Kinetic and mechanistic investigations of the formation of polyimides under homogeneous conditions

Abstract

This paper describes kinetic and mechanistic studies of the homogeneous formation of highperformance polyimides. Controlled molecular weights and nonreactive phthalimide end groups were emphasized. NMR spectroscopy, nonaqueous titration, and solution viscosity measurements were the principal techniques utilized. The disappearance of the amic acid groups was followed to quantitative conversion via nonaqueous titration with tetramethylammonium hydroxide. The homogeneous solution imidization processes were well described by auto-acid-catalyzed second-order kinetics. The effects of heteroatom electron-donating and -withdrawing bridging groups (0 and SOz) in the diamines and dianhydrides on imidization rates were investigated, and a possible reaction mechanism for the solution imidization processes was proposed. Imidization of 4,4'-oxydianiline/4,4'-oxydiphthalic anhydride poly(amic acid) was investigated at three different temperatures (140,150, and 180 O C ) . Two-dimensional 'H-lH correlation spectroscopy and intrinsic viscosity measurements provided direct evidence for partial degradation of the poly(amic acid) backbone structures. Complete imidization, including rehealing of the broken chains, was achieved under proper reaction conditions, and the implication of these findings was considered to be very significant for the synthesis of thermally stable high-performance polyimides. For polyimide systems containing benzophenonetetracarboxylic dianhydride (BTDA), direct evidence for network formation involving imine branching and cross-linking was observed by high-field lH NMR spectroscopy and the formation of gels was discussed as a function of reaction conditions. One might anticipate that all ketone-containing polyimides could, to varying degrees, display this behavior.

Comparison of one-pot and two-step polymerization of polyimide from BPDA/ODA

“…In the course of the film preparation from the solution, the embrittlement occurs when the film is prepared from the polyamic acid solution, while it did not occur in the case of that from the solution of the one-pot method. A molecular weight of polyimide film is almost the same as that of precursor poly- Figure 11 Mechanical properties as a function of cure temperature for thermally staged films by two-step polymerization.…”

Preventing gelation in polyisoimide synthesis

“…Figure 1 shows 1 H NMR spectra of poly(amic acid)s and polyisoimide gel. As reported in previous work 12 where 1 H± 1 H correlation spectroscopy was utilized for decoding the 1 H NMR spectrum of partially imidized 4,4'-ODA/ODPA poly(amic acid), the up®eld-shifted peak at 6.60 ppm in spectrum B is due to ortho protons with respect to amine groups in the terminal aromatic moieties. In Fig 1(A), no peaks are observed at 6.60 ppm, which con®rms that poly(amic acid)s are successfully end-capped with phthalic anhydride.…”

Effect of the solvent type and polymerization conditions on the curing kinetics, thermal and viscoelastic performance of poly(amide-imide) resins

“…On the other hand, the solvent is a media in which the PAI reactions occur. The postcuring reaction is extremely important for the final structure formation and occurs at elevated temperatures, when the solvent is evaporated [7,10]. In the present study, effect of both curing conditions and solvent type on the polymerization kinetics and final properties of PAI resins was investigated.…”

“…60-80 wt%) brings difficulties for investigation of the curing kinetics of these resins by thermal analysis. Some authors report the determination of the curing kinetics of polyimides using FTIR or NMR analysis [6][7][8][9]. Detecting the increase of the imide bands intensity during the chemical reaction, the conversion can be determined with quite high accuracy.…”