Thermal and rheological properties of miscible polyethersulfone/polyimide blends

Blends of an aromatic polyethersulfone (commercial name Victrex) and a polyimide (commercial name Matrimid 5218), the condensation product of 3,3′,4,4′-benzophenone tetracarboxylic dianhydride and 5(6)-amino-1-(4′-aminophenyl)-1,3,3′-trimethylindane, were studied by differential scanning calorimetry, dynamic mechanical analysis, and rheological techniques. The blends appeared to be miscible over the whole range of compositions when cast as films or precipitated from solution in a number of solvents. After annealing above the apparent phase boundary, located above T_g, the blends were irreversibly phase separated indicating that the observed phase boundary does not represent a true state of equilibrium. Only a narrow “processing window” was found for blends containing up to 20 wt % polyimide. Rheological measurements in this range of compositions indicated that blending polyethersulfone with polyimide increases the complex viscosity and the elastic modulus of the blends. For blends containing more than 10 wt % polyimide, abrupt changes in the rheological properties were observed at temperatures above the phase boundary. These changes may be consistent with the formation of a network structure (due to phase separation and/or crosslinking). Blends containing less than 10 wt % polyimide exhibited stable rheological properties after heating at 320°C for 20 min, indicating the existence of thermodynamic equilibrium.     

Rodlike/flexible polyimide composite films prepared from soluble poly(amic diethyl ester) precursors: Miscibility,structure, and properties

Homogeneous precursor/precursor solutions with various compositions were obtained with appreciably high solid contents in N-methyl-2-pyrrolidone from soluble poly(amic diethyl ester) precursors of rodlike poly(p-phenylene biphenyltetracarboximide) (BPDA-PDA) and flexible poly(4,4′-oxydiphenylene biphenyltetracarboximide) (BPDA-ODA), which are hydrolytically more stable as well as more soluble than the corresponding poly(amic acid)s being equilibrated with the constituent monomers. Both optical microscopic and light scattering measurements showed that the dried precursor blend films and resultant polyimide composite films were optically transparent, regardless of compositions and process conditions. The composite films showed a single T_g behavior. However, for the composite of 30 wt % BPDA-PDA dispersed in the matrix of 70 wt % BPDA-ODA, a smectic crystalline-like aggregation of the BPDA-PDA component was detected on wide-angle x-ray diffraction patterns, indicative of microscopic phase separation between the two components. This phase separation was not detected on the optical microscopy, light scattering, and dynamic mechanical thermal analysis because of their resolution limits: Optical microscopy has a resolution of submicrometers, whereas dynamic mechanical thermal analysis and light scattering have a resolution of ca. 50 Å. Therefore, it is speculated that in the composite films BPDA-PDA and BPDA-ODA polyimide molecules have demixed on the scale of a few nanometers. The mean long periodicity, which was estimated from the small-angle x-ray scattering pattern, varied from 134 to 170 Å as the content of BPDA-ODA component increased. In addition, mechanical properties of the composite films were characterized. ©1995 John Wiley & Sons, Inc.     

Chain orientation and anisotropies in optical and dielectric properties in thin films of stiff polyimides

Thin films of poly(p-phenylene biphenyltetracarboximide) (BPDA-PDA), prepared by thermal imidization of the precursor poly(amic acid) on substrates, have been investigated by optical waveguide, ultraviolet-visible (UV-VIS), infrared (IR), and dielectric spectroscopies. The polyimide films exhibit an extraordinarily large anisotropy in the refractive indices with the in-plane index n_∥ = 1.806 and the out-of-plane index n_⊥ = 1.589 at 1064 nm wavelength. No discernible effect of the film thickness on this optical anisotropy is found between films of ca. 2.1 and ca. 7.8 μm thickness. This large birefringence is attributed to the preferential orientation of the biphenyltetracarboximide moieties with their planes parallel to the film surface, coupled with the strong preference of BPDA-PDA chains to align along the film plane. The frequency dispersion of the in-plane refractive index n_∥ is consistent with the results calculated by the Lorentz–Lorenz equation from the UV-visible spectrum exhibiting several absorption bands in the 170–500 nm region. The contribution from the IR absorption in the range 7000–400 cm,^?1 computed by the Spitzer-Kleinmann dispersion relations from the measured spectra, adds ca. 0.046 to the in-plane refractive index n_∥. Tilt-angle–dependent polarized IR results indicate nearly the same increase for the out-of-plane index n_⊥. Application of the Maxwell relation then leads to the out-of-plane dielectric constant ε^⊥ ? 2.7 at 1.2 × 10¹³ Hz, as compared with the measured value of ca. 3.0 at 10⁶ Hz. Assuming this small difference to remain the same for the in-plane dielectric constants ε_∥, we obtain a very large anisotropy in the dielectric properties of these polyimide films with the estimated in-plane dielectric constant ε_∥ ? 3.4 at 1.2 × 10¹³ Hz, and ε_∥ ? 3.7 at 10⁶ Hz. © 1992 John Wiley & Sons, Inc.     

