Surface morphology and Flory-Huggins interaction strength in UCST blend system comprising poly(4-methyl styrene) and isotactic polystyrene

The surface morphology and polymer-polymer interaction parameter (χ₁₂) of UCST blend systems comprising isotactic polystyrene and poly(4-methyl styrene) (P4MS) were investigated using atomic-force microscopy (AFM) and differential scanning calorimetry (DSC). From the measured glass transition temperature and the specific heat increments (ΔC_p) at T_g, it was found that the P4MS dissolved more easily in the iPS rich-phase than did the iPS in the P4MS rich-phase. AFM result also supported that the compatibility increased more in the regions of P4MS-rich compositions than in the regions of PS-rich compositions of the PS/P4MS blends. From the measured T_g’s and apparent weight fractions of iPS and P4MS dissolved in each phase, the values of the Flory-Huggins interaction parameter (χ₁₂) were determined to be 0.0163-0.0232 depending on the composition. These results indicate that the χ₁₂ is quite dependend on the apparent volume fraction of the polymers dissolved in each phase. The values of χ₁₂ calculated from this work (method based on T_g’s of phases) were lower than those estimated using an earlier method based on the UCST or clarity temperatures. All values of χ₁₂ are greater than the values of interaction parameter at the critical point (χ₁₂)_c. This fact indicates that the iPS/P4MS blend are immiscible for all blend compositions. The surface of the phase-separated blend system was mostly covered with the P4MS rich-phase owing to its lower surface free energy in comparison with that of the neat iPS. The mechanism of surface phase separation for the P4MS blends with aPS or iPS is governed by two factors: (1) difference in the solubility of the two polymers in the solvent and (2) surface free energy.     

Decreasing miscibility with greater heterogeneity in ternary polymer blend: poly(cyclohexyl methacrylate), poly(α‐methyl styrene) and poly(4‐methyl styrene)

A ternary blend system comprising poly(cyclohexyl methacrylate) (PCHMA), poly(α‐methyl styrene) (PαMS) and poly(4‐methyl styrene) (P4MS) was investigated by thermal analysis, optical and scanning electron microscopy. Ternary phase behaviour was compared with the behaviour for the three constituent binary pairs. This study showed that the ternary blends of PCHMA/PαMS/P4MS in most compositions were miscible, with an apparent glass transition temperature (T_g) and distinct cloud‐point transitions, which were located at lower temperatures than their binary counterparts. However, in a closed‐loop range of compositions roughly near the centre of the triangular phase diagram, some ternary blends displayed phase separation with heterogeneity domains of about 1 µm. Therefore, it is properly concluded that ternary PCHMA/PαMS/P4M is partially miscible with a small closed‐loop immisciblity range, even though all the constituent binary pairs are fully miscible. Thermodynamic backgrounds leading to decreased miscibility and greater heterogeneity in a ternary polymer system in comparison with the binary counterparts are discussed. © 2003 Society of Chemical Industry     

New miscible blends composed of polysulfone and poly(1-vinylpyrrolidone-co-acrylonitrile) copolymers and their phase behavior

The miscibility of polysulfone, PSf, blend with poly(1-vinylpyrrolidone), PVP, and that of PSf blend with poly(1-vinylpyrrolidone-co-acrylonitrile) copolymers, P(VP-AN), containing various amount of VP were explored. Even though PSf did not formed miscible blends with PVP when both components had high molecular weight, it formed miscible blend with PVP by decreasing molecular weight of PVP. PSf also formed homogeneous mixtures with P(VP-AN) containing AN from 2 to 16 wt%. These miscible blends underwent phase separation on heating caused by LCST-type (lower critical solution temperature-type) phase behavior. The phase separation temperature of miscible blends first increases with AN content, goes through a maximum centered at about 8 wt% AN. Interaction energies of binary pairs involved in blends were evaluated from the observed phase boundaries using the lattice-fluid theory. The decline of the contact angle between water and blend film by increasing P(VP-AN) content in blend indicated that the hydrophobic properties of PSf could be improved by blending with P(VP-AN) copolymers.     

