Compatibility and mesophase separation in blends of α-helical polyglutamates

Blends composed of the α-helical polymers, poly-L-glutamates [(? NHC^αHRC′O? )_n, R = ? CH₂CH₂COO? (CH₂)_m(C₆H₅] (Lm) and the corresponding D enantiomers (Dm), have been studied by x-ray diffraction and viscoelastic measurements. Binary blends of L2, D2, L3, and D3 are compatible and form isomorphous mixed crystals at all compositions, whereas other pairs, with the exception of L1/D1, are incompatible. The demixing process is described for a ternary system consisting of L1, D3, and a diluent chloroform at 40°C. The phase diagram comprises four regions, I, IA, A, and AA, with increasing polymer concentration; I: isotropic, A: anisotropic, IA: I–A biphasic, and AA: A–A biphasic. The IA biphasic gap is greater in the ternary system than in the binary ones. The high-molecular-weight component (D3) is partitioned into the A phase in the IA region. The AA separation originates from incompatibility of the polymers. The phase behavior is discussed on the basis of the Abe-Flory theory by incorporating the polymer-polymer interaction parameter.     

Analysis of phase structure and evolution of PP/PEOc blends during quiescent molten-state annealing process from SEM patterns. Part II. Co-continuous morphology

The influence of quiescent molten-state annealing process on the phase structure and morphology of poly(propylene)/poly(ethylene-co-octene) blends with co-continuous morphology was studied using scanning electron microscopy (SEM). The structure parameter called characteristic length (L) was calculated by the pattern analysis of SEM micrographs to describe morphological variation with annealing time during molten-state annealing process under quiescent condition. Moreover, the potential fractal behavior of the phase structure and morphology of PP/PEOc?=?50/50 blend during the process were discussed. The histograms of P(L/L _m ) obtained at various annealing time fell on a master curve, demonstrating the self-similar growth of the phase structure of the blends during quiescent molten-state annealing process.     

Comparative study of the phase behavior of liquid-crystalline components in closely related blends and copolyesters

Phase behavior of blends of a liquid-crystalline (LC) polymer with a non-LC polymer and of a series of copolymers containing mesogenic and nonmesogenic units was studied by thermal, optical, and dynamic mechanical methods. The polymers composing the blends and the copolymers had the same constituent monomers. The blends exhibited phase separation over the whole range of compositions studied as observed by DSC and dynamic mechanical analysis. Two glass transition temperatures (T_g) corresponding to the two components and independence of melting (T_m) and isotropization temperatures (T_i) to changes in composition were observed for the blends. The copolymers did not show phase separation over most of the composition range studied. Only one T_g corresponding to that of the major component could be detected for the copolymers, and the T_g was found to increase with an increase in the amount of nonmesogenic monomer in the copolymers. The difference in phase behavior was explained on the basis of the chemical environment of the constituent units in the blends and in copolymers. Phase inversion in the blends was observed by microscopy when the blends contained 60 mol% or more of the non-LC polymer.     

Poly(ε-caprolactone) + unsaturated isophtalic polyester blends: Thermal properties and morphology

Miscibility of blends composed by a linear unsaturated polyester (LUP) with poly(ε-caprolactone) (PCL) of different molecular weights (M_w = 50 × 10³, 18 × 10³ and 2 × 10³) has been studied. The blends were subjected to different thermal treatments and have been studied by FT-IR spectroscopy, differential scanning calorimetry (DSC) and scanning electronic microscopy (ESEM). FT-IR results allow proving the miscibility of the blends at temperatures above the melting temperature of neat PCL. DSC measurements confirm the existence of a crystalline phase corresponding to neat PCL. The crystallization of PCL is observed in a wide range of blends composition, being detected in all the blend compositions when the crystallization time increases. Thermograms show clearly the glass transition temperatures of samples that have been rapidly quenched from the melt. However, the change in the heat flow corresponding to the glass transition temperatures is difficult to detect in samples with high PCL crystallization degree. The analysis of the results indicates that the morphology of the amorphous phase is heterogeneous for LUP + PCL blends and changes depending on the thermal treatment. The ESEM measurements, confirm the heterogeneity of the amorphous phase. The decrease of the molecular weight of the PCL favours the miscibility of the blends.     

