Thermodynamic interactions in blends of poly(4-tert-butyl styrene) and polyisoprene by small-angle neutron scattering

The thermodynamic interactions between poly(4-tert-butyl styrene) [P(4tBS)] and 1,4-polyisoprene (PI; both hydrogenous) were obtained as functions of the temperature, PI molecular weight, and blend composition through the examination of miscible ternary blends of these two components with a common miscible labeled polymer [90% 1,2-deuterated polybutadiene (dPBD)] with small-angle neutron scattering. The thermodynamic interaction parameters between P(4tBS) and dPBD and between P(4tBS) and PI increased with increasing temperature and were consistent with lower critical solution temperature behavior. Although the binary blends of P(4tBS) and dPBD exhibited phase separation at elevated temperatures, the thermodynamic interaction parameters between P(4tBS) and PI remained large and negative and independent of the PI molecular weight. Finally, the thermodynamic interactions for PI and P(4tBS) depended strongly on the ratio of PI to P(4tBS) and were also sensitive to the amount of dPBD present in the ternary blend. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3204–3217, 2004     

Excess volume of mixing and equation of state theories

Equation-of state theories of Flory and of Sanchez and Lacombe describe both enthalpy and volume of mixing of binary systems using single component properties and only one binary parameter X₁₂. We have evaluated this parameter from literature enthalpy data for numerous mixtures of two aromatic hydrocarbons, of alkanes with aromatic compounds, and of alkanes with carbonyl compounds. We have used this X₁₂ for calculation of excess volumes and compared the results with our previously measured experimental data. The agreement was fair for mixtures of two nonpolar components. Nevertheless, mixtures containing either cyclohexane or benzene displayed anomalies that could be traced to special packing of molecules in these compounds when pure. For mixtures of carbonyl compounds with alkanes, the theories predicted the qualitative trends correctly, but the quantitative agreement was rather poor. These results tend to support a model in which the enthalpy(cohesive energy) is inversely proportional to volume (as in the theories considered) only for dispersive interaction. When polar-polar interactions are involved, the dependence of excess volume on the excess enthalpy is much weaker.     

Excess and partial excess molar volumes of mixing trimethyl- and triethylphosphate with water

Excess and excess partial molar volumes of mixing of the systems trimethylphosphate (TMP) and triethylphosphate (TEP) with water were determined at 15, 20, 25, 30 and 35°C. Negative deviation from ideal behavior were observed for the two systems studied, with a minimum at x _TMP =0.40 and x _TEP =0.35. Excess volume values in general decrease with temperature, and are smaller for the TMP-water system.     

Excess and partial excess molar volumes of mixing of N,N-dibutyl-2-ethylhexamide with dodecanol

Excess and excess partial molar volumes of mixing of the system N,N-dibutyl-2-ethylhexylamide (DBEHA) + dodecanol (DDA) were determined at 25, 35, 45, 55 and 65°C. The excess molar volumes exhibit a maxima at each temperature at approximatelyx _DBEHA = 0.3 and a minima close tox _DBEHA = 0.9. The values of the excess volumes in general increase with the temperature. The partial excess molar volumes are calculated from the smoothed data and the results are discussed in the light of postulated amide-alcohol interactions.     

Excess volume of mixing and excess enthalpies of mixing of ethyl iodide + aromatic hydrocarbons at 25°C

The excess volumes and enthalpies of mixing of binary mixtures of ethyl iodide with benzene, toluene, o-xylene, m-xylene and p-xylene have been measured experimentally over the whole composition range at 25°C. Qualitatively the data have been explained on the basis of electron donoracceptor interactions between the ethyl iodide and aromatic hydrocarbons and also on the loss of favorable orientational order of the pure components. Flory's theory correctly predicts the sign and to some extent magnitude of the V _E and H ^E values.     