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

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.     

Miscibility and intermolecular specific interactions in blends of poly(hydroxyether of bisphenol A) and poly(4-vinyl pyridine)

The blends of poly(hydroxyether of bisphenol A) (phenoxy) with poly(4-vinyl pyridine) (P4VPy) were investigated by differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR) and high-resolution solid-state nuclear magnetic resonance (NMR) spectroscopy. The single, composition-dependent glass transition temperature (T_g) was observed for each blend, indicating that the system is completely miscible. The sigmoid T_g-composition relationship is characteristic of the presence of the strong intermolecular specific interactions in the blend system. FTIR studies revealed that there was intermolecular hydrogen bonding in the blends and the intermolecular hydrogen bonding between the pendant hydroxyl groups of phenoxy and nitrogen atoms of pyridine ring is much stronger than that of self-association in phenoxy. To examine the miscibility of the system at the molecular level, the high resolution ¹³C cross-polarization (CP)/magic angle spinning (MAS) together with the high-power dipolar decoupling (DD) NMR technique was employed. Upon adding P4VPy to the system, the chemical shift of the hydroxyl-substituted methylene carbon resonance of phenoxy was observed to shift downfield in the ¹³C CP/MAS spectra. The proton spin-lattice relaxation time T₁(H) and the proton spin-lattice relaxation time in the rotating frame T_1ρ(H) were measured as a function of the blend composition. In light of the proton spin-lattice relaxation parameters, it is concluded that the phenoxy and P4VPy chains are intimately mixed on the scale of 20-30 Å.     

Dynamic mechanical and tensile properties of poly(N-vinyl pyrrolidone)-poly(ethylene glycol) blends

Mechanical properties of miscible blends of high molecular weight poly(N-vinyl pyrrolidone) (PVP) with a short-chain, liquid poly(ethylene glycol) (PEG) of molecular weight 400 g/mol have been examined as a function of PVP-PEG composition and degree of hydration. The small-strain behavior in the linear elastic region has been evaluated with the dynamic mechanical analysis and compared with the viscoelastic behavior of PVP-PEG blends under large strains in the course of uniaxial drawing to fracture and under cyclic extension. A strong decoupling between the small-strain and the large strain properties of the blends has been observed, indicative of a pronounced deviation from rubber elasticity in the behavior of the blends. This deviation, also seen on tensile tests under fast drawing, is attributed to the peculiar phase behavior of the blends and the molecular mechanism of PVP-PEG interaction. Nevertheless, for the PVP blend with 36% PEG, under comparatively low extension rates, the reversible contribution to the total work of deformation up to ε=300% has been found to be maximum at around 70%, while the blends containing 31 and 41% PEG behave rather as an elastic-plastic solid and a viscoelastic liquid, respectively.     

Poly(hydroxyether sulfone) and its blends with poly(ethylene oxide): miscibility, phase behavior and hydrogen bonding interactions

Poly(hydroxyether sulfone) (PHES) was synthesized through polycondensation of bisphenol S with epichlorohydrin. It was characterized by Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance spectroscopy and differential scanning calorimetry (DSC). The miscibility in the blends of PHES with poly(ethylene oxide) (PEO) was established on the basis of the thermal analysis results. DSC showed that the PHES/PEO blends prepared by casting from N,N-dimethylformamide (DMF) possessed single, composition-dependent glass transition temperatures (T_gs), indicating that the blends are miscible in amorphous state. At elevated temperatures, the PHES/PEO blends underwent phase separation. The phase behavior was investigated by optical microscope and the cloud point curve was determined. A typical lower critical solution temperature behavior was observed in the moderate temperature range for this blend system. FTIR studies indicate that there are the competitive hydrogen bonding interactions upon adding PEO to the system, which was involved with the intramolecular and intermolecular hydrogen bonding interactions, i.e. -OH?OS, -OH?-OH and -OH versus ether oxygen atoms of PEO between PHES and PEO. In terms of the infrared spectroscopic investigation, it is judged that from weak to strong the strength of the hydrogen bonding interactions is in the following order: -OH?OS, -OH?-OH and -OH versus ether oxygen atoms of PEO.     

