Hexafluoroisopropylidene Bis Research Articles

Branched polyamide/poly (acrylonitrile) blend membranes: synthesis, characterisation and pervaporation applications

ABSTRACTHerein, a novel branched polyamide (BPA-1and BPA-2) was synthesised by direct polycondensation using branched polyethyleneimine and two different dicarboxylic acids (adipic acid and Hexafluoroisopropylidene bis benzoic acid) as monomers. The newly developed BPA was blended with poly (acrylonitrile) (PAN) separately at ratio of 3:1 (BPA/PAN) to form a branched BPA/PAN membrane via the solution-casting method. The prepared membrane was characterised using FTIR, X-ray, SEM and TGA and so that used for the dehydration of alcohols by pervaporation process. The experimental results revealed that the permeation flux of the BPA/PAN membrane increased with increasing feed ethanol concentration and feed temperature, but an increase in the number of carbon atoms inalcohol results in an increase in the permeation rate. The best separation performance could be achieved for the BPA-2/PAN membrane at 60°C for 80% ethanol in the feed with a total flux of 925 g m−2 h−1 and a separation selectivity of 1696.

Some aspects of polybenzimidazoles’ synthesis in Eaton reagent under different temperatures and microwave irradiation

Solution polycondensations of 3,3′-diaminobenzidine with two dicarboxylic acids, 4,4′-oxybis(benzoic acid) and hexafluoroisopropylidene bis(benzoic acid) to obtain two different polybenzimidazoles, OPBI and CF3PBI, correspondingly, were studied in terms of formation of processable polymers and insoluble crosslinked gel. The syntheses were conducted in Eaton’s reagent using conventional heating (CH) at 100, 140 and 180 °C and microwave irradiation (MW) at 90 and 100 °C. The content of gel fraction was lesser using high temperature conditions under CH. The MW-assisted syntheses resulted in acceleration of polycondensations, but an abrupt growth of the insoluble gel was also observed under these conditions. The FTIR data showed that MW irradiation stimulated the side acylation reactions, and OPBI suffered more from the side acylation than CF3PBI.

Eaton’s reagent in polybenzimidazole synthesis

The polycondensations of 3,3′-diaminobenzidine with two acids, 4,4′-oxybis(benzoic acid) and hexafluoroisopropylidene bis(benzoic acid), were conducted in Eaton’s reagent at the unusually high temperature of 180°C and under microwave irradiation at 90°C. Both protocols resulted in soluble polybenzimidazoles, OPBI and CF3PBI, of high molecular weights in very short reaction times. The synthesized polybenzimidazoles exhibited high thermostability and excellent mechanical properties. The influence of the reaction conditions on the polymer structure and molecular weights was studied. The “microwave effect” was demonstrated by comparison of the polycondensations conducted under microwave irradiation and conventional heating.

Effect of substituent polarity, bulk, and substitution site toward enhancing gas permeation in dibromohexafluorobisphenol‐a based polyarylates

AbstractThe gas permeation properties of polyarylates were tuned by varying nature and site of substituents present on both of its monomers, viz., bisphenol and dicarboxylic acid. The phenyl rings of hexafluorobisphenol‐A were substituted in asymmetric manner by polar bromine to obtain dibromohexafluorobisphenol‐A. This bisphenol was polymerized with equimolar mixture of iso‐ and terephthalic acid (base case), bromo‐ and nitroterephthalic acid (polar group substituted acids), 4,4′‐hexafluoroisopropylidene bis(benzoic acid), and t‐butyl isophthalic acid (bulky group containing acids). Physical properties and gas permeation properties of these polyarylates were investigated to assess combined effects of asymmetric nature of bisphenol substitution, polar nature of substituent bromine, hexafluoroisopropylidene group present at the bridge position of bisphenol, and substituent present on the acid moiety. The combination of these substituent types led these polyarylates to lie near Robeson upper bound. The gas sorption analysis and estimation of diffusivity in these polyarylates shed a light on observed variations in gas permeation properties by attempted structural variations. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 3156–3168, 2007

Synthesis and characterization of polyimides and co-polyimides having pendant benzoic acid moiety

A novel diamine monomer, 2,4-diamino-4′-carboxy diphenyl ether had been synthesized. Several polyimides were prepared by reacting this diamine with commercially available dianhydrides, such as benzophenone tetracarboxylic acid dianhydride (BTDA), 4,4′-bis{hexafluoroisopropylidene bis (phthalic anhydride)}(6-FDA), oxydiphthalic anhydride (ODPA) and 3,3′,4,4′-biphenyltetracarboxylic acid dianhydride (BPDA). Furthermore, copolymers from the resulting diamine and oxydianiline (ODA) with 6 FDA were also synthesized. The inherent viscosities of the polymers were 0.42–0.67dlg−1. The polymers have good solubility in polar aprotic solvents, high thermal stability up to 410°C in nitrogen and high glass transition temperatures (Tg) ranging from 260–330°C. These polymers formed tough flexible films by solution casting.

