Thermal Rearrangement of Functionalized Polyimides: IR-Spectral, Quantum Chemical Studies, and Gas Permeability of TR Polymers

Abstract

Thermal rearrangement of polyimides with OH side groups results in insoluble products (TR polymers) that reveal extremely high gas permeability combined with good permselectivity. However, the mechanism of the formation of these polymers remains unclear, as well as there are some doubts about their chemical structure. In order to elucidate this problem, infrared (IR) spectra of TR polymers were recorded and compared with those of several polyimide precursors. IR spectra in the range 400−4000 cm −1 showed numerous bands that evidenced the formation of aromatic lactam structure in the final products of thermal rearrangement, while only weak bands indicated the presence of benzoxazole structure. It was also shown that thermal rearrangement of functionalized polyimides studied leads to highly permeable TR polymers: permeability coefficients (P) increased by a factor of 5−20, compared to those of the polyimide precursors.

Gas separation membranes made through thermal rearrangement of ortho-methoxypolyimides

“…Nonetheless, it can be presumed that by applying the very high temperatures used to force the intramolecular rearrangement, both lactams and benzoxazoles could be formed, and that the final composition is greatly affected by the final temperature and the heating protocol. In this regard, it is to remark that there is a spectroscopic indication of polyimide persistence, apart from the merging of bands attributable to lactams, as the characteristic IR bands of imide at about 1778, 1720, 1550 and 725 cm -1 remained in the IR spectra reported by Kostina et al, and that is so also for most of the TR-PBOs prepared from ortho-esterpolyimides reported until now [26,46].…”

“…It is well documented that pyrolysis of methoxy aromatic compounds proceeds via the homolytic scission of the (H3C)-O linkage, with the subsequent loss of CH3 as methane or ethane and recombination of the phenoxy radical to phenol [37]. If this mechanism is accepted as a hydroxypolyimides at temperatures over 400 ºC [26,46]. They have postulated that the formation of rigid cyclolactams, and not only polybenzoxazoles, is responsible of the chain conformational changes which lead to the observed strong effects on physical properties, and particularly to the dramatic increase of fractional free volume and hence of gas diffusivity.…”

“…The thermal rearrangement of ortho-methoxy-polyimides to TR-PBOs was very early reported [26], but a conscientious study of the process was not done at that time, nor any investigation on gas permeation properties was performed. Additionally, polybenzoxazoles have been attained from ortho-methoxy aromatic polyamides in some instances, mainly looking for a substantial thermal resistance increment of the precursor polyamides [27].…”

Thermal, optical and photoinduced properties of a series of homo and co-polyimides with two kinds of covalently bonded azo-dyes and their supramolecular counterparts

“…Homo-polymers were synthesized from diamine with hydroxyl groups, that is, 3,3 0 -dihydroxybenzidine and bicy cle[2,2,2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride (PI-1-OH) or 4,4 0 -(hexafluoroisopropylidene)bis(phthalic anhydride) (PI-2-OH), while co-polymer was obtained from both of dianhydrides and 3,3 0 -dihydroxybenzidine (co-PI-OH). Homo-polymers PI-1-OH and PI-2-OH have already been reported [34][35][36][37][38][39]. Polymer PI-1-OH has been used for investigation of the aggregation behavior of organic-soluble polymers [34], while PI-2-OH has been characterized by gas transport measurements [35][36][37][38][39].…”

“…Homo-polymers PI-1-OH and PI-2-OH have already been reported [34][35][36][37][38][39]. Polymer PI-1-OH has been used for investigation of the aggregation behavior of organic-soluble polymers [34], while PI-2-OH has been characterized by gas transport measurements [35][36][37][38][39]. Functionalized azo-polymers were obtained by the Mitsunobu reaction of the precursors and the DR13 and/or AzPy-2 chromophores.…”