Reaction-induced Phase Separation Research Articles

Interfacial reaction induced phase separation in LaxHfyO films

Amorphous LaxHfyO films containing La at concentrations (x) of 50 and 20% were prepared by atomic layer deposition on ultrathin SiO2 films (1 nm). We examined the electronic structures and microstructures of the LaxHfyO films by x-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), energy dispersive x-ray spectroscopy (EDS), and x-ray diffraction (XRD). Phase separation into La2O3 and HfO2 was observed in the LaxHfyO films subjected to annealing temperatures over 900 °C, although the mixture of La2O3 and HfO2 is thermodynamically stable. The structural changes that occurred as the result of phase separation were dependent on the concentrations of La and Hf in the films. During the annealing treatment, silicate was produced due to interfacial reactions and the interfacial reactions were found to be dependent on the La2O3 content in the LaxHfyO films, which has a significant influence on the phase separation process and resulting film structure.

Influence of addition of silica particles on reaction-induced phase separation and properties of epoxy/PEI blends

Polyether imides (PEI)/silica nanocomposites, prepared by sol–gel process, were used to modify the epoxy resin (ER), and the effect of silica particles on reaction-induced phase separation and mechanical properties of these systems were investigated. SEM images of the fracture surface of ER/PEI/silica composites showed an interesting morphology transformation with the increase of silica particle content. SEM–EDX results indicated that silica particles once formed in the PEI gradually migrated and concentrated in epoxy-rich region during the phase separation because of the better affinity between silica particles and epoxy resin. FTIR measurement and rheological test confirmed that the silica particles make the polymerization reaction of epoxy faster and the dynamic DSC results demonstrated that the activation energy of these systems decreased with the increase of the silica particles. Mechanical measurements approved that the introducing of PEI/silica nanocomposites into the epoxy could lead to great improvement of the impact strength and storage module.

Preparation of poly(2-oxy-6-naphthoyl) and copolymers using reaction-induced phase separation during direct polymerization in the presence of boronic anhydride

Poly(2-oxy-6-naphthoyl) was prepared using reaction-induced phase separation during direct polymerization of 2-hydroxy-6-naphthoic acid in the presence of boronic anhydrides. Various unique morphologies such as spheres, spheres with needles, cone-like crystals were obtained as precipitates. Copolymers with 4-hydroxybenzoic acid were also studied.

Rheology and pressure–volume–temperature behavior of the thermoplastic poly(acrylonitrile-butadiene-styrene)-modified epoxy-DDS system during reaction induced phase separation

The rheology and volume shrinkage characteristics of an epoxy matrix based on diglycidyl ether of bisphenol-A (DGEBA) cured with 4,4′-diaminodiphenylsulfone (DDS) and those containing poly(acrylonitrile-butadiene-styrene) (ABS) at compositions ranging from 0 to 12.9 wt% were monitored in situ using rheometry and pressure–volume–temperature (PVT) analysis. This investigation has focused on the importance of cure rheology on microstructure formation, using rheometry. The relationship between rheological properties and the phase separation process was carefully explored. The evolution of storage modulus, loss modulus, and tan δ was found to be closely related to the evolution of complex phase separation. It was found that complex viscosity profiles follow an exponential growth with curing at various temperatures. The characteristic relaxation time of viscosity growth can be described by the WLF equation. In the second part of this manuscript PVT measurements carried out to understand the volume shrinkage of the blend matrix with respect to cure are described. Volume shrinkage is highest for a neat epoxy system, the volume shrinkage decreased linearly up to 6.9 wt% ABS then it shows a different trend for the 10 and 12.9 wt% ABS modified epoxy blend. Investigation of the volume shrinkage behavior in these blends by various techniques confirms that the shrinkage behavior is influenced by thermoplastic phase separation during cure.

Reaction-Induced Phase Separation and Structure Formation in Polymer Blends

The peculiarities of reaction-induced phase separation and the structure formation in semi- and full interpenetrating polymer networks and in the blends of linear polymers formed in situ are analyzed. It is shown that for most of these systems phase separation proceeds viathe spinodal decomposition mechanism resulting in the formation of interconnected spatially periodic structures. The possible ways for the structure regulation of the composites produced are considered.

