三维骨架聚合物的孔径调控及其滤光效应

利用二阶段相分离控制方法制备不同孔径的三维骨架聚合物及配位聚合物材料.在第一阶段的反应诱导相分离中,通过加入十二烷基苯磺酸作为相分离抑制剂,控制了环氧树脂在聚乙二醇介质中固化反应的相分离速率和程度;在第二阶段,将处于亚稳状态的聚合物用ZnSO4或CdSO4水溶液处理,在配合作用的推动下发生二次相分离,并稳定三维骨架结构,最终实现了在1~2μm范围内调节孔径大小.研究了三维连续孔道在充满二乙烯基苯高折射液体后的滤光特性,通过引入金属离子改变固体材料折射率的方法,验证了光在高折射液相中的全反射效应,并从定性角度建立三维骨架材料的孔径及分布与透射光波长范围之间的关系,对新光学现象给出了初步解释.     

Effects of Hofmeister Anions on the LCST of PNIPAM as a Function of Molecular Weight

The effect of a series of sodium salts on the lower critical solution temperature (LCST) of poly(N-isopropylacrylamide), PNIPAM, was investigated as a function of molecular weight and polymer concentration with a temperature gradient microfluidic device under a dark-field microscope. In solutions containing sufficient concentrations of kosmotropic anions, the phase transition of PNIPAM was resolved into two separate steps for higher molecular weight samples. The first step of this two step transition was found to be sensitive to the polymer's molecular weight and solution concentration, while the second step was not. Moreover, the binding of chaotropic anions to the polymer was also influenced by molecular weight. Both sets of results could be explained by the formation of intramolecular and intermolecular hydrogen-bonding between polymer chains. By contrast, the hydrophobic hydration of the isopropyl moieties and polymer backbone was found to be unaffected by either the polymer's molecular weight or solution concentration.     

Conditions of formation of liquid crystals from biopolymer solutions

Using the representation of a completely stiff macromolecule as a long rigid rod and the representation of a semiflexible macromolecule as a chain of freely rotating connected effective rigid rods, the conditions of formation of the liquid-crystalline phase in the solutions of such macromolecules are obtained and the diagram of states for the corresponding phase transitions in the variables temperature-volume fraction of polymer in the solution is constructed.     

Solid-state polymerization of oxetanes. II. Investigation of the growth of the polymer phase as related to the mechanism of polymerization

The radiation-induced solid-state polymerization of 3,3-bischloromethyloxetane (BCMO) was investigated by direct observation of the development of the morphology of the growing polymer phase in single crystals of the monomer. Electron microscopy shows that the polymerization gives rise to amorphous polymer in the first step. The polymer forms irregular platelets which aggregate into larger units without reflecting the crystalline order of the monomer. Subsequent to polymerization, the amorphous polymer crystallizes to the β-modification of poly-BCMO. If the partially polymerized crystals are extracted by solvents of the monomer, crystallization of the polymer is enhanced, and morphological artifacts arise which were previously mistaken for the true morphology of the “as polymerized” polymer. The copolymerization behavior of solid solutions of 3-ethyl-3-chloromethyloxetane (ECMO) and BCMO does not differ from the liquid bulk copolymerization with respect to copolymer composition, which is different from the composition of the monomer mixture. It is concluded that the polymer chains grow in noncrystalline zones as in a polymerization in the liquid state by which amorphous polymer is formed. No lattice control was observable in this solid-state polymerization.     

Interfacial properties of compressible polymer solutions

A chemomechanical model for the interfacial concentration and density in compressible polymer solutions is formulated using variational principles. The nonlinear model with boundary conditions obtained from phase equilibrium calculations gives the coupled concentration and density profiles. The couplings between chemical and mechanical balances are identified and efficient ways to calculate the interfacial structure is identified. A specific model appropriate to high‐pressure processing of the polyolefins is developed using the modified Sanchez Lacombe equation of state. Bakker's formula for the interfacial tension is adapted to compressible polymer solutions. The structure and tension of a flat interface is characterized using the developed model and material properties of three molecular weight hydrogenated polybutadiene; the main variables of interest were the pressure, polymer molecular weight, and temperature. The relation between the pressure profile across the interface and the interfacial tension is characterized. Scaling power laws for interfacial tension and interfacial thickness as a function of pressure are obtained and contrasted with the corresponding laws observed and predicted for incompressible polymer solutions. It is found that the modified Sanchez Lacombe‐based power law prediction predictions for compressible solutions in terms of pressure quenches are similar to those from those obtained by the Flory‐Huggins incompressible model for temperature quenches. The present results provide the basis for the future study of the kinetics of pressure‐induced phase separation in compressible polymer solutions. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 640–654, 2009     

