Effect of supercritical carbon dioxide on the crystallization and melting behavior of linear bisphenol A polycarbonate

The crystallization and melting behavior of bisphenol A polycarbonate treated with supercritical carbon dioxide (CO₂) has been investigated with differential scanning calorimetry. Supercritical CO₂ depresses the crystallization temperature (T_c) of polycarbonate (PC). The lower melting point of PC crystals increase nonlinearly with increasing treatment temperature. This indicates that the depression of T_c is not a constant at the same pressure. T_c decreases faster at a higher treatment temperature than at a lower temperature. The leveling off of the depression in T_c at higher pressures is due to the antiplasticization effect of the hydrostatic pressure of CO₂. The melting curves of PC show two melting endotherms. The lower melting peak moves to a higher temperature with increasing treatment temperature, pressure, and time. The higher temperature peak moves toward a higher temperature as the treatment temperature is increased, whereas this peak is independent of the treatment pressure, time, and heating rate. The double melting peaks observed for PC can be attributed to the melting of crystals with different stability mechanisms. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 280–285, 2004     

An in situ study of plasticization of polymers by high-pressure gases

A high-pressure differential scanning calorimetric technique is described for studying polymer plasticization by compressed gases at pressures to 100 atm. The in situ measurements avoid problems due to gas desorption encountered with conventional DSCs, thus providing an accurate way to determine the change in glass transition temperature, T_g, with pressure, p. The entire T_g–p curve can be established in less than 2 days. The glass transition was observed as a sharp step in the case of 100–200-μm thin samples, whereas thicker samples gave a broad transition; highly reproducible results were obtained for the thin samples. For PS–CO₂, the measured T_gs under various pressures were found to be in good agreement with literature values. Results for the systems PS–HFC134a, PVC–CO₂, and PC–CO₂ are also reported. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 977–982, 1998     

On the plasticization of poly(2,6-dimethyl phenylene oxide) by CO2

Change in the glass transition temperature, T_g, of poly(2,6-dimethyl phenylene oxide), PPO, due to the dissolved CO₂ has been measured as a function of the gas pressure, p, using a high-pressure DSC cell. At 61.2 atm, the highest pressure studied, T_g is depressed by 31.6°C. The depression in T_g is found to be linear with pressure, with dT_g/dp of ?0.5°C atm^?1. The experimental results are in fair agreement with those calculated from a quasilattice solid-solution model for polymer-diluent systems. The present results, however, differ markedly from a recent investigation on PPO-CO₂ system which reported a depression in T_g of 226°C at 60 atm and a dT_g/dp of ?3.8°C atm^?. © 1994 John Wiley & Sons, Inc.     

Effect of isopropylidene replacement on gas transport properties of polycarbonates

The gas sorption and transport properties of a series of polycarbonates in which the isopropylidene unit of bisphenol A polycarbonate has been replaced with another molecular group are presented. Two new materials, bisphenol of norbornane polycarbonate (NBPC) and bisphenol Z polycarbonate (PCZ), are compared with several polymers which have been studied previously in this laboratory, including bisphenol A polycarbonate (PC), hexafluorobisphenol A polycarbonate (HFPC), and bisphenol of chloral polycarbonate (BCPC). The effect of molecular structure on chain mobility and chain packing is related to the gas transport properties. Dynamic mechanical thermal analysis and differential scanning calorimetry are used to judge chain mobility, while x-ray diffraction and free volume calculations give information about chain packing. Permeability measurements were made for He, H₂, O₂, N₂, CH₄, and CO₂ at 35°C over a range of pressures up to 20 atm. Sorption experiments were also done for N₂, CH₄, and CO₂ under the same conditions. The permeability coefficients of these polymers rank in the order HFPC ? NBPC>PC>BCPC ? PCZ for all of the gases. With the exception of BCPC, this order correlates well with fractional free volume. The low gas permeability of BCPC is attributed to a polarity effect. In general, bulky and relatively immobile substituents, as in HFPC and NBPC, can yield improved separation characteristics. The polar group of BCPC and the flexible cyclohexyl substituent of PCZ result in relatively low gas permeability.     