Functionalized Nanoporous Membranes from Reactive Triblock Polymers

Hydrophilic and stimuli responsive nanoporous poly(dicyclopentadiene) membranes are prepared using reactive ABC triblock polymers consisting of a chemically etchable ‘A’ block, poly(lactide), various functionalized ‘B’ blocks, and a metathesis-reactive ‘C’ block, poly(styrene-stat-norbornenylethylstyrene).A membrane with a bicontinuous structure is formed by reaction-induced phase separation during the metathesis crosslinking of dicyclopentadiene in the presence of the ABC triblock polymers. Selective etching of the poly(lactide) block exposed the functionality contained in the B block. Hydrophilic membranes are prepared from a triblock polymer with a poly(N,N-dimethylacrylamide) B midblock as evidenced by static contact angle measurements in comparison to AC diblock templated membranes. Temperature responsive membranes are prepared from a triblock polymer with a poly(N-isopropylacrylamide) B block.

Layered structure formation in the reaction-induced phase separation of epoxy/polysulfone blends

In an epoxy/polysulfone blend, the reaction-induced phase separation behavior and the final morphology were investigated. Three distinct morphological structures were obtained. Sea-island and nodular structures were observed at lower and higher polysulfone contents, respectively. A three-layered structure was obtained in the middle polysulfone concentration range. In order to understand the formation of three-layered structure, phase separation process was studied using time-resolved light scattering, phase-contrast optical microscope and scanning electron microscope. Bicontinuous structure formed uniformly in the whole sample at the beginning of phase separation. After the phase structure grew for a certain time, large domains formed and developed. Then, the large epoxy-rich domains gradually flew to the outer space of the sample film. This process assisted the formation of the three-layered structure. The mechanism of the formation of the three-layered structure was discussed based on the different viscoelastic properties of the components.

Modulating the Porosity of Cryogels by Influencing the Nonfrozen Liquid Phase through the Addition of Inert Solutes

The freezing of monomeric mixtures is known to concentrate solutes in a nonfrozen phase in the area surrounding the ice crystals. The concentration of such solutes is determined by the freezing temperature. Although salts or solvents do not directly react in the polymerization reaction, they do change the composition and properties of the nonfrozen phase. In this study, we investigated the influence of the addition of various salts and solvents on the structure of macroporous hydrogels formed in a semifrozen state through aqueous free-radical polymerization. The change in composition of the nonfrozen phase was studied using NMR to monitor the freezing of water, and the structural changes of the gels were observed using scanning electron microscopy. It was found that the addition of methanol or acetone caused the formation of reaction-induced phase separation polymerization due to cryoconcentration, which caused a significant increase of methanol or acetone in the nonfrozen phase. This resulted in a material with bimodal pore size distribution with pores of 10-80 μm in diameter caused by cryogelation, and with pores in the polymeric matrix with a diameter of less than 1 μm due to the reaction-induced phase separation. Addition of salts to the monomeric mixture resulted in a structure with only pores of 10-80 μm in diameter due to cryogelation. Increasing the amount of salts added resulted in the formation of thicker pore walls and thus a slight reduction in pore size compared to a sample with no added solute. The possibility of changing the structure and properties of the gels by adding different solutes could open up new applications for these materials, for example, chromatography applications.

Submicrometer Thermoplastic Vulcanizates Obtained by Reaction-Induced Phase Separation of Miscible Poly(Ε-Caprolactone)/Dimethacrylate Systems

Abstract Reaction-induced phase separation of initially miscible mixtures of poly(Ε-caprolactone) (PCL) and elastomer precursors based on difunctional methacrylate resins was applied to prepare thermoplastic vulcanizates (TPVs) with rubber particle sizes ranging from 80 to 900 nm. The radicals formed by the peroxide decomposition initiate the formation of a cross-linked rubber network with gel contents exceeding 90%, but also abstract hydrogen atoms from the aliphatic moieties in PCL. This leads to the formation of PCL-grafted rubber particles, which show a high nucleating efficiency for crystallization of the PCL matrix. It is demonstrated that the tensile and elastic properties of these TPVs are determined by a complex interplay of the morphology, the type of elastomer precursor, the extent of PCL grafting, the crystallinity, and the lamellar thickness. The materials showed a rheological behavior that is typical for TPVs, for which the melt changes from an elastic to a viscous behavior above a critical stress.