Preparation of a unique microporous structure via two step phase separation in the course of drying a ternary polymer solution

A unique porous polymeric film was prepared by drying a ternary polymer solution: a polystyrene (PS), polyethylene glycol (PEG), and toluene solution. Highly ordered micropores, ranging from 5 to 12 mum in diameter, were formed on the film surface, and the rim of each micropore was surrounded by a ring of PEG. The effects of the weight ratio of the polymer blend and molecular weight of the polymer (PEG) on the porous structure were investigated. Based on in situ visual observation and light scattering measurements, the formation mechanism of the porous structure was speculated to be a two step phase separation: the phase separation into PEG-rich and PEG-poor (i.e., PS-rich) phases occurred first at the surface area of the ternary solutions, where polymers were condensed due to solvent evaporation. The PEG-rich phase became droplets and had an ordered structure on the surface. The PEG-poor phase became a matrix where PS and solvent coexisted as a single phase solution. Secondary phase separation then followed in the PEG droplets, which was induced by further solvent evaporation, and formed into solvent-rich and PEG-rich domains within the droplets. Solvent evaporation and secondary phase separation created a cavity structure in each PEG droplet structured on the film surface.     

A Comprehensive Study on the Full Series of Alkali-Metal Selenocyanates AI[SeCN] (AI=Li−Cs)

The full series of quasibinary alkali-metal selenocyanates was synthesized either by oxidation of the respective cyanides (A=Li−Rb) or by metathesis (A=Cs). For Li[SeCN] only ball-milling and subsequent annealing led to the isolation of the quasibinary selenocyanate. Their structures were refined from single-crystal and powder X-ray data. The respective solid-state IR and Raman spectra were interpreted with the aid of solid-state quantum-mechanical calculations and DSC-TGA measurements allowed for extraction of melting points. Only for Li[SeCN] a possible phase transition was observed that is discussed on the basis of VT-PXRD experiments. It is also the only quasibinary selenocyanate to form a hydrate (Li[SeCN] ⋅ 2H₂O).     

Synergistic effects in flows of mixtures of wormlike micelles and hydroxyethyl celluloses with or without hydrophobic modifications

This work presents experimental results on simple shear and porous media flow of aqueous solutions of two hydroxyethyl celluloses (HEC) and two hydrophobically modified hydroxyethyl celluloses (HMHEC) with different molecular weights. Mixtures of these polymers with a cationic surfactant, cetyltrimethylammonium p-toluenesulfonate (CTAT) were also studied. Emphasis was given to the range of surfactant concentrations in which wormlike micelles are formed. The presence of hydrophobic groups, the effect of the molecular weight of the polymers, the surfactant and polymer concentrations, and the effect of the flow field type (simple shear versus porous media flow) were the most important variables studied. The results show that the shear viscosity of HEC/CTAT solutions is higher than the viscosities of surfactant and polymer solutions at the same concentrations, but surface tension measurements indicate that no complex formation occurs between CTAT and HEC. On the other hand, a complex driven by hydrophobic interactions was detected by surface tension measurements between CTAT and HMHEC. In this case, the viscosity of the mixture increases significantly more (up to four orders of magnitude at high CTAT concentrations) in comparison with HEC/CTAT aqueous solutions. Increments in the molecular weight of the polymers increase the interaction with CTAT and the shear viscosity of the solution, but make phase separation more feasible. In porous media flow, the polymer/CTAT mixtures exhibited higher apparent viscosities than in simple shear flows. This result suggests that the extensional component of the flow field in porous media flows leads to a stronger interaction between the polymer and the wormlike micelles, probably as a consequence of change of conformation and growth of the micelles.     

