Phase Behavior Of Poly Research Articles

Phase behavior of poly(4‐tert‐butylstyrene‐stat‐4‐tert‐ butoxystyrene)/polyisoprene blends with competitive interactions

AbstractThe phase behavior of statistical copolymers composed of (4‐tert‐butylstyrene) (B) and (4‐tert‐butoxystyrene) (O), abbreviated as s‐BO, with polyisoprene (I) was investigated by optical microscopic (OM) observation and small‐angle neutron scattering (SANS) measurements. It has been known that B/I blend shows lower critical solution temperature (LCST) type phase diagram, while O/I blend has upper critical solution temperature (UCST) type one. Several blends of s‐BOs having mol fraction of B, mB, comparable to 0.50, with I showed both UCST and LCST type phase diagram. Furthermore, UCST type phase behavior was observed for blends having small mB, while LCST type one was for that of large mB at all used temperatures. Hence, the phase behavior of s‐BO/I blend can be understood as a result of the competition of two interactions having opposite temperature dependence. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 2272–2280, 2009

Thermodynamic study on phase transitions of poly(benzyl methacrylate) in ionic liquid solvents

Abstract The lower critical solution temperature (LCST) phase behavior of poly(benzyl methacrylate) (PBnMA) in room-temperature ionic liquids (ILs) was studied by considering the effect of the chemical structure of ILs on the phase separation temperature (T c). It was found that the LCST behavior of PBnMA was observed in ILs containing [NTf2] anions and PF6 anions. T c changed significantly with a small change in the chemical structures of the cations. High-sensitivity differential scanning calorimetry (DSC) was successfully performed for studying the LCST phase separation of PBnMA in two different imidazolium-based ILs. Endothermic peaks corresponding to the phase separation of PBnMA from the ILs were clearly observed at ca. 100 °C in the DSC thermograms. It was experimentally verified for the first time that the negative enthalpy and entropy change of mixing of PBnMA in ILs caused the LCST phase separations. The absolute values of the thermodynamic parameters for the phase transition of PBnMA in ILs obtained in this study were much lower than those reported in previous studies for aqueous polymer solutions that exhibit LCST phase behavior, such as poly(N-isopropylarylamide) and poly(vinyl methyl ether). Small changes in the thermodynamic parameters resulted in a large change in the phase separation temperature even by small changes in the chemical structure of the ILs and polymers. The microscopic desolvation process detected from the DSC measurements was inferred to have occurred before the macroscopic phase separation detected from turbidity measurements. The dependence of the endothermic peak temperatures on the DSC scan rate was observed even at slow scan rates. These results indicate that the phase separation of PBnMA from ILs is characterized by extremely slow kinetics.

Thermal and FTIR analysis of the miscibility and phase behaviour of poly (isobutyl methacrylate-co-4-vinylpyridine)/poly (styrene-co-acrylic acid) systems

The miscibility and phase behaviour of poly (isobutyl methacrylate-co-4-vinylpyridine) containing 20 mol% of 4-vinylpyridine (IBM4VP20) and poly (styrene-co-acrylic acid) containing 27 or 32 mol% of acrylic acid (SAA27 or SAA32) mixtures were investigated by DSC, TGA and FTIR spectroscopy in the 25–180 °C temperature range. The results showed that sufficient specific carboxyl–pyridine hydrogen bonding interactions occurred between these copolymers and led to miscible blends as cast from THF and to inter-polymer complexes of significantly improved thermal stability when butan-2-one is the common solvent. The self-association effect on the inter-polymer interactions was evidenced by the decrease of complexation yields, observed when the carboxylic content is increased above 27 mol% as with SAA32. The trend of phase behaviour predicted by a thermodynamic analysis of the specific interactions of hydrogen bonding type that occurred between the two components of the SAA27/IBM4VP20 blends, neglecting the weak carboxyl–ester interactions and the functional group accessibility effect, carried out using the Painter–Coleman association model that considers the screening effects, is in a fair agreement with the experimental results. Moreover an LCST is predicted to occur at relatively high temperature.