A light-scattering study of phase separation kinetics in polystyrene/poly(2-chlorostyrene) blends

The angular dependence of the intensity of scattered light from polystyrene/poly(2-chlorostyrene) blends was measured as a function of time in early and late stages of phase separation. The results were discussed in terms of Cahn's theory and scaling law for the late stage. Some distinctive behaviors which had not been found in other polymer blends were observed: the intensity of low-angle scattering increased significantly during phase separation, possibly because of inhomogeneities in density. In the power laws k_m α t_? and I_m α t_θ for the time (t) evolution of the peak position k_m and peak heigh I_m of the structure function in the late stage; the value of ? was around ?1, almost independent of composition and temperature; the ratio |θ/?| was less than the theoretical value 3. Possible explanations for these behaviors are discussed in relation to the glass transition.     

Cellulose Dissolution in Mixtures of Ionic Liquids and Dimethyl Sulfoxide: A Quantitative Assessment of the Relative Importance of Temperature and Composition of the Binary Solvent

We studied the dissolution of microcrystalline cellulose (MCC) in binary mixtures of dimethyl sulfoxide (DMSO) and the ionic liquids: allylbenzyldimethylammonium acetate; 1-(2-methoxyethyl)-3-methylimidazolium acetate; 1,8-diazabicyclo [5.4.0]undec-7-ene-8-ium acetate; tetramethylguanidinium acetate. Using chemometrics, we determined the dependence of the mass fraction (in %) of dissolved cellulose (MCC-m%) on the temperature, T = 40, 60, and 80 °C, and the mole fraction of DMSO, χ_DMSO = 0.4, 0.6, and 0.8. We derived equations that quantified the dependence of MCC-m% on T and χ_DMSO. Cellulose dissolution increased as a function of increasing both variables; the contribution of χ_DMSO was larger than that of T in some cases. Solvent empirical polarity was qualitatively employed to rationalize the cellulose dissolution efficiency of the solvent. Using the solvatochromic probe 2,6-dichloro-4-(2,4,6-triphenylpyridinium-1-yl)phenolate (WB), we calculated the empirical polarity E_T(WB) of cellobiose (a model for MCC) in ionic liquid (IL)–DMSO mixtures. The E_T(WB) correlated perfectly with T (fixed χ_DMSO) and with χ_DMSO (fixed T). These results show that there is ground for using medium empirical polarity to assess cellulose dissolution efficiency. We calculated values of MCC-m% under conditions other than those employed to generate the statistical model and determined the corresponding MCC-m% experimentally. The excellent agreement between both values shows the robustness of the statistical model and the usefulness of our approach to predict cellulose dissolution, thus saving time, labor, and material.     

Thermodynamic investigation of MF-MgF<Subscript>2</Subscript> (M = Na,K) system

The molar Gibbs energy of formation of NaMgF₃(s) in NaF-MgF₂ system and KMgF₃(s) and K₂MgF₄(s) in KF-MgF₂ system has been determined using an electromotive force (e.m.f.) technique. For this purpose, fluoride cell has been constructed for each compound using CaF₂(s) as the solid electrolyte. From the measured e.m.f. values and required Gibbs energy data available in the literature, ?_fG^o_m(T) for NaMgF₃(s), KMgF₃(s), and K₂MgF₄(s) have been calculated. To determine the stability domains of NaMgF₃(s), KMgF₃(s), and K₂MgF₄(s), the binary phase diagram NaF(s)-MgF₂(s) and KF(s)-MgF₂(s) and ternary phase diagram Na-Mg-F₂ and K-Mg-F₂ have been calculated and chemical potential diagrams of Na-Mg-F-O and K-Mg-F-O system were calculated.     

Thermodynamic properties of resveratrol in dimethyl sulfoxide

In this article, the enthalpies of dissolution of resveratrol in dimethyl sulfoxide (DMSO) were measured using a RD496-2000 Calvet microcalorimeter at 298.15?K under atmospheric pressure. The differential enthalpy (??_dif H _m) and molar enthalpy (??_sol H _m) of dissolution of resveratrol in DMSO were determined, and the relationship between heat and the amount of solute was also established. Based on the thermodynamic and kinetic knowledge, the corresponding kinetic equation, half-life, ??_sol H _m, ??_sol S _m, ??_sol G _m, the relative partial molar enthalpy (??_sol H _m(partial)) and the relative apparent molar enthalpy (??_sol H _m(app)) of the dissolution process were obtained. The results showed that this study not only provided a simple method for the determination of the half-life for a drug, but also offered a theoretical reference for the clinical application of resveratrol.     

