Positive photosensitive polyimides with cyclobutane structure

A new family of positive photosensitive polyimide (PPI) systems composed of solvent soluble polyimides (Pls) with cyclobutane (CBDA) structures and diazonaphthoquinone compounds (DNQ) has been prepared. Heat and catalytic imidizations were carried out to obtain CBDA Pls; the former was better than the latter in controlling the molecular weight of the Pl. The ? OH groups in the Pls were easily acetylated during catalytic imidization, so ? COOH groups were selected as weak acidic groups in the Pls. The ? COOH groups were also effective in giving the Pls an alkaline solubility. Therefore, Pls having ? COOH groups were superior to those having ? OH groups for PPI systems. The photosensitive properties of various PPl systems containing ? COOH were found to vary with the fraction of ? COOH groups in the Pls, the content of DNQ in the systems, and the molecular weight of the Pls.     

FTIR studies of polyimides. II. Factors affecting quantitative measurement

Measurement of imidization by IR spectroscopy has frequently been reported to give results that are either insensitive to changes in the latter part of the cure or in conflict with observations by other methods. However, an analysis of imide formation using the 1370 cm^?1 band (C? N stretch) in conjunction with the 1500 cm^?1 aromatic band as an internal standard appears capable of giving precise, internally consistent measurements for the most commonly used polyimide structures, for samples that are measured in transmission. Measurements of imide content in ultrathin films by grazing incidence reflection spectroscopy appear to be at least semiquantitative. © 1993 John Wiley & Sons, Inc.     

A novel type of Si-containing poly(urethane-imide)s: synthesis, characterization and electrical properties

A novel type of a Si-containing poly(urethane-imide) (PUI) was prepared by two different methods. In the first method, Si-containing polyurethane (PU) prepolymer having isocyanate end groups was prepared by the reaction of diphenylsilanediol (DSiD) and toluene diisocyanate (TDI). Subsequently the PU prepolymer was reacted with pyromellitic dianhydride (PMDA) or benzophenonetetracarboxylic dianhydride (BTDA) in N-methyl pyrolidone (NMP) to form Si-containing modified polyimide directly. In the second method, PU prepolymer was reacted with diaminodiphenylether (DDE) or diaminodiphenylsulfone (DDS) in order to prepare an amine telechelic PU prepolymer. Finally, the PU prepolymer having diamine end groups was reacted with PMDA or BTDA to form a Si-containing modified polyimide. Cast films prepared by second method were thermally treated at 160 °C to give a series of clear, transparent PUI films. Thermogravimetric analysis indicated that the thermal degradation of PUI starts at 265 °C which is higher than degradation temperature of conventional PU, confirming that the introduction of imide groups improved the thermal stability of PU.To characterize the modified polyimides and their films, TGA, FTIR, SEM and inherent viscosity analyses were carried out. The dielectrical properties were investigated by the frequency-capacitance method. Dielectric constant, dielectric breakdown strength, moisture uptake and solubility properties of the films were also investigated.     

Direct patterning of poly(amic acid) and low‐temperature imidization using a crosslinker,a photoacid generator,and a thermobase generator

A positive‐type photosensitive polyimide (PSPI) based on poly(amic acid) (PAA), a crosslinker 1,1,1‐tris{4‐[2‐(vinyloxy)ethoxy]phenyl}ethane (TVPE), a photoacid generator (PAG) (5‐propylsulfonyloxyimino‐5H‐thiophen‐2‐ylidene)‐2‐(methylphenyl)acetonitrile (PTMA), and a thermobase generator (TBG) t‐butyl 2,6‐dimethylpiperidine‐1‐carboxylate (BDPC) has been developed as a promising material in microelectronics. The PAA was prepared from 3,3′,4,4′‐biphenyltetracarboxylic dianhydride (BPDA) and 4,4′‐oxydianiline (ODA) in dimethyl sulfoxide (DMSO). The PSPI, consisting of PAA (69 wt %), TPVE (21 wt %), PTMA (3 wt %), and BDPC (7 wt %), showed high sensitivity of 21 mJ/cm² and a high contrast of 6.8 when it was exposed to a 436‐nm line (g‐line), postbaked at 90 °C for 5 min, and developed with 1.69 wt % TMAHaq. A clear positive image of 8 μm line and space pattern was printed on film, which was exposed to 50 mJ/cm² of g‐line by a contact printing mode and fully converted to the corresponding polyimide (PI) pattern on heating at 200 °C, confirmed by FTIR spectroscopy. Thus, this system will be a good candidate for next generation PSPIs. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3362–3369, 2009     