Quasibinary amorphous phase in a three-dimensional system of particles with repulsive-shoulder interactions

We report a computer-simulation study of the equilibrium phase diagram of a three-dimensional system of particles with a repulsive-step potential. Using free-energy calculations, we have determined the equilibrium phase diagram of this system. At low temperatures, we observe a number of distinct crystal phases. However, under certain conditions the system undergoes a glass transition in a regime where the liquid appears thermodynamically stable. We argue that the appearance of this amorphous low-temperature phase can be understood by viewing this one-component system as a quasibinary mixture.     

ChemInform Abstract: Phase Relations in the System NaIn-Sn and the Crystal Structures of the Intermediate Compounds NaInSn2 and NaInSn4.

The phase diagram of the quasibinary NaIn-Sn system is determined and, except for Na₂In₂Sn₃ which is stable only in the range 134-365 °C, single crystals of the intermediate phases are grown from the melt and their structures are determined.     

Phase equilibria in polymer solutions

A theoretical study of phase equilibria in multicomponent polymer solutions is presented. The treatment is based on the virial expansion of the osmotic pressure. A program for the numerical determination of phase diagrams is worked out and applied to the polystyrene-cyclohexane system. The present approach is compared with the Flory-Huggins theory of polymer solutions, which is shown to represent a special class of approximations in the present treatment.     

Kinetically stable structures in the nonlinear theory of spinodal decomposition

A nonlinear diffusion equation is used to study the spinodal decomposition of binary polymer mixtures. The structure of steady-state solutions is analyzed. The free energy of the system for the solutions is shown to be a nonincreasing time function. The solution with the minimum free energy is the only stable solution and corresponds to complete phase separation in the system. A numerical analysis shows that transition to complete equilibrium takes place through a succession of fast concentration structure changes interspersed by periods in which the process is abruptly showed down. The free energy of the system is almost constant in the kinetically stable periods. All these facts indicate a relaxation process of an absolutely new type. Slow variables are introduced to describe the spinodal decomposition in macroscopic regions. These variables govern the spatial transformation of the forms and sizes of microphases. The perturbation theory is used to derive the equations for slow variables. The final relations of the simplest type give an exponential time dependence of the average size of a microphase. The problem of a contact of two pure components that are not compatible in the entire composition range is set.     

A Mechanisms and Kinetics Study of Polymeric Thin-Film Deposition in Glow Discharge

Polymeric thin-film deposition in a capacitively coupled rf glow discharge of styrene has been investigated. A kinetic scheme for the polymerization was proposed in which initiation of monomers by electron impact was followed by propagation and termination as in conventional polymerization, the initiation rate constant being a function of electron temperature alone. Four mechanism models were examined, depending on where each reaction step takes place: in the gas phase or on the substrate. Free-radical polymerization was assumed. Experiments were carried out at pressures ranging from 0.25 to 1.05 Torr and at voltages and currents that yielded cold and stable discharges. Substrate temperature was controlled. Deposition rate was determined by weighing. A regression program was used in addition to experimental tests in which substrate temperature was varied. The best approximation to the plasma polymer deposition process was found to be the following model: monomers are activated in the gas phase by electron bombardment and subsequently diffuse to the substrate where they propagate and terminate, adsorption of monomers on the substrate playing an important role. A rate expression relating polymer film deposition rate to the experimental variables is presented.     

Liquid-liquid equilibria of polymer solutions: Applicability of extended Redlich-Kister expansion

We developed a simple and improved expression for the Helmholtz energy of mixing which uses a Taylor series of an exponential function based on extending the Redlich-Kister expansion. This model incorporates the chain-length dependence of polymers and specific interactions such as hydrogen bonds. The proposed model can accurately predict most phase diagrams of various binary polymer solutions including upper critical solution temperature (UCST), lower critical solution temperature (LSCT), both UCST and LCST, and closed miscibility loops. Our model fits experimental data of the complex phase behavior of polymer solutions well.     