Study of free volume in high-vinyl polybutadiene/cis-polyisoprene blends using positron annihilation spectroscopy

High-Vinyl Polybutadiene (HVBD)/cis-Polyisoprene (CPI) blends were characterized by Differential Scanning Calorimetry (DSC) and Positron Annihilation Lifetime Spectroscopy (PALS). A single DSC glass transition temperature T_g is observed, whose composition dependence strongly deviates from additivity, and shows an apparent cusp when the weight fraction of HVBD ≈ 0.75. The free-volume hole size, V_h, and the scaled fractional free volume, h_ps/C, = I₃V_h were determined by PALS from the orthopositronium (o-Ps) intensities, I₃, and lifetimes, τ₃, over a temperature range encompassing T_g and the temperature at which “positronium bubble” formation occurs. In the glass, V_h and h_ps/C are smaller for CPI than for HVBD, but the thermal expansion coefficient for hole volume, α_f, is larger in the melt for CPI than for HVBD; thus, an iso-hole volume temperature occurs in these blends at T_iso ≈ −34°C. Above and below T_iso, V_h and h_ps/C each show a negative departure from additivity. A quantitative interpretation of the cusp in the composition dependence of T_g can be obtained, via a modified analysis of Kovacs, using free-volume quantities from PALS, with the ratio of scaling constants C_CPI/C_HVBD as an adjustable parameter. At high temperatures, the positron bubble size is smaller in CPI than in HVBD. This agrees with the observation that the thermal expansivity of hole volume, and, hence the internal pressure are larger in the equilibrium melt of CPI. The effect of e⁺-irradiation on the o-Ps intensity was investigated. I₃ decreases more rapidly in the melt as T → T_g, and then more slowly in the glass, suggesting that the effect is due to trapping of radical or ionic species which inhibit o-Ps formation. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 861–871, 1998     

Pressure–volume–temperature properties and free volume parameters of PEO/PMMA blends

Melt-miscible polymer blends of poly(ethylene oxide)/atactic poly(methyl methacrylate (PEO/a-PMMA)) were prepared by melt-mixing and characterized by pressure–volume–temperature (PVT) dilatometry in the pressure and temperature range of 0 to 200 MPa and 20 to 200°C, respectively. The PVT data were analyzed in terms of two equations of state (EOS). The empirical Tait EOS was applied in the glassy, semicrystalline, and equilibrium melt state, and the Simha-Somcynsky EOS theory was applied in the equilibrium melt and glassy state. The Simha-Somcynsky EOS theory contains a free volume function. The temperature, pressure, and composition dependence of the free volume fraction h calculated from the Simha-Somcynsky EOS theory was studied. As a function of blend composition we observe that the free volume fraction, thermal expansivity, and compressibility all deviate mainly positively from linearity while the specific volume deviates mainly negatively from linearity. These findings are reconciled with composition-dependent free volume parameters, the free volume and cell volume as well as with self- and cross-interaction parameters derived from the Simha-Somcynsky EOS theory as applied to polymer mixtures. Moreover, the pressure dependence of glass and melting transitions as well as crystallization kinetics have been investigated. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 1061–1080, 1998     

A new formula for the entropy of mixing in polymer systems and free volume

The famous equations of Flory-Huggins for the entropy of mixing with one highmolecular component are of great importance for polymer physics. But Gujrati stated in 1980 [12] that these equations cannot be exact. This is why we derived a new formula for the dependence of the entropy from the fraction of vacant sites in a quasi-lattice. It differs significantly from that of Huggins and still more from that of Flory in the case of low free volume. The equations of Flory-Huggins are correct with reference to low polymer content only.If our formula for entropy is used instead of that of Huggins an important result of the theory of Gibbs-DiMarzio is called in question. The increase of thermal expansion at the glass transition cannot be explained by an increase of vacant sites. A growth of the number of unoccupied sites according to the thermodynamic equilibrium condition would bring about a far too great thermal expansion coefficient. From estimations of the energy of interaction between polymer molecules, which can be found in literature, it follows that the increase of entropy is far too small to enable the formation of vacant sites above the glass transition. It is unambiguously shown that the free volume, commonly regarded to be the decisive quantity with respect to glass transition, cannot consist of holes as considered in the quasi-lattice model and in many theoretical treatments.     

