Alexander A. Kuznetsov

One-Pot Polyimide Synthesis in Carboxylic Acid Medium

The melts of aromatic carboxylic acids such as benzoic acid (BA) at 130–160 °C were shown to be excellent media for the one-pot synthesis of high molecular weight, completely cyclicized polyetherimides (PEIs) from the corresponding diamines and tetracarboxylic acid dianhydrides. According to the data on the cyclodehydratation (CD) kinetics of oligomeric amic acid model compounds, the rate of cyclicization of transient polyamic acids in BA at 140 °C is very high, and the polymer chain growth proceeds via the polyaddition of completely cyclicized PEI oligomers with amino and anhydride end groups. Tetracarboxylic acids in BA at 140 °C were shown to react with aromatic diamines to obtain high molecular weight PEIs as well as the corresponding dianhydrides. The effect of the total concentration of comonomers and the presence of an ‘inert’ diluent on the kinetics of the growth of the inherent viscosity in the polycyclocondensation of diamines and dianhydrides is discussed from the point of view of the mechanism of the process. The prospect of a novel synthetic approach in polyimide synthesis is discussed, including obtaining new homopolyimides based on extremely-low-reactivity monomers; new statistical, regular, alternating copolyimides and block copolyimides; two-component blends with one glass transition point, and PEIs based on AB-type heteromonomers.

New AB Polyetherimides Obtained by Direct Polycyclocondensation of Aminophenoxy Phthalic Acids

The one-pot, high temperature, catalytic synthesis of polyetherimides (PEIs) in molten benzoic acid was investigated. The synthesis was conducted using the AB monomers, 4-aminophenoxy phthalic acid (IIa) and 3-aminophenoxy phthalic acid (IIb). Both Homo and co-PEIs with different ratios of substituted AB IIa and IIb were prepared and characterized by Fourier transform infrared spectroscopy, differential scanning calorimetry and wide angle X-ray diffraction. The solubility of the polymers in a variety of solvents was also investigated. Homo-poly-lib is an amorphous thermoplastic that is soluble in CHC13 DMS8 and amide-type solvents. Homo-poly-IIa has a locally ordered structure and is insoluble. Properties of the IIa/IIb copolymers depend strongly on their composition. When the IIa/Hlb ratio is 30: 70 or less, co-PEIs behave as thermoplastic substances soluble in chloroform. At an IIa/lIb ratio in the starting mixture of 40: 60 or higher, the properties of co-PEIs are similar to that of poly-IIa.

High Temperature Polyimide Synthesis in "Active" Medium: Reactivity Leveling of the High and the Low Basic Diamines

The kinetics associated with the reaction of aromatic and aliphatic diamines with phthalic anhydride in glacial acetic acid was studied. This model system was intended to simulate the synthesis of polyimides from diamines and dianhydrides in molten benzoic acid. The reaction proceeds in two discrete steps, the first acylation occurs by the reaction of the diamine with phthalic anhydride followed by cy-clodehydration of the corresponding bis-(o-carboxyamides). The focus of the work was on the influence of chemical composition and basicity of the diamines on the kinetics. Kinetic and thermodynamic characteristics of model reactions were determined. It was established that acylation of aromatic and aliphatic diamines in acid medium proceeds as a reversible second-order reaction catalyzed by acid medium. On the basis of kinetic data obtained, an explanation is given for the observed phenomenon of reactivity leveling of diamines regardless of the basicity.

New Alternating Copolyimides by High Temperature Synthesis in Benzoic Acid Medium

The one-pot high temperature catalytic polycyclocondensation of diamines and dianhydrides in molten benzoic acid (BA) was studied. Due to specific features of molten BA as a solvent, obtaining new random and alternating copolyimides (CPIs) becomes possible. Several series of CPIs containing the moieties of different diamines (para- and meta- aromatic, hinged aromatic, aliphatic C6-C12, cardo-, adamanthane containing) in different combinations to each other as well as corresponding homopolyimides were synthesized using one-, two-, or three-portions of comonomer loading. Polymers were characterized by means of viscosimetry, solubility evaluation, DSC and WAXD.

Chain microstructure of soluble copolyimides containing moieties of aliphatic and aromatic diamines and aromatic dianhydrides prepared in molten benzoic acid

Two series of high-molecular-weight copolyimides CPI-1 and CPI-2 containing five-membered imide cycles have been prepared by high-temperature polycondensation in molten benzoic acid (BA) at 140°C from a pair of aromatic/aliphatic diamines (9,9-bis(4-amino)fluorene (AFL) and 1,12-dodecamethylene diamine (DDA)) and one dianhydride (4,4′-oxydiphthalic anhydride (in CPI-1 series) or (1,3-phenylene)-bis(4-oxyphtalic anhydride) (in CPI-2 series)) using different order of the components loading. The diamines moiety distribution in chain was analyzed by means of high resolution carbon nuclear magnetic resonance. It is found that CPI-1 and CPI-2 samples prepared using one-shot comonomers/intermonomer loading have random moieties distribution, whereas the samples prepared using stepwise addition of dianhydride to the mixture of two diamines have multiblock (MB) chain microstructure. Thus, despite complicated scheme of CPIs synthesis in molten BA including several reactions, the process as a whole displays a feature typical for ideal one-stage interbipolycondensation of symmetrical components with independent groups. The average block length increases when DDA and dianhydride are added together slowly to AFL solution in molten BA. The phase morphology of CPI-2 was studied by means of differential scanning calorimeter. The data obtained demonstrate symptoms of microphase separation in nascent powders of MB CPI-2.