Structure and properties of blends containing ethylene-methacrylate copolymers

The preparation, melting point, degree of crystallinity, mechanical properties, and morphology of a family of blends composed of a transition-metal-neutralized carboxylate semicrystalline ionomer (metal-neutralized ethylene-methacrylate copolymer) and an amorphous copolymer (styrene-4-vinyl pyridine copolymer) are described. These polymeric materials contain low levels (≤ 10.0 mol %) of interacting groups which are capable of forming interpolymeric complexes. These interactions are best described as transition metal-pyridine coordination complexes. A general characteristic of these blend systems is that the mechanical properties and morphology are directly influenced by the nature of the counterion and the specific composition ratio of amorphous to semicrystalline component. A nontransition metal counterion (sodium) is weakly interacting at best, while a transition metal counterion (zinc) is strongly interacting. Morphological studies (polarized-light microscopy and small-angle light-scattering measurements) confirm that the glassy component, if nonassociating, resides primarily in the interspherulite region, while the associating species will behave in a similar manner only after the stoichiometric ratio is reached. The morphology directly influences the stress-strain behavior of these blends. It is noteworthy that the spherulite size remains unchanged with nonassociating blends while a 50% reduction is noted in the associating blends. Thermal and wide-angle x-ray scattering measurements confirm the lamellar structure is unaffected by these associations. © 1992 John Wiley & Sons, Inc.     

Microdeformation in thin films of 3FDA/PMDA polyimide and polyimide nanofoams

Transmission electron microscopy has been used to investigate the microdeformation behavior of thermally imidized thermoplastic pyromellitic dianhydride/1,1-bis(4-amino-phenyl)-1-phenyl-2,2,2 trifluoroethylene (3FDA/PMDA) polyimide films with a T_g of ～ 440°C, prepared by solution casting of a polyamic ester precursor. Failure of the films at room temperature was by unstable cracking at about 5% strain, accompanied by homogeneous shear deformation at the crack tips. As the temperature was raised to above 100°C, zones of mixed shear and crazing were observed, and a stick-slip mode of cracking. Above about 300°C shear was once again the dominant deformation mechanism and the films became fully ductile. In films containing porosity on a scale of a few nanometers, prepared by thermal degradation/imidization of a 3FDA/PMDA/poly α-methyl styrene graft copolymer, film failure at room temperature was also by unstable cracking, but a zone of multiple craze-like features was observed at crack tips, rather than a single shear deformation zone. The increase in extent of this zone of craze-like features as the temperature was raised was again associated with an increase in crack stability. ©1995 John Wiley & Sons, Inc.     

Comparative studies of flexible aliphatic ternary/binary benzoxazines and their copolymers: Thermal and dynamic mechanical properties

Aliphatic ternary benzoxazine (Bz) based from triamine with long chain, as well as flexible binary Bz, was successfully synthesized, which was named as BzT and BzD respectively. The corresponding polybenzoxazines (PBz) rooting from BzT and BzD (PBzT and PBzD) respectively and their copolybenzoxazines (co-PBzs) were obtained to improve the mechanical and thermal properties via chemical cross-linking. The onset polymerization temperatures of the copolymers decreased from 189.1°C to 143.9°C, and the exothermic peak temperature reduced significantly from 232.5°C to 217°C as the content of BzT increased from 0 wt% to 100 wt% in the copolymers. The value of char yield at 800°C increased gradually from 21.5 wt% for PBzD to 28.7 wt% for PBzT. The increasing crosslink density resulted higher glass transition temperatures and improved storage moduli in glassy region because of the introduction of BzT.     

