Phase Separation Of Poly Research Articles

Studies on the Phase Separation of Poly(Ether Imide)‐Modified Cyanate Ester Resin

A high temperature thermosetting bisphenol‐A dicyanate (BADCy) was blended with a novel thermoplastic poly(ether imide) (PEI) at various composition. The phase separation behavior during isothermal curing was studied by differential scanning calorimeter (DSC), time‐resolved light scattering (TRLS), scanning electron microscopy (SEM), and rheological measurements. The results suggested that the phase structure changed from separated phase, via co‐continuous phase, to phase inversion with the increase of the PEI content. The curing conversion of BADCy was slightly affected by the composition in the blend and the curing rate was decreased with the increase of PEI content. The co‐continuous phase morphology was attributed to a spinodal decomposition. The initial concentration of PEI had an effect on the rheological behavior during phase separation. It was found by tensile test that the blend with 15 wt.% PEI had higher tensile strength and elongation at break than that without PEI.

Intermolecular interactions in poly(2,6-dimethyl-1,4-phenylene oxide)/poly(styrene) blends from the study of FT-IR spectra at various temperatures

Intermolecular interactions and phase separation in poly(2,6-dimethyl-1,4-phenylene oxide)/polystyrene (PPO/PS) blends have been studied by FT-IR spectroscopy. Infrared measurements of absorption bands provide a valuable method for the study of interactions between polymers in compatible blends. The influence of temperature changes on the absorption bands, the PPO/PS miscible blend and the corresponding homopolymers have been investigated. From the study of spectra obtained at several temperatures, ranging from +250 °C to −180 °C, useful evidence has been found. FT-IR spectra in the region 4 000–450 cm−1 of PPO at −180 °C (bottom), at room temperature (middle), and at +250 °C (top).

Phase Separation of Poly(N-isopropylacrylamide) in Mixtures of Water and Methanol: A Spectroscopic Study of the Phase-Transition Process with a Polymer Tagged with a Fluorescent Dye and a Spin Label

The thermoreversible phase transition of poly(N-isopropylacrylamide) randomly labeled with a spin label, 4-amino-2,2',6,6'-tetramethylpiperidine 1-oxide (TEMPO), and a fluorescent dye, 4-(pyren-1-yl)butyl (PNIPAM-Py-T), in different H2O/MeOH mixtures was studied by turbidimetry, continuous-wave electron paramagnetic resonance spectroscopy (CW-EPR), and fluorescence spectroscopy. The macroscopic phase diagram of PNIPAM-Py-T in H2O/MeOH measured by turbidimetry was identical to those of poly(Nisopropylacrylamide) (PNIPAM) and of TEMPO-labeled PNIPAM (PNIPAM-T) in H2O/MeOH mixtures. However, distinct differences among the three polymers were detected in their solvent-dependent EPR and fluorescence-spectroscopic properties. The EPR spectra were analyzed in terms of the isotropic hyperfine coupling constants, which monitor the variation in environmental polarity of the radical labels occurring for the conformational transitions of the polymer as a function of temperature, as well as the correlation time for reorientation motion, the increase of which is indicative of the increased viscosity of the radical environment and interactions occurring between the radical and other surface groups of the precipitated polymer, if compared to the soluble polymer. The fluorescence of Py in PNIPAM-Py-T displayed contributions from isolated excited pyrenes (monomer emission) and from preformed pyrene ground-state aggregates (excimer emission). The quantum efficiencies of monomer and excimer emission were monitored as a function of solvent composition. By the two experimental approaches, we demonstrate the profound influence of the PNIPAMattached pyrene units in increasing the hydrophobicity of the nanodomains formed upon heat-induced precipitation of PNIPAM-Py-T.

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

AbstractTemperature‐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

Phase Separation in Poly(N,N-diethylacrylamide)/D2O Solutions and Physical Gels as Studied by1H NMR Spectroscopy

The structural-dynamic changes during temperature-induced phase separation in poly(N,N-diethylacrylamide) (PDEAAm)/D 2 O solutions and physical gels in a broad range of concentrations (c = 0.5-50 wt.-%) were studied by conventional high-resolution and MAS 1 H NMR spectra. In the whole concentration range, irrespective of whether the studied system is a solution (c 5 wt.-%), the phase transition is manifested by line brondening (linewidth 3.6 kHz) of a major part of PDEAAm anits, evidently due to the formation of compact globular-like structures. 1 H. MAS NMR spectra have shown that this broadening is not due to near-static dipolar interactions. The respective motion is effectively isotropic with correlation time 1 μs, probably corresponding to Brownian tumbling of the whole globular particles. The thermotropic phase transition, as revealed by NMR, is not discontinuous, but 6 K broad (302-308 K). Above the LCST transition, the fraction p * of PDEAAm segments in globular-like structures is between 0.94-1.0, independent of the polymer concentration. At temperatures below the LCST a certain preaggregation of PDEAAm is indicated by smaller line broadening (linewidths 100 Hz) in the 1 H NMR spectra.