Oxygen barrier,free volume,and blending properties of polyamide 12/poly (vinyl alcohol) blends

Oxygen permeation rates, average volumes of free‐volume‐cavities (V_f), and fractional free volumes (F_v) of polyamide 12 (PA12)/poly(vinyl alcohol) (PVA) (ie, PA12_xPVA⁰⁵_y, PA12_xPVA⁰⁸_y, and PA12_xPVA¹⁴_y) blend films with varying PVA degrees of polymerization reduced to a minimum value when their PVA contents reached a corresponding optimal value, respectively. The minimum oxygen permeation rates, V_f, and F_v values obtained for the optimal PA12_xPVA^z_y blown films were reduced considerably with decreasing PVA degrees of polymerization. Experimental findings from dynamic mechanical analysis, differential scanning calorimetry, wide angle X‐ray diffraction, and Fourier transform infrared spectroscopy of the PA12_xPVA^z_y blend series suggest that PA12 and PVA in PA12_xPVA^z_y are miscible to some extent at the molecular level when their PVA contents are near and less than the corresponding critical values. The considerably enhanced oxygen barrier properties of the PA12_xPVA^z_y blend films with optimized compositions are attributed to the significantly reduced local free volume characteristics.     

Positron annihilation lifetime studies of changes in free volume on cross-linking cis-polyisoprene,high-vinyl polybutadiene,and their miscible blends

Measurements of average free volume hole sizes, 〈v_f〉, and the fractional free volumes, f_ps, in vulcanized cis-polyisoprene (CPI), high-vinyl polybutadiene (HVBD), and their 50 : 50 blend were made via determination of orthopositronium annihilation lifetimes. The results are compared to corresponding data on the uncured materials. On crosslinking, 〈v_f〉 decreases in the rubbery state but remains essentially unchanged in the glass. This is consistent with the expectation that the crosslinks greatly restrict the thermal expansion of the chains above the glass transition temperature (T_g) but have less influence on the packing density in the glass. Scaling relationships between 〈v_f〉, f_ps, the thermal expansion coefficient α_f = df_ps/dt, and T_g are examined. We find that 〈v_f〉_g, the hole volume at T_g, and f_ps,g, the fractional free volume at T_g, each increase significantly with increasing T_g. This behavior is consistent with previous observations reported in the literature and has been interpreted as a manifestation of the kinetic character of the glass transition. High-T_g polymers need a larger free volume to pass into the liquid state. The change in expansion coefficient on passing from the glass to the liquid, Δα_f = α_f,l − α_f,g, increases slowly with T_g, as predicted by free volume theory. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2754–2770, 1999     

Solid state NMR study of hydrogen bonding, miscibility, and dynamics in multiphase polymer systems

The application of solid state NMR (SS NMR) to the study of multiphase polymer systems is growing rapidly. This article aims to provide an overview of the current state of development of this field, paying particular attention to the study of hydrogen bonding in hydrogen-bonded polymer materials through SS NMR investigations. The effection of hydrogen bonds on the miscibility, phase separation and dynamic behavior of selected systems will also be discussed, based on work during the last 10 to 15 years.     

Measurements of excess enthalpies at high temperature and pressure using a new type of mixing unit

A flow mixing unit (calorimetric cell and auxiliary devices) has been designed for measuring the enthalpy of mixing or reaction of two fluids (gas+liquid or liquid+liquid). The indicator of the heat effect is a differential heat flux calorimeter, SETARAM C-80, allowing measurements at temperatures up to 300°C. The mixing cell is made of a stainless-steel capillary (o.d 1.6 mm, length 2.4m) which is coiled in a cylindrical form and tightly fitted in the thermopile well of the calorimeter. The fluids are delivered from the high pressure piston pumps and circulated through the system at controlled flow rates ranging from 100 to 1500 L-min^–1. The tests were carried out at pressures up to 20 MPa. Special care was taken to allow good thermostatting of fluids entering the mixing cell. Check measurements were made with one liquid-liquid system (C₂H₅OH+H₂O) and one gas-liquid system (CO₂+C₆H₅CH₃); our enthalpies of mixing agreed with the literature values in most cases to 2%. For the system ethanol+water the experiments have been also performed at temperature of 250°C and pressures of 15 and 20 MPa. The endothermal mixing effect was higher than expected indicating an increase in the excess heat capacity.     