Phase Behavior of Poly(N-isopropylacrylamide) Nanogel Dispersions: Temperature Dependent Particle Size and Interactions

The phase behavior of poly(N-isopropylacrylamide) nanoparticles dispersed in aqueous medium is investigated as a function of temperature using static and dynamic light scattering techniques. The diameter, d of the particles, as determined by dynamic light scattering measurements on dilute dispersion showed a decrease in size from 273 nm at 25 degrees C to 114 nm at 40 degrees C as function of temperature with a sudden collapse of particle volume (volume phase transition) at 32.4 degrees C. Further this nanoparticle dispersion is found to turn turbid beyond volume phase transition. Static light scattering measurements on samples with intermediate concentration and high concentration showed liquid-like order and crystalline order respectively. The intensity of the Bragg peak of the crystallized sample when monitored as a function of temperature showed crystal to liquid transition at 26.2 degrees C and a fluid to fluid transition at 31 degrees C. The occurrence of melting at a volume fraction of 0.85 and the absence of change in number density across the fluid-to-fluid transition suggest that interparticle interaction is repulsive soft-sphere below the volume phase transition. The reported results on the phase behavior of poly(N-isopropylacrylamide) nanogel suspensions are discussed in the light of the present results.

Phase Behavior of Poly(vinylpyrrolidone) Containing Amorphous Solid Dispersions in the Presence of Moisture

The objective of this study was to investigate the phase behavior of amorphous solid dispersions composed of a hydrophobic drug and a hydrophilic polymer following exposure to elevated relative humidity. Infrared (IR) spectroscopy, differential scanning calorimetry (DSC) and moisture sorption analysis were performed on five model systems (nifedipine-poly(vinylpyrrolidone) (PVP), indomethacin-PVP, ketoprofen-PVP, droperidol-PVP, and pimozide-PVP) immediately after production of the amorphous solid dispersions and following storage at room temperature and elevated relative humidity. Complete miscibility between the drug and the polymer immediately after solid dispersion formation was confirmed by the presence of specific drug-polymer interactions and a single glass transition (T(g)) event. Following storage at elevated relative humidity (75-94% RH), nifedipine-PVP, droperidol-PVP, and pimozide-PVP dispersions formed drug-rich and polymer-rich amorphous phases prior to crystallization of the drug, while indomethacin-PVP and ketoprofen-PVP dispersions did not. Drug crystallization in systems exhibiting amorphous-amorphous phase separation initiated earlier (<6 days at 94% RH) when compared to systems that remained miscible (>or=46 days at 94% RH). Evidence of moisture-induced amorphous-amorphous phase separation was observed following storage at as low as 54% RH for the pimozide-PVP system. It was concluded that, when an amorphous molecular level solid dispersion containing a hydrophobic drug and hydrophilic polymer is subjected to moisture, drug crystallization can occur via one of two routes: crystallization from the plasticized one-phase solid dispersion, or crystallization from a plasticized drug-rich amorphous phase in a two-phase solid dispersion. In the former case, the polymer is still present in the same phase as the drug, and can inhibit crystallization to a greater extent than the latter scenario, where the polymer concentration in the drug phase is reduced as a result of the amorphous-amorphous phase separation. The strength of drug-polymer interactions appears to be important in influencing the phase behavior.

Phase behavior of poly(3-alkylthiophene)/polystyrene blends

Abstract Phase diagrams of blends consisting of poly(3- n -alkylthiopene) having four different n -alkyl side chain lengths ( n = 4, 6, 8, 12) and polystyrene (PS) were obtained by turbidity measurement. All of the P3AT/PS blends employed in this study exhibited the upper critical solution temperature (UCST) type phase behavior. From n = 4 [poly(3-butylthipene)] to n = 6 [poly(3-hexylthipene)], the miscibility between P3AT/PS blends decreased, but with further increase in the value of n , the miscibility increased. Thus, the miscibility of the P3HT/PS blend becomes the least among four blend pairs. This interesting phase behavior depending on n was successfully illustrated via the combination of Monte Carlo simulation and molecular dynamics.