Synthesis of branched polyimides based on 9,9-bis(4-aminophenyl)fluorene and an oligomeric trianhydride, a 1,3,5-triaminotoluene derivative

A new three-arm reactive oligomer (A3) with three end anhydride groups is prepared via the high-temperature cyclocondensation of 1,3,5-triaminotoluene disulfate with excess 2,2-propylidene-bis(phenyl-4-oxyphthalic acid) dianhydride in molten benzoic acid at 140°C in the presence of [2.2.2]-diazobicyclooctane. A branched polyimide is synthesized via the one-step high-temperature catalytic polycondensation of oligomer A3 with 9,9-bis(4-aminophenyl)fluorene in benzoic acid at 140°C via scheme (A3 + B2) and characterized.

13C-NMR analysis of chain microstructure of copolyimides on the basis of 2,2-bis[(3,4-dicarboxyphenoxyl)-phenyl]-propane dianhydride synthesized in molten benzoic acid

Three series of copolyimides CPI-1, CPI-2 and CPI-3 were prepared in molten benzoic acid, based on 2,2-bis-[(3,4-dicarboxyphenoxy)-phenyl]-propane dianhydride (intermonomer) and three pairs of diamines (comonomers): aromatic/aliphatic (CPI-1, CPI-3) and moderate basic aromatic/low basic aromatic (CPI-2). The chain microstructure of copolyimides was determined by means of the high resolution 13C NMR spectroscopy. It was found that microstructure of copolyimides depends on the order of comonomers/inermonomer loading. The one-shot loading of comonomers/intermonomer mixture leads to random copolymer whereas slow addition of intermonomer to the mixture of two comonomers leads to preferentially multi-block copolymer.

One-pot high-temperature synthesis of polyimides in molten benzoic acid: Kinetics of reactions modeling stages of polycondensation and cyclization

For aromatic and aliphatic diamines of significantly different basicities, the kinetics of acylation with phthalic anhydride in glacial acetic acid in the range 16–70°C and of imidization of corresponding bis(o-carboxyamides) in acetic acid at 140°C has been studied. The reactions under study model the stages of polycondensation and intramolecular cyclization, respectively, in the high-temperature catalytic synthesis of polyimides in molten benzoic acid. It has been established that the acylation of amino groups in acetic acid proceeds as a reversible reaction and is catalyzed by the acidic medium. The kinetic and thermodynamic parameters of the above-mentioned model reactions have been determined, and the effect of the chemical structure of diamines on these parameters has been assessed. On the basis of the experimental data obtained for the model reactions, it is inferred that, in the synthesis of polyimides in benzoic acid, the overall rate of the process is determined by the rate of the intramolecular cyclization. A low sensitivity of the cyclization reaction to a change in the structure of the starting diamines explains why high-molecular-mass polyimides can be prepared at comparable rates under these conditions from both high-and low-basicity diamines.

Chemical structure-transport behavior relationship for polyimides and copolyimides based on rigid and flexible dianhydrides

Gas-separation membrane characteristics of a number of new polyimides containing common dianhydride and diamine moieties, including two copolymers of the regular structure, have been investigated. The densities of polymer films have been measured, and the permeability and diffusion coefficients of H2, CO, CO2, and CH4 gases have been estimated. The values of free volume, solubility coefficients of these gases, and selectivities of gas separation have been determined. The transport parameters of polyimides depend on the combination of rigid and flexible dianhydride and diamine fragments. The combination of rigid dianhydride fragments with rigid diamine moieties and of flexible dianhydride fragments with symmetric flexible diamine moieties is the most promising for membrane applications.

One-pot synthesis of semicrystalline polyamide imide based on 4,4’-diaminobenzanilide and 2,2-propylidene-bis(1,4-phenyleneoxy)diphthalic anhydride in molten benzoic acid:

High-temperature thermoplastic semicrystalline polyamide imide (PAI) with Tg = 250°C, and Tm = 370°C was synthesized from 4,4’-diaminobenzanilide, and 2,2-propylidene-bis (1,4-phenyleneoxy) diphthalic anhydride using three different methods: one-pot high-temperature catalytic polycondensation in molten benzoic acid (BA), low-temperature polycondensation (LTP) in dimethylacetamide (DMAA) followed by chemical imidization, and LTP followed by imidization. The influence of the synthetic route on the crystallinity of PAI was studied by wide-angle X-ray scattering. The PAI synthesized in molten BA comprised a reactive oligomer, which on heating up to 360°C easily transformed into high-molecular-weight PAI. The thermal and rheological properties of the high-molecular-weight PAI thus prepared were studied using differential scanning calorimetry, trimellitic acid, thermogravimetric analysis, and capillary viscosimetry. The rheological characteristics indicate that the obtained PAI can be melt processed by extrusion and hot pressing at 370–380°C.