Preparation Of Polyimides Research Articles

New fluorene‐based thermally stable five‐ and six‐membered rings polyimides with enhanced solubility

AbstractA novel ester diamine, 9‐(3,5‐diaminobenzoyloxy) fluorene, as a new monomer for preparation of polyimides was synthesized via two successive reactions. In the first step, reaction of 3,5‐dinitrobenzoylchloride with 9‐hydroxy fluorene in the presence of sodium hydroxide led to preparation of 9‐(3,5‐dinitrobenzoyloxy) fluorene. Second reaction was reduction of the nitro groups by tin (II) chloride and fuming hydrochloric acid to produce 9‐(3,5‐diaminobenzoyloxy) fluorene. The new diamine containing bulky fluorene group was characterized and polycondensed with different dianhydrides via two methods to produce polyimides. The new five‐membered and six‐membered ring polyimides were characterized and their properties including solubility behavior, inherent viscosity, thermal behavior and stability, and crystallinity were studied. They exhibited favorable balance of physical and thermal properties and their solubility were improved without sacrificing their thermal stability. Six‐membered rings polyimides showed higher thermal stability and lower solubility in comparison to related five‐membered ring polyimides. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Preparation and properties of polyimide solvent‐resistant nanofiltration membrane obtained by a two‐step method

AbstractThis study investigated the preparation of polyimide solvent‐resistant nanofiltration membranes by a two‐step method (casting the membrane first and then crosslinking by the thermal imidization method). The influences of polymer concentration, thickness of membranes, temperature of the imidization, phase inversion time and thermal imidization procedure were studied. The membranes with the highest rejection rate of Fast Green FCF (molecular weight 808.86 g mol−1) were prepared in the following conditions: polymer concentration 13 wt%, phase inversion time 1 h, membrane thickness 150 µm and thermal imidization procedure 200 °C for 2.5 h, 250 °C for 2 h and 300 °C for 2 h in a vacuum environment; the heating rate was 5 °C min−1. The membrane was stable in most of the solvents tested and the fluxes of some common solvents were equal to or higher than a number of commercial solvent‐resistant nanofiltration membranes. A much higher rejection of dyes in water than in methanol was observed in the filtration experiments and a new way to explain it was developed. Copyright © 2011 Society of Chemical Industry

Environmentally friendly route for the preparation of solvent resistant polyimide nanofiltration membranes

Organic Solvent Nanofiltration (OSN) is an emerging membrane separation process with the potential to replace traditional separation techniques. Its advantages include lower energy consumption than alternatives such as distillation, easy up scaling and flexibility. However, manufacturing OSN membranes involves a number of stages contributing towards the discharge of hazardous chemicals as waste. Thus the environmental advantages of employing OSN are to some extent cancelled out by the waste released during OSN membrane production. This paper describes a process for the preparation of polyimide integrally skinned asymmetric OSN membranes with adjustable molecular weight cut off (MWCO). Previously reported methods for producing polyimide based OSN membranes are modified in the presented work without compromising the performance of the membranes. The toxic solvents used to form polymer dope solution, i.e.dimethylformamide (DMF)/1,4-dioxane are replaced by an environmentally friendly dimethyl sulfoxide (DMSO)/acetone solvent system. In order to further diminish the environmental impact, isopropanol was successfully replaced with water in the crosslinking step. Scanning electron microscope images revealed that membranes with spongy matrix without macrovoids were obtained regardless the DMSO/acetone ratio.

PHASE SEPARATION OF POLY(AMIC ACID-CO-IMIDE) SOLUTION

Poly(amic acid-co-imide) (PA-I) is an intermediate for preparation of polyimide from polyamic acid (PAA). Phase separation does not appear for the solution until a certain imidization degree. The experimental results of a rotation viscometer and FT-IR analysis showed that the critical point of phase separation (CPPS) was related to the imidization methods (thermal or chemical imidization) and the backbone structures (flexible ODPA-ODA or semi-rigid PMDA-ODA). Phase separation time is shorted with the increase of the initial PAA concentration, acetic anhydride amount, or temperature. When phase separation occurs, the solution viscosity increases, while the imidization degree is almost constant as the initial PAA concentration rises. The greater the chain mobility, the higher the imidization degree at phase separation point. At CPPS, higher imidization degree and lower solution viscosity are obtained in the thermal imidization than in the chemical imidization; ODPA-ODA system exhibits higher imidization degree and better solubility than that of PMDA-ODA system.