Miscibility studies of poly(3-octylthiophene)/poly(ethylene-co-vinylacetate) blends with a solvatochromatic shift in the solid state

The mixing of electrically conducting polymers in the undoped state with flexible polymers has been limited due to the stiffness of the delocalized coplanar backbone. The substitution with alkyl side chains has resulted in the distortion of the aromatic rings in the backbone with an increase of the flexibility. The alkyl substituents also prevent the thiophene back-bones from packing together, thus making blending with other polymers promising. We have investigated the phase behavior of poly(3-octylthiophene) (P3OT) with a flexible polymer, poly(ethylene-co-vinylacetate) (vinylacetate composition 20%, EVA20), and defined a miscibility window based on melting point data, on cloud point measurements, and on analysis by optical microscopy. The miscible region has been studied by UV-VIS and CPMAS NMR spectroscopies. A UV absorption in the visible region originates from a π-π ^* transition in the delocalized structure of P3OT, and a change in the length of the conjugated segment in the backbone results in a shift of this absorption. A gradual solvatochromatic shift of P3OT in the solid state with dilution was observed in the miscible region. T₁ relaxation times for the methylene carbons in solid state show a gradual change in the relaxation process as a function of composition. © 1995 John Wiley & Sons, Inc.     

Effect of selected structural parameters of styrene–butadiene block copolymers on their compatibilization efficiency in polystyrene/polybutadiene blends

The effects of the block length and block number of linear styrene–butadiene (S–B) block copolymers on their compatibilization efficiency in blending polystyrene with polybutadiene were studied. For this purpose, two sets of model S–B copolymers and both homopolymers were prepared by anionic polymerization. Diblocks, triblocks, or pentablocks of S–B copolymers were blended with these homopolymers, and the structures and some end‐use properties of the blends were determined. The supramolecular structure (determined by small‐angle X‐ray scattering), morphology (determined by transmission and scanning electron microscopy), and stress‐transfer characteristics (impact and tensile strengths) of the blends were chosen as criteria for the compatibilization efficiency of the copolymers used. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2612–2623, 2002     

Determination of the intermolecular interaction parameters in the water-amide systems based on the data of the excess thermodynamic functions

The molar excess enthalpiesH ^E for the water +N-methyl-2-pyrrolidinone binary mixtures have been measured as functions of mole fraction at 298.15, 308.15 and 318.15 K, using isoperibol rotating calorimeter. A hydrogen bonding pairs model proposed by Luzar was fitted to the experimental dataH ^E,G ^E for the binary mixtures of water with hexamethylphosphoric triamide, N,N-dimethylformamide, N,N-dimethylacetamide and N-methyl-2-pyrrolidinone.     

Solid‐state NMR studies of cis‐1,4‐polyisoprene crosslinked with dicumyl peroxide in the presence of triallyl cyanurate

The network of dicumyl peroxide (DCP)/triallyl cyanurate (TAC) crosslinked cis‐1,4‐polyisoprene was studied by solid‐state NMR techniques such as direct‐polarization (DP), cross‐polarization (CP), and proton T₂ experiments. Line broadening and cis/trans isomerization of mobile carbons were observed in the DP experiments. The information on rigid carbons of network structures was observed with the CP technique. Motional heterogeneity was examined by proton T₂ relaxation experiments. Decreases in long T₂ (T_2L) values from the mobile non‐network structures and short T₂ (T_2S) values from the rigid network structures were observed with an increase in peroxide or coagent concentration. The percentage of T_2S in T₂ relaxation, which is related to network density, was observed to increase with peroxide and coagent addition. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1417–1423, 2000     

Heat of mixing in polymer blends based on poly(vinyl acetate)

Knowledge of the heat of mixing is very important in order to evaluate the interaction parameter, according to the Patterson theory. In this work we illustrate the results regarding some polymer blends, based on poly(vinyl acetate) and some polyacrylates with different substituent groups. In this way it is possible to understand the effect of the lateral group hindrance, as it will be illustrated in the paper.     

