature on the optical and structural properties of three samples of polypropylene fibres (having different deniers) has been studied over the temperature range (28–67^oC). A hot-stage attached with the Pluta microscope has been modified for this purpose. The effect of temperature on the refractive indices (n, n), the mean polarizabilities per unit volume (P^ll, P) and the optical orientation function f(θ) have been investigated for each sample. The thermal coefficients of the refractive indices were determined. The refractive index profiles are also provided at different temperatures for each of the three tested samples. Microinterferograms are given for illustration.     

Preparation of Room‐Temperature Ionic Liquids by Neutralization of 1,1,3,3‐Tetramethylguanidine with Acids and their Use as Media for Mannich Reaction

Abstract

New room‐temperature ionic liquids (ILs) were prepared by neutralization of 1,1,3,3‐tetramethylguanidine with different acids under ambient condition. The density, viscosity, decomposition temperature, electronic conductivity, and miscibility with some commonly used solvents were determined. As an example of the applications of the new ILs, the reaction of benzaldehyde, aniline, and acetophenone was carried out in the ILs. The ILs are easily prepared in large scale.     

Polymer Structures and Glass Transition: A Molecular Dynamics Simulation Study

Full atomistic molecular dynamics (MD) simulations on five polymers with different chain backbone (C—C, Si—O, and C—O) and different side groups (—H, one —CH₃, and two —CH₃) are performed to study the effects of chain flexibility and side groups on the glass transition of polymers. Molecular dynamics simulations of NPT (constant pressure and constant temperature) dynamics are carried out to obtain specific volume as a function of temperature for polyethylene (PE), poly(propylene) (PP), polyisobutylene (PIB), poly(oxymethylene) (POM), and poly(dimethylsiloxane) (PDMS). The volumetric glass transition temperature has been determined as the temperature marking the discontinuity in slope of the plots of V–T simulation data. Various energy components at different temperatures of the polymers are investigated and their roles played in the glass transition process are analyzed. In order to understand the polymer chain conformations above and below the glass transition temperature, dihedral angle distributions of polymer chains at various temperatures are also studied.     

Usefulness of Hysteresis Curves for Studying Temperature Effects on Ises Responses

Abstract

A procedure for study of the effects of the temperature on the response of ion-selective electrodes in which isothermal hysteresis cum determined at several concentrations are used for obtaining the temperature variation parameters (isothermal slope and potential coefficients and isopotential points) is proposed. The procedure was tested against the classic procedure in which calibration curves are obtained at different temperatures. 'All -solid-state' Ag₂S and Ag₂S/Agl electrodes with sensors applied to silver- and copper-loaded epoxy supports (and commercial electrodes, for comparison) were used for this purpose. The values of the temperature parameters obtained by the two procedures (in the raw 10–60°C) are compared. This comparison show that the present procedure yields acceptable values of temperature parameters for cases like the studied where the hysteresis is not very produced.     

Determination of salutary parameters to facilitate bio-energy production from three uncommon biomasses using thermogravimetric analysis

Fuels derived from biomass are renewable as well as environment friendly. In this study, three biomasses viz. husk of areca nut (Areca catheu), trunks of moj (Albizzia lucida), and bon bogori (Ziziphus rugosus) available in North-East region of India were tested as potential biofuel sources. The accentuation of this study was to determine the kinetic parameters using thermogravimetric (TG) technique under air and nitrogen atmosphere. The experiments were carried out within temperature range 300–973 K under air and nitrogen atmosphere at four different heating rates viz. 5, 10, 15, and 20 K min^?1, respectively. The mass losses at different lumps in the TG graphs were estimated. The first-order kinetic parameters such as activation energy and pre-exponential factor were calculated for different reaction zones for all the three biomass samples. Effects of atmosphere on combustion characteristics (e.g., peak temperature, ignition temperature, and reactivity index) of biomasses were also determined in this study. Areca nut husk has highest ignition temperature (526.38 K) and reactivity index (0.21) but moj has highest peak temperature (597.91 K) along with highest activation energy (348.04 kJ mol^?1) and pre-exponential factor (1.12 × 10²⁴ min^?1), respectively.     

