Branched versus linear oligo(dimethylsiloxane): Differences in their thermodynamic interaction with solvents

The thermodynamic behavior of linear and of branched oligo(dimethylsiloxane) (O‐DMS) solutions was studied by means of vapor pressure measurements and vapor pressure osmometry at different temperatures for the thermodynamically favorable solvent THF. The branched material required for that purpose was synthesized and afterwards fractionated by means of the single solvent acetone to eliminate components of low degrees of branching. The Flory‐Huggins interaction parameters, χ, for the systems THF/O‐DMS as a function of composition pass a minimum at all temperatures (25, 40, and 60 °C) in the case of the branched material. For the unbranched oligomer such a minimum is only observed at 60 °C. At 40 °C the results are ambigous whereas the dependence is definitely linear at 25 °C. This exceptional behavior of the linear product at the latter temperature is tentatively attributed to the formation of favorable orientational order in the pure state under these conditions. At high oligomer concentrations THF interacts more favorably with the branched material, however, this preference is reversed upon dilution. All measured composition dependencies of χ can be modeled quantitatively by an approach accounting for chain connectivity and for the ability of the oligomers to change their conformation upon dilution. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1309–1318, 2010     

结晶分级技术在支化聚乙烯研究中的应用

介绍了近年发展起来的几种结晶分级技术及其在支化聚乙烯结构表征及性能研究方面的应用。利用升温淋洗分级技术(TREF),可根据结晶特性的不同将高分子分离成多个分布较窄的级份,通过分别表征各级份的链结构,从而可获得高分子链结构方面较为准确的信息。基于差示扫描量热技术(DSC)发展起来的两类热分级技术,主要包括逐步结晶热分级(SC)和连续自成核退火分级(SSA)技术,虽然不能从物理上对高分子进行分级,但通过选择适当的操作参数,也能得到一系列与升温淋洗分级实验类似的链结构信息,并且具有设备简单、操作方便、样品用量少、耗时短等优点。本文结合我们自己的工作,对各种分级技术的原理、实验操作及应用进行了系统综述,并展望了结晶分级技术发展的某些可能趋势。     

Characterization of polyethylenes by x-ray diffraction and 13C-NMR: Temperature studies and the nature of the amorphous halo

X-ray diffraction patterns of linear and branched polyethylenes typically show two sharp reflections and an amorphous halo. The position of the halo depends on branch content and temperature. A single curve describes the position of the halo maximum (2θ_halo) for a range of liquid hydrocarbons and polyethylenes in the 20–140°C range. At temperatures well below their melting point, branched polymers give 2θ_halo values which differ significantly from those observed for the liquid Linear polymers show a greater divergence, indicating that some of the material giving rise to the halo is much better packed than in the liquid.Parallel ¹³ C NMR spin-lattice relaxation studies suggest that this relatively ordered material has a trans conformation but a low average T_1c value. © 1993 John Wiley & Sons, Inc.     

Polymer Incompatibility Caused by Different Molecular Architectures: Modeling via Chain Connectivity and Conformational Relaxation

The calculation of phase diagrams for blends of linear and branched polymers made up of identical monomeric units is modeled using an approach that subdivides the mixing process into two steps: i) contact formation between the different components, keeping their chain conformations and the volume of the system constant; and, ii) relaxation of the macromolecules into their equilibrium state by molecular rearrangements. It is assumed that step (ii) causes shape‐induced polymer incompatibility and that the degree of branching can be quantified in terms of the volumes the isolated coils of the branched polymer occupy in relation to the volume the linear product with the same molecular weight occupies. Under these premises, it is possible to work out how the critical conditions depend on the molar masses of the components and on the degree of branching of the non‐linear polymer by means of only one system‐specific parameter, measuring the effects of conformational relaxation. Detailed phase diagrams show how the binodal and spinodal conditions reflect the conformational variability of the blend components.

     

Synthesis and Characterization of a Branched Poly(Methacrylamide): Thermal Stability and Molecular Simulation Studies of Their Blends With Vinylic Polymers

The synthesis of a poly(diethylaminoethyl methacrylamide) (BP), based on a lineal methacrylamide with diethylaminoethyl branches was carried out. Thermal behavior was studied by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). Relatively high thermal stability is found. Blends with poly(methylmethacrylate) (PMMA), poly(acrylic acid) (PAA) and poly(monomethyl itaconate) (PMMI) were prepared. Their thermal properties in blends were studied together with miscibility, in order to improve thermal properties of vinylic polymer blends. An increase of thermal stability was found for certain blend compositions. By FTIR analysis, higher band displacements were found for low BP compositions. AFM and molecular simulation analysis were carried out in order to elucidate the structural origin leading to thermal stability and miscibility increases. Hydrophobic interactions among methyl end groups of BP and methylene groups of vinylic polymers should be the responsible of miscibility and thermal stability increases.     