Phase Behavior of Polystyrene-block-poly(2-vinylpyridine) Copolymers in a Selective Ionic Liquid Solvent

The phase behavior of poly(styrene-block-2-vinylpyridine) copolymer solutions in an imidazolium bis(trifluoromethane)sulfonamide ([Im][TFSI]) ionic liquid has been studied using small-angle X-ray scattering (SAXS) and optical transmission characterization. Through scaling analysis of SAXS data, we demonstrate that the [Im][TFSI] ionic liquid behaves as a selective solvent toward one of the blocks. We observe lyotropic and thermotropic phase transitions that correspond qualitatively to the phase behavior observed in block copolymer melts and block copolymer solutions in molecular solvents. In addition, we have studied the thermal properties of block copolymer solutions in the ionic liquid using differential scanning calorimetry and wide-angle X-ray scattering. We observe distinct composition regimes corresponding to the change in the block copolymer’s glass transition temperature, Tg, with respect to the concentration of polymer in ionic liquid. At high block copolymer concentrations, a “salt-like” regime corresponding to an increase in the block copolymer Tg is observed, while at intermediate block copolymer concentrations, a “solvent-like” regime corresponding to a decrease in the block copolymer Tg is observed. An unusual thermal transition consisting of crystallization and subsequent melting of the ionic liquid is observed at the lowest block copolymer concentration characterized.

Rheology and morphology change with temperature of SEBS/hydrocarbon oil blends

The effect of hydrocarbon oil incorporation on the rheological and phase behaviors of poly(styrene-b-(ethylene-co-butylene)-b-styrene) (SEBS) has been investigated. SEBS-A1 (neat SEBS) shows a presence of very long relaxation time mode even at the highest temperature carried out here. On the other hand, G′ of SEBS-A3 (oil concentration = 50 wt %) drastically decreases with increase of temperature at a critical temperature, which can be assigned to be order–disorder transition (ODT). The critical temperature was determined by two rheological criteria. Incorporation of hydrocarbon oil affects the ODT temperature. The rheological response is very sensitive to a few temperature increases around the ODT temperature. Above the critical temperature, G′ finally yields the terminal flow in the low frequency range. The morphological observation at various temperatures was determined using atomic force microscopy (AFM) equipped with environmental controller. This enabled in situ observation of structural change of SEBS induced by temperature and phase transition. We found that the layered texture, mostly aligned along the surface can be seen for SEBS-A1 ranging from room temperature to 230 °C, though the image contrast reduced by an increase of temperature. SEBS-A3 showed sphere domains at room temperature and also remains the structure at a critical temperature. The phase separated structure disappeared almost completely above ODT temperature, which was confirmed by the rheologial criteria. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 955–965, 2009

Phase behavior study of poly(N‐tertbutylacrylamide‐co‐acrylamide) in the mixture of water–methanol: The role of polymer–nonsolvent second‐order interactions

AbstractThe phase behavior of poly(N‐tertbutylacrylamide‐co‐acrylamide) (PNTBAM) in pure water and mixture of water–methanol is studied at different temperatures. The different compositions of PNTBAM are prepared by free‐radical polymerization technique and their phase behavior is studied by turbidimetry. The effects of copolymer and solvent composition on the phase behavior of the copolymers are discussed. It has been suggested that the inhomogenities in polymer chains are responsible for lowering the rate of phase transition by increasing the N‐tertbutylacrylamide (NTBAM) and methanol contents in copolymer and mixture, respectively. For the first time we have revealed that there are second‐order binary interactions in the water–methanol which are dominant in the special range of copolymer composition. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 455–462, 2009