Synthesis and Characterization of Novel Polyimides Derived from 1,4‐Bis(4‐aminophenoxymethylene) Cyclohexane (BAMC) and Two Aromatic Dianhydrides

A novel diamine monomer containing the alicyclic unit 1,4‐bis(4‐aminophenoxymethylene) cyclohexane (BAMC) was synthesized successfully and employed in the preparation of polyimides with two aromatic dianhydrides by a two‐step procedure. Experimental results indicate that the resulting polyimides show exceptional thermal properties with glass transition temperatures of 306.7°C and 254.4°C, and temperatures at 5% weight loss of 461.5°C and 470.0°C in nitrogen. Wide‐angle X‐ray diffraction measurements reveal that these polyimides are almost amorphous with little crystallization. All of the polyimide films show good transparency in the visible region; the transmittances of the polyimide films at 500 nm are over 70%.

Multi-month thermal aging of electro-optic polymer waveguides: Synthesis, fabrication, and relaxation modeling

The preparation of polyimides containing side-chain chromophores and the long-term aging performance of poled films are described. These materials were compared to guest–host polycarbonate films. Mach–Zehnder optical interferometers were fabricated from these polymers that contained CLD- and FTC-type chromophores. Changes in optical properties were monitored for months at four temperatures ranging from ambient to 110°C. The isothermal relaxation data were modeled using both a stretched exponential equation and a power law in time equation. The temperature dependency of the time constants of these equations was modeled using a new activation-energy equation: ln(τ/τp)=ER(1+tanh[(Tc−T)/D])/2RT+Ep/RT where Tc is the central temperature of the transition zone, D is the breadth of the zone, and Es are the activation energies of rigid and pliable materials. Multi-year high-temperature stability of the poled guest–host and side-chain materials was predicted.

One-pot synthesis of polyimides via Ni-catalyzed coupling of bis(chlorophthalimide)s

A one-pot synthesis method for the preparation of polyimides containing biphenyl units was developed via nickel-catalyzed coupling reaction of bis(chlorophthalimide)s which were prepared from chlorophthalic anhydrides and diamines in xylene. The resulting polyimides had inherent viscosities of above 0.60 dL g −1. In the meantime, the copolymerizations from a mixture of three isomeric bis(chlorophthalimide)s gave the polymers with inherent viscosities of 0.36–0.55 g dL −1. The solubility and film formability of the copolymers were better than those of homopolymers from bis(4-chlorophthalimide). The 10% weight loss of these polyimides was between 470 and 531 °C.

Comparison of one-step and two-step methods of polyimidization and substitution effect in the synthesis of new poly(ester-imide)s with bulky pendent group

New naphthalene-ring containing ester diamines, as new monomers for the preparation of polyimides were synthesized via two successive reactions. Nucleophilic reaction of 3,5-dinitrobenzoylchloride with 1-naphthol and 2-naphthol in the presence of sodium hydroxide led to the preparation of 1- and 2-(3,5-dinitrobenzoyloxy)naphthalene, respectively. Next step was reduction of them by hydrazine hydrate/Pd–C to produce 1- and 2-(3,5-diaminobenzoyloxy)naphthalene. All the prepared compounds were characterized by common spectroscopic methods. These ester containing aromatic diamines with pendent naphthalene group were used to prepare soluble polyimide copolymers via two different methods: catalyzed one-step high-temperature polycondensation in m-cresol, and two-step polycondensation in NMP and subsequent chemical dehydration. The obtained poly(ester-imide)s were characterized and their properties were studied. One-step and two-step methods for the preparation of five-membered ring polyimides were compared. Polymers prepared through one-step method showed higher yield and inherent viscosities and therefore better physical properties.

A novel direct method for preparation of aromatic polyimides via microwave-assisted polycondensation of aromatic dianhydrides and diisocyanates

Possibility of imide structure formation under microwave irradiation of molecules containing anhydride and isocyanate functional groups was investigated. The microwave-assisted polycondensation of aromatic diisocyanates and dianhydrides for preparation of polyimides was studied. The effect of microwave irradiation time and power, solvent nature, solid content of monomers, effect of catalyst, effect of polymerization reactor material and possibility of pressure development during polymerization, on the inherent viscosity of prepared polyimides were discussed. Experimental results showed that polymers obtained via this method had superior inherent viscosity and yield in comparison to the polymers obtained via conventional solution method.