Viscoelastic phase separation in polyethersulfone modified bismaleimide resin

The polymerization-induced phase separation process of polyethersulfone (PES) modified bismaleimide resin, 4,4′-bismaleimidodiphenylmethane (BDM), was investigated by time resolved light scattering (TRLS) and scanning electronic microscopes (SEM). At the blends with 10 wt% and 12.5 wt% PES, a phase inversion structure was found by SEM. TRLS results displayed clearly the spinodal decomposition (SD) mechanism and the exponential decay procedure of scattering vector q_m, which followed Maxwell-type relaxation equation. The characteristic relaxation time τ for the blends can be described by the Williams-Landel-Ferry equation. It demonstrated experimentally that the phase separation behaviors in these PES modified bismaleimide blends were affected by viscoelastic effect.     

The enthalpies and kinetic of dissolution of diterpenoid derivative—paclitaxel in aqueous NaCl solutions at 309.5 K

The enthalpies of dissolution of paclitaxel in normal saline were measured using a RD496-2000 Calvet Microcalorimeter at 309.65 K under atmospheric pressure. The differential enthalpy (Δ_dif H _m ) and molar enthalpy (Δ_sol H _m) of dissolution of paclitaxel innormal saline were determined. The corresponding kinetic equation described the dissolution process was elucidated to be dα/dt = 10^?3.57(1 ? a)^1.15. Moreover, the half-life, Δ_sol H _m , Δ_sol G _m and Δ_sol S _m of the dissolution process were also obtained. This work will provide a potential reference for the clinical application of paclitaxel.     

Monte Carlo simulation of phase separations of block copolymers and of corresponding blends

The Monte Carlo method has been used to simulate the phase separations of block copolymers and of corresponding blends with very high concentration (sum of volume fractions of blocks A and B: ϕ_A + ϕ_B = 0,9545). Our main findings are as follows: (1) The mixing is nonrandom even in the athermal limit. (2) The nonselective good solvent molecules (ϕ_V = 0,0455) are mostly located at the interface between A- and B-rich phases, thus, it is not true that solvent and monomeric units will remain mixed at all temperatures. (3) Even for the same microscopic A-B interaction energy, ε, and at the same temperature, the Flory-Huggins parameter χ of block copolymers is always higher than that of corresponding blends, and the χ values of block copolymers and corresponding blends have different ε-dependencies. (4) The critical values of χ both for block copolymer and corresponding blend are obtained and compared with the meanfield theoretical predictions. It is found that the ratio of χ_c (block)/χ_c (blend) is qualitatively compatible with the prediction of the Flory-Leibler theory.     

Poly(butylene terephthalate)/poly(ε-caprolactone) blends: Influence of PCL molecular mass on PBT melting and crystallization behavior

The isothermal crystallization kinetics and melting behavior of poly(butylene terephthalate) (PBT) in binary blends with poly(ε-caprolactone) (PCL) was investigated as a function of PCL molecular mass by differential scanning calorimetry and optical microscopy. The components are miscible in the melt when oligomeric PCL (M_w = 1250) is blended with PBT, whereas only partial miscibility was found in mixtures with higher molecular mass (M_w = 10,000 and 50,000). The equilibrium melting point of PBT in the homopolymer and in blends with PCL was determined through a non-linear extrapolation of the T_m = f(T_c) curve. The PBT spherulitic growth rate and bulk crystallization rate were found to increase with respect to plain PBT in blends with PCL1250 and PCL10000, whereas addition of PCL50000 causes a reduction of PBT solidification rate. The crystallization induction times were determined by differential scanning calorimetry for all the mixtures through a blank subtraction procedure that allows precise estimation of the crystallization kinetics of fast crystallizing polymers. The results have been discussed on the basis of the Hoffman-Lauritzen crystallization theory and considerations on both the transport of chains towards the crystalline growth front and the energy barrier for the formation of critical nuclei in miscible and partially miscible PBT/PCL mixtures are widely debated.     