Effects of high-pressure CO2 on the glass transition temperature and mechanical properties of polystyrene

Hydrostatic pressure usually increases the glass transition temperature T_g of a polymer glass by decreasing its free volume; if the pressurizing environment is soluble in the polymer, however, one might expect an initial decrease in T_g with pressure as the polymer is plasticized by the environment. Just such a minimum in the T_g of polystyrene (PS) is observed as the pressure of CO₂ gas is increased over the range 0.1–105 MPa from both ultrasonic (1 MHz) measurements of Young's modulus E and static measurements of the creep compliance J. A time-temperature-pressure superposition law is obeyed by PS which allows a master curve for the compliance to be constructed and shift factors to be determined. A master curve for E is then obtained by using the Boltzmann superposition principle. The compliance J reaches a maximum, and E and T_g reach minima, at a CO₂ pressure of ca. 20 MPa at both 34 and 45°C, which are above the critical temperature (31°C) of CO₂. At the minimum, T_g is 41 at 45°C and 36 at 34°C, the larger depression at 34°C evidently corresponding to the higher solubility of CO₂ at the lower temperature. The plasticization effect due to CO₂ can be isolated by subtracting the effect of hydrostatic pressure alone from the experimental data. The results leave no doubt that at high pressures CO₂ gas is a severe plasticizer for polystyrene.     

Indentation of poly(methyl methacrylate) under high‐pressure gases

The variation of the indentation hardness of a high molecular weight poly(methyl methacrylate) (PMMA) subjected to CO₂ and Ar at high pressure was measured in situ. The samples were subjected to gas exposure for 3 h at 40 °C before a conical indenter of an included angle at 105 °, with a fixed load of 0.237 kg, was applied for a loading time of 60 s. The data show that both CO₂ and Ar reduce the hardness of PMMA to a comparable extent at low pressures. The hardness of PMMA subjected to Ar indicates a minimum at about 4 MPa and then increases. CO₂ produced a monotone decreasing trend in hardness in the pressure range studied, and the glass‐transition temperature (T_g) was achieved at about 6.0 MPa. The change in hardness is attributed to plasticization of the polymer matrix that is more extensive for CO₂. The relationship between the change in hardness for this PMMA subjected to high‐pressure CO₂, the corresponding change in the T_g, and the associated swelling of the polymer is discussed. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 3020–3028, 2001     

Gas sorption and transport in substituted polycarbonates

The effects of molecular structure manipulation of polycarbonates on sorption and transport of various gases were studied using tetramethyl, tetrachloro, and tetrabromo substitutions onto the aromatic rings of bisphenol A polycarbonate. Solubility and permeability measurements were made at 35°C over the pressure range of 1–20 atm for a variety of gases, namely CO₂, CH₄, O₂, N₂, and He. A threefold to fourfold increase in permeability was caused by the tetramethyl substitution, whereas the tetrachloro and tetrabromo substitutions reduced the permeability relative to the tetramethyl substitution. Lower activation energies for transport were found for the tetramethyl polycarbonate relative to the unsubstituted polycarbonate. Permeability coefficients were factored into solubility and diffusion coefficients. Sorption levels increased for all substitutions, but among the substituted polymers the levels remain practically the same. Solubility data were analyzed in terms of the dual sorption model. The Henry's law solubility coefficients obtained from this analysis were found to be consistent with a predictive equation developed for rubbery polymers. The usual correlation for predicting the Langmuir sorption capacity of the model overestimates the values for the substituted polycarbonates, and a proposal for the cause of this is offered. Thermal expansion of these polymers was measured using dilatometry, and the results are used in the interpretation of the sorption data. Diffusion phenomena are explained by segmental mobility and free volume considerations. The effects of CO₂ exposure history on sorption and transport were also investigated.     

Effects of polar group incorporation on crazing of glassy polymers: Styrene–acrylonitrile copolymer and a dicyano bisphenol polycarbonate

The degree of swelling and attendant reduction in the glass transition temperature have been determined for a 70% styrene–30% acrylonitrile copolymer in a large number of organic liquids. The critical strain ?_c for crazing or cracking has been determined also in air and in each agent. Limited crazing data have been obtained also on a dicyano bisphenol polycarbonate in which the CN groups take the place of the methyl groups in bisphenol A (BPA) polycarbonate. The two resins are compared with polystyrene and BPA polycarbonate, respectively, in terms of crazing resistance, swelling, and other properties. In both systems CN incorporation raises ?_c (air) and reduces susceptibility to liquids of low solubility parameter δ; T_g and shear yield stress are raised in the polycarbonate but not in the styrene system. The volume efficiency of CN in raising ?_c (air) is greater in the polycarbonate system than the styrene system; for the rise in polymer solubility parameter, CN efficiency is apparently reversed. These changes are discussed in terms of the differences in molecular architecture of the two systems. For glassy polymers, ?_c (air) is shown to depend in semiquantitative fashion on polymer T_g, δ, and resistance to shear deformation.     