Phase behavior of blends containing amorphous poly(resorcinol phthalate‐block‐carbonate) and semicrystalline polyesters

AbstractThe phase behavior of poly(resorcinol phthalate‐block‐carbonate) (RPC) with engineering polyesters was investigated by using differential scanning calorimeter (DSC) and dynamic mechanical analysis. RPC was found to form miscible blends with poly(ethylene terephthalate) (PET), poly(butylene terephthalate) (PBT), and poly(cyclohexylmethylene terephthalate) (PCT), but was partially miscible with poly(1,4‐cyclohexanedimethylene‐1,4‐cyclohexanedicarboxylate) (PCCD) in the melt state and below the melting temperature (Tm). The degree of melting‐point depression indicates that the RPC is most miscible with PCT followed by PET and then PBT. Furthermore, with the help of empirical DSC data and the Nishi–Wang equation, the interaction parameters between RPC and PET, PBT, and PCT were quantified to be −0.36, −0.33, and −0.54, respectively. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Irreversible phase behavior of the ternary blends of poly(ethylene terephthalate)/poly(ethylene‐2,6‐naphthalate)/poly(ethylene terephthalate‐ co‐ethylene‐2,6‐naphthalate)

AbstractThe phase behavior of Poly(ethylene terephthalate)/Poly(ethylene‐2,6‐naphthalate)/Poly(ethylene terephthalate‐co‐ethylene‐2,6‐naphthalate) (PET/PEN/P(ET‐co‐EN)) ternary blends in molten state was evaluated from differential scanning calorimetry (DSC) and NMR results as well as optical microscopic observations. Copolymer of ethylene terephthalate and ethylene‐2,6‐naphthalate was prepared by a condensation polymerization, which was a random copolymer with an intrinsic viscosity (IV) of 0.3 dL/g. The phase diagram of the ternary blends revealed that the miscibility of ternary blends in molten state was dependent on the fraction of P(ET‐co‐EN) in the blends and holding time of the blends at high temperatures above 280°C. With increase in the holding time, the fraction of copolymer in the blends necessary to induce the immiscible to miscible transition decreased. For the blends with longer holding time at 280°C, the phase diagram in molten state was irreversible against the temperature, although a reversibility was found for the blends with short holding time of 1 min at 280°C. The irreversibility of phase behavior was not explained simply by the increase of copolymer content produced during heat treatment. Complex irreversible physical and chemical interactions between components and change of phase structure of the blend in the molten state might influence on the irreversibility. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Dispersion Polymerization of Methyl Methacrylate using Poly(HDFDMA-co-MMA) as a Surfactant in Supercritical Carbon Dioxide

New surfactants, random copolymers of heptadecafluorodecyl methacrylate (HDFDMA) and methyl methacrylate (MMA), were synthesized at 343.2 K and 30 MPa in supercritical carbon dioxide (scCO2) with varying HDFDMA/MMA ratios. 1H NMR and FT-IR were used to confirm the structure and to determine the composition of the resulting copolymers. The phase behavior of poly(HDFDMA-co-MMA) in CO2 was obtained by means of a variable volume view cell, which will be used to select the polymerization condition. After that, dispersion polymerization of methyl methacrylate (MMA) in scCO2 was performed using 2,2′-azobis(isobutyronitrile) (AIBN) as the initiator and poly(HDFDMA-co-MMA) with various MMA mole fraction as a surfactant. The new surfactant, poly(HDFDMA-co-MMA), whose MMA content is lower than 12.3 wt %, shows comparable capacity to produce PMMA particles compared to poly(HDFDMA) surfactant. The resulting PMMA particles, such as those produced using poly(HDFDMA) homopolymer as a surfactant, could also be produced with poly(HDFDMA-co-MMA) up to 12.3 wt % MMA.