Sorption and diffusion of water vapor in polyimide films

Sorption and diffusion of water vapor are investigated gravimetrically for polyimide films. The activity dependence of the solubility and diffusion coefficients, S and D, respectively, is classified under four types: (1) constant S and D type, (2) dual-mode sorption and transport type, (3) dual-mode type followed by a deviation due to a plasticization effect at high vapor activity, and (4) constant S and D type followed by a deviation due to water cluster formation at high activity. For the dual-mode type, the Henry's law component is much larger than the Langmuir component except at low activity, and therefore deviation in behavior from the first type is small. S is larger for polyimides with higher content of polar groups such as carbonyl, carboxyl, and sulfonyl. D is larger for polyimides with a higher fraction of free space, with some exceptions. The polyimide from 3,3′,4,4′-biphenyltetracarboxylic dianhydride and dimethyl-3,7-diaminodibenzothiophene-5, 5-dioxide belongs to the third type and displays both large S and large D. The polyimide from 2,2-bis(3,4-dicarboxyphenyl) hexafluoropropane dianhydride and 4,4′-oxydianiline belongs to the fourth type, and has the largest D but rather small S because of the hydrophobic C(CF₃)₂ groups. © 1992 John Wiley & Sons, Inc.     

Mean centering of ratio spectra as a new spectrophotometric method for the analysis of binary and ternary mixtures

In this paper a new and very simple method was developed for the simultaneous determination of binary and ternary mixtures, without prior separation steps. This method is based on the mean centering of ratio spectra. The mathematical explanation of the procedure is illustrated. After modeling procedure, the method has been successfully applied to the simultaneous analysis of binary mixtures of mefnamic acid and paracetamol and ternary mixtures of acetylsalysilic acid, ascorbic acid and paracetamol. The analytical characteristics of the method such as detection limit, accuracy, precision, relative standard deviation (R.S.D.) and relative standard error (R.S.E.) was calculated. The results showed that the proposed method is simple, rapid, accurate and precise method for analysis of binary and ternary mixtures.     

Phase behaviour of star-shaped binary mixtures of triphenylbenzenes,triphenylboroxines and triphenyltriazines

ABSTRACT

Star-shaped nonaalkoxy-1,3,5-triphenyltriazines were prepared and their mesomorphism was investigated by differential scanning calorimetry (DSC), polarised optical microscopy (POM) and X-ray diffraction (WAXS and SAXS). Compounds with chain lengths C₉ – C₁₂ displayed enantiotropic hexagonal columnar mesophases over a wide range of temperature. Their similarity in molecular size and mesomorphism prompted us to study their binary mixtures with previously reported planar 1,3,5-triphenylboroxines and propeller-shaped 1,3,5-triphenylbenzenes. All three compounds are fully miscible in their hexagonal columnar mesophases, but mixtures of planar with propeller-shaped compounds generated columnar stacks that contain only one type of molecule to avoid their shape incompatibility. However, the two types of columnar stacks were fully miscible which circumvented macroscopic phase separation.     

Influence of curing temperature on the optical properties of fluorinated polyimide thin films

The influence of curing temperature (CT) on the optical properties of 6FDA/ODA poly(amic acid)-polyimide (PAA-PI) films was characterized by measuring ATR-FT-IR spectra, refractive index (RI) and birefringence of the films. The results showed that the infrared absorption intensity of characteristic peaks (IAICP) corresponding to the imide ring and the RI of PAA-PI films reached their maxima when the films had been cured at 270 °C, while the magnitude of birefringence (|Δn|) of the films reached its minimum as CT rose up to 330 °C. However, the RI decreased as CT was between 270 °C and 330 °C. Both the RI and |Δn| of the film increased obviously when CT increased after 330 °C. We think this is due to the interchain crosslink reaction (ICCR) above 330 °C and can be an evident proof of ICCR. And the evidences supporting ICCR was also discussed via IR differential spectra.     

Mesomorphic and ferroelectric properties of FLCP/FLC binary mixtures

We have prepared several ferroelectric polysiloxanes with two and three benzenic ring moieties. The siloxane backbone is favorable to ferroelectric S phase formation, and the chiral S phase is observed in all of the polymers. Some of the spontaneous polarizations are very high, more than 100 nC/cm² (10^?3 C/m²) and the response times are less than 1 ms near the I-S or S_a–SS transition. Several binary mixtures between FLC copoly-siloxanes and different low molar mass LC have been studied, and have shown the complete miscibility of these two components and richer mesomorphic sequences than for the polymers alone; for example, an N^*–S_a sequence.     

