A predictive approach based on the Simha–Somcynsky free‐volume theory for the effect of dissolved gas on viscosity and glass transition temperature of polymeric mixtures

The gas concentration and pressure effects on the shear viscosity of molten polymers were modeled by using a unified approach based on a free volume theory. A concentration and pressure dependent “shift factor,” which accounts for free volume changes associated with polymer‐gas mixing and with variation of absolute pressure as well as for dilution effects, has been herein used to scale the pure polymer viscosity, as evaluated at the same temperature and atmospheric pressure. The expression of the free volume of the polymer/gas mixture was obtained by using the Simha and Somcynsky equation of state for multicomponent fluids. Experimental shear viscosity data, obtained for poly(ε‐caprolactone) with nitrogen and carbon dioxide were successfully predicted by using this approach. Good agreement with predictions was also found in the case of viscosity data reported in the literature for polystyrene and poly(dimethylsiloxane) with carbon dioxide. Free volume arguments have also been used to predict the T_g depression for polystyrene/carbon dioxide and for poly(methyl methacrylate)/carbon dioxide mixtures, based on calculations performed, again, with the Simha and Somcynsky theory. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1863–1873, 2006     

Gas transport in vulcanized natural rubber‐cellulose. II. Composites

This work reports the transport of carbon dioxide, oxygen, and nitrogen in amorphous membranes of vulcanized natural rubber reinforced with regenerated cellulose. The values of the permeability coefficient of carbon dioxide, oxygen, and nitrogen in the composites with 25% of cellulose, measured at 25 °C and 15 cmHg of pressure, are roughly one‐third of those measured in the same conditions for these gases in natural rubber. The isotherms representing the variation of both the permeability and diffusion coefficients of the gases with pressure present a relatively sharp increase in the region of low pressures, attributed to changes in the free volume. The analysis of the permeability characteristics of the membranes in terms of the free‐volume theory suggests that gas transport is severely hindered in both the cellulose phase and the cellulose–rubber interphase of the composites. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 393–402, 2000     

Simultaneous measurement of the solubility of nitrogen and carbon dioxide in polystyrene and of the associated polymer swelling

New experimental results for the solubility of nitrogen and carbon dioxide in polystyrene are reported, accompanied by data on the change in volume of the polymer caused by the sorption process. The two phenomena were measured simultaneously with a combined technique, in which the quantity of penetrating fluid introduced into the system was evaluated by pressure‐decay measurements in a calibrated volume, whereas a vibrating‐wire force sensor was employed for weighing the polymer sample during sorption inside of the high‐pressure equilibrium cell. The use of the two techniques was necessary because the effects of swelling and solubility could not be decoupled in a single gravimetric or pressure‐decay measurement. The sorption of nitrogen in polystyrene was studied along three isotherms from 313 to 353 K at pressures up to 70 MPa. The sorption of carbon dioxide was measured along four isotherms from 338 to 402 K up to 45 MPa. The results are compared with values from the literature when possible, although our data extend significantly the pressure ranges of the latter. The uncertainties affecting our measurements with nitrogen are 1 mg of N₂/g of polystyrene in solubility and 0.1% of the volume of the polymer. For carbon dioxide, the uncertainties are 5 mg of N₂/g of polystyrene and 0.5% respectively, carbon dioxide being about 1 order of magnitude more soluble than nitrogen. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2063–2070, 2001     

Sorption and swelling of semicrystalline polymers in supercritical CO2

The equilibrium sorption and swelling behavior of four different polymers—poly(methyl methacrylate), poly(tetrafluoroethylene), poly(vinylidene fluoride), and the random copolymer tetrafluoroethylene–perfluoromethylvinylether–in supercritical CO₂—are studied at different temperatures (from 40 to 80 °C) and pressures (up to 200 bar). Swelling is measured by visualization, and sorption through a gravimetric technique. From these data, the behavior of amorphous and semicrystalline polymers can be compared, particularly in terms of partial molar volume of CO₂ in the polymer matrix. Both poly(methyl methacrylate) and the copolymer of tetrafluoroethylene exhibit a behavior typical of rubbery systems. On the contrary, polymers with a considerable degree of crystallinity, such as poly(tetrafluoroethylene) and poly (vinylidene fluoride), show larger values of partial molar volume. These can be related to the limited mobility of the polymer chains in a semicrystalline matrix, which causes the structure to “freeze” during the sorption process into a nonequilibrium state that can differ significantly from the actual thermodynamic equilibrium. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1531–1546, 2006     