Preparation and phase behavior of poly(4‐trimethylsilylstyrene)‐block‐polyisoprene

Three poly(4‐trimethylsilylstyrene)‐block‐polyisoprenes (TIs), the molecular weights of which were 82,000, 152,000 and 291,000 (TI‐82K, TI‐152K, and TI‐291K), were synthesized by sequential anionic polymerizations. The component polymers were a miscible pair that presented a lower critical solution temperature phase diagram if blended. The TI phase behavior was investigated with transmission electron microscopy. The order–disorder transition could be observed at a temperature between 200 °C (the ordered state) and 150 °C (the disordered state) for the block copolymer TI‐152K. The block copolymer TI‐82K presented the disordered state at 200 °C, whereas TI‐291K was in the ordered state at 150 °C. With the Flory–Huggins interaction parameter between poly(4‐trimethylsilylstyrene) and polyisoprene, which was evaluated by small‐angle neutron scattering for the block copolymers, the TI phase behavior could be reasonably explained by mean‐field theory. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1214–1219, 2005     

Miscibility and phase behavior in atactic polystyrene and poly(o-chlorostyrene-co-p-chlorostyrene) blends: Effect of polystyrene molecular weight and copolymer composition

Miscibility in blends of random copolymers of o-chlorostyrene and p-chlorostyrene [P(oClSy-co-pClS_1-y)] with 8 atactic polystyrene (aPS) fractions has been studied at temperatures ranging from 150°C to 300°C. Miscibility windows whose size depends on the molecular weight of the PS and on the copolymer composition, y, were observed for each blend. From these data, the temperature dependence of the three segmental interaction parameters required to describe this system were obtained.     

聚合物共混物的相容性及相分离

综述了聚合物共混物相容性和相分离的研究现状。介绍了聚合物共混物的相容性理论,影响相容性的因素及改善和相容性的方法和表征相容性的手段。聚合物共混物的相分离机理制约着材料的性能,旋节分离和成核－增长相分离分别形成不同的形态结构。旋节分离和成核－增长相分离所对应的动力学过程是不同的,散射光强与相分离时间分别满足指数和幂指数关系。     

PVDF membrane formation by diffusion‐induced phase separation‐morphology prediction based on phase behavior and mass transfer modeling

The equilibrium phase behavior of water (nonsolvent)‐DMF (solvent)‐PVDF system at 25°C was investigated via both theoretical and experimental approaches. Using binary interaction parameters, χ_ij, obtained previously, the theoretical phase boundaries were computed and were found to match closely the measured binodal and crystallization‐induced gelation data. Membranes were prepared using the isothermal immersion‐precipitation processes in various dope and bath conditions. The formed membranes demonstrated a broad spectrum of morphologies: At one extreme, asymmetric structure was obtained featuring a continuous tight skin and a sublayer composed of parallel macrovoids and cellular pores; at the other limit, skinless microporous membrane was produced with spherical particles packed into a bi‐continuous structure. The crystalline characters of PVDF gels and membranes were examined by small angle light scattering, scanning electron microscopy, and differential scanning calorimetry techniques. In addition, diffusion trajectories and concentration profiles in the membrane solution before precipitation were calculated for the immersion process. These results predicted reasonably the various morphologies observed in the membranes. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2079–2092, 1999     

Properties of star-branched and linear chains in confined space: a computer simulation study

We studied the properties of simple models of linear and star-branched polymer chains confined in a slit. The polymer chains were built of united atoms and were restricted to a simple cubic lattice. Two macromolecular architectures of the chain linear and star-branched with three branches (of equal length) were studied. The excluded volume was the only potential introduced into the model and thus, the system was athermal. The chains were put between two parallel and impenetrable surfaces. Monte Carlo simulations with a sampling algorithm based on chain’s local changes of conformation were carried out. The differences and similarities in the global size and the structure and of linear and star-branched chains were shown and discussed.     

Deuteration-induced structural phase transition versus quantum paraelectric behavior: Quantum chemical modeling of H/D bonded materials

On the examples of the K₃(H/D)(SO₄)₂ family (I), the derivatives of 9-hydroxyphenalenone (II) and chromous acids α-(H/D)CrO₂ (III) the problem of the deuteration-induced structural phase transition (SPT) is considered using pseudospin dynamic Ising model formalism. The pseudospin Hamiltonian parameters – tunneling integrals Ω(H/D) and Ising model coupling parameters J_ij(H/D) along with molecular field parameters J₀(H/D) have been evaluated on the base of quantum chemical models and various computational techniques. The crystal-chemistry factors that influence on the values of these parameters are discussed. For I and II solids zero-dimensional character of the H-bond network is believed to be the main reason of the deuteration-induced SPT, although the pronounced geometrical (H/D) isotope effect (0.04 Å) also may play a noticeable role for I. Meanwhile for III such SPT is due to the giant (0.1 Å) geometrical (H/D) isotope effect.     