Preparation, structure and properties of porous polyimide films via PAA/PU alloy

A new route to porous polyimide (PI) films with pore sizes in the nanometer regime was developed. A polyamic acid (PAA)/polyurethane (PU) blend with PU as the disperse phase was first prepared via in situ polymerization of pyromellitic dianhydride and 4,4-oxydianiline in PU solutions. Porous PI films were obtained from PAA/PU films by thermolysis of PU at 360°C and imidization of PAA at 300°C, respectively. Fourier transform infrared spectroscopy and thermal gravimetric analysis were used to detect the imidization and thermolysis processes of PAA/PU blends under thermal treatment. The microporous structure of the PI films was observed by transmission electron microscopy. It was found that the size and content of pores increased with an increase in the PU mass fraction in the PAA/PU blend up to 20%. Because of the existence of nanopores, the dielectric constant of PI films decreased by a wide margin and was less than 2.0 at a PU mass fraction of 20%. It implies that this is an effective means to reduce the dielectric constant of PI, but it also causes the decrease of tensile strength and the rise of water absorption. Translated from Chemistry Journal of Chinese Universities 2006, 27(1): (in Chinese)     

Structure and infrared emissivity of silicon-containing polyimide/BaTiO3 nanocomposite films

Silicon-containing polyimide/BaTiO₃ nanocomposite films were prepared by the direct mixing of silicon-containing polyamic acid and BaTiO₃ nanoparticles under ultrasonic wave irradiation, followed with thermal imidization. Structure and thermal properties were measured with FTIR, XPS, SEM, DSC and TGA. The results showed that the compatibility of BaTiO₃ and a polyimide might be improved by the introduction of dimethylsilylene groups into the backbone of a polyimide; and BaTiO₃ nanoparticles in the nanocomposites tended to form clusters. The clusters coalesced into a more uniform structure at a higher BaTiO₃ filling than at a lower one.The interfacial interaction between BaTiO₃ and the silicon-containing polyimide resulted in the increase of the glass transition and the thermal decomposition temperature. It was found that the nanocomposites exhibited lower infrared emissivity value than the pure polyimide and the magnitude of infrared emissivity value was related to the content of BaTiO₃ in the nanocomposites.     

Excess properties of binary alkanol-ether mixtures and the application of the ERAS model

Experimental results are reported of excess molar volumes V^E and excess molar enthalpies H^E for binary mixtures of 1-propanol, 2-propanol, 1-butanol and 2-butanol with diisopropyl ether (DIPE) and dibutyl ether (DBE) at 298.15 K. A vibrating-tube densitometer was used to determine V^E, and H^E was measured using a quasi-isothermal flow calorimeter. The applicability of the ERAS model has been investigated for describing the experimental data as well as literature data of alkanol-ether mixtures containing DBE or dipropyl ether (DPE).     

Caloric properties of mixtures of refrigerants R22 / R114

The nonazeotropic refrigerant mixture chlorodifluoromethane (R22) and 1,2-dichlorotetrafluoroethane (R114) has been frequently suggested as a working fluid in cooling systems and heat pump applications. However, especially for mixtures exact and reliable measurements of the caloric properties are often missing, so that calculations with equations of state yield results of great uncertainty. In spite of the CFC-ozone problem of this mixture it can be considered as an exemplary mixture to set up accurate equations of state.

Therefore measurements with an isenthalpic throttle calorimeter were carried out for three different compositions of the mixture. The measured isenthalps could be reproduced within the experimental accuracy by polynomials. Together with the specific heat capacity of the pure components the measurements lead to several caloric properties in the liquid-, vapour- and critical region. The caloric properties can also be calculated by equations of state (EOS). It turned out that the results obtained from Bender's EOS with interaction parameters fitted to the experiments lead to a good agreement with the experimental data.     

Dielectric properties of binary mixtures of n-methylbenzenesulfonamide

The dielectric permittivities of binary mixtures of N-methylbenzenesul-fonamide (N-MBS) with benzyl alcohol, 1,2-dichloroethane, 1,4-dioxane and hexamethylphosphortriamide were measured as a function of mole fraction over the whole composition range at 30 and 50°C. The excess dielectric permittivities and the excess molar polarizations were also calculated. The excess dielectric permittivities ^E and excess molar polarizations P_E were found to be negative for N-methylbenzene-sulfonamide mixtures with benzyl alcohol and 1,4-dioxane, ^E values were positive and P^E values negative for mixtures with 1,2-dichloroethane, and ^E and P^E values were clearly positive for mixtures with hexamethylphosphortriamide. The results are discussed in terms of the strength of the dipolar and hydrogen-bonding interactions between the molecules in various binary mixtures.     