Upper critical solution temperature—type cononsolvency of poly(N,N-dimethylacrylamide) in water—organic solvent mixtures

The behaviour of linear poly(N,N-dimethylacrylamide) (PDMAM) chains was studied by turbidimetry and viscometry in mixtures of water with the polar organic solvents methanol, dioxane and acetone. The swelling-deswelling behaviour of PDMAM gels in the same solvent mixtures was also investigated. Contrary to the behaviour in water-methanol mixtures, in water-dioxane and water-acetone mixtures a significant shrinkage of polymer chains and deswelling of polymer gels, followed by phase separation, was observed for high organic solvent fractions. Cononsolvency phenomena were found to be temperature-dependent, as demixing occurred upon decreasing temperature. This upper critical solution temperature (UCST) phase separation behaviour in mixed solvents was studied by turbidimetry and compared to the well-known lower critical solution temperature (LCST) behaviour of poly(N-isopropylacrylamide) (PNIPAM) in similar solvents mixtures.     

Immiscibility–miscibility phase transitions in blends of poly(L‐lactide) with poly(methyl methacrylate)

BACKGROUND: The nature of phase transitions and apparently irreversible phase homogenization upon heating in blends of biodegradable poly(L ‐lactide) (PLLA) with poly(methyl methacrylate) (PMMA) were proven using differential scanning calorimetry, polarized optical microscopy, scanning electron microscopy and ¹H NMR spectroscopy. The complex phase behaviour in this blend system is puzzling and is a matter of debate; this study attempts to clarify the true nature of the phase behaviour. RESULTS: A PMMA/PLLA blend is immiscible at ambient temperature but can become miscible upon heating to higher temperatures with an upper critical solution temperature (UCST) at 230 °C. The blends, upon rapid quenching from the UCST, can be frozen into a quasi‐miscible state. In this state, the interaction strength was determined to be χ₁₂ = ? 0.15 to ? 0.19, indicating relatively weak interactions between the PLLA ester and PMMA acrylic carbonyl groups. CONCLUSION: The absence of chemical exchange reactions above the UCST and phase reversibility back to the original phase separation morphology, assisted by solvent re‐dissolution, in the heat‐homogenized PLLA/PMMA blend was shown. Verification of UCST behaviour, phase diagrams and solvent‐assisted phase reversibility were experimentally demonstrated in PMMA/PLLA blends. Copyright © 2008 Society of Chemical Industry     

Miscibility and phase behavior in blends of phenolphthalein poly(ether sulfone) and poly(hydroxyether of bisphenol A)

Miscibility and phase behavior in the blends of phenolphthalein poly(ether sulfone) (PES-C) with poly(hydroxyether of bisphenol A) (PH) were investigated by means of differential scanning calorimetry (DSC), high resolution solid state nuclear magnetic resonance spectroscopy (NMR) and Fourier transform infrared spectroscopy (FTIR). It was found that the homogeneity of the as-prepared blends depended on the solvents used; N,N-dimethylformamide (DMF) provided the segmental mixing for PH and PES-C, which is confirmed by the behavior of single, composition-dependent glass transition temperatures (T_g's). To examine the homogeneity of the blends at the molecular level, the proton spin-lattice relaxation times in the rotating frame T_1ρ(H) were measured via ¹³C CP/MAS NMR spectroscopy as a function of blend composition. In view of the T_1ρ(H) values, it is concluded that the PH and PES-C chains are intimately mixed on the scale of 20-30 Å. FTIR studies indicate that there were the intermolecular specific interactions in this blends, involved with the hydrogen-bonding between the hydroxyls of PH and the carbonyls of PES-C, and the strength of the intermolecular hydrogen bonding is weaker than that of PH self-association. At higher temperature, the PH/PES-C blends underwent phase separation. By means of thermal analysis, the phase boundaries of the blends were determined, and the system displayed the lower critical solution temperature behavior. Thermogravity analysis (TGA) showed that the blends exhibited the improved thermal stability, which increases with increasing PES-C content.     