Emulsion polymerization of vinyl acetate. II

The emulsion polymerization of vinyl acetate was investigated at low ionic strengths and has quite unusual kinetics. The rate of polymerization is dependent on the initiator concentration to the first power and independent of soap concentration. In seeded polymerizations, the rate of polymerization depends on initiator to the 0.8 power, particle concentration to the 0.2 power, and monomer volume to 0.35 power. In all cases the rate of polymerization is almost independent of monomer concentration in the particles until 85–90% conversion. These results were rationalized by the following mechanism: (a) polymerization initiates in the aqueous phase because of the solubility of the monomer and is stabilized there by adsorption of ionic soap on the growing polymer molecule; (b) the growing polymer is swept up by a particle at a degree of polymerization (under our conditions) of about 50–200. Growth continues in the particle. This sweep-up is activation-controlled as both particle and polymer are charged. (c) Chain transfer to the acetyl group of monomer gives a new small radical which cyclizes to the water-soluble butyrolactonyl radical, and reinitiates polymerization in the aqueous phase; (d) the main termination step is reaction of an uncharged butyrolactonyl radical with a growing aqueous polymer radical. A secondary reaction at low ionic strength is sweep-up of an aqueous radical by a particle containing a radical. At high ionic strength, this is the major termination step. The unusual kinetic steps are justified by data from the literature. They are combined with the usual mechanisms operating for vinyl acetate polymerization and kinetic equations are derived and integrated. The integral equations were compared with the experimental data and shown to match it almost completely over the whole range of experimental variables.     

New polymer systems exhibiting microphase separation transition with the formation of nano-microstructures

The concept of microphase separation was up to now widely applied mainly to the conformational transitions in block-copolymer solutions and melts. However, recently it became obvious that this concept has a much more general meaning. It was shown that microphase separation transition can be observed in random copolymers, interpenetrating polymer networks, polyelectrolyte mixtures, poor solvent polyelectrolyte solutions, ionomer solutions and melts, polymer blends and solutions with nonlocal entropy of mixing. In all these examples the emerging microdomain structures correspond to the nanometer scale, therefore the study of these effects can lead to the new ways of obtaining polymer materials with controlled nano-microstructure. In this presentation the review of our recent findings on microphase separation in some of the above-mentioned systems will be presented. 1. The problem of microphase separation in the systems containing weakly charged polyelectrolytes (polyelectrolyte mixtures and poor solvent polyelectrolyte solutions) will be considered. From the methodic point of view, it will be shown that this problem can be solved by direct minimization of the free energy, without the use of “weak segregation” or “strong segregation” assumptions which are common in the theory of block-copolymers. The final phase diagrams exhibit wide macroscopic phase separation regions, which is their main difference from the corresponding phase diagrams for block-copolymer systems. The formation of microdomains is thus coupled with macroscopic phase separation: in most of the cases microdomain structure is formed in one of the coexisting phases after macroscopic phase separation takes place [1] - [2]. 2. The formation of the multiplet structure in ionomer melts and solutions can be also considered as the microphase separation in the random copolymer system with the formation of the “micelles” (or clusters) of ionic links. The parallels with micelle formation in block-copolymer systems can be established if one considers a new “superstrong segregation regime” for block-copolymer microstructures. This regime can be indeed observed for diblock copolymers with one ionomeric and one neutral block [3]. 3. The microphase separation transition in ordinary polymer blends and solutions is also possible. The conditions for this effect are: (i) significant entropic contribution to polymer/polymer or polymer/solvent miscibility, (ii) the nonlocal character of this contribution with a high value of the nonlocality radius. It is argued that one can expect that the entropy nonlocality radius increases in the vicinity of the glass transition for the blend or polymer solutions (in the latter case solvent molecules act like “poor solvent plasticisers”). Computer simulation data supporting the theoretical prediction of microphase separation transition in these systems will be presented [4] - [5].     