Phase Behaviour of Poly(styrene‐co‐methacrylic acid)/ Poly(styrene‐co‐N,N‐dimethylacrylamide)/Poly(styrene‐co‐4‐vinylpyridine) Ternary Blends by DSC and FTIR

AbstractSummary:we have investigated by DSC and FTIR the miscibility and phase behaviour of binary and ternary blends of different ratios of poly(styrene‐co‐methacrylic acid) containing 15 mol% of methacrylic acid (SMA15) with poly(styrene‐co‐N,N‐dimethylacrylamide) containing 17 mol% of N,N,‐dimethylacrylamide (SAD‐17) and poly(styrene‐ co‐4‐vinylpyridine) containing 15 mol% of 4‐vinylpyridine. SMA15 is miscible with both SAD17 and S4VP15 and interacts more strongly with S4VP15 than with SAD17 as evidenced by the positive deviations from linear average line observed with these blends and the appearance of new bands in the 1800–1550 cm−1 region. This behaviour is known as ΔK effect. The FTIR study confirms that though the specific intermolecular interactions that occurred with each pair of the SMA15/S4VP15 and SMA15/SAD17 binary components are of different strength, they still exist in the ternary blend. Even though the three binary polymer pairs are individually miscible, the ternary system of SMA15/S4VP15/SAD17 exhibits only partial miscibility with small loop of immiscibility due to a significant ΔK effect. These results obtained by DSC and FTIR are in a fair agreement with theoretical prediction applying the Painter‐Coleman association model.

Phase Behavior of Symmetric Sulfonated Block Copolymers

Phase behavior of poly(styrenesulfonate-methylbutylene) (PSS-PMB) block copolymers was studied by varying molecular weight, sulfonation level, and temperature. Molecular weights of the copolymers range from 2.9 to 117 kg/mol. Ordered lamellar, gyroid, hexagonally perforated lamellae, and hexagonally packed cylinder phases were observed in spite of the fact that the copolymers are nearly symmetric with PSS volume fractions between 0.45 and 0.50. The wide variety of morphologies seen in our copolymers is inconsistent with current theories on block copolymer phase behavior such as self-consistent field theory. Low molecular weight PSS-PMB copolymers (<6.2 kg/mol) show order−order and order–disorder phase transitions as a function of temperature. In contrast, the phase behavior of high molecular weight PSS-PMB copolymers (>7.7 kg/mol) is independent of temperature. Due to the large value of Flory–Huggins interaction parameter, χ, between the sulfonated and non-sulfonated blocks, PSS-PMB copolymers with PSS and PMB molecular weights of 1.8 and 1.4 kg/mol, respectively, show the presence of an ordered gyroid phase with a 2.5 nm diameter PSS network. A variety of methods are used to estimate χ between PSS and PMB chains as a function of sulfonation level. Some aspects of the observed phase behavior of PSS-PMB copolymers can be rationalized using χ.

Lyotropic Phase Behavior of Poly(ethylene oxide)−Poly(butadiene) Diblock Copolymers: Evolution of the Random Network Morphology

The phase behavior of poly(ethylene oxide)−poly(butadiene) (PEO-PB) diblock copolymers mixed with water was studied using small-angle X-ray scattering (SAXS), cryogenic scanning electron microscopy (cryo-SEM), cryogenic transmission electron microscopy (cryo-TEM), and dynamic mechanical spectroscopy. Two sets of diblocks were synthesized by adding different lengths of PEO to hydroxy terminated PB with degrees of polymerization NPB = 46 and 170. Two-component mixtures were investigated as a function of block composition and copolymer molecular weight, between 1 and 100 wt % polymer content. Melt phase behavior is consistent with established theory and known experimental behavior for diblock copolymers. Various lyotropic liquid crystalline structures, notably lamellae (L), hexagonally packed cylinders (H), and spheres (S) arranged on cubic (body-centered cubic, face-centered cubic) lattices, were documented as a function of water content. At the higher molecular weights (NPB = 170), a random network phase (N) was identified over a sizable portion of the phase portrait, located between hexagonally ordered cylinders and ordered lamellae. This new structure, along with branching of cylindrical micelles in the dilute limit, bear a striking similarity to experimentally observed and theoretically predicted phase behavior in certain ternary water/oil/surfactant systems. These findings demonstrate that block copolymer surfactants are characterized by at least four structural building blocks—spheres, cylinders, bilayers, and branched cylinders—above a threshold molecular weight.