Sorption and diffusion of carbon dioxide in single-phase polystyrene/poly(vinylmethylether) blends

The sorption and transport properties of CO₂ in miscible PS/PVME blends at 20°C are reported as a function of pressure from 1 to 15 atm. The complex shape of isotherms for glassy blends and the concentration-dependent diffusion coefficient for rubbery blends reveal a plasticization by sorbed CO₂. The significant depression in T_g has to be taken into account in the analysis of the sorption data. Diffusion coefficient for CO₂ passes through a minimum when plotted against the blend composition. Such a behavior can be quantitatively related to the negative volume mixing of the PS/PVME system in the framework of the theories based on unoccupied volume. © 1996 John Wiley & Sons, Inc.     

Gas sorption in poly(vinyl benzoate)

High-pressure sorption (up to 50 atm) for CO₂, N₂, and Ar in poly(vinyl benzoate) (PVB) was studied at temperatures from 25 to 70°C by a gravimetric method utilizing an electromicrobalance. The results are described by Henry's law above the glass transition temperature T_g for all gases. The dual-mode sorption model, Henry's law plus a Langmuir isotherm, applies to the sorption isotherms of N₂ and Ar in the glassy state, and the dual-mode parameters are given. For CO₂, a new type of sorption isotherm is observed below T_g. The isotherm is concave to the pressure axis in the low-pressure region and turns into a straight line with increasing CO₂ pressure which can be extrapolated back to the coordinate origin. The linear part of the isotherm is characteristic of the rubbery state, while the nonlinear part stems from glassystate behavior. The “glass transition solubility” of CO₂, at which PVB film changes from the glassy to the rubbery state, decrease as the temperature increases. The disappearance of microvoids, that is, the decrease of the Langmuir capacity, may be due to a large plasticizing effect of sorbed CO₂. The difference between the N₂ and Ar isotherms and the CO₂ isotherm is discussed from this standpoint.     

High‐pressure rheology and viscoelastic scaling predictions of polymer melts containing liquid and supercritical carbon dioxide

High‐pressure rheological behavior of polymer melts containing dissolved carbon dioxide (CO₂) at concentrations up to 6 wt % were investigated using a high‐pressure extrusion slit die rheometer. In particular, the steady shear viscosity of poly(methyl methacrylate), polypropylene, low‐density polyethylene, and poly(vinylidene fluoride) with dissolved CO₂ were measured for shear rates ranging from 1 to 500 s^?1 and under pressure conditions up to 30 MPa. The viscosity of all samples revealed a reduction in the presence of CO₂ with its extent dependent on CO₂ concentration, pressure, and the polymer used. Two types of viscoelastic scaling models were developed to predict the effects of both CO₂ concentration and pressure on the viscosity of the polymer melts. The first approach utilized a set of equations analogous to the Williams–Landel–Ferry equation for melts between the glass‐transition temperature (T_g) and T_g + 100 °C, whereas the second approach used equations of the Arrhenius form for melts more than 100 °C above T_g. The combination of these traditional viscoelastic scaling models with predictions for T_g depression by a diluent (Chow model) were used to estimate the observed effects of dissolved CO₂ on polymer melt rheology. In this approach, the only parameters involved are physical properties of the pure polymer melt that are either available in the existing literature or can be measured under atmospheric conditions in the absence of CO₂. The ability of the proposed scaling models to accurately predict the viscosity of polymer melts with dissolved high‐pressure CO₂ were examined for each of the polymer systems. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 3055–3066, 2001     

High-pressure calorimetric study of plasticization of poly(methyl methacrylate) by methane,ethylene, and carbon dioxide

Glass transition in the system poly(methyl methacrylate)/compressed gas was studied as a function of the gas pressure p using a high-pressure Tian-Calvet heat flow calorimeter. Measurements were made on PMMA-CH₄-C₂H₄, and ;-CO₂ at pressures to 200 atm. All three gases plasticize the polymer leading to depression of the glass transition temperature T_g. Trends in the T_g depression were the same as those reported for the solubility of these gases in PMMA; the higher the solubility the larger the depression in T_g. CO₂ was found to be the most effective plasticizer producing a depression of about 40°C at a pressure of about 37 atm. In the low-pressure limit, the pressure coefficient of the glass transition temperature (dT_g/dp) was found to be about −0.2°C atm^-1 for PMMA-CH₄, the same as that observed for polystyrene-CH₄. For PMMA-C₂H₄, the pressure coefficient was −0.7°C atm^-1, which is lower than the value of −0.9°C atm^-1 observed for PS-C₂H₄. The pressure coefficient for PMMA-CO₂ was found to be about −1.2°C atm^-1, which is larger than the value of −0.9°C atm^-1 observed for PS-CO₂. © 1996 John Wiley & Sons, Inc.     