Measurement and prediction of solubilities and diffusion coefficients of carbon dioxide in starch–water mixtures at elevated pressures

The solubility and diffusion coefficient of carbon dioxide in intermediate‐moisture starch–water mixtures were determined both experimentally and theoretically at elevated pressures up to 16 MPa at 50 °C. A high‐pressure decay sorption system was assembled to measure the equilibrium CO₂ mass uptake by the starch–water system. The experimentally measured solubilities accounted for the estimated swollen volume by Sanchez–Lacombe equation of state (S‐L EOS) were found to increase almost linearly with pressure, yielding 4.0 g CO₂/g starch–water system at 16 MPa. Moreover, CO₂ solubilities above 5 MPa displayed a solubility increase, which was not contributed by the water fraction in the starch–water mixture. The solubilities, however, showed no dependence on the degree of gelatinization (DG) of starch. The diffusion coefficient of CO₂ was found to increase with concentration of dissolved CO₂, which is pressure‐dependent, and decrease with increasing DG in the range of 50–100%. A free‐volume‐based diffusion model proposed by Areerat was employed to predict the CO₂ diffusivity in terms of pressure, temperature, and the concentration of dissolved CO₂. S‐L EOS was once more used to determine the specific free volume of the mixture system. The predicted diffusion coefficients showed to correlate well with the measured values for all starch–water mixtures. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 607–621, 2006     

Chromatographic investigation of the effect of dissolved carbon dioxide on the glass transition temperature of a polymer and the solubility of a third component (additive)

The effect of dissolved carbon dioxide on the glass transition temperature of a polymer, PMMA, has been investigated using molecular probe chromatography. The probe solute was iso-octane, and the specific retention volumes of this solute in pure PMMA and mixtures of PMMA with CO₂ were measured over a temperature range of 0 to 180°C and CO₂ pressures from 1 to 75 atm. The amount of CO₂ dissolved in the polymer was calculated from a model fit to previously published solubility data determined chromatographically. Classical van't Hoff-type plots were used to determine the glass transition temperature of CO₂-impregnated PMMA from low pressure up to 46 atm of CO₂. Solvent-induced plasticization was observed with the glass transition temperature decreasing by about 40°C. At some pressures, glass transitions at low temperatures could not be determined from the van't Hoff plots because of the proximity of the polymer glass transition temperature to the gas–liquid transition temperature for CO₂. For these pressures, a new method was developed to determine the glass transition composition. The glass transition pressure was then calculated from the measured composition and temperature using an isotherm model. In every case, the glass transition temperature decreased linearly with increasing concentration of CO₂ in the polymer. However, at higher compositions, the glass transition pressure decreased with increasing composition and decreasing temperature. The observed retention volume of iso-octane with PMMA in a glassy state was correlated with an adsorption model developed from a theory for liquid–solid chromatography derived by Martire. This model accurately described the observed decrease in retention of iso-octane by adsorption on the surface of glassy PMMA with increasing concentration of CO₂ dissolved in the polymer. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. B Polym. Phys. 36: 2537–2549, 1998     

Effect of molecular weight on the diffusion coefficient of carbon dioxide in polystyrene

The permeability and time lag at pressures below 1 atm were measured for carbon dioxide in five polystyrene samples with different molecular weights at 25 to 40°C. The apparent permeability coefficient decreases with increasing carbon dioxide pressure and also decreases with increasing molecular weight of polystyrene, whereas the apparent diffusion coefficient calculated from time lag increases with pressure and is independent of molecular weight. Parameters for the partial-immobilization model were determined from the apparent diffusion and permeation coefficients by using a nonlinear least-squares optimization program without using sorption data. The results suggest that the void-saturation constant C′_H decreases as the molecular weight of the polymer increases or as the chain-end free volume decreases. The significance of these observation and their interpretation is discussed in terms of free-volume theory for glassy polymers.     