Structure and properties of rubber/organic montmorillonite nanocomposites prepared by in situ anionic intercalation polymerization

Polybutadiene (PB), polyisoprene (PI), and styrene–butadiene rubber/organic montmorillonite (OMMT) nanocomposites (NCs) were prepared by in situ anionic intercalation polymerization. The intercalation structure, chemical constitution, and morphology of the rubber/OMMT NCs were characterized with X‐ray diffraction, H NMR spectroscopy, and transmission electron microscopy; the thermal and dynamic mechanical properties of the rubber/OMMT NCs were characterized with differential scanning calorimetry, thermogravimetric analysis, and dynamic mechanical analysis. The mechanical properties of PB/OMMT NC were also tested. The results showed that a certain extent of exfoliated rubber/OMMT could be prepared by anionic in situ intercalation polymerization. The incorporation of OMMT obviously changed the microstructure content of PB and PI: the concentrations of the 1,2‐unit, 3,4‐unit, and trans‐1,4‐unit increased dramatically with an increasing concentration of OMMT, and the concentration of the cis‐1,4 structure decreased. The addition of OMMT‐DK1B and OMMT‐DK4 had little effect on the molecular weight and molecular weight distribution, but the addition of OMMT‐DK1 reduced the molecular weight of rubber, and the molecular weight distribution became broad. The glass‐transition temperature, weight‐loss temperature, storage modulus, and loss modulus of the NCs evidently increased, but tan δ decreased. OMMT apparently enhanced the rubber matrix; for example, the breaking strength and hardness of PB/OMMT NC crosslinked rubber increased greatly, but the tear strength and permanent deformation did not change much. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1344–1353, 2005     

Characterization of blends of poly(vinyl chloride) and poly(N‐vinyl pyrrolidone) by FTIR and 13C CP/MAS NMR spectroscopy

Blends of poly(vinyl chloride) (PVC) with Poly(N‐vinyl pyrrolidone) (PVP) were investigated by Fourier infrared spectroscopy (FTIR) and high‐resolution solid‐state ¹³C cross‐polarization/magic angle spinning (CP/MAS) nuclear magnetic resonance (NMR) spectroscopy. The intermolecular interactions between PVP and PVC are weaker than the self‐association of PVP and the inclusion of the miscible PVC results in the decreased self‐association of PVP chains, which was evidenced by the observation of high‐frequency shift of amide stretching vibration bands of PVP with inclusion of PVC. This result was further substantiated by the study of ¹³C CP/MAS spectra, in which the chemical shift of carbonyl resonance of PVP was observed to shift to a high field with inclusion of PVC, indicating that the magnetic shielding of the carbonyl carbon nucleus is increased. The proton spin‐lattice relaxation time in the laboratory frame (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 to give the information about phase structure. It is concluded that the PVC and PVP chains are intimately mixed on the scale of 20–30Å. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2412–2419, 1999     

Effect of Structure on Excess Partial Volumes and Deviation in Molar Viscosity of Some Aqueous-Ethylene Glycols Mono Alkyl Ether

The data obtained for density, viscosity, and dielectric constant are used for the study of the physical properties of 2-ethoxy ethanol-water mixtures. Density measurements showed the presence of contraction in the volume of the mixture and also in the partial molal volume of the components. Viscosity data provided supporting evidence of interaction between the two solvents. The dielectric data for the system were studied in terms of a deviation fraction, δD, representing the deviation from an ideal volume mixture. The results are also compared with the data obtained in the literature for water-2-methoxy ethanol and water-ethylene glycol mixtures.