Life tests of lithium/fluorocarbon cells

Long-term (15 years) tests of lithium/fluorocarbon cells (Li-CF _x ) are performed using the full-scale and accelerated storage in a wide temperature range. Regularities governing the capacity loss of the cells in different storage modes are discovered. The self-discharge rate constants are determined for different temperatures. A mechanism is proposed, which explains the cell self-discharge by the occurrence of a number of chemical reactions that lead to the loss of active fluorine and the electrode passivation. The activation energy for the self-discharge process is determined     

Microstructural characterisation and behaviour in different salt solutions of sodium polymethacrylate-g-PEO comb copolymers

Different polycarboxylate polymers (PCPs) have been characterised and their microstructure investigated by size exclusion chromatography, ¹H and ¹³C nuclear magnetic resonance spectroscopy. These polymers are comb-like with a sodium polymethacrylate backbone (PMAANa) on which poly(ethylene oxide) (PEO) chains are randomly grafted as shown by ¹³C NMR measurements. Since they are mostly used as superplasticisers in cementeous applications, their behaviour has been investigated at high pH in various salt solutions; average radii were determined at room temperature by static and dynamic light scattering and phase diagrams were determined as a function of temperature. We tried to evaluate the influence of different parameters (ion valence, cations, anions, PCP molecular weight, PEO length and grafting degree). A few experiments on homopolymers (PEO and PMAANa) have been equally performed in order to better understand the behaviour of PCPs in solution.     

环形聚苯乙烯的稀溶液性质——Ⅰ. 环己烷溶液的θ温度

本工作采用光散射测定第二维利系数的方法, 确定了环形聚苯乙烯在环己烷溶液中的θ温度为30 ℃, 比线形聚苯乙烯的θ温度低4.5 ℃。在此温度下及35 ℃, 环形聚苯乙烯(1×10~4相似文献   

Conductance Study and Thermodynamics of Some Substituted Ammonium Salts with Crown Ethers in Aqueous Solution

A conductance study of the interaction between substituted ammonium ions with three crown ethers in aqueous solution has been carried out at different temperatures. The formation constants of the 1 : 1 complexes at various temperatures were determined from the molar conductance-mole ratio data and found to vary in the order 18C6 > 15C5 > 12C4 for the same salt and with the same crown, the formation constants vary in the order (C2H5)3NHCl > (C2H5)4NBr > (CH3)3NPhI.The enthalpy and entropy of complexation were determined from the temperature dependence of the formation constants. The results indicate that the complexation process is enthalpy unfavored and entropy favored. The influence on the thermodynamic data for different parameters such as cavity size of crown ethers and nature of salt are discussed.     

Synthesis and Properties of Nonionic Surfactants from Rosin-Imides Maleic Anhydride Adduct

Ester-adduct derivatives of rosin were synthesized by reacting rosin with polyethylene glycol 600 (PEG 600) or 2000 (PEG2000) and maleic anhydride (MA) at elevated temperature. These derivatives were evaluated for acid number, FTIR spectroscopy, molecular weight (Mw), and polydispersity. The derivatives were soluble in organic solvents; aqueous solubility was pH dependent. Rosin-imides were synthesized from a rosin ester-maleic anhydride adducts. It was condensed with diaminobutane or triethylene tetramine to obtain rosinimides. This imide was etherified by reaction with PEG in the presence of β,β′-dichlorodiethyl ether as a linking agent and NaOH as a catalyst. The surface properties of the prepared surfactants were determined by measuring the surface tension at different temperatures. The surface tension, critical micelle concentration and surface activities were determined at different temperatures. Surface parameters such as surface excess concentration (Γmax), the area per molecule at interface (Amin), and the effectiveness of surface tension reduction (πCMC) were determined from the adsorption isotherms of the prepared surfactants. Some thermodynamic data for the adsorption process were calculated and are discussed.     