Continuous precipitation polymerization of acrylic acid in supercritical carbon dioxide: The polymerization rate and the polymer molecular weight

The precipitation polymerization of acrylic acid in supercritical carbon dioxide was studied in a continuous stirred tank reactor with 2,2′‐azobis(2,4‐dimethylvaleronitrile) as the free‐radical initiator. The reactor temperature was between 50 and 90 °C, the pressure was 207 bar, and the average residence time was between 12 and 40 min. The product polymer was a white, dry, fine powder that dissolved in water. A wide range of polymer molecular weights (5–200 kg/mol) was obtained. The effects of the operating variables on the polymerization rate and on the polymer molecular weight were evaluated. The observed kinetics suggested that polymerization took place in both the supercritical fluid and the precipitated polymer particles. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2546–2555, 2005     

Solubility and partial molar volume of carbon dioxide and ethane in crosslinked poly(ethylene oxide) copolymer

Experimental solubility and sorptive dilation data are reported for carbon dioxide and ethane in a crosslinked poly(ethylene oxide) (XLPEO) rubbery copolymer. Five different temperatures (253 ≤ T(K) ≤ 308) were considered, with a maximum gas pressure of 2.09 MPa (20.6 atm). The polymer was prepared by photopolymerization of a solution containing 70 wt % poly(ethylene glycol) methyl ether acrylate (PEGMEA) and 30 wt % poly(ethylene glycol) diacrylate (PEGDA). Sorption isotherms were described by the Flory‐Huggins model. For each gas, the Flory‐Huggins interaction parameter was a decreasing function of temperature and did not show a composition dependence. Dilation and sorption data were combined to calculate the partial molar volume (PMV) of the gases in the polymer, which was an increasing function of temperature. Based on a comparison with literature data for a XLPEO homopolymer prepared from pure PEGDA over the same range of operating conditions, an effect of the network composition on both gas solubility and PMV was found. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 456–468, 2010     

Molar mass distributions and viscosity behavior of perfluorinated sulfonic acid polyelectrolyte aqueous dispersions

Perfluorinated sulfonic acid polyelectrolyte aqueous dispersions originating from similar polymer feed stocks and having similar compositions can have order‐of‐magnitude viscosity differences that are dependent on the manufacturing process. To better understand this phenomenon at the molecular level, a size exclusion chromatography method incorporating static light scattering detection was developed. The initial apparent mass distributions were broad and bimodal for all dispersions. A high‐molar‐mass shoulder was consistent with a previously postulated aggregate structure, and the evidence suggested that molecular aggregation accounted for viscosity variability. The apparent weight‐average molar masses ranged from 1.3 × 10⁶ to 3.9 × 10⁶ g mol^?1. Upon the heating of the dispersions at or above 230 °C, the aggregate structure was broken down, and this resulted in similar low‐viscosity dispersions that had monomodal mass distributions. The weight‐average molar masses were reduced to approximately 2.5 × 10⁵ g mol^?1, and the polydispersities were approximately 1.7–1.8. Shear thinning with higher viscosities and apparent molar masses was rationalized with intrinsic viscosity and other measurements, which supported an anisotropic aggregate structure, with particles that could be significantly overlapped at nominal 11% concentrations. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 421–428, 2005     

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     

Rheology of polydimethylsiloxane swollen with supercritical carbon dioxide

Viscosity curves were measured for polydimethyl siloxane (PDMS) melts swollen with dissolved carbon dioxide at 50 and 80°C for shear rates ranging from 40 to 2300 s⁻¹, and for carbon dioxide contents ranging from 0 to 21 wt %. The measurements were performed with a capillary extrusion rheometer modified for sealed, high-pressure operation to prevent degassing of the melt during extrusion. The concentration-dependent viscosity curves for these systems are self-similar in shape, exhibiting low-shear rate Newtonian plateau regions followed by shear-thinning “power-law” regions. Considerable reduction of viscosity is observed as the carbon dioxide content is increased. Classical viscoelastic scaling methods, employing a composition-dependent shift factor to scale both viscosity and shear rate, were used to reduce the viscosity data to a master curve at each temperature. The dependence of the shift factors on polymer chain density and free volume were investigated by comparing the shift factors for PDMS-CO₂ systems to those obtained by iso-free volume dilutions of high molecular weight PDMS. This comparison suggests that the free volume added to PDMS upon swelling with dissolved carbon dioxide is the predominant mechanism for viscosity reduction in those systems. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys, 35: 523–534, 1997     