Equilibrium structure and spectroscopic constants of maleic anhydride

The quadratic, cubic, and semi-diagonal quartic force fields of maleic anhydride have been calculated at the MP2 level of theory employing the cc-pVTZ basis set. The spectroscopic constants derived from the force field are in excellent agreement with the corresponding experimental values. The semi-experimental equilibrium structure has been derived from experimental ground state rotational constants and rovibrational corrections calculated from the cubic force field. This semi-experimental equilibrium structure is in excellent agreement with the ab initio structures computed at the CCSD(T) level of theory and it is closer to the ab initio structure than the purely experimental (or empirical) structures r ₀, r _m⁽¹⁾, and r _m⁽²⁾ obtained by microwave spectroscopy as well as the equilibrium structure derived from gas-phase electron diffraction data.     

Phase behavior,morphology, and mechanical properties of polyethylene-copolymer blends

Binary blends of unbranched polyethylene (PE) and 5-10% model ethylene-butene random copolymers are used to determine the effects of composition heterogeneity on phase separation in the melt, semicrystalline morphology, plane strain fracture toughness J_C and tensile modulus and yield strength. Slowly cooled samples of melt-miscible blends are appreciably tougher (J_C = 5.2 kJ/m²) than unblended PE (J_C = 2.7 kJ/m²). A blend with the same average short chain branch concentration, but which is phase separated in the melt state, has J_C= 3.3 kJ/m²; dispersed domains of amorphous polymer have little effect on toughness. Enhanced toughness is associated with nonuniform morphology formed on slow cooling “one phase” melts composed of chains with different amounts of branching. The relative number of chemically different chains, as opposed to absolute branch concentrations, seems most important. Tensile properties are relatively unaffected by blending at these levels. Results from these model blends are used to consider the properties of compositionally heterogeneous ethylene copolymers. © 1994 John Wiley & Sons, Inc.     

Solid-state NMR study of biodegradable starch/polycaprolactone blends

Abundant literature exists on starch or modified starch blended with biodegradable polyesters to achieve good performance with cheap compost plastics. The level of miscibility in these blends is one of the most relevant parameters. In the present study, solid-state ¹H and ¹³C NMR spectra, as well as carbon spin-lattice relaxation times T₁(C) and proton spin-lattice relaxation times T₁(H) and proton spin-lattice relaxation times in the rotating frame T_1ρ(H) of biodegradable starch (or starch formate)/polycaprolactone (PCL) (or polyester (PE) oligomers) blends and samples of the neat components were measured. From the T_1ρ(H) and T₁(H) relaxation times it follows that blends starch/PCL, starch/PE-oligomers and starch formate/PE-oligomers are phase separated even on the scale of 20-110 nm. On the contrary starch formate/PCL blend is phase separated on the scale 2.5-12 nm but homogeneously mixed on the scale 20-90 nm. Moreover, shorter T₁(C) and especially T_1ρ(H) values found for the starch or starch formate component in all these blends in comparison with neat samples show that molecular mobility of starch and starch formate segments is affected by blending. This indicates some miscibility also in phase separated blends which can happen in amorphous channels of starch.     

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

The 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, m_B, 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 m_B, while LCST type one was for that of large m_B 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     

Phase separation in mixtures of poly(ethylene glycol monomethylether) and poly(propylene glycol) oligomers

Time-resolved light scattering was employed to investigate kinetics of phase separation in mixtures of poly (ethylene glycol monomethylether) (PEGE)/poly (propylene glycol) (PPG) oligomers. Phase diagrams for PEGE/PPG of varying molecular weights were established by means of cold point measurements. The oligomer mixtures reveal an upper critical solution temperature (UCST). Several temperature quench experiments were carried out with a 60/40 PEGE/PPG blend by rapidly quenching from a single phase (69°C) to two-phase temperatures (66–61°C) at 1°C intervals. As is typical for oligomer mixtures, the early stage of spinodal decomposition (SD) was not detected. The kinetics of phase decomposition was found to be dominated by the late stage of SD. Time-evolution of scattering intensity was analyzed in accordance with nonlinear and dynamical scaling theories. The time dependence of the peak intensity I_m and the corresponding peak wavenumber q_m was found to follow the power-law {I_m(t)? t^α, q_m(t)? t^-β} with the values of α = 3 ± 0.3 and β = 1 ± 0.2, which are very close to the values predicted by Siggia. This process has been attributed to a coarsening mechanism driven by surface tension. In the temporal scaling analysis, the structure function reveals university with time, suggesting self-similarity. Phase separation dynamics in 60/40 PEGE/PPG resembles the behavior predicted for off-critical mixtures.     