Synthesis and characterization of novel polyimides starting from 1,2‐bis(p‐dimethylaminobenzylideneimino)alkane homologues and various dianhydrides

AbstractThe objective of this research was the preparation of polyimides from 1,2‐bis(p‐dimethylaminophenylimino)alkane homologues and various dianhydrides in N‐methylpyrrolidone by one‐stage polycondensation. The monomers were prepared via condensation of p‐dimethylaminobenzaldehyde and the corresponding diamines, 1,4‐diaminobutane, 1,3‐diaminopropane and 1,2‐diaminoethane. The influence of the incorporation of this moiety into the polymer backbone on the properties of the polyimides has been evaluated. The thermogram of the polyimides indicated that PI‐10 to PI‐32 had Tg values ranging from 181 to 290 °C. The inherent viscosities of the polymers ranged from 0.99 to 2.05 dl g−1, and the highest solubility was obtained without significant loss of the thermal properties. Copyright © 2004 Society of Chemical Industry

Preparation of Polyimides by Using Mixtures of Tetrahydrofuran and Methanol and Their Properties

Reaction conditions of the preparation of solutions of polyamic acids in the tetrahydrofuran/methanol mixed solvent (THF/MeOH) were studied. The polyamic acids were based on pyromellitic dianhydride and 4,4’-oxydianiline. Transparent solutions were prepared at 5 wt% and lower concentrations of polyamic acid in the THF/MeOH mixture with component weight ratio ranging from 4:1 to 1:1. The properties of the final polyimide films were compared with those prepared by using N-methyl-2-pyrrolidone as the solvent.

Preparation and structure of polyimides derived from H complexes of benzophenonetetracarboxylic acid with diaminodiphenyl ether

The possibility of using H complexes of dialkyl dihydrogen 3,3',4,4'-benzophenonetetracarboxylates and 4,4'-diaminodiphenyl ether and of polyimides prepared therefrom as polyimide foam materials, carbon-reinforced plastics, and foam composites was examined.

Preparation and Properties of Novel Aromatic Polyimides from 4,4′-Diamino-4″ -Hydroxytriphenylamine and Aromatic Tetracarboxylic Dianhydrides

Novel aromatic polyimides containing hydroxytriphenylamine units were prepared from 4,4′-diamino-4″-hydroxytriphenylamine 1 and various aromatic tetracarboxylic dianhydrides 2. The glass transition temperatures ( Tgs) of these polyimides were in the range of 274–388 °C and the 10% weight loss temperatures ( T d10s) were above 462 and 511 °C in air and nitrogen respectively. Polyimide 4f prepared from diamine 1 and 4,4′-hexafluoroisopropylidenebis(phthalic anhydride) (6FDA) was soluble not only in organic solvents such as N-methyl-2-pyrrolidone, N, N-dimethylacetamide, N, N-dimethylformamide, 1, 3-dimethyl-2-imidazolidone and dimethyl sulfoxide but also in tetramethylammonium hydroxide aqueous solution. Other resulting polyimides were not soluble in organic solvents. The resulting polyimides 4 possessed Tgs about 20–70 °C higher and poorer solubilities than the previously reported polyimides prepared from 4,4′-diaminotriphenylamine and various aromatic tetracarboxylic dianhydrides. These results indicated that polymer properties such as thermal behaviour and solubilities were influenced by the intermolecular interaction of hydrogen bonding due to hydroxy units.

Preparation of polyimides derived from biphenyltetracarboxylic dianhydrides and aromatic diamines bearing alkylene spacers

Four series of aromatic polyimides (PIs V–VIII) composed of biphenyltetracarboxylic dianhydrides (BPDAs) and aromatic diamines bearing alkylene spacers were prepared by two methods. Most polymers could be readily prepared in a one-step method for the combination of a-BPDA with α,ω-bis(3-aminophenoxy)alkanes, a-BPDA with α,ω-bis(4-aminophenoxy)alkanes, and s-BPDA with α,ω-bis(3-aminophenoxy)alkanes. However, the polymerization of s-BPDA with α,ω-bis(4-aminophenoxy)alkanes gave powders. On the other hand, all four monomer combinations afforded the desired polyamic acid solution in a two-step method. These polymer solutions could be cast into tough and flexible films, which were characterized by their inherent viscosity, differential scanning calorimetry, thermogravimetric analysis, and dynamic mechanical spectrometry measurements. The glass transition temperatures (Tgs) of the polymers were in the range of 110–240°C, but they were not clearly defined for PIs VIII and VI. The 5% weight loss temperatures were around 450°C for all prepared PIs. For PI VIII an “odd–even” behavior of the tensile properties of the films was detected, corresponding to the reported behavior of the melting temperatures. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2404–2413, 1999

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.