Solubility in the binary and ternary system for poly(alkyl acrylate)-supercritical solvent mixtures

Experimental cloud-point data to 210 ‡C and 2,200 bar are presented for binary and ternary mixtures of poly(methyl acrylate)-CO₂-methy acrylate and poly(ethyl acrylate)-CO₂, propylene, and 1-butene-ethyl aerylate systems. The accuracy of the experimental apparatus was tested by comparing the measured pressure-temperature phase behavior data of the poly(ethyl acrylate)-CO₂ system obtained in this study with those of Rindfleisch et al. [1995]. The phase behaviors for the system poly(methyl acrylate)-CO₂-methyl acrylate were measured in changes of pressure-temperature slope, and with cosolvent concentrations of 0, 5.0, 13.7, 25.3, and 43.3 wt%, respectively. With 48.3 wt% methyl acrylate to the poly(methyl acrylate)-CO₂ solution significantly changes, the phase behavior curve takes on the appearance of a typical lower critical solution temperature (LCST) boundary. The impact of ethyl acrylate on the cloud-point for the poly(ethyl acrylate)-CO₂ system shows the change of slope of the phase behavior curves from negative to positive with ethyl acrylate concentration of 0, 8.2, and 25.0 wt%. The cloud-point behavior for the poly(ethyl acrylate)-CO₂-39.5 wt% ethyl acrylate system shows an LCST curve. The solubility curve to ∼150 ‡C and 1,650 bar for poly(ethyl acrylate)-propylene-ethyl acrylate system shows the change of pressure-temperature diagram and with ethyl acrylate concentration of 0, 7.2 and 21.0 wt%. Also, when 41.1 wt% ethyl acrylate was added to the poly(ethyl acrylate)-propylene solution, the phase behavior curve showed the LCST region. The high pressure phase behavior of poly(ethyl acrylate)-1-butene-0, 3.1, 8.1, 18.5 and 30.7 wt% ethyl acrylate system presented the change of pressure-temperature curve from the UCST region to U-LCST region as the ethyl acrylate concentration increased.     

Miscibility with positive deviation in Tg-composition relationship in blends of poly(2-vinyl pyridine)-block-poly(ethylene oxide) and poly(p-vinyl phenol)

Phase behavior and miscibility with positive deviation from linear T_g-composition relationship in a copolymer/homopolymer blend system, poly(2-vinyl pyridine)-block-poly(ethylene oxide) (P2VP-b-PEO)/poly(p-vinyl phenol) (PVPh), were investigated by differential scanning calorimetry (DSC), Fourier-transform infrared spectroscopy (FT-IR) and solid-state ¹³C nuclear magnetic resonance (¹³C NMR), optical microscopy (OM), and scanning electron microscopy (SEM). Optical and electron microscopy results as well as NMR proton spin-lattice relaxation times in laboratory frame () all confirmed the miscibility as judged by the T_g criterion using DSC. In comparison to the literature result on a homopolymer/homopolymer blend of P2VP/PVPh, fitting with the Kwei equation on the T_g-composition relationship for the block-copolymer/homopolymer blend of P2VP-b-PEO/PVPh blend system yielded a smaller q value (q = 120) for P2VP-b-PEO/PVPh than that for P2VP/PVPh blend (q = 160). The FT-IR and ¹³C NMR results revealed hydrogen-bonding interactions between the pendant pyridine group of P2VP-b-PEO and phenol unit in PVPh, which is responsible for the noted positive deviation of the T_g-composition relationship. Comparison of the shifts of hydroxyl IR absorbance band, reflecting the average strength of H-bonding, indicates a decreasing order of P2VP/PVPh > P2VP-b-PEO/PVPh > PEO/PVPh blends. The PEO block in the copolymer segment tends to defray the interaction strength in the P2VP-b-PEO/PVPh blends because of relative weaker interaction between PEO and PVPh than that between P2VP and PVPh pairs. A comparative ternary (P2VP/PEO)/PVPh blend was also studied as the controlling experiments for comparison to the P2VP-b-PEO/PVPh blend. The thermal behavior and interaction strength in (P2VP/PEO)/PVPh ternary blends are discussed with those in the P2VP-b-PEO/PVPh copolymer/homopolymer blend.     