Phase Separation in Poly(N,N-diethylacrylamide)/D2O Solutions and Physical Gels as Studied by 1H NMR Spectroscopy

Phase Separation in Poly(N,N-diethylacrylamide)/D2O Solutions and Physical Gels as Studied by 1H NMR Spectroscopy

Relationship between dynamic rheological behavior and phase separation of poly(methyl methacrylate)/poly(styrene-co-acrylonitrile) blends

On the basis of phase separation temperatures (Ts) for poly(methyl methacrylate)/poly(styrene-co-acrylonitrile) blends of different compositions, measured by small angle laser light scattering, we have studied dynamic rheological behavior of these blends at different temperatures below, near and above Ts. The results showed that the time–temperature superposition principle could be applied and the linear viscoelastic response emerged in the terminal region at temperatures below Ts. However, it was found that the breakdown of time–temperature superposition principle appeared, and viscoelastic response deviated from the linear behavior in the terminal region at temperatures near and above Ts.

Phase separation in poly(N‐isopropyl acrylamide)/water solutions. II. Salt effects on cloud‐point curves and gelation

AbstractThe cloud‐point temperatures (Tclo's) of poly(N‐isopropyl acrylamide) (PNIPAM)/water solutions with NaCl, NaBr, or NaI were measured. All these salts reduced the Tclo's of PNIPAM/water solutions to different extents, in the following order: NaCl > NaBr > NaI. The higher the concentration of the added salt was, the more greatly Tclo dropped. A dynamic viscoelasticity investigation of the PNIPAM/water solutions with the salts indicated that during phase separation, the system changed from a homogeneous fluid into a physically crosslinked network, and the addition of salts also reduced the temperature at which this change began. The gelation temperature (Tgel) and the scaling exponent of the PNIPAM/water solutions with NaBr were obtained with dynamic scaling theory, and Tgel was found to be close to Tclo. That the addition of salts to the solution decreased Tclo and Tgel to the same extent further proved that the network structure was formed with the phase separation in the PNIPAM/water solutions. © 2001 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 901–907, 2001

Thermal reversible gelation during phase separation of poly(N-isopropyl acrylamide)/water solution

Thermal reversible gelation during phase separation of poly(N-isopropyl acrylamide)/water solution

On the nature of morphological features in phase-separated (PEO) nNaSCN mixtures: a SAXS investigation

The SAXS technique is used to throw light on the morphology of phase-separated poly(ethylene oxide) n –sodium thiocyanate [(PEO) n NaSCN] mixtures. A temperature-dependent investigation is reported for (PEO) 4.5NaSCN. (PEO) n NaSCN mixtures show a complex phase behaviour. At the investigated composition, a crystalline complex (CC) is formed between PEO and NaSCN. The considered composition is representative of thermodynamic states where three different phases coexist simultaneously: crystalline PEO (CPEO), amorphous PEO (APEO) and crystalline complex (CC). Various SAXS data analysis approaches are presented to understand the nature of these coexisting phases. Invariant analysis shows a bimodal behaviour which seems to be related to the melting of CPEO and a different process occurring well before the melting of the CC. Electron density correlation function analysis shows a well defined border between a complex morphology with bimodal lamellae (when both CPEO and CC coexist) and a simple pseudo-two-phase model (when CPEO is melted and only CC lamellae persist). A detailed knowledge of the system morphological details is then obtained as a function of temperature.

Synthesis and characterization of poly(urethane-benzoxazine) films as novel type of polyurethane/phenolic resin composites

Poly(urethane-benzoxazine) films as novel polyurethane (PU)/phenolic resin composites were prepared by blending a benzoxazine monomer (Ba) and PU prepolymer that was synthesized from 2,4-tolylene diisocyanate (TDI) and polyethylene adipate polyol (MW ca. 1000) in 2 : 1 molar ratio. DSC of PU/Ba blend showed an exotherm with maximum at ca. 246 °C due to the ring-opening polymerization of Ba, giving phenolic OH functionalities that react with isocyanate groups in the PU prepolymer. The poly(urethane-benzoxazine) films obtained by thermal cure were transparent, with color ranging from yellow to pale wine with increase of Ba content. All the films have only one glass transition temperature (Tg ) from viscoelastic measurements, indicating no phase separation in poly(urethane-benzoxazine) due to in situ polymerization. The Tg increased with the increase of Ba content. The films containing 10 and 15% of Ba have characteristics of an elastomer, with elongation at break at 244 and 182%, respectively. These elastic films exhibit good resilience with excellent reinstating behavior. The films containing more than 20% of Ba have characteristics of plastics. The poly(urethane-benzoxazine) films showed excellent resistance to the solvents such as tetrahydrofuran, N,N-dimethyl formamide, and N-methyl-2-pyrrolidinone that easily dissolve PUs. Thermal stability of PU was greatly enhanced even with the incorporation of a small amount of Ba. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4165–4176, 2000

