Soluble aromatic polyimides based on 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane: Synthesis and properties

Abstract

SYNOPSISAromatic polyimides were synthesized from 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane (6F-OH diamine) and different aromatic dianhydrides by a one-step hightemperature polycondensation, or by a two-step procedure using either thermal or chemical imidization of poly(amic acids), PAA. The obtained polyimides were compared in terms of their chemical structure, molecular weight, mechanical and thermal properties. The reaction of 6F-OH diamine with different aromatic dianhydrides in amide solvents at room temperature resulted in the formation of PAA with moderate molecular weight (tinh I 0.7 g/ dL). The thermal imidization of these PAAs led to brittle hydroxy polyimides (PI-6F-OH). In contrast, chemical imidization of similar PAAs in acetic anhydride and pyridine brought about flexible self-supporting polyimide films. The FTIR analysis indicated that the latter process was accompanied by an esterification of the OH groups in the diamine moieties, resulting in the formation of the polymers with side acetate groups (PI-6F-Ac). The high molecular weight hydroxy polyimides, suitable for preparation of films with good tensile properties, were synthesized by a one-step high-temperature polycondensation in phenolic solvents. All obtained polyimides were well soluble in common organic solvents. The highest solubility was observed for PI-6F-Ac. It was found by means of FTIR and TGA that the polyimides with the R group (R = OH or acetate) in orto position to the nitrogen atom in the diamine moiety underwent a rearrangement to benzoxazoles above 300°C. The starting temperature and conversion of this rearrangement reaction were controlled by the type of R group. The imide-to-benzoxazole rearrangement shifted to lower temperatures, and higher conversion was encountered for the polyimides with side acetate group, PI-6F-Ac, obtained by chemical imidization. 0 1996 John Wiley & Sons, Inc.

Thermal Rearrangement of Poly(o-hydroxyimide)s Synthesized from 4,6-Diaminoresorcinol Dihydrochloride

“…Polyimides 2 were stable up to 400 • C and remarkable sign of the benzoxazole ring could not be found. For instance, when the film of 2c was heated at 500 • C and 550 • C, no significant decreasing of the absorption bands characteristic for imide carbonyl and appearing of a small new absorption band at about 1556 cm −1 (typical band for benzoxazoles 13,14 ) was observed. The results of IR spectra indicate that part of the imide ring converted to PBO, while the rearrangement was not completed, and imide structure still existed even after heating at 550 • C. Figure 1 presents thermogravimetric (TG) analysis curves of 2b before and after treatment at 550 • C. In the case of the before heat treatment, weight decrease is observed at 390 • C, whereas the sample after heat treatment did not show any change at this tempera- ture.…”

“…After heating at 450 • C, all films became brittle. FT-IR spectra showed small changes of the absorption bands after heating at 450 • C in comparison with polymers before 13,14 ) appeared after heating at 400 • C. The results of IR investigation indicated that functionalized PIOHs were not converted to PBOs by heating up to 450 • C As it was found that thermal conversion from PIOHs 2 to PBOs 3 seemed to be difficult because of rigid structure of DAR, preparation of PBO by thermal conversion of poly(o-hydroxyamide)s (PAOHs) [16][17][18][19][20][21][22] that were prepared from DAR was investigated as comparison. Such rearrangement to PBOs has been described to occur at lower temperatures.…”

“…14 In the next step, hydroxyl group of 2 was chemically modified by acetylation with acetic anhydride and silylation with tertbutyldimethylsilyl chloride. It was expected that such chemical modification of the polymers 2 decreased the temperature of their rearrangement to PBOs 3 and improved solubility of 2.…”

“…After the first synthesis of poly(3,3 -dihydroxy 4,4 -diphenylene) pyromellitimide and thermal conversion to the corresponding PBO was reported by Kardash et al in 1967, 24 several studies have been reported. [10][11][12][13][14][15] Although PIOHs has been prepared from the smallest diamino-diphenol monomer, 4,6-diaminoresorcinol, 25 it is noteworthy that no report was found concerning the thermal rearrangement of PIOHs synthesized from 4,6-diaminoresorcinol to PBOs that are expected to possess high modulus and high strength because of their compact rigid rod structure.…”

Synthesis and Properties of Novel Polyimides Containing Fluorinated Alkoxy Side Groups

“…[3] In most of cases, the introduction of fluorinated groups was carried out by chemical modification of aromatic diamines. [4,5] Some of the widely used approaches are based on the incorporation of a trifluoromethyl group directly attached to an aromatic group [6] or on the incorporation of a hexafluoroisopropylidene group in meta or para position of phenyl [7] or phenoxyphenyl groups. [8,9] Fluoroalkyl modified building blocks can for example be synthesised by condensation of bisphenol A or bisphenol AF with 2-chloro-5-nitrobenzotrifluoride followed by reduction.…”