Densities and excess molar volumes for binary mixtures of N,N-dimethylformamide+ 1,2-dimethoxyethane

Densities are reported for N,N-dimethylformamide and 1,2-dimethoxyethane binary mixtures at different mole fractions covering the whole miscibility range and at 19 temperatures ranging from –10 to 80°C. The experimental density data have been fitted by empirical relations and the excess volumes by a Redlich-Kister equation. The 11 N,N-dimethylformamide and 1,2-dimethoxyethane adduct appears to be stable throughout the temperature range. A comparison with other DMF containing mixtures is made.     

NMR studies of water in polyimide films

Commercial polyimide films containing up to ～ 3 wt % water have been studied by proton, deuteron, and oxygen-17 nuclear magnetic resonance (NMR). Comparisons between NMR results and previous dielectric relaxation (DR) results for a variety of Kapton films show that there is a one-to-one correspondence between specific dielectric loss peaks and features of the ²H or ¹⁷O NMR spectra. It is concluded that water molecules, which interact only weakly with the polymer, reside in the polyimide matrix in two configurations, randomly oriented single molecules and chains of water molecules oriented perpendicular to the plane of the film. The correspondence between NMR and DR observed in water in Kapton extends to water in Upilex and to methanol and acetic acid in Kapton. © 1995 John Wiley & Sons, Inc.     

Preparation and properties of polysilsesquioxanes: Polysilsesquioxanes and flexible thin films by acid‐catalyzed controlled hydrolytic polycondensation of methyl‐ and vinyltrimethoxysilane

Polymethylsilsesquioxane (PMS) and polyvinylsilsesquioxane (PVS) were prepared by acid‐catalyzed controlled hydrolytic polycondensation of methyl‐ and vinyltrimethoxysilane (MTS and VTS), respectively. The spinnabilities and molecular weights of polysilsesquioxanes were easily controlled by the reaction conditions, such as the molar ratios of water, hydrochloric acid, and methanol to MTS or VTS; nitrogen flow rate; temperature; and stirring rate. PMS and PVS showed spinnability of more than 200 cm when their molecular weights were up to 42,000 (PMS) and 19,000 (PVS) M_w. Transparent, colorless, and flexible films of 0.02–0.10 mm thick were prepared by casting a 20 wt % acetone–methanol (V/V = 1) solution of PMS and PVS on a polymethylpentene shale, followed by heating at 80°C for 3 weeks. The tensile strength of the films, approximately 26 (PMS) and 17 (PVS) MPa, was found to be correlated with the structure of the polysilsesquioxanes. The surface contact angle and electroconductivity of films were also measured. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1017–1026, 1999     

Characterization of thermal diffusion of polystyrene in binary mixtures of THF/dioxane and THF/cyclohexane

The thermal diffusion coefficient (D_τ) was determined for three polystyrene standards of different molecular masses in binary mixtures of tetrahydrofuran/dioxane and tetrahydrofuran/cyclohexane of various compositions. The D_τ values were obtained by combining retention data from thermal field-flow fractionation measurements with diffusion data from dynamic light scattering experiments. In agreement with earlier work of Schimpf and Giddings, the thermal diffusion coefficient was found to be virtually independent of the molecular mass of the polymers. In the binary mixtures of tetrahydrofuran and dioxane, both good solvents for polystyrene, the D_τ value was approximately equal to the average of the D_τ values in the pure solvents, weighted according to the mole fractions of the solvents in the mixture. However, for polystyrene in binary mixtures of tetrahydrofuran and cyclohexane this linear behavior of the thermal diffusion phenomenon was not observed. The addition of cyclohexane to tetrahydrofuran has initially only a minor effect on the molecular and thermal diffusion coefficients of the polystyrene standards. Because cyclohexane is a theta solvent for polystyrene, the preferential solvation of polystyrene by tetrahydrofuran could be an explanation for these results. © 1996 John Wiley & Sons, Inc.