Isothermal phase behavior of Nylon-6, -66, and -610 polyamides in formic acid–water systems

Concentration-dependent ternary interaction parameters are experimentally determined for the polyamide homopolymers, Nylon-6, -66, -610, and for the Nylon-66/610/6 terpolymer in formic acid-water systems. The binodal envelope, the tie lines, and the crystallization isotherms at 25°C are given for each of the ternary systems. © 1994 John Wiley & Sons, Inc.     

Influence of binary interactions on phase behavior of water/ dimethylsulfoxide/ polyethersulfone casting solution: Thermodynamic modeling

Prediction and control of membrane morphology using multi‐phase thermodynamic knowledge are of growing interest. The water/dimethylsulfoxide/polyethersulfone ternary system is a widely used casting dope for the preparation of MF, UF, and NF membranes. In the current study, Flory–Huggins (F–H) model was applied to predict the behavior of this ternary system during phase inversion. Titration method was applied to generate cloud point data. The prediction accuracy of the F–H model was directly dependent on the binary interactions of the system components. The compressible regular solution (CRS) model predicts the binodal location using only the pure component properties as the input parameters. Accordingly, the influence of binary parameters on the location of the binodal curves was investigated. The predicted binodal points showed superior accordance with the experimental data, where the binary interaction between nonsolvent (water) and solvent (DMSO) was overlooked. In addition, the modelling results emphasized on the pivotal importance of the interactions between polymer (PES) and nonsolvent (water) on the phase inversion and thus, on the control of the membrane morphology. The CRS model offered a greater conformity with the experimental results in comparison with the F–H theory. Copyright © 2013 John Wiley & Sons, Ltd.     

Solid and liquid phase equilibria and solid-hydrate formation in binary mixtures of water with amines

Solid and liquid phase diagrams have been constructed for {water+triethylamine,or+N,N-dimethylformamide(DMF) or+N,N-dimethlacetamide (DMA)} Solid-hydrates form with the empirical formulae N(C2H5)3 3H2O,DMF 3H2O,DMF 2H2O,DMA 3H2O and (DMA)2 3H2O.All are congruently melting except the first which melts incongruently.The solid-hydrate formation is attributed to hydrogen bond.The results are compared with the references     

Novel phase behavior in adsorbed film of fluoroalkanol and cationic surfactant mixture

The surface tension of the aqueous solution of the binary mixture of 1H,1H-heptafluoro-1-butanol (FC4OH) and dodecyltrimethylammonium bromide (DTAB) was measured as a function of the total molality of the mixture and the composition (mole fraction in the surfactant mixture) of DTAB at 298.15 K under atmospheric pressure to examine the phase behavior in the adsorbed film. The results of the surface tension measurement were analyzed by the thermodynamic procedure proposed by us and the composition of the mixed adsorbed film in equilibrium with their bulk solution was calculated. Three different phases of the adsorbed film appeared by a subtle balance between the attractive interaction of the polar head groups and weak dispersion interaction of the hydrophobic chains. In the low-concentration regime, FC4OH molecules and DTAB molecules form a gaseous film and mix attractively in the whole composition by the long-range ion–dipole attraction between hydrophilic groups. The effect of the attractive dispersion interaction between CH and CF chains became more influential in the expanded film within a restricted composition region, where it should be noted that the interaction between CH and CF is weaker than that between CH chains or between CF chains alone. Furthermore, the adsorbed films at two specific compositions are stabilized by the stoichiometric arrangements of the molecules, which help ion–dipole attraction, in them.     

Morphology of solidified polysulfone structures obtained by wet phase separation

Evidence is presented that all three theoretically predicted modes of phase separation take place in the ternary system polysulfone(PSf)/N,N-dimethyl acetamide(DMA)/water during the process of wet phase separation (WPS). The elementary process of solidification is reconsidered with regard to the (non-) equilibrium phase separation. Cast solutions with more than 15 wt% of PSf undergo nucleation and growth of the polymer lean phase with formation of separation membranes characterised by a cellular structure. When cast solutions with about 5-7 wt% of PSf undergo WPS, somewhere inside the ternary system conditions are established so that alongside other solidified PSf structures the bicontinuous spinodal structures superimposed by bead-like structures are also formed. Variety of lacy PSf structures with less/more polymer beads is the manifestation of the primary phase separation by the spinodal mode superimposed by the secondary phase separation taking place by heterogeneous nucleation and growth of the polymer rich phase mode. Latex formation during the WPS will also be explained. Skin formation on the cast solution - coagulation bath interface by direct accumulation of polymer is established regardless of the PSf content in the cast solution.     