Some aspects of preparation of fluorine-containing polyimides

Polyimides based on 4,4′-(hexafluoroisopropylidene)diphthalic anhydride and 4,4′-(hexafluoroisopropylidene)dianiline with controlled and uncontrolled molecular weight were prepared. The products with controlled molecular weight were terminated with 4- tert-butylaniline. The synthesized poly(amic acid)s were transformed into polyimides using both thermal solid state and solution imidization. Molecular parameters of the prepared polymers were evaluated by viscometry, size exclusion chromatography and n.m.r. spectroscopy. The properties of polyimides prepared by both methods were compared.

Polyimide/Polyimide Molecular Composite Films: Difference between Reactive Oligoimide and Reactive Polyimide as the Matrix Component

Polyimide/polyimide molecular composite (MC) films were prepared by blending precursor solutions of a rigid polyimide and a reactive oligoimide or a reactive polyimide that contains acetylene units in the backbone in a 7:3 ratio, followed by casting, drying and thermal imidization at 300 °C. 3, 3′, 4, 4′-Biphenyltetracarboxylic dianhydride (BPDA), pyromellitic dianhydride (PMDA), p-phenylenediamine (PDA), oxydianiline (ODA) and 3, 3′-diaminodiphenylacetylene ( m-intA) were used as acid dianhydride and diamine monomers for the preparation of polyimide. The rigid components were prepared from PMDA or BPDA and PDA. The matrix components were prepared from PMDA or BPDA and ODA or m-intA. The polyimide/polyimide MCs have exotherm on DSC due to the reaction of internal acetylene units, which indicates that the MC films are laminate processable. Tensile measurements revealed that the tensile modulus of the MCs utilizing reactive oligoimides is 20–30% higher than that of the MCs utilizing reactive polyimides. Viscoelastic analyses of the MC films showed that the crosslinking of the acetylene units gave polyimides that have a very high glass transition temperature.

Polyimide-Silica Gel Hybrids Containing Metal Salts: Preparation via the Sol-Gel Reaction

A facile preparation of polyimide–silica gel hybrids by the simultaneous in-situ formation of polyimides during the hydrolysis–condensation of tetramethoxysilane (TMOS) is reported here. The hydrolysis and condensation of TMOS was carried out in a solution of DMAc containing 5% LiCl, CaCl2 or ZnCl2 and the seven-membered cyclic polyimide intermediate. The seven-membered cyclic intermediates, precursors of polyimides, were derived from the low-temperature polycondensation of dianhydrides [benzophenonetetracarboxylic dianhydride (BTDA), pyromellitic dianhydride (PMDA), and 4,4-bis(hexafluoroisopropylidene)phthalic dianhydride (6FDA)] and di-isocyanates [isophorone di-isocyanate (IPDI), toluene di-isocyanate (TDI), hexamethylene di-isocyanate (HDI) and 4,4′-diphenylmethane di-isocyanate (MDI)]. These intermediates could readily be converted to the corresponding polyimides. Films were cast from the resulting mixtures and the solvent was gradually evaporated at 130 °C to result in the formation of clear, transparent, pale yellow or amber-colored hybrid films in which the salts were dispersed at the molecular level. Pyrolysis of polyimide–silica gel hybrids at 600 °C gave mesoporous silica. Silica gel obtained from hybrids HPI-8 (containing no salt) and HPI-11 (containing ZnCl2) had a pore radius (BJH method) of 2.9 nm, while that from hybrid HPI-9 (containing LiCl) had a pore radius of 11.4 nm. The surface areas (BET method) obtained were 203 m2 g−1, 19 m2 g−1 and 285 m2 g−1, while the pore volumes were 0.373 cm3 g−1, 0.158 cm3 g−1 and 0.387 cm3 g−1, respectively, for samples obtained from hybrids HPI-8, HPI-9 and HPI-11. © 1997 by John Wiley & Sons, Ltd.

Synthesis of multinuclear asymmetrical diamines based on 4-(nitrophenoxy)phthalic acids

Four new N -(aminophenyl)-4-(aminophenoxy)phthalimides, which can be used as monomers for the preparation of polyimides, have been synthesised from 4-( p - and m -nitrophenoxy)phthalic acids.

Synthesis and Characterization of Polyimides Based on Furan Resins

Abstract Preparation of polyimides was carried out by the Diels-Alder (DA) reaction of furan resin namely; Poly [4-(2-furanyl)-3-methylbutan-2-one] with different types of bismaleimides. The reaction was carried out in solution as well as in bulk and this was followed by aromatization of tetrahydrophthalimide intermediate. The molecular structure of resultant polyimides was established by elemental analysis and IR spectral studies. Thermogravimetric technique was used to evaluate thermal behaviour. The glass and carbon fiber reinforcement using lab synthesized polyimides was attempted for the preparation of composites.