Upper critical solution temperature type phase behavior of poly(styrene-co-acrylonitrile) blends with poly(styrene-co-n-phenyl maleimide) and their interaction energies

To enhance the heat resistance of poly(styrene-co-acrylonitrile-co-butadiene), ABS, miscibility of poly(styrene-co-acrylonitrile), SAN, with poly(styrene-co-n-phenyl maleimide), SNPMI, having a higher glass transition temperature than SAN was explored. SAN/SNPMI blends casted from solvent were immiscible regardless of copolymer compositions. However, SNPMI copolymer forms homogeneous mixtures with SAN copolymer within specific ranges of copolymer composition upon heating caused by upper critical solution temperature, UCST, type phase behavior. Since immiscibility of solvent casting samples can be driven by solvent effects even though SAN/SNPMI blends are miscible, UCST-type phase behavior was confirmed by exploring phase reversibility. When copolymer composition of SNPMI was fixed, the phase homogenization temperature of SAN/SNPMI blends was increased as AN content in SAN copolymer increased. To understand the observed phase behavior of SAN/ SNPMI blend, interaction energies of blends were calculated from the UCST-type phase boundaries by using the lattice-fluid theory combined with a binary interaction model.

Influence of Side Chain Length on the Self-Assembly of Hairy-Rod Poly(9,9-dialkylfluorene)s in the Poor Solvent Methylcyclohexane

We report on the phase behavior of poly(9,9-dihexylfluorene) (PF6), poly(9,9-diheptylfluorene) (PF7), poly(9,9-dioctylfluorene) (PF8), poly(9,9-dinonylfluorene) (PF9), and poly(9,9-didecylfluorene) (PF10) in methylcyclohexane (MCH). After a heating−cooling cycle, in the 10−50 mg/mL concentration range, PF6/MCH, PF7/MCH, PF8/MCH, and PF9/MCH systems were found to be gel-like, while PF10/MCH appears less viscous. PF6/MCH, PF7/MCH, PF8/MCH, and PF9/MCH form large (10−100 nm) sheetlike assemblies (thickness of 2−3 nm). The larger length scale structures of these sheets show an odd−even dependence on the side chain (spacer) length: the PF6 and PF8 sheets are broader and thinner, whereas PF7 and PF9 sheets are thicker with a putative double layer structure. PF10 does not follow this sequence, and only part of the polymer is assembled into a sheetlike structure, the rest remaining dissolved at the molecular level. PF8/MCH and PF9/MCH mixtures also have lower length scale crystalline structures with an internal period corresponding to the periodicity observed in the solid-state β phase of PF8. Vestiges of crystalline domains are found for PF6 and PF7 but not for PF10. PF7/MCH, PF8/MCH, and PF9/MCH systems contain the conformational isomer Cβ, of those chains observed in the β phase, while this is not observed with other polymer/MCH systems.

Phase behavior on the binary and ternary mixtures of poly(isooctyl acrylate) + supercritical fluid solvents + isooctyl acrylate and CO2 + isooctyl acrylate system

