Thermal Degradation Of Polyimides Research Articles

A study of the stabilization of vertical alignment for liquid crystals by increasing the side-chain rigidity of polyimides

A series of polyimides (PIs) with various side-chain structures were prepared via copolymerization of pyromellitic dianhydride, 3,3′-dimethyl-4,4′-methylenediamine and three functional diamines: 4-(4-octyloxybenzoyloxy)biphenyl-3′,5′-diaminobenzoate (C8-BPDA), 4-octyloxybiphenyl-3′,5′-diaminobenzoate (C8-PDA) and 4-(4-butoxybenzoyloxy)biphenyl-3′,5′-diaminobenzoate (C4-BPDA). PIs derived from C8-BPDA and C4-BPDA exhibited excellent rubbing resistance in comparison with PI from C8-PDA and the pretilt angle could be controlled over 89° after rubbing. Thermogravimetric analysis showed that the thermal degradation of PIs under nitrogen atmosphere occurred above 320 °C, and PI derived from C8-BPDA showed the best thermal stability. Wide-angle X-ray diffraction patterns indicated an amorphous morphology of the PIs, and the PIs also had outstanding solubility in polar aprotic solvents. The resultant PI films were light colored and maintained high transparency in the visible light region. By increasing the rigidity of side-chains, the rubbing resistance and the thermal stability of PIs could be promoted at the same time. © 2012 Society of Chemical Industry

Preparation, Characterization and Thermal Degradation of Polyimide (4-APS/BTDA)/SiO2 Composite Films

Polyimide/SiO2 composite films were prepared from tetraethoxysilane (TEOS) and poly(amic acid) (PAA) based on aromatic diamine (4-aminophenyl sulfone) (4-APS) and aromatic dianhydride (3,3,4,4-benzophenonetetracarboxylic dianhydride) (BTDA) via a sol-gel process in N-methyl-2-pyrrolidinone (NMP). The prepared polyimide/SiO2 composite films were characterized using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM) and thermogravimetric analysis (TGA). The FTIR results confirmed the synthesis of polyimide (4-APS/BTDA) and the formation of SiO2 particles in the polyimide matrix. Meanwhile, the SEM images showed that the SiO2 particles were well dispersed in the polyimide matrix. Thermal stability and kinetic parameters of the degradation processes for the prepared polyimide/SiO2 composite films were investigated using TGA in N2 atmosphere. The activation energy of the solid-state process was calculated using Flynn–Wall–Ozawa’s method without the knowledge of the reaction mechanism. The results indicated that thermal stability and the values of the calculated activation energies increased with the increase of the TEOS loading and the activation energy also varied with the percentage of weight loss for all compositions.

Characterization and Thermal Degradation of Polyimide Derived from 5-amino-2(p-aminophenyl) Benzoxazole Monomer with Pyromellitic Dianhydride

- 5-amino-2(p-aminophenyl) benzoxazole (AAPB) and its derived polyimide prepared with pyromellitic dianhydride (PMDA) were synthesized successfully. Their structures were characterized by FT-IR, 1H NMR, Element analysis, 13C NMR, Solid-state 13CNMR, DSC, TG and XRD. The polyimide was synthesized via a conventional two-stage method. The intermediate poly (amic acid) had inherent viscosity of 1.06dL/g and could be thermally converted into light yellow polyimide film. The polyimide showed excellent solvent resistance and good thermal stability. The glass transition temperature (Tg) was found to be 314°C, the decomposition started at a temperature above 500°C in air and above 550°C in argon atmosphere. The thermal degradation of the polyimide was studied by thermogravimetric analysis (TGA) in order to determine the actual reaction mechanisms of the decomposition process. The apparent activation energy (Ea) was obtained following Flynn-Wall-Ozawa method. The activation energies of different mechanism models and pre-exponential factor (A) were determined by Coats-Redfern method. Compared with the value obtained from the Ozawa method, the actual reaction mechanism obeyed three-dimensional diffusion model, Jander equation (D3) with integral form g(α)=[1-(1-α)1/3]2.

Thin polymer films from polyimide vacuum thermal degradation with and without a glow discharge

Polyimide-like thin films were deposited by thermal degradation of polyimide with and without simultaneous activation by a glow discharge excited using an r.f. planar magnetron. The films deposited without discharge are similar in composition to conventional polyimide, whereas the deposition with plasma results in cross-linked coatings with composition typical for plasma polymers e.g. prepared by r.f. sputtering of polyimide. AFM reveals rough surface topography for the films evaporated without plasma. The application of plasma leads to very smooth plasma polymer films.

Effect of the mole ratios of silane-modified polyvinylimidazoles on adhesion promotion of the polyimide/ copper system

Polyvinylimidazoles (PVIs) modified with vinyltrimethoxysilane (VTS) and y-methacryloxypropyltrimethoxysilane (γ-MPS) in different mole fractions were used as adhesion promoters (primers) for the polyimide (PI)/copper interface. The effects of the compositions of the silane-modified PVI copolymers on the lap shear strength between PI and copper were investigated at different bonding temperatures. Contact angle measurements and scanning electron microscopic (SEM) analysis were performed to characterize the interfacial phenomena between PI and the primer, and Fourier transform infrared (FTIR) spectroscopy was employed to investigate the thermo-oxidative degradation of PI at the different bonding temperatures and the locus of failure after the lap shear test. In the PI/γ-MPS-modified PVI/copper system, γ-MPS-modified PVI containing a lower γ-MPS content showed higher lap shear strengths, but the behavior was opposite in the PI/VTS-modified PVI/copper system. In particular, VTS-modified PVI with a 1: 1 silane/VI mole ratio showed the best performance for adhesion promotion of the PI/copper interface at all bonding temperatures. The interfacial adhesion strength between PI and the primer was a crucial factor for adhesion promotion of the PI/γ-MPS-modified PVI/copper system. In the PI/VTS-modified PVI/copper system, however, the primer's capability to suppress the thermal degradation of PI at the bonding temperature was the main factor in controlling the adhesion strength.

Kinetics of the thermal degradation of polyimides

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.

Thermal degradation of polyimides—I. Investigation of the role of isoimide structure on degradation process

The structures of isoimide cycles in polyimides were elucidated from i.r. and 13C NMR spectra of N-phenylphthalimide and N-phenylphthalisoimide. Using i.r. and gas-chromatographic data, conversion of isoimide cycles to the imide form was studied as a function of temperature. This process is irreversible, precluding the presence of the isoimide form at high temperature.

Effects of some methodological factors on quantitative characteristics of thermal stability of polyimide materials

Thermogravimetry and differential thermal analysis of films and fibres prepared from polypyromellitimidediphenyl oxide were carried out with standard Derivatograph and Du Pont-951 thermoanalyzers. The results were used for the investigation of some methodological factors affecting the processes of thermal degradation of polyimides, and the quantitative characteristics of these processes. It was shown that the pattern of thermal degradation of polyimide and its thermal characteristics depend on the construction of the sample holders, on the weight of the sample and on its packing in the holder. It is concluded that strict standardization of conditions of comparative thermal analysis and a detailed description of the conditions of carrying out the analysis are necessary to obtain comparable results.