Raman spectroscopic investigation of the phase behavior and phase transitions in a poly(methyl methacrylate)‐carbon dioxide system

Laser Raman spectroscopy, in conjunction with an optical high‐pressure cell, was used to investigate the poly(methyl methacrylate)‐carbon dioxide system. The Raman shifts associated with carbon dioxide molecules in the gas phase and those dissolved in the polymer were used to derive sorption kinetics of carbon dioxide and the carbon dioxide‐induced phase changes in the polymer. Measurements were made in the temperature and pressure ranges in which this system is known to exhibit retrograde vitrification behavior. The Raman results on the sorption kinetics and on the onset of plasticization were in agreement with those obtained by gravimetric and calorimetric techniques, respectively. This technique provides a versatile and rapid way of characterizing polymer‐gas systems and information that so far has been obtainable only through painstaking and time‐consuming techniques. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2214–2217, 2003     

High-precision gravimetric technique for determining the solubility and diffusivity of gases in polymers

An in situ gravimetric technique, employing an electrobalance, is described for determining the solubility and diffusivity of gases in polymers over extended ranges of temperature and pressure. Solubilities of CO₂ in polystyrene at 35°C were measured as a test case; the results are in excellent agreement with the literature values determined by the pressure decay method. Solubility and diffusivity results are also reported for PVC-CO₂ at 35°C and for PS-1,1,1,2-tetrafluoroethane at 30, 90, and 120°C. A comparison with other studies shows the in situ method to be more efficient and precise than the ones based on weighing the gas-saturated polymer under ambient conditions. The kinetics of gas sorption were analyzed in terms of two data reduction techniques to derive diffusion coefficients. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 2025–2032, 1998     

Equation of state of poly(dimethylsiloxane) melts

The pressure–volume–temperature (PVT) properties of three commercial samples of poly(dimethylsiloxane) are studied experimentally and theoretically in the temperature range 25–150°C and for pressure to ∼ 3 kbar. The Tait equation is employed to represent the data at elevated pressure. Isothermal compressibilities are computed for the three samples. The melt data are analyzed in terms of the Simha–Somcynsky hole theory, and scaling parameters of pressure, volume, and temperature are obtained. Satisfactory agreement between theory and experiment is found over the entire range of experimental pressures. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 841–850, 1998     

Synthesis,cure, and composite properties of mixed allyl/propargyl cyclopentadiene resins

A series of thermosetting resins were synthesized via phase transfer reaction of allyl chloride and propargyl bromide with cyclopentadiene in the presence of a strong base. Feed ratios of 1 : 1, 3 : 1, and 5 : 1 allyl chloride to propargyl bromide were used to give resins with varying amounts of propargyl and allyl functionality. In all cases the resins could be thermally cured, without added catalyst, at temperatures below 275°C to give black, glassy, brittle materials with densities of 1.15. TGA evaluation of the resins, with heating to 1000°C, resulted in carbon yields ranging from 48 to 66% with increasing propargyl functionality causing increased values. Physical mixtures of ACP and PCP resins were also made and evaluated. Cure of the mixed materials also occurred below 275°C, and carbon yields were comparable to the corresponding APCP resin. APCP/carbon fiber composites gave good mechanical properties with flexural modulus values of 115–130 GPa and flexural strength values of 1000 MPa. Carbonization of 1 : 1 APCP/carbon fiber composites provided materials with interlaminar strength values of approximately 1.14 MPa. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 2869–2876, 1998     

Alternating copolymerization of carbon dioxide and cyclohexene oxide catalyzed by silicon dioxide/Zn?CoIII double metal cyanide complex hybrid catalysts with a nanolamellar structure