Optical Properties of Polyimide Thin Films. Effect of Chemical Structure and Morphology

The optical properties of polyimide (PI) thin films with various backbone structures were investigated with prism coupler. PI films were prepared from two types of dianhydrides: pyromellitic dianhydride (PMDA) and 4,4’-hexafluoroisopropylidene bis(phthalic anhydride) (6FDA), and two type of diamines: 4,4’-oxydiphenylene diamine (ODA) and p-phenylene diamine (PDA). To relate the free volume change with refractive indices in PI thin films, the fractional free volume and the average refractive index were estimated for PI thin films. The fractional free volume of PI thin films varied from 0.2168 to 0.3865, and was in the following increasing order: PMDA-PDA < PMDA-ODA < 6FDA-ODA < 6FDA-PDA. The average refractive indices varied from 1.5778 to 1.7427, and were in the following increasing order: 6FDA-PDA < 6FDA-ODA < PMDA-ODA < PMDA-PDA. Morphological structure of the films was characterized with wide-angle X-ray diffraction (WAXD) analysis. The birefringence for different PIs was measured from in-plane and out-of-plane refractive indices using the prism coupler technique. The birefringence of PI film was in the following order: PMDA-PDA > PMDA-ODA > 6FDA-PDA ≍ 6FDA-ODA. Finally the effect of film thickness on birefringence was determined by preparing PI films having various backbone structures with different thickness. Thus effect of morphological structure, including their in-plane orientation and molecular packing on optical properties of PI thin films were studied.

Synthesis and characterization of dye-containing fluorinated polyimide thin films

Lightguiding polyimide based thin films have been extensively studied for their good optical properties. By doping the polyimide matrix with different concentrations of dye molecules, active structures can be produced. In this work, thin films of fluorinated polyimide containing rhodamine B (RB) have been obtained by a two-step solvent based method. The precursor resin has been spin coated on silica substrates and cured at temperatures ranging from 80 to 250°C, providing about 5 μm thick films. 4,4′-Hexafluoroisopropylidene bis diphthalic anhydride (6FDA) and 4,4′-diaminobenzophenone (DAB) have been used as precursor monomers. Dye concentration ranging from 0.5 to 1.5 wt.% has been chosen. Optical emission and absorption spectra have been collected in order to study spectroscopic and aggregation characteristics of rhodamine as a function of doping and curing parameters. The waveguiding properties and the refractive index of the films have been analyzed by prism coupling method.

Damage-depth profiling of ion-irradiated polyimide films with a variable-energy positron beam

Various polyimide layers [2.2–2.6 μm of hexafluoroisopropylidene bis(phthalic anhydride-oxydianiline), pyromellitic dianhydride-oxydianiline, and 3,3′-4,4′-biphenyltetracarboxylic dianhydride-p-phenylenediamine] spin-coated on silicon substrates were studied with a variable-energy positron beam in combination with a Doppler-broadened annihilation radiation technique. From the experiments, the thickness of the layers was estimated with the VEPFIT routine. These values corresponded well to the values determined from interferometry and ellipsometry. Irradiation of the polyimides with 1 × 1015 boron ions/cm2 at an energy of 180 keV led to a strong chemical modification of the irradiated top layer. This caused the inhibition of positronium formation in the irradiated layer, which was observed as a lowering of the annihilation line S parameter. The thickness of the modified layer was estimated to be 700–800 nm. This value did not agree with the ellipsometric measurements but corresponded to the maximum implantation depth of boron ions calculated with TRIM (Transport of Ions in Matter) code. The positron results appeared somewhat larger than the TRIM estimates. Reasons for these relations are discussed. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 3062–3069, 2000

Study on the preparation and properties of copolyimides based on hexafluoroisopropylidene bis(3,4-phthalic anhydride) and 1,12-di(4-aminophenoxy)dodecane