Structure-property behavior of poly(dimethylsiloxane) based segmented polyurea copolymers modified with poly(propylene oxide)

Poly(propylene oxide) (PPO) was incorporated in a controlled manner between poly(dimethylsiloxane) (PDMS) and urea segments in segmented polyurea copolymers and their solid state structure-property behavior was investigated. The copolymers contained PDMS segments of MW 3200 or 7000 g/mol and an overall hard segment content of 10-35 wt%. PPO segments of MW 450 or 2000 g/mol were utilized. Equivalent polyurea copolymers based on only PDMS as the soft segment (SS) component were used as controls. The materials (with or without PPO) utilized in this study were able to develop microphase morphology as determined from dynamic mechanical analysis (DMA) and small angle X-ray scattering (SAXS). DMA and SAXS results suggested that the ability of the PPO segments to hydrogen bond with the urea segments results in a limited inter-segmental mixing which leads to the formation of a gradient interphase, especially in the PPO-2000 co-SS containing copolymers. DMA also demonstrated that the polyureas based on only PDMS as the SS possessed remarkably broad and nearly temperature insensitive rubbery plateaus that extended up to ca. 175 °C, the upper temperature limit depending upon the PDMS MW. However, the incorporation of PPO resulted in more temperature sensitive rubbery plateaus. A distinct improvement in the Young's modulus, tensile strength, and elongation at break in the PPO-2000 and PDMS-7000 containing copolymers was observed due to inter-segmental hydrogen bonding and the formation of a gradient interphase. However, when PPO was incorporated as the co-SS, the extent of stress relaxation and mechanical hysteresis of the copolymers increased relative to the segmented polyureas based on the utilization of only PDMS as the soft segment component.     

Miscibility and phase behavior of poly(D,L-lactide)/poly(p-vinylphenol) blends

The miscibility of poly(D ,L -lactide) (PDLLA) and poly(p-vinylphenol) (PVPh) blends has been studied by differential scanning calorimetry and Fourier transform infrared spectroscopy (FTIR). Phase separation was observed in blends over a wide composition range. A PDLLA-rich phase was found to coexist with an almost pure PVPh phase. The quenched blend samples showed two glass transitions (T_gs), except for a blend with a low PVPh content. However, the T_g value of the PDLLA-rich phase showed a gradual increase with increasing PVPh content. No evidence of interassociation (hydrogen bond formation) between PDLLA and PVPh was found by FTIR. The phase behavior of the blends was simulated using an association model. The results suggested that the equilibrium constant of interassociation between PDLLA and PVPh was small. The phase compositions of the two separated phases were calculated using Fox, Gordon-Taylor, and Couchman equations. The amount of PVPh in the PDLLA-rich phase increased with increasing PVPh content in the blend. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 811–816, 1998     

Temperature- and pH-sensitive membrane formed from blends of poly(vinylidene fluoride)-graft-poly(N-isopropylacrylamide) and poly(acrylic acid) microgels