Air‐stable hybrid catalysts of silicon dioxide/double metal cyanide complexes (Si‐DMCCs) based on Zn₃[Co(CN)₆]₂ (ZHCC) were prepared by an in situ sol–gel method. The Si‐DMCCs showed low crystallinity and a nanolamellar structure with a thickness of ～40–60 nm. In particular, a lamellar structure of regular hexagonal shape was observed for Si‐DMCCs with low SiO₂ content. These catalysts had very high catalytic activity for alternating copolymerization of cyclohexene oxide (CHO) and carbon dioxide. A turnover number of 11,444, turnover frequency of 3815 h^?1, and apparent efficiency of 7.5 kg polymer/g ZHCC (～24.0 kg polymer/g Zn) were achieved at 3.8 MPa and 100 °C. The poly(cyclohexenylene carbonate) (PCHC) polymers obtained were completely atactic with a molecular weight (M_n) of ～10 kg/mol and polydispersity of 2.0–3.0. The PCHCs had a structure of nearly alternating CHO and CO₂ units, with a molar fraction of carbonate units of 0.44–0.47. Preliminary investigations of the mechanism suggest that nucleophilic attack by neighboring oxygen atoms is involved in copolymerization initiation with Zn? Co^III DMCCs. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3128–3139, 2008     

Electron paramagnetic resonance spin probe study of carbon dioxide‐induced polymer plasticization

Steady‐state electron paramagnetic resonance (EPR) spectroscopy using nitroxide spin probes has been used to investigate the plasticization of poly(vinyl acetate) and poly(ethyl methacrylate) by carbon dioxide. By varying the CO₂ pressure at constant ambient temperature, the glass transition for each polymer could be depressed to 25 °C. This effect has been quantified by a parameter P_50G, obtained by plotting the EPR spectral width as a function of CO₂ pressure. Certain spin probes showed free volume distribution effects, manifested in the EPR spectra as “double peaks.” Possible reasons for this phenomenon are presented and discussed, and the efficacy of CO₂ as a plasticizer is clearly demonstrated by direct comparison with di‐n‐butyl phthalate. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2097–2108, 2005     

Pure and mixed gas acetone/nitrogen permeation properties of polydimethylsiloxane [PDMS]

The permeability of polydimethylsiloxane [PDMS] to acetone, nitrogen, and acetone/nitrogen mixtures has been determined at 28°C. In pure gas experiments, the permeability of PDMS to nitrogen was 245 × 10⁻¹⁰ cm³(STP) · cm/cm² · s · cmHg and was independent of pressure. The permeability of PDMS to acetone vapor increased exponentially with increasing acetone pressure. PDMS is much more permeable to acetone than to nitrogen; acetone/nitrogen selectivity increases from 85 to 185 as acetone partial pressure in the feed increases from 0 to 67% of saturation. In mixed gas permeation experiments, the nitrogen permeability coefficient is independent of acetone relative pressure and is equal to the pure gas permeability coefficient. The acetone permeability coefficient has the same value in both mixed gas and pure acetone permeation experiments. Average acetone diffusivity in PDMS, determined as the ratio of permeability to solubility, decreases with increasing acetone concentration due to mild clustering of acetone in the polymer (because acetone is a poor solvent for PDMS) and changes in the polymer–penetrant thermodynamic interactions which influence diffusion coefficients. A Zimm–Lundberg analysis of the acetone sorption isotherm is also consistent with acetone clustering in PDMS. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36 : 289–301, 1998     

Partial molar volume of paracetamol in water, 0.1 M HCl and 0.154 M NaCl at T = (298.15, 303.15, 308.15 and 310.65) K and at 101.325 kPa

The apparent molar volume of paracetamol (4-acetamidophenol) in water, 0.1 M HCl and 0.154 M NaCl as solvents at (298.15, 303.15, 308.15 and 310.65) K temperatures and at a pressure of 101.325 kPa were determined from the density data obtained with the help of a vibrating-tube Anton Paar DMA-48 densimeter. The partial molar volume, V_m, of paracetamol in these solvents at different temperatures was evaluated by extrapolating the apparent molar volume versus molality plots to m = 0. In addition, the partial molar expansivity, E^°, the isobaric coefficient of thermal expansion, α_p, and the interaction coefficient, S_v, have also been computed. The expansivity data show dependence of E^° values on the structure of the solute molecules.