Copolyimides were prepared from hexafluoroisopropylidene bis(3,4-phthalic anhydride) (6FDA), 1,12-di(4-aminophenoxy)dodecane and 4,4′-diaminodiphenylether through a solution co-polycondensation reaction followed by a chemical imidization reaction. It was observed that copolyimides prepared with any diamine molar ratio studied (1,12-di(4-aminophenoxy)dodecane/4,4′-diaminodiphenylether=7/3∽1/9) were soluble in polar organic solvents such as N-methyl-2-pyrrolidone (NMP), N, N-dimethylacetamide (DMA), dimethylformamide (DMF) and m-cresol, tetrahydrofuran (THF) and chloroform, while the corresponding homopolyimides were insoluble. Wide angle X-ray diffraction (WAXD) results show a clear relationship between the crystallinity tendency and the solubility of polyimides. High crystallinity tendency leads to low organo-solubility. The glass transition temperature of a copolyimide was in good agreement with Fox’s equation for random copolymers. The long flexible chains in the backbone of copolyimides are the least thermally stable part.

Study on preparation and properties of polyimides containing long flexible chains in the backbone

Polyimides containing long flexible chains in the backbone were prepared from α,ω-di(4-aminophenoxy)alkanes and hexafluoroisopropylidene bis(3,4-phthalic anhydride) (6FDA), benzophenone-3,3′,4,4′-tetracarboxylic acid dianhydride (BDTA), diphenylether-3,3′,4,4′-tetracarboxylic acid dianhydride (EDTA). Polyimides prepared from 6FDA (except that from 6FDA and α,ω-di(4-aminophenoxy)dodecane) were observed to be soluble in strong polar organic solvents, while those from BTDA and ETDA were not soluble. The glass transition temperature ( T g) of a 6FDA based polyimide decreases with the increase of the length of the flexible chains linearly. The initial thermal decomposition temperatures of polyimides studied were found to be 450∼490°C in N 2 and independent of the length of the flexible chains.

Preparation and properties of novel fluorinated polyimides based on 2,2?,6,6?-tetrafluorobenzidine

Fluorinated polyimides were prepared from 2,2′,6,6′-tetrafluorobenzidine and four conventional dianhydride monomers by a solution polycondensation reaction followed by a chemical imidization. Polyimide based on 2,2′,6,6′-tetrafluorobenzidine and hexafluoroisopropylidene bis(3,4-phthalic anhydride) (6FDA) is soluble in organic solvents such as NMP, DMA, DMF, THF, chloroform, and acetone while those based on 2,2′,6,6′-tetrafluorobenzidine and pyromellitic dianhydride (PMDA), benzophenone-3,3′,4,4′-tetracarboxylic acid dianhydride (BTDA), diphenylether-3,3′,4,4′-tetracarboxylic acid dianhydride (ETDA) are not. Polyimide from 2,2′,6,6′-tetrafluorobenzidine and 6FDA possesses high optical transparency at 350–700 nm and has a in-plane refractive index of 1.558 at 632.8 nm. All polyimides exhibit glass transition temperatures above 350°C. They also possess very high thermal stability. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 1605–1609, 1998

Synthesis and Properties of Highly Fluorinated Polyimides

A series of polyimides was synthesized to facilitate the study of several structure/property relationships, including relative permittivity, moisture absorption, free volume, and viscoelastic transitions. This series was based on hexafluoroisopropylidene bis(phthalic anhydride) and various diamines, with the intention of having a number of fluorine/hydrogen and symmetric/asymmetric analog sets. Since several of the fluorinated diamines were exceptionally unreactive, a multistep polycondensation polymerization technique was developed to obtain materials of sufficient molecular weight for property evaluation. Effects of fluorine incorporation on the aforementioned properties are reported

Cure Studies of Fluorinated Polyamic Acids by Thermal-IR

AbstractThe thermal curing chemistry of a fluorinated polyamic acid based on 6FDA (hexafluoroisopropylidene bis(phthalic anhydride)) and APBP (4,4′-bis(4-aminophenoxy)biphenyl) was studied by thermal-IR spectroscopy. Anhydride formation was observed at intermediate cure temperatures and maximized at approximately 220°C. The degree of anhydride formation was affected by the solvent, being least in 2-methoxyethyl ether and increasing in the solvent order: 2-methoxyethyl ether &lt; NMP &lt; 2-(2-ethoxy)ethoxyethanol. In addition to the back reaction of amic acid to anhydride and amine, at least one additional mechanism of anhydride formation is observed. The onset of the second mechanism of anhydride formation is coincident with the onset of imidization, which leads us to propose that water generated by imidization can react with anhydride during the curing process, before escaping from the film, to form diacid. Cyclization of diacid to anhydride is proposed as the second mechanism of anhydride formation.