AbstractExperimental cloud‐point data to the temperature of 180 °C and the pressure up to 2000 bar are presented for ternary mixtures of poly(isooctyl acrylate) + supercritical fluid solvents + isooctyl acrylate systems. Cloud‐point pressures of poly(isooctyl acrylate) + CO2 + isooctyl acrylate system is measured in the temperature range of 60–180°C and to pressures as high as 2000 bar with isooctyl acrylate concentration of 0–44.5 wt. This system changes the pressure–temperature slope of the phase behavior curves from upper critical solution temperature (UCST) region to lower critical solution temperature (LCST) region as the isooctyl acrylate concentration increases. Poly(isooctyl acrylate) does dissolve in pure CO2 to the temperature of 180°C and the pressure of 2000 bar. The phase behavior for poly(isooctyl acrylate) + CO2 + 9.5, 14.8, 30.6, and 41.9 wt % dimethyl ether (DME) mixture show the curve changes from UCST to LCST as the DME concentration increases. Also, the cloud‐point curves are measured for the binary mixtures of poly(isooctyl acrylate) in supercritical propane, propylene, butane, and 1‐butene. High pressure phase behaviors are measured for the CO2 + isooctyl acrylate system at 40, 60, 80, 100, and 120°C and pressure up to 200 bar. This system exhibits type‐I phase behavior with a continuous mixture‐critical curve. The experimental results for the CO2 + isooctyl acrylate system are modeled using the Peng‐Robinson equation of state. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008

Phase behavior of poly(3-hydroxybutyrate)/poly(3-hydroxybutyrate- co-3-hydroxyvalerate) blends

Miscibility, molecular interactions and crystallinity of blends of poly(3-hydroxybutyrate) [P(3HB)] with poly(3-hydroxybutyrate- co-3-hydroxyvalerate) [P(3HB- co-3HV)] were studied in this work. P(3HB)/P(3HB- co-3HV)-6%3HV blends were prepared by casting and characterized by differential scanning calorimetry (DSC) and X-ray diffraction (XRD). The results for the glass transition temperatures ( T g) and the melting temperatures ( T m) showed that most of the blends are miscible in amorphous and melting phases. A good agreement between values of experimental T gs for miscible blends and those predicted by Fox equation was achieved. XRD analyses confirmed the crystallinity degrees found by DSC. Measurement of T m depression for the blends allowed to determine the Flory-Huggins interaction parameter ( χ 12) using the Nishi-Wang equation. The value of χ 12 obtained is negative, indicating miscibility of the components of the blends, which is in agreement with DSC experiments.

Difference in Lower Critical Solution Temperature Behavior between Random Copolymers and a Homopolymer Having Solvatophilic and Solvatophobic Structures in an Ionic Liquid

The solubility and phase behavior of poly(benzyl methacrylate) (PBzMA) and poly(styrene-co-methyl methacrylate) (P(St-co-MMA)) in a hydrophobic ionic liquid, 1-ethyl-3-methylimidazolium bis(trifluoromethane sulfone)imide ([C(2)mim][NTf(2)]), have been explored as a function of temperature. Although both polymers have solvatophobic phenyl groups and solvatophilic methacrylate groups in the structure, their distribution on the polymer chains is quite different. In PBzMA, both structures are incorporated in each monomer unit, whereas in P(St-co-MMA)s the distribution is statistically determined by the monomer reactivity ratio of St and MMA. Both polymer solutions in [C(2)mim][NTf(2)] become turbid with an increase in temperature (lower critical solution temperature (LCST) behavior). The turbidity change occurs sharply at 100 degrees C for PBzMA, whereas it is sluggish for P(St-co-MMA)s. The LCST-type phase-separation temperature for P(St-co-MMA)s decreases with an increase of the St composition. The sluggish phase separation for P(St-co-MMA)s has been explained in terms of the presence of the MMA sequences along the polymer chain, which inhibits the St aggregation to a certain extent. The dynamic light scattering (DLS) measurements for PBzMA reveal that the hydrodynamic radius of PBzMA suddenly changes at 100 degrees C; below this temperature, no aggregation is observed. This result strongly implies that the coil-to-collapse transition is of the first-order type. It has been demonstrated that the LCST-type phase separation of the polymers in an ionic liquid is greatly affected by the distribution of the solvatophilic and solvatophobic groups on the polymer chains.