Effect of solute hydrophobicity on phase behaviour in solutions of thermoseparating polymers

 Two-phase systems consisting of a polymer rich phase and polymer depleted phase, where the polymer is either ethyl(hydroxy ethyl)cellulose (EHEC) or Ucon (a random copolymer of ethylene oxide and propylene oxide), have been studied. Both of these polymers can be separated from an aqueous solution by either temperature increase or addition of cosolutes. The polymers are thermoseparating and phase separate in water solutions at the cloud point temperature. Two types of EHEC have been studied: one with a cloud point at 60 °C and the other at 37 °C. The Ucon polymer used in this study has a cloud point at 50 °C. Ternary phase diagrams of polymer/water/cosolute systems have been investigated. When a strongly hydrophilic or hydrophobic cosolute is added to an EHEC- or Ucon–water solution, a phase separation occurs already at, or below, room temperature. As cosolutes, hydrophobic molecules like phenol, butyric and propionic acid, and hydrophilic molecules like glycine, ammonium acetate, sodium carboxylates (acetate to valerate), were studied. The polymer rich phase formed when mixing polymer, water and cosolute was strongly enriched or depleted with hydrophobic or hydrophilic cosolutes, respectively. The two phase region increased for propionic acid, butyric acid and phenol as a result of increased cosolute hydrophobicity. The opposite occurred in the series sodium acetate, sodium butyrate and sodium valerate. The effect of temperature on the phase behaviour has also been investigated. Model calculations based on Flory–Huggins theory of polymer solutions are presented, in form of a phase diagram, which semiquantitatively reproduce some experimental results. Received: 5 July 1996 Accepted: 4 November 1996     

Attenuated total reflectance/fourier transform infrared studies on the phase‐separation process of aqueous solutions of poly(n‐isopropylacrylamide)

Temperature‐induced phase separation of poly(N‐isopropylacrylamide) in aqueous solutions was studied by attenuated total reflectance (ATR)/Fourier transform infrared spectroscopy. The main objectives of the study were to understand, on a molecular level, the role of hydrogen bonding and hydrophobic effects below and above the phase‐separation temperature and to derive the scenario leading to this process. Understanding the behavior of this particular system could be quite relevant to many biological phenomena, such as protein denaturation. The temperature‐induced phase transition was easily detected by the ATR method. A sharp increase in the peaks of both hydrophobic and hydrophilic groups of the polymer and a decrease in the water‐related signals could be explained in terms of the formation of a polymer‐enriched film near the ATR crystal. Deconvolution of the amide I and amide II peaks and the O? H stretch envelope of water revealed that the phase‐separation scenario could be divided, below the phase‐separation temperature, into two steps. The first step consisted of the breaking of intermolecular hydrogen bonds between the amide groups of the polymer and the solvent and the formation of free amide groups, and the second step consisted of an increase in intramolecular hydrogen bonding, which induced a coil–globule transition. No changes in the hydrophobic signals below the separation temperature could be observed, suggesting that hydrophobic interactions played a dominant role during the aggregation of the collapsed chains but not before. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 1665–1677, 2001     

Synthesis of poly(1.4.-benzamide) in solutions of randomly coiled polymers

The polycondensation of p-aminobenzoic acid by the use of triphenylphospine and hexachloroethane is described. One way to obtain a mixed solution of rigid rod and flexible coil polymers is the polycondensation of the rigid chains in a solution of a flexible polymer matrix. Results on matrix polycondensation of poly(p-benzamide) in solutions of poly(methyl methacrylate), poly(methyl methacrylate-co-styrene), polystyrene and polyacrylonitrile are reported. It is shown that there exists an interrelation between the phase behavior of the mixed polymer solutions and the influence of the matrix polymer on the synthesis of poly(1.4.-benzamide). The ternary phase diagrams of the rigid rod/flexible coil polymer solutions were determined.     

The Influence of Ion Pair Formation on the Phase Behavior of Polyelectrolyte Solutions

In this paper we calculate the phase diagrams of polyelectrolyte solutions taking into account the possibility of ion pair formation between counterions and ions on polymer chains with their subsequent aggregation in multiplets. Multiplets play a role of reversible physical crosslinks between different polymer chains. Furthermore, we assume that the dielectric constant, and hence the binding energy of ion pairs and multiplets, depends on the volume fraction of polymer in the solution. We have shown that ion pairing and multiplet formation leads to instability of the homogeneous phase, so that at some conditions the phase separation can proceed even in good solvent. Another qualitatively new feature of the behavior of polyelectrolyte solutions is the emergence of a triple point on the phase diagram. The effect of the solvent polarity and the polarity of the dry polymer on the general form of the phase diagram is studied in detail.