Prototropic tautomers of 5‐methylcytosine and enthalpy changes of their protonation,deprotonation, and deamination: Hybrid density functional B3LYP study

Molecular and thermodynamic properties such as geometric parameters, dipole moments, vibrational frequencies, the first ionization potentials, relative tautomerization energies, and tautomeric equilibrium constants of all prototropic tautomers of 5‐methylcytosine have been studied at the hybrid density functional level B3LYP/6‐31+G(d,p). The methylation on the C5 atom does not lead to significant geometric deformation of the pyrimidine structures of the corresponding tautomers of cytosine, which maintains the similar stability order. The tautomeric species 2‐oxo‐4‐amino [T(0)], 2‐hydroxy‐4‐amino [T(1‐2s) and T(1‐2t)], and trans‐2‐oxo‐4‐imino [T(3‐4t)] are predominated in the gas phase. The zwitterionic conformers of tautomerism [T(1‐4)] and protonation [P(4), P(1‐2s‐4), P(1‐2t‐4), and P(1‐3‐4)] are investigated for the first time due to their close relationship with deamination during genetic repair. Enthalpy changes (Δ_rH) of protonation, deprotonation, and deamination are calculated for these tautomeric species at room temperature; it is noted that the relative enthalpies [δ(ΔH)] of the tautomers are rationalized well in terms of a second‐order polynomial of the sum of the mean Δ_rH values of protonation and deprotonation processes. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002     

Kinetics of the droplet formation at the early and intermediate stages of the spinodal decomposition in homopolymer blends

The kinetics of the droplet formation during the spinodal decomposition (SD) of the homopolymer blends has been studied by numerical integration of the Cahn‐Hilliard‐Cook equation. We have found that the droplet formation and growth occurs when the minority phase volume fraction, f_m , approaches the percolation threshold value, f_thr = 0.3 ± 0.01. The time for the formation of the disperse droplet morphology (coarsening time) depends only on the equilibrium minority phase volume fraction, f_m . f_m approaches its equilibrium value logarithmically at the late SD stages, and, therefore, the coarsening time decreases exponentially as the average volume fraction or the quench depth decrease. Since the temporal evolution of the total interfacial area does not depend on the quench conditions and blend morphology, the average droplet size and the droplet number density is determined by the coarsening time. Within the time scale studied, the droplet number density decreases with time as t ^{–0.63±0.03}; the average mean curvature decreases as t ^{–0.35±0.05}; the average Gaussian curvature decreases as t ^{–0.42±0.03}, and the average droplet compactness ˜V/S^3/2 where S is the surface area and V is the volume) approaches a spherical limit logarithmically with time. The droplets with larger area have lower compactness and in the low compactness limit their area is a parabolic function of compactness. The size and shape distribution functions have been also investigated.     

Blends of poly(butylene terephthalate) and a polyarylate before and after transesterification

Blends of poly(butylene terephthalate) (PBT) and a copolyester of bisphenol-A with 50% terephthalate-50% isophthalate (PAr), before and after transesterification, have been studied by thermal and dynamic mechanical tests to determine crystallinity and phase behavior. Blends without transesterification, as prepared by solution precipitation, show a single T_g, indicating amorphous miscibility of PBT and PAr. A melting-point depression for PBT crystals is not observed; this means that PBT crystallizes excluding PAr and the entropy of melting is small. The highest fractional crystallinity for PBT is obtained at 20-35% of PAr. Transesterified blends were obtained by holding the physical blends at 250°C for up to 16 h. The transesterified systems show higher T_g's than the corresponding physical blends and also show a marked melting-point depression and lesser PBT crystallinity at the corresponding increased PAr content.