Membrane formation via phase separation induced by penetration of nonsolvent from vapor phase. II. Membrane morphology

Phase separation of poly(vinylidene fluoride) dimethylformamide solution was induced by the penetration of water vapor, and the porous membrane was formed. As the humidity in the gas phase increased, membrane morphology changed in the order of dense, porous (cellular), and lacy-like structures. At the higher humidity condition, spherical bead structure was observed, which is likely to be crystalline spherulite. With the increase of the initial polymer concentration, less pores were formed in the case of the lower humidity of 20%, whereas more distinguished spherical structures were formed in the case of higher humidity of 40%. The obtained membrane morphologies were discussed based on both the calculated composition paths during the process and the phase diagram. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 171–178, 1999

On the Formation of Colloidally Dispersed Phase-Separated Poly(N-isopropylacrylamide)

ADVERTISEMENT RETURN TO ISSUEPREVNoteOn the Formation of Colloidally Dispersed Phase-Separated Poly(N-isopropylacrylamide)Karinne Chan, Robert Pelton, and Ju ZhangView Author Information McMaster Centre for Pulp and Paper Research, Department of Chemical Engineering, McMaster University, Hamilton, Ontario, Canada L8S 4L7 Cite this: Langmuir 1999, 15, 11, 4018–4020Publication Date (Web):May 6, 1999Publication History Received16 September 1998Revised11 March 1999Published online6 May 1999Published inissue 1 May 1999https://doi.org/10.1021/la9812673Copyright © 1999 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views638Altmetric-Citations64LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit Read OnlinePDF (38 KB) Get e-AlertsSUBJECTS:Colloidal particles,Ionic strength,Particle size,Polymer particles,Polymers Get e-Alerts

Effect of filler on kinetics and energy of activation of phase separation in poly(methyl methacrylate)/poly(vinyl acetate) blend

Effect of filler on kinetics and energy of activation of phase separation in poly(methyl methacrylate)/poly(vinyl acetate) blend

Effect of filler on kinetics and energy of activation of phase separation in poly(methyl methacrylate)/poly(vinyl acetate) blend

The effect of a filler on the rate and energy of activation of phase separation was studied for binary poly(methyl methacrylate)/poly(vinyl acetate) blends (system with LCST) using light scattering. It was found that the rate of phase separation of the filled blends at close quench depth AT = T-T s is much lower as compared with the unfilled one at close quench depth. The activation energy for the filled blends is lower than that of unfilled blends. The drop of the rate of phase separation and of the activation energy in filled systems is explained by the formation of a border layer at the interface with solid where molecular packing is less dense and molecular mobility is restricted in comparison with unfilled polymer. Equal rates of phase separation or the equilibrium state may be achieved at higher quench depth for the filled blend.

Effect of filler on kinetics and energy of activation of phase separation in poly(methyl methacrylate)/poly(vinyl acetate) blend

Effect of filler on kinetics and energy of activation of phase separation in poly(methyl methacrylate)/poly(vinyl acetate) blend

DSC study of main relaxations in the poly(imide-dimethylsiloxane) block copolymers

The segmentai dynamics in a series of alternating, phase-separated poly(imidedimethylsiloxane) (PI/PDMS) block copolymers has been studied by differential scanning calorimetry (DSC) over the temperature range of 100–630 K, covering the regions of the glass transition and β-relaxation for soft and rigid blocks. The PI blocks had degrees of polymerization that ranged from 6 to 30, and the PDMS moiety content varied from 10 to 47 mass%. Complex behavior of the low-temperature, PDMS block glass transition characteristics was shown, and the conditions for maintaining the PI domains with high T g, providing thermal stability for these block copolymers, were ascertained. The peculiarities of segmentai dynamics and its heterogeneity observed within the glass transition could be interpreted by using as a basis the concept of the common segmentai nature of the α- and β-transitions in flexible-chain polymers.