Porous epoxies by reaction induced phase separation of removable alcohols: Control of spheroidal pore size by mass fraction, cure temperature, and reaction rate

AbstractPorous organic and inorganic materials with both random and controlled microstructures have utility in a variety of fields including catalysis, sensors, separations, optical platforms, tissue engineering, hydrogen storage, micro‐electronics, medical diagnostics, as well as other applications. This work highlights a simple and general technique for tuning the pore size in crosslinking polymeric systems by adding a solvent poragen that phase separates during the curing process (reaction induced phase separation). The pore size can be controlled over large length scales ranging from microns to well below 100 nanometers. In this system an amine cured epoxy resin was reacted in the presence of the sacrificial poragen octadecanol, which is removed by vacuum‐assisted evaporation once the epoxy components have reacted to form a solid, porous matrix. The importance of the present approach is based on the simplicity of the chemical formulation, the ease by which other epoxide or amine chemistries may be substituted for the two reactive components, and the control of pore size down to the nanometer scale by the addition of a small amount of catalyst. © 2010 Wiley Periodicals, Inc.† J Appl Polym Sci, 2010

Formation of Nanostructured Poly(dicyclopentadiene) Thermosets Using Reactive Block Polymers

Nanostructured thermosets were prepared by reaction-induced phase separation (RIPS) using a metathesis-cross-linkable monomer in the presence of a metathesis-reactive block polymer. Mixtures of poly(norbornenylethylstyrene-s-styrene)-b-poly(lactide) (PNS−PLA) and dicyclopentadiene (DCPD) in tetrahydrofuran were cross-linked using the second generation Grubbs catalyst. Small-angle X-ray scattering analysis of a series of cured films containing PNS−PLA with varied PLA block lengths and 0−83 wt % DCPD indicated the presence of nanophase-separated disordered morphologies postcuring in most cases. Scanning electron microscopy of cured films after removal of the PLA phase revealed that a majority of the films exhibited a bicontinuous structure. Mechanistic investigations demonstrated that cross-linking the PNS block into the matrix was vital in preventing macrophase separation, and the morphologies observed were relatively unaffected by variations in the concentration of the catalyst. We propose a general mecha...

Poly(2,5-benzimidazole) nanofibers prepared by reaction-induced crystallization

Morphological control of poly(2,5-benzimidazole) (PBI) was examined by reaction-induced phase separation of oligomers during polymerization to prepare nanofibers. Three monomers, 3,4-diaminobenzoic acid (DABA), 3,4-diacetoamidebenzoic acid (DAcBA) and phenyl 3,4-diaminobenzoate (PDAB), were used to synthesize PBI. Polymerizations were carried out at 350 °C in a mixture of dibenzyltoluene isomers. Polymerization of DABA yielded spheres with plate-like crystals on their surface. Polymerization of DAcBA yielded almost no precipitates because of the high solubility of DAcBA oligomers. By contrast, polymerization of PDAB yielded aggregates of PBI nanofibers (of which the average diameter was ∼60 nm), which resembled nonwoven fabrics. These fibers were formed by precipitation of (2,5-benzimidazole) oligomers and their subsequent polymerization into a developing crystal structure. The structure of the monomer significantly influenced the morphology of the PBI product, and PDAB was preferable for the preparation of PBI nanofibers. The temperature of 10% N2 weight loss in these nanofibers was in the range of 634–644 °C and they were thermally stable. The network aggregates of poly(2,5-benzimidazole) nanofibers were prepared by the polymerization of phenyl 3,4-diaminobenzoate at 350 °C in a mixture of dibenzyltoluene isomers. The average diameter of the fibers was ∼60 nm. These fibers were formed by the crystallization of oligoimidazoles and the subsequent polymerization in them.

Using two-dimensional time resolved light scattering to study the cure reaction induced phase separation process of epoxy-amine-polyethersulfone blend with secondary phase separation

The generalized two-dimensional correlation analysis based on time-resolved light scattering patterns (2D TRLS) has been employed to study the phase separation process of an epoxy-amine-polyethersulfone blend in which the secondary phase separation takes place. The results of the 2D TRLS provided more detailed information that was not readily observed in the 1D TRLS patterns. (i) During the first process of phase separation, the sequential order of coarsening in size of the domains among the larger and smaller ones has been reversed between the diffusion regime and the hydrodynamic regime. (ii) The change of the larger domains in size, due to the hydrodynamic flow in the late stage of the first phase separation process, keeps on taking place earlier than that of the new domains appeared in the secondary phase separation process. (iii) During the secondary phase separation process the size growth of the smaller domains takes place earlier than that of the larger ones, probably due to the assumption that the coarsening mode could decrease the interface tension more quickly.