Temperature- and pH-responsive membranes prepared from blends of poly(vinylidene fluoride)-graft-poly(N-isopropylacrylamide)(PVDF-g-PNIPAM) copolymer and poly(acrylic acid) (PAA) microgels in N,N-dimethylformamide (DMF) solution by phase inversion method. PAA microgels help PNIPAM chains largely enrich onto membrane surface. Furthermore, adding PAA microgels increases the porous size, porosity and hydrophilic property of the blend membrane. The membranes show temperature-sensitivity between 30 and 35 °C, and pH-sensitivity between pH 3 and 5 on permeating aqueous solutions. Meanwhile, the blend membranes keep good antifouling property even if one of the hydrophilic components becoming hydrophobic in response to temperature or pH stimuli, which is superior to single-sensitive PVDF membrane.     

Crystallization and phase separation in blends of high stereoregular poly(lactide) with poly(ethylene glycol)

The effect of cooling rate on crystallization and subsequent aging of high stereoregular poly(lactide) (PLA) blended with poly(ethylene glycol) (PEG) was studied by thermal analysis and by direct observation of the solid state structure with atomic force microscopy (AFM). Blending with PEG accelerated crystallization of PLA. When a PLA/PEG 70/30 (wt/wt) blend was slowly cooled from the melt, PLA crystallized first as large spherulites followed by crystallization of PEG. The extent of PLA crystallization depended on the cooling rate, however, for a given blend composition the PEG crystallinity was proportional to PLA crystallinity. The partially crystallized blend obtained with a cooling rate of 30 °C min⁻¹ consisted of large spherulites dispersed in a homogeneous matrix. The blend was not stable at ambient temperature. With time, epitaxial crystallization of PEG on the edges of the spherulites depleted the surrounding region of PEG, which created a vitrified region surrounding the spherulites. Further from the spherulites, the homogeneous amorphous phase underwent phase separation with formation of a more rigid PLA-rich phase and a less-rigid PEG-rich phase. Decreasing the amount of PEG in the blend decreased the crystallization rate of PLA and increased the nucleation density. The amount of PLA crystallinity did not depend on blend composition, however, PEG crystallinity decreased to the extent that PEG did not crystallize in a PLA/PEG 90/10 (wt/wt) blend.     

Segregation morphology of poly(3-hydroxybutyrate)/poly(vinyl acetate) and poly(3-hydroxybutyrate-co-10% 3-hydroxyvalerate)/poly(vinyl acetate) blends as studied via small angle X-ray scattering

Segregation morphology of poly(3-hydroxybutyrate) (PHB)/poly(vinyl acetate) (PVAc) and poly(3-hydroxybutyrate-co-10% 3-hydroxyvalerate) (P(HB-co-10% HV)/PVAc blends crystallized at 70 °C have been investigated by means of small angle X-ray scattering (SAXS). Morphological parameters including the crystal thickness (l_c) and the amorphous layer thickness (l_a) were deduced from the one-dimensional correlation function (γ(z)). Blending with PVAc thickened the PHB crystals but not the P(HB-co-10% HV) crystals. On the basis of the composition variation of l_a, and the volume fraction of lamellar stacks (?_s) revealed that PHB/PVAc blends created the interlamellar segregation morphology when the weight fraction of PVAc (w_PVAc)≤0.2 and the interlamellar and interfibrillar segregation coexisted when w_PVAc>0.2, while P(HB-co-10% HV)/PVAc blends yielded the interfibrillar segregation morphology at all blend compositions. For both PHB/PVAc and P(HB-co-10% HV)/PVAc blends, the distance of PVAc segregation was promoted by increasing PVAc composition and the distance of PVAc segregation in P(HB-co-10% HV)/PVAc blends was greater than in PHB/PVAc at a given PVAc composition. The crystal growth rate played a key role in controlling the segregation of PVAc.     