Drug Microencapsulation by PLA/PLGA Coacervation in the Light of Thermodynamics. 1. Overview and Theoretical Considerations

□ Phase separation of poly(lactide) (PLA) and poly(lactide-co-glycolide) (PLGA), often called “coacervation” in the pharmaceutical field, is one of the classical methods for peptide drug microencap-sulation in biodegradable polyesters. Although numerous studies have used this technique, the underlying physicochemical mechanisms of polyester coacervation under conditions of microsphere production have not been well-described yet. Moreover, the quality of microen-capsulation in terms of drug loading efficiency and residual organic solvents is often not entirely satisfactory and depends greatly on the specific drug and polymer used. The first part of this contribution reviews briefly the scientific and patent literature on PLA/PLGA coacervation. Then, the underlying physicochemical principles of polyester coacervation are discussed and relevant thermodynamic models presented. More specifically, attempts were made to clarify the necessary characteristics of polymers, solvents, and coacervating and hardening agents for successful phase separation and microsphere formation. These basic considerations may contribute to a better understanding of the boundary conditions crucial for efficient drug microencapsulation by polyester coacervation.

Relationship between drawability of poly(vinyl alcohol) films prepared from semi-dilute solutions and phase separation of the solutions studied in terms of stereo-regularity and degree of polymerization

The phase separation of poly(vinyl alcohol) (PVA) in dimethyl sulfoxide/water mixtures was investigated by using light scattering techniques in terms of the degree of polymerization and stereo-regularity. Atactic (at-) and syndiotactic (st-) PVA, the degrees of polymerization ( P) being 17 900 and 1980, respectively, were used as test specimens. The analysis was mainly performed in comparison with previous results obtained for at-PVA ( P = 2000) whose degree of polymerization is similar to that ( P = 1980) of st-PVA, but lower than that ( P = 17 900) of at-PVA used in the present work. The phase separation occurred rapidly when the content of dimethyl sulfoxide in the mixed solvent was 50–70vol%. This tendency was found to be significant for st-PVA with high stereo-regularity, but to be almost independent of the degree of polymerization of at-PVA. The logarithm of scattered intensity from at- and st-PVA solutions increased linearly with time in the initial stage of the phase separation. If this phenomenon could be analysed within the framework of the linear theory of spinodal decomposition proposed by Cahn ( J. Chem. Phys., 1965, 42, 93) the phase diagram of st-PVA was classified into four regions: (I) a homogeneous sol region, (II) a sol region under spinodal temperature, indicating only spinodal decomposition, (III) a gel region under the spinodal curve, indicating simultaneous advance of both gelation and spinodal decomposition, and (IV) a gel region above the spinodal line, independent of liquid—liquid separation. On the other hand, for at-PVA, region II could not be observed and region IV existed only in a very narrow temperature range, which is similar to the result observed for at-PVA ( P = 2000) solutions in previous work. The drawability of the dried gel film was affected by the composition of the solvent mixture and by quenching temperature of the solutions, but it was hardly affected by the stereo-regularity. This interesting phenomenon is discussed in terms of morphology of gels and films, as studied by crystallinity, X-ray diffraction, birefringence and small angle light scattering under Hv polarization condition. As the results show, it turned out that the greatest significant drawability is related to a continuous tissue with honeycomb-like structure associated with rapid phase separation of PVA solutions due to thermodynamic instability.

N.m.r. investigation of phase separation in poly(N-isopropyl acrylamide)/water solutions

1H and 13C n.m.r. spectra of poly(N-isopropyl acrylamide) (PNIPA) in D 2O and CDCl 3 were measured at several temperatures encompassing the lower critical solution temperature (LCST) about 32°C of the PNIPA/water solution, using a high resolution n.m.r. spectrometer (500 MHz for proton). The PNIPA/CDCl 3 is homogeneous in the temperature ranging from 16 to 36°C and the hydrogen bonds of the amide groups are weakened by the solvation of CDCl 3 and broken by heating. In the PNIPA/D 2O solution, the proton and 13C spectra are well resolved below the LCST. Whereas at temperatures above the LCST, all the resonance peaks except that for water proton became broad and the spectra lost their fine structure. The integral intensity of the water proton relative to that of the lone proton in the isopropyl group increases with increasing temperature, suggesting that some water molecules appear to be released out of the hydrated shells around the polymer chains. When the solution was heated from 22 to 35°C, the spin-lattice relaxation time T 1 for the proton of the methyl group in the isopropyl residue increased, while that for the protons of the methylene and methyne groups of the backbone chain decreased. This indicates that during heating the relaxation of the isopropyl side chain slows down and that of the main chain speeds up. The phase separation was qualitatively interpreted with the Nemethy-Scheraga model for the hydrophobic bonding.