Synthesis and characterization of polycarbonates based on bisphenol S by melt transesterification

Several sulfone-containing polycarbonates, having inherent viscosity 0.25–0.30 dL g⁻¹ in N,N-dimethylformamide (DMF), were prepared by melt polycondensation of diphenyl carbonate (DPC) with various aromatic and aliphatic diols, in the presence of zinc acetate as transesterification catalyst. The polycarbonates were examined with IR spectra, inherent viscosity, solubility, tensile strength, contact angle, DSC and TGA. Almost all polymers were soluble in DMF, pyridine, N-methyl pyrrolidinone (NMP), THF, phenol and dimethylsulfoxide (DMSO), partially soluble in nitrobenzene, but insoluble in acetone. Polycarbonate with introduced ether linkages leads to enhanced flexibility and elongation strength. The contact angle of the polycarbonate based on bisphenol S was found in the range 42–80°, smaller than that of polycarbonates based on bisphenol AF and bisphenol A. The wettability of polycarbonate films based on bisphenol S remarkably increased with increasing oxyethylene unit in polymer chain. The smaller values of T_d of PC-3-PC-7 than of PC-1 is attributed to the flexible ether linkage. The thermal stability of a brominated aromatic polycarbonate (PC-2) is less than that of the unbrominated one (PC-1). The brominated aromatic polycarbonate (PC-2) has good flame retardency, as indicated by the large limiting oxygen index 56. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 2453–2460, 1997     

Gas transport properties of poly(arylether bissulfone)s and poly(arylether bisketone)s

The transport properties of the poly(arylether bissulfone) based on bisphenol A (PBSF) and the poly(arylether bisketone) s based on bisphenol A (PBK) and bisphenol S (PBK-S) are reported at 35°C. Comparisons are made with the polysulfone and the polycarbonate also based on bisphenol A to determine the effect of the long, rigid bisketone and bissulfone groups on polymer properties. A direct comparison also is made between PBK and PBSF, which differ only by their ketone and sulfone groups. The bulkier sulfone group increases free volume and T_g more than the ketone group. This results in higher solubility and diffusivity coefficients for the bissulfone versus the bisketone polymer, both of which contribute to higher permeability coefficients. © 1993 John Wiley & Sons, Inc.     

A new technique for measuring retrograde vitrification in polymer–gas systems and for making ultramicrocellular foams from the retrograde phase

A stepwise temperature‐ and pressure‐scanning thermal analysis method was developed to measure glass‐transition temperature T_g in the two‐phase polymer–gas systems as a function of gas pressure p, and was used to confirm recent theoretical predictions that certain polymer–gas systems exhibit retrograde vitrification, that is, they undergo rubber‐to‐glass transition on heating. A complete T_g‐p profile delineating the glass–rubber phase envelope was established for the PMMA‐CO₂ system. The retrograde vitrification behavior observed, where at certain gas pressures the polymer exists in the rubbery state at low and high temperatures and in the glassy state at intermediate temperatures, was similar to that reported previously based on the creep‐compliance measurements. The existence of the rubbery state at low temperatures was used to generate foams by saturating the polymer with CO₂ at 34 atm and at temperatures in the range −0.2 to 24 °C followed by foaming at temperatures in the range 24 to 90 °C. Foams with very fine cell structure never reported before could be prepared by this technique. For example, PMMA foams with average cell size of 0.35 μm and cell density of 4.4 × 10¹³ cells/g were prepared by processing the low temperature rubbery phase. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 716–725, 2000     

Rheological and mechanical properties of antiplasticized and rubber-toughened bisphenol A polycarbonate

The addition of a high-T_g aromatic diluent to bisphenol A polycarbonate (PC) reduced T_g and melt viscosity while raising elastic modulus and yield stress substantially. Ultimate tensile elongation and impact toughness were badly affected. However, the addition to these antiplasticized blends of a small amount of a rubber modifier restored impact toughness and elongation but left the blend with increased melt fluidity and ambient stiffness re: neat PC. The key to this rebalancing of the properties of PC was found to be the disappearance of the plane strain crack instability that is a hallmark of the neat resin. The deformation mechanism in all the rubber-containing blends in all failure tests, regardless of geometric constraint and strain rate was found to be shear flow alone. The large plastic zone seen at the plane strain crack tip appears to involve rubber particle cavitation as well. © 1995 John Wiley & Sons, Inc.     