Phase-Separated Conetwork Structure Induced by Radical Copolymerization of Poly(dimethylsiloxane)-α,ω-diacrylate and N,N-Dimethylacrylamide

Phase-separated conetwork structure was induced by a radical copolymerization of telechelic polymer, (polydimethylsiloxane-α,ω-diacrylate (PDMS-DA)), and N,N-dimethylacrylamide (DMAA). The structure development was investigated by in situ SAXS measurement. A mixture of PDMS-DA and DMAA was transparent and homogeneous and gave no peak in SAXS profile. The radical copolymerization of both initiated at 303−363 K was successfully done to form fully transparent objects. Peak was observed in SAXS from the resulting polymer, which can be interpreted in terms of Teubner−Stray model, involving a polymer morphology with given a periodicity. The analysis of time evolution of the SAXS profiles (in site measurement) revealed that the phase separation occurred via the spinodal decomposition mechanism. The morphology was fixed by solidification of the sample due to cross-linking and glass transition during reaction-induced phase separation. The final structure was interpreted fairly using Teubner−Stray model. Thus, the final structure of the PDMS-DA/DMAA copolymer sample was found to be a bicontinuous and periodic structure (conetwork) in nanometer scale. The structure was also confirmed by TEM.

Morphology evolution of polysulfone nanofibrous membranes toughened epoxy resin during reaction-induced phase separation

The phase separation process and morphology evolution of 5 wt% polysulfone (PSF) nanofibrous membranes toughened epoxy resin at different temperatures were investigated by synchrotron radiation small angel X-ray scattering (SR-SAXS), phase contrast microscopy (PCM) and scanning electron microscopy (SEM). The onset time of phase separation obtained by different methods was basically identical. As the curing proceeded at constant temperature, the scattering peak corresponding to the maximum scattering intensity shifted to a smaller scattering vector ( q m ), and the average diameters of PSF spheres increased, which showed a phase separation pattern of nucleation and growth mechanism. PSF spheres exhibited random alignment in “sea-island” morphology, which was attributed to the in situ phase separation of PSF nanofibers. Also, the effects of phase separation kinetics on the phase morphology and fracture toughness of nanofibrous membranes toughened epoxy resin were investigated. Results showed that the phase separation process was faster than the curing reaction process, which implied that the diffusion coefficient of PSF in epoxy resin increased with increasing the curing temperature, resulting in the increase of PSF sphere size that in turn improved the fracture toughness at higher temperature.

Ultrasonic Online Tracking of Reaction-Induced Phase Separation

On-line tracking of reaction-induced phase separation has been realized for the first time by using high frequency ultrasonic wave,which is based on the Rayleigh scattering of ultrasonic wave on the interface of a multiphasic system.The new technology was employed to track the curing reaction of epoxy resin in PEG medium.The investigation involved the effects of concentration,reaction medium,amount of curing agent and temperature on the reaction-induced phase separation.Based on an intensive analysis of spinodal demixing(SD) in this curing system,a physical model has been put forward,in which two processes have been abstracted to describe the reaction-induced phase separation.One is the process of phase separation,and the other is phase isolation.In the related mathematical model the scattering intensity of ultrasonic wave is expressed as a function of the rates of both phase separation and phase isolation,by which the experimental data from ultasonic tracking have been explained reasonably.The on-line tracking technology found that under high concentration or by raising the reaction temperature the phase separation would be suppressed by polymerization to yield phase structures with high connectivity.In PEG2000 medium and under high concentration a hysteresis effect of function l(t) was found and the SD mechanism was supported.The phase separation is also influenced by the weight ratio of epoxy resin and curing agent,a ratio of 4/1 was proved to suitable for the completion of both phase separation and polymerization.The new technology made it possible to realize a real-time analysis of the changing of multiphasic structure during the phase separation,which might provide an experimental basis for the control of phase separation.