Two-dimensional condensation in camphor-10-sulphonic acid films at the mercury/electrolyte interface

The electrosorption properties of camphor-10-sulphonic acid (CS) in different electrolytes (Na₂SO₄, LiClO₄, KNO₃, KCl, KBr, KJ) were investigated experimentally by ac polarographic measurements at different temperatures. Depending on the type of electrolyte and on the temperature, film condensation was observed.The Frumkin interaction coefficient, determined from the critical degree of coverage, does not depend linearly on the reciprocal temperature as would be the case in correspondence to the temperature dependence of the pit width. This contradiction does not occur if the interaction coefficient is determined from the critical degree of coverage using the lattice gas model. The temperature dependence of the pit width of the differential capacity-potential curves, found in the experiment, can be theoretically described by both these models. The interaction coefficient in the models is inversely proportional to the temperature. Furthermore, the parameters of the standard free energy of adsorption, the interaction energy, the interaction coefficient of the Frumkin isotherm, the adsorption coefficient, and the maximal surface concentration of CS in the film were estimated and compared.     

用DSC测量葡萄糖溶液部分玻璃化转变温度的新方法

用差示扫描量热仪, 采用经过退火处理的连续扫描法, 以不同浓度(20%、45%)的葡萄糖溶液为研究对象, 研究了退火温度对Tgf(部分结晶的玻璃化转变温度)的影响, 给出了确定Tg′(部分玻璃化转变温度)的新方法. 研究发现, 不同退火温度下的Tgf不同. 在−50 ℃以上退火, Tgf随着退火温度的增大而减小; 在−50 ℃以下退火, Tgf随着退火温度的增大而增大, 都有很好的线性关系. 不同浓度的溶液具有相似的规律. 提出从Tgf确定Tg′的方法: Tgf在−50 ℃上下随退火温度变化线的交点所对应的部分结晶玻璃化转变温度即为Tg′. 使用该方法测得葡萄糖的Tg′为−55 ℃.     

Molecular Dimension and Interaction Parameters of Polyacrylamide in Water‐N,N‐Dimethylformamide Mixtures

The intrinsic viscosities [η] of polyacrylamide (PAM) having different average molecular weights are measured in various mixtures of water (good solvent) and N, N dimethyl formamide (DMF, nonsolvent) at different temperatures. The observed results show a significant variation of cosolvency as a function of solvent composition (?_DMF). The nature of curves in [η] vs. ?_DMF plot at different temperatures indicates the existence of two antagonistic effects. The unperturbed dimensions (K_θ) of the polymer are determined by a number of methods, which agree well with each other. The temperature coefficient of unperturbed dimension (K′), molecular extension factors (α_n), characteristic ratio (C_α) and chain rigidity (σ) are evaluated and the effects of temperature, solvent composition are discussed. The volume related parameter V_E and shape factor ν were also computed, which shows the shape of polymer molecules to be more or less spherical in solution.     

Crystal polymorphism of local anaesthetic drugs

Crystal polymorphs of pramocaine hydrochloride (PRCNC) and pramocaine (PRCN) free base were produced and characterized by means of thermomicroscopy, differential scanning calorimetry (DSC), FTIR- and FT-Raman-spectroscopy as well as X-ray-powder diffractometry. The relative thermodynamic stabilities of all forms were determined and are represented in semi-schematic energy/temperature diagrams. PRCN, which is a viscous liquid at room temperature and insoluble in water, was found to exist in two different crystal forms with the melting points 23.5°C (mod. I°) and 12.5°C (mod. II). The water-soluble PRCNC crystallizes in three different crystal modifications. Mod. II° is the thermodynamically stable form at room temperature and is present in commercial products. This form is obtained by crystallization from solvents and transforms on heating at about 95°C into the high temperature form mod. I which melts at 171.0°C. Both compounds show conformational polymorphism with forms of low kinetic stability. This revised version was published online in July 2006 with corrections to the Cover Date.     

A phase transition study for two homologues of the terephthalylidene bis-4-n-alkylanilines

The variation of density with temperature across different phases for two homologues of the terephthalylidene bis-4-n-alkylaniline series (TBAA7 and TBAA9) was determined to locate the phase transitions. The temperature dependence of the thermal expansion coefficient and the estimated pressure dependence of the transition temperatures together with the reported experimental P-T data are discussed.