Transport of carbon dioxide and methane in glassy aromatic polyesters

Solubilities and diffusivities of CO₂ and CH₄ in two aromatic polyesters [Ardel® poly(bisphenol A phthalate) (PAr) and poly(phenolphthalein phthalate) (PPha)] and one polycarbonate [Lexan® (PC)], generated from independent sorption and permeation measurements at 35°C and up to 25 atm, are compared. The permeability ratio for CO₂ over CH₄, at 20 atm and 35°C, ranges from 24 for PC, to 21 for PAr, and 27 for PPha. However, the permeability of PPha and PAr are 40 and 120% higher, respectively, than that of PC. Less than 21% change in the gas diffusivity was observed; therefore, a major portion of the observed higher permeability of PPha and PAr is attributed to an increase in the gas solubility. These data are interpreted qualitatively in terms of changes in the calculated packing density, chain torsional mobility of the polymer, and gas-polymer attraction.     

Electrical properties of a novel fluorinated polycarbonate

The relative permittivity, loss and dielectric strength have been measured for a polycarbonate-based material, tetraaryl bisphenol A polycarbonate, that has been fluorine substituted (DiF p-TABPA-PC). The new material has a glass transition temperature, T_g = 489 K, that is higher than that for either conventional bisphenol A polycarbonate (BPA-PC) for which T_g = 421 K or for a copolymer of tetraaryl bisphenol A (TABPA) and bisphenol A (BPA) (TABPA-BPA-PC) for which T_g = 464 K. In addition, the dielectric strength of DiF p-TABPA-PC is almost identical to that for purified BPA-PC and slightly larger than the value for TABPA-BPA-PC. The relative permittivity and loss measurements were carried out from 10 to 10⁵ Hz over a wide temperature range and at pressures up to 0.25 GPa. Variable temperature results for the α relaxation and both temperature and pressure results for the γ relaxation regions are reported. The α relaxation exhibits standard behavior. The γ relaxation exhibits unusual characteristics such as a strong increase in peak height as temperature increases and a strong decrease in peak height with increasing pressure. The data for the γ relaxation have been analyzed using several formulations. Expressions for the peak height and peak position based on a two state (inequivalent well) model and the resulting parameters are discussed in terms of the insight they provide into the molecular mechanisms responsible for the sub-T_g relaxation. Ab initio SCF results for a related model compound are presented. Finally, the real part of the relative permittivity for the new polymer is about 10% higher than for BPA-PC.     

Phase transition of polycarbonate in blends with liquid crystal

Phase transition temperatures of polycarbonate film consisting of micron-sized liquid crystalline droplets were investigated using differential scanning calorimetry (DSC) and thermo-optical analysis (TOA) methods. Both a decrease in (T _g ) and (T _m ) of the polycarbonate with an increase of liquid crystal (LC) content in the sample were observed. The decrease ofT _g is related to the plastifying effect of a low molecular weight LC substance remaining soluble in the polycarbonate matrix. A fraction of the liquid crystal contained in the droplets was estimated on the basis of theT _g decrease.     

Phosphonyl/hydroxyl hydrogen bonding–induced miscibility of poly(arylene ether phosphine oxide/sulfone) statistical copolymers with poly(hydroxy ether) (phenoxy resin): Synthesis and characterization

High molecular weight bisphenol A or hydroquinone‐based poly(arylene ether phosphine oxide/sulfone) homopolymer or statistical copolymers were synthesized and characterized by thermal analysis, gel permeation chromatography, and intrinsic viscosity. Miscibility studies of blends of these copolymers with a (bisphenol A)‐epichlorohydrin based poly(hydroxy ether), termed phenoxy resin, were conducted by infrared spectroscopy, dynamic mechanical analysis, and differential scanning calorimetry. All of the data are consistent with strong hydrogen bonding between the phosphonyl groups of the copolymers and the pendent hydroxyl groups of the phenoxy resin as the miscibility‐inducing mechanism. Complete miscibility at all blend compositions was achieved with as little as 20 mol % of phosphine oxide units in the bisphenol A poly(arylene ether phosphine oxide/sulfone) copolymer. Single glass transition temperatures (T_g) from about 100 to 200°C were achieved. Replacement of bisphenol A by hydroquinone in the copolymer synthesis did not significantly affect blend miscibilities. Examination of the data within the framework of four existing blend T_g composition equations revealed T_g elevation attributable to phosphonyl/hydroxyl hydrogen bonding interactions. Because of the structural similarities of phenoxy, epoxy, and vinylester resins, the new poly(arylene ether phosphine oxide/sulfone) copolymers should find many applications as impact‐improving and interphase materials in thermoplastics and thermoset composite blend compositions. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1849–1862, 1999