A novel PMR polyimides (TMBZ-15) based on substituted benzidines is examined and compared to state-of-the-art PMR-15. The
mechanism for the thermal decomposition of two specific PMR polyimides is obtained using TG/FTIR/MS techniques. In order to
verify the pathway of polyimide degradation, a pyrolysis/GC-MS technique was employed to evaluate the organic degradation
products, particularly the larger components that are destroyed in traditional TG/MS. A proposed degradation mechanism involves
two main stages of decomposition, each of which produce a variety of products. The first group includes aromatic hydrocarbons,
aromatic amines and nitriles, which correspond to partial fragments of polymer chains. The second group consists largely of
fluorene, naphthalene and phenanthrene, which are attributed to the isomerization, rearrangements and cyclizations of the
aforementioned pyrolyzates at high temperature.
Authors:Y.-J. Song, S.-H. Meng, F.-D. Wang, C.-X. Sun, and Z.-C. Tan
Polyimide BTDA-ODA sample was prepared by polycondensation or step-growth polymerization method. Its low temperature heat capacities were measured by an adiabatic calorimeter in the temperature range between 80 and 400 K. No thermal anomaly was found in this temperature range. A DSC experiment was conducted in the temperature region from 373 to 673 K. There was not phase change or decomposition phenomena in this temperature range. However two glass transitions were found at 420.16 and 564.38 K. Corresponding heat capacity increments were 0.068 and 0.824 J g–1 K–1, respectively. To study the decomposition characteristics of BTDA-ODA, a TG experiment was carried out and it was found that this polyimide started to decompose at ca 673 K.
Curves obtained by controlled rate TG of polyimide film in air are quite different from those obtained by conventional constant rate heating TG. A two step mass loss was observed during the constant rate heating TG, while mass loss proceeded as a single step process in the controlled rate TG. To elucidate the cause for this difference, kinetic analysis was made, and it was found that the reaction mechanism in a lower temperature range is different from those in a higher temperature range. The lower temperature decomposition is a single step process, and the higher temperature decomposition is a two-step process. The reason for the difference is that only the low temperature single step process is observed in the controlled rate TG, while both reactions are observed in the constant heating rate TG along with the temperature increase. This speculation was confirmed by isothermal TG. These facts show us another usefulness of controlled rate TG. To analyze the three types of TG data together, the Friedman—Ozawa method was used, and it is demonstrated to be the most appropriate and reliable.
Authors:Muhammad Bisyrul Hafi Othman, Rafiza Ramli, Zulkifli Mohamad Ariff, Hazizan Md Akil, and Zulkifli Ahmad
In the last 80 years, the synthesis of aromatic polyimides (PIs) has seen a tremendous increase within a wide range of applications, particularly in insulation materials [ 1 , 2 ] and high performance polymers [ 3
A number of temperature and kinetic parameters of thermal degradation of polyimides over the temperature range from 20 to 1000° have been determined on the basis of thermogravimetric investigations of a polyimide sample obtained from pyromellitic dianhydride and diaminodiphenyl ether. It was shown that such kinetic parameters as the reaction order and the activation energy of thermal degradation are directly dependent on the conditions under which the thermal analysis is carried out. It was found that when the static and dynamic conditions of the environment of a polymer sample are varied, the thermochemical processes occurring in a polyimide over the temperature range investigated are drastically changed.
A commercially available polyimide fiber was investigated as a possible precursor for the formation of carbon fibers. The
thermal response of the fiber was thoroughly investigated using DSC, TMA and TG. These responses were dependent on the atmosphere
and tension during scanning. The fiber was stabilized at high temperatures both in inert and oxidative environments and the
effect of these stabilization treatments on the structure and properties of the fiber was carefully followed. During heating,
the fiber showed shrinkage tendency at small tensions, but at higher tensions the fibers could be stretched. Among the two
environments investigated, air was more effective than nitrogen in getting a more stable fiber.
Authors:Y. Li, N. Obando, F. Tschen, and R. J. Morgan
Thermal analysis of phenylethynyl end-capped imide oligomer AFR-PEPA-4
was performed to characterize cure reaction, thermal stabilities and semicrystalline
behavior of AFR-PEPA-4 oligomer and its cured polyimide. Cured AFR-PEPA-4
polyimide showed high Tgs
up to 418C. Both AFR-PEPA-4 oligomer and polyimide exhibit excellent
thermal stabilities comparable to PETI-5 polyimides. AFR-PEPA-4 imide oligomer
has a Tm of 330C
and exhibits spherulite crystalline morphology in the film. The crystallinity
in AFR-PEPA-4 films could not be regenerated under any annealing conditions
after the initial melt.
The results of thermoanalytical investigations of polyimides are considered. It is shown that combined application of methods of thermal analysis makes it possible not only to determine the thermal and structural characteristics of polyimide articles but also to observe the formation of polyimides, their thermal degradation and transformation into new structures under the influence of high temperatures.
Authors:Young Ho Kim, Bong Seok Moon, F. W. Harris, and S. Z. D. Cheng
A new high molecular weight polyimide based on 4,4′-oxidiphthalic anhydride (ODPA) dianhydride and 2,2′-dimethyl-4,4′-diaminobiphenyl (DMB) diamine has been synthesizedvia a one-step polymerization method. This polyimide is soluble in phenolic solvents. Films from 7 to 30 μm thick were cast from the polymer solution and show in-plane orientation on a molecular scale detected by Fourier transform infrared spectroscopy experiments. This anisotropic structure leads to anisotropic optical properties arising from two different refractive indices along the inplane and out-of-plane directions. ODPA DMB possesses high thermal and thermo-oxidative stability. The glass transition temperature has been determined to be 298 °C. Dynamic mechanical analyses show two relaxation processes appearing above room temperature: the β- and the α-relaxation processes. The α-relaxation corresponds to the glass transition while the β-relaxation is a secondary relaxation process associated with the non-cooperative subsegmental motion.
The space charge trapping/detrapping in thermally charged polyimide (PI) samples have been studied by means of “Final Thermally
Stimulated Discharge Current” (FTSDC). We investigate the effects associated with space charge behavior in PI near glass transition
region. The FTSDC spectra consist of space charge peak attributed trapping of charges at different trapping levels. The peak
positions are found to be very sensitive with poling time, discharging time, and heating rate. The apparent activation energy
distributed in the range from 0.51 to 1.12 eV, and the charge released has been found to be varying with poling temperature
(Tp) and poling time (tc)/discharging time (td). The decay of space charge (Q) resembled an agreement with interfacial polarization.