Tuning commercial diesel to microemulsified and blended form: phase behavior and implications

Abstract

Microemulsification and blending of commercial diesel is under constant research for possible fuel application. Microemulsions (ME) were prepared using diesel (D), kerosene (K), diesel and kerosene mixtures at various proportions (D?+?K) (oil phase: O), Triton X-100 surfactant (S), n-butanol, isobutanol (i-butanol), n-pentanol and n-octanol cosurfactants (C), and aqueous phase (W) containing water or brine for the study. Electrical conductance studies and temperature-induced separation of phase have been adopted for recognizing the o/w, w/o and bicontinuous zones. Dye probing has been done to explain the mass transfer among these phases. Percent of solubilization of oil in water has been enumerated in some of the ME. The possible fuel applications of the microemulsions are predicted from their density and flame brightness.     

Crystallization and melting of narrow composition distribution polyethylenes: Investigation and implications of crystal thickening

The crystal structure produced during the isothermal crystallization of polyethylene (PE) copolymers with a broad range of comonomer concentrations was determined by the measurement of the melting endotherms directly after crystallization. PE copolymers with higher concentrations of short‐chain branches (≥10 branches per 1000 total carbon atoms) exhibited strong resistance to crystal thickening during isothermal crystallization. Negligible thickening, estimated to be only about 0.1 nm in 10 min of isothermal crystallization, was observed. The side‐chain branches apparently acted as limiting points of chain incorporation into the crystals, which exhibited great resistance to the modification of their position, that is, crystal thickening. Even with long periods (up to 8 h) of isothermal storage, crystal thickening was very small or negligible, about 0.3 nm. The crystal thickness was calculated from differential scanning calorimetry data. The behavior of copolymers with lower branching concentrations and the unbranched PE homopolymer was quite different from that of the copolymers with higher branching. Polymers with low or no branching exhibited the initial crystallization of a thinner crystal population, which thickened substantially with increasing time. The thickening observed for these lower or unbranched polymers was an order of magnitude larger, that is, 1.6–2.0 nm in 10 min of isothermal crystallization. Copolymers with higher concentrations of branching had relatively short sequence lengths of ethylene units between branch points, and this resulted in strong control over the crystal thickness by the branch points and great resistance to crystal thickening, even with long times of isothermal crystallization. Copolymers with low concentrations of branching had relatively long sequence lengths of ethylene units between branch points, and this resulted in little control over the crystal thickness by the branch points and rapid crystal thickening upon isothermal crystallization. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 235–246, 2003     

Rubidium and lithium butanoates binary phase diagram

The temperature and enthalpy vs. composition diagrams of the binary system [xC₃H₇CO₂Li+(1–x)C₃H₇CO₂Rb], where x=mole fraction, were determined by differential scanning calorimetry (DSC). This binary systems displays the formation of two mixed salts with a composition 1:1 and 1:2, which melt incongruently at T _fus=590.5 K, with Δ_fus H _m=11.6 kJ mol^–1, and congruently at T _fus=614.5 K, with Δ_fus H _m=20.2 kJ mol^–1, respectively. The phase diagram also presents an ionic liquid-crystalline phase in a wide temperature range: 95 K.     

Phase behavior of methoxypolyoxyethylene dodecanoate as compared to polyoxyethylene dodecyl ether and polyoxyethylene methyl dodecyl ether

The phase behavior of binary systems composed of water and nonionic surfactants were investigated. The nonionic surfactants studied were the methoxypolyoxyethylene dodecanoates (R₁₁COO(EO) _n CH₃,n=4.9, 6.1, 7.3, 9.3, and 12.8, wheren is the average number of oxyethylene units).The phase behaviors of R₁₁COO(EO) _n CH₃ were compared with those of the polyoxyethylene dodecyl ethers (R₁₂O(EO) _p H) and polyoxyethylene methyl dodecyl ethers (R₁₂O(EO) _q CH₃) which have been previously reported. It was found that the R₁₁COO(EO) _n CH₃s have lower cloud points and lower upper limit temperatures for the existence of the mesophase as compared to the other two types. A R₁₁COO(EO)_12.8CH₃/water system had favorable solution properties for practical use, such as a relatively narrow hexagonal liquid crystalline region and a lower melting point than the ordinary alcohol ethoxylate type nonionics.