Crystallization and phase separation kinetics in blends of linear low-density polyethylene copolymers

We have systematically studied the crystallization and liquid-liquid phase separation (LLPS) kinetics in statistical copolymer blends of poly(ethylene-co-hexene) (PEH) and poly(ethylene-co-butene) (PEB) using primarily optical microscopy. The PEH/PEB blends exhibit upper critical solution temperature (UCST) in the melt and crystallization temperature below the UCST. The time evolution of the characteristic morphology for both crystallization and LLPS is recorded for blends at various compositions and following a quench from initial homogenous melts at high temperature to various lower temperatures. The crystallization kinetics is measured as the linear growth rate of the super structural crystals, whereas the LLPS kinetics is measured as the linear growth rate of the characteristic length of the late-stage spinodal decomposition. The composition dependence crystallization kinetics, G, shows very different characteristics at low and high isothermal crystallization temperature. Below 116 °C, G decreases with increasing PEB content in the blend, implying primarily the composition effect on materials transport; whereas at above 116 °C, G shows a minimum at about the critical composition for LLPS, implying the influence of the LLPS. On the other hand, LLPS kinetics at 130 °C is relatively invariant at different compositions in the two-phase regime. The length scale at which domains are kinetically pinned, however, depends strongly on the composition. In a blend near critical composition, a kinetics crossover is shown to separate the crystallization dominant and phase separation dominant morphology as isothermal temperature increases.     

Miscible blends of poly(vinyl phenyl ketone hydrogenated) and poly(styrene-co-4-vinylpyridine)

Miscibility behavior over a wide composition range was detected for polymer blends of poly(vinyl phenyl ketone hydrogenated) (PVPhKH) with poly(styrene-co-4-vinylpyridine) (PS-co-4VPy). Differential scanning calorimetry (DSC) and thermo mechanical analysis (TMA) reveal that each composition has only one glass transition temperature. The variation of the glass transition temperature with composition for PVPhKH/PS-co-4VPy miscible blends follows the Gordon-Taylor equation. FTIR analysis of this binary system indicates the existence of hydrogen bonding between pyridine ring of PS-co-4VPy and hydroxyl groups insert into PVPhKH. This specific interaction has a decisive influence in the phase behavior of PVPhKH/PS-co-4VPy blends.     

Experimental verification on UCST phase diagrams and miscibility in binary blends of isotactic, syndiotactic, and atactic polypropylenes

Issues in blends of polymers of the same chemical repeat unit but with different tacticities were addressed by investigating on the phase behavior and interaction strength of binary blends of three polypropylenes of different tacticities, i.e., isotactic polypropylene (iPP), syndiotactic polypropylene (sPP), and atactic polypropylene (aPP) using polarized optical microscopy (POM) and differential scanning calorimetry (DSC). Although blends of polypropylenes have been widely studied in the past, there are still on-going debates on true phase behavior (miscibility vs. upper critical solution temperature (UCST) or immiscibility). Except for several earlier theoretical predictions based on the Flory-Huggins mean field theories, UCST behavior had not been experimentally proven for blends of sPP/iPP or aPP/sPP, owing to interference from PP crystallinity. In addition, interaction strength of the blends of different tactic polypropylenes is yet to be established. Using the method of equilibrium melting points, the Flory-Huggins interaction parameter of the aPP/iPP blend was shown to possess a significantly negative value (χ₁₂ = −0.21), which proves that the blend is indeed miscible in the melted amorphous as well as semicrystalline states as previously reported in the literature. However, the interaction parameters for the sPP/iPP and aPP/sPP blends were found to be nearly zero (χ₁₂ = −0.02 and −0.0071, respectively, at T = 150-180 °C), indicating that the interactions in two blends are weak and that the corresponding phase behavior for them borders on immiscibility at ambient temperature. This study also utilized novel approaches in constructing UCST phase diagrams by separating the amorphous phase domains from the crystalline spherulites, yielding data plausible for experimentally determining the UCST in iPP/sPP blend vs. aPP/sPP blend.