Preparation and characterization of single-hole macroporous organogel particles of high toughness and superfast responsivity

Crosslinked macroporous polymer particles containing a single large hole in their surfaces were prepared by solution crosslinking of butyl rubber (PIB) in benzene using sulfur monochloride (S 2Cl 2) as a crosslinking agent. The reactions were carried out within the droplets of frozen solutions of PIB and S 2Cl 2 at −18 °C. Spherical millimeter-sized organogel beads with a polydispersity of less than 10% were obtained. The particles display a two phase morphology indicating that both cryogelation and reaction-induced phase separation mechanisms are operative during the formation of the porous structures. The beads exhibit moduli of elasticity of 1–4 kPa, much larger than the moduli of conventional nonporous organogel beads formed at 20 °C. The gel particles also exhibit fast responsivity against the external stimulus (solvent change) due to their large pore volumes (4–7 ml/g). The gel beads prepared at −18 °C are very tough and can be compressed up to about 100% strain during which almost all the solvent content of the particles is released without any crack development. The sorption–squeezing cycles of the beads show that they can be used in separation processes in which the separated compounds can easily be recovered by compression of the beads under a piston.

Polymer‐based monolithic columns in capillary format tailored by using controlled in situ polymerization

This review introduces to the readers our new perspectives of polymer-based monolithic column with a high performance for small solutes such as drug candidates, illustrating the fabrication of LC columns in capillary. First, we briefly reviewed the status quo of polymer-based monolithic columns, comparing with silica monoliths. The miniaturization of LC system with higher throughput (shorter analytical time) was stressed conceptually, along with a fine permeable bicontinuous monolithic structure with submicron domain size (skeletal thickness + pore size) for higher performance. Second, from these perspectives, our column preparation was described, while our specially designed porogenic solvents were introduced as a controller of the monolithic morphology via reaction-induced phase separation. Specifically, monolithic columns were exemplified in two polymer formats, that is, one monolith prepared by free radical polymerization of glycerin 1,3-dimethacrylate, GDMA, and the other prepared by stepwise polymerization of newly introduced multifunctional epoxy and diamino monomers. Both monolithic columns in capillary format demonstrated a fine bicontinuous structure, affording a good compatibility of the efficiency (H) and permeability (D). Especially, the epoxy-based column showed an excellent separation impedance, E (=H(2)/D). Our micro-HPLC data were discussed along with a prototyped wired chip device.

Polyoxometalate-based protic alkylimidazolium salts as reaction-induced phase-separation catalysts for olefin epoxidation

Two protic alkylimidazolium polyoxometalates, together with two corresponding aprotic N-methyl-alkylimidazolium polyoxometalates were synthesized and characterized by the methods of NMR, IR and TGAetc. Then, these salts were employed as catalysts for the epoxidation of cyclooctene in different media. The novel protic N-dodecylimidazolium peroxotungstate [HDIm]2[{WO(O2)2}2(μ–O)] was found to be a room temperature liquid molten salt (ionic liquid) and the most effective catalyst for the epoxidation of cyclooctene among these salts. The ionic liquid catalyst [HDIm]2[{WO(O2)2}2(μ–O)] can also be extended to the epoxidation of some other substrates. On the basis of this experimental observation, an efficient reaction-induced phase-separation catalyst system has been developed in this work. The reaction system can switch from tri-phase to emulsion and then to biphase and finally to all the catalyst self-precipitating at the end of the reaction, which made the recovery and reuse of the present catalyst very convenient.

Effect of non-reactive solvent on the formation and properties of porous epoxy thermosets formed via reaction-induced phase separation

BACKGROUND: A reaction-induced process for producing controlled-porosity epoxy thermosets with the aid of solvents is presented. The curing reactions were carried out in diglycidyl ether of bisphenol A and 4,4′-diaminodicyclohexylmethane systems in the presence of appropriate solvents. RESULTS: The phase separation during the polymerization with appropriate solvent was characterized using dynamic light scattering. Supercritical carbon dioxide was used to extract the solvent from the epoxy resin matrix. The morphology and the porosity within the epoxy thermosets were investigated using scanning electron microscopy and atomic force microscopy as a function of solvent content. The results showed that porous epoxy networks with average pore size ranging from 1 to 20 µm were obtained, and the size of pores could be varied by changing the solvent content. Thermal properties were investigated using differential scanning calorimetry and thermogravimetric analysis. The introduction of solvent decreased the glass transition temperature and the thermal stability of the epoxy thermosets but showed no influence on the degradation of the main networks. CONCLUSION: Porous epoxy thermosets have been successfully fabricated through a novel reaction-induced phase separation process with the aid of appropriate solvents. They should open a wide range of opportunities for new applications. Copyright © 2008 Society of Chemical Industry