Effect of carbon nanotubes and their dispersion on thermal curing of polyimide precursors

The process of thermal imidization reaction is significant for temperature and time control in the polyimide industry. Here, we report the effect of carbon nanotubes and their states of dispersion on the thermal imidization of the precursor films of polyimide (poly(amic acid)) for the first time. The curing process was followed by measuring Fourier transform-infrared (FT-IR) spectra, fluorescence spectra, thermogravimetric-differential scanning calorimeter (TG-DSC) properties and the refractive indices of films. It was found that by evenly dispersing 1 wt% of carbon nanotubes assisted by a dispersant in the poly(amic acid),the full imidization temperature of the polyimide can be reduced from 300 °C to 250 °C. Different states of distribution of CNTs were observed by light microscopy and scanning electron microscopy, and proved that a better dispersion of carbon nanotubes dramatically enhanced the speed of imidization. Moreover, the DSC results showed that lower decomposition temperature of poly(amic acid) could be obtained with more uniform distribution of carbon nanotubes, which means the process of cyclodehydration of the poly(amic acid) was accelerated.     

Rodlike/flexible polyimide composite films prepared from soluble poly(amic diethyl ester) precursors: Miscibility,structure, and properties

Homogeneous precursor/precursor solutions with various compositions were obtained with appreciably high solid contents in N-methyl-2-pyrrolidone from soluble poly(amic diethyl ester) precursors of rodlike poly(p-phenylene biphenyltetracarboximide) (BPDA-PDA) and flexible poly(4,4′-oxydiphenylene biphenyltetracarboximide) (BPDA-ODA), which are hydrolytically more stable as well as more soluble than the corresponding poly(amic acid)s being equilibrated with the constituent monomers. Both optical microscopic and light scattering measurements showed that the dried precursor blend films and resultant polyimide composite films were optically transparent, regardless of compositions and process conditions. The composite films showed a single T_g behavior. However, for the composite of 30 wt % BPDA-PDA dispersed in the matrix of 70 wt % BPDA-ODA, a smectic crystalline-like aggregation of the BPDA-PDA component was detected on wide-angle x-ray diffraction patterns, indicative of microscopic phase separation between the two components. This phase separation was not detected on the optical microscopy, light scattering, and dynamic mechanical thermal analysis because of their resolution limits: Optical microscopy has a resolution of submicrometers, whereas dynamic mechanical thermal analysis and light scattering have a resolution of ca. 50 Å. Therefore, it is speculated that in the composite films BPDA-PDA and BPDA-ODA polyimide molecules have demixed on the scale of a few nanometers. The mean long periodicity, which was estimated from the small-angle x-ray scattering pattern, varied from 134 to 170 Å as the content of BPDA-ODA component increased. In addition, mechanical properties of the composite films were characterized. ©1995 John Wiley & Sons, Inc.     

Influence of curing temperature on the optical properties of fluorinated polyimide thin films

The influence of curing temperature (CT) on the optical properties of 6FDA/ODA poly(amic acid)-polyimide (PAA-PI) films was characterized by measuring ATR-FT-IR spectra, refractive index (RI) and birefringence of the films. The results showed that the infrared absorption intensity of characteristic peaks (IAICP) corresponding to the imide ring and the RI of PAA-PI films reached their maxima when the films had been cured at 270 °C, while the magnitude of birefringence (|Δn|) of the films reached its minimum as CT rose up to 330 °C. However, the RI decreased as CT was between 270 °C and 330 °C. Both the RI and |Δn| of the film increased obviously when CT increased after 330 °C. We think this is due to the interchain crosslink reaction (ICCR) above 330 °C and can be an evident proof of ICCR. And the evidences supporting ICCR was also discussed via IR differential spectra.     

Physicochemical and thermal effects of pendant groups,spatial linkages and bridging groups on the formation and processing of polyimides

Aromatic polyimides are known for their remarkable thermal and chemical properties which are greatly influenced by their precursors. In this study, we report synthesis and characterization of four different aromatic polyimides. The four different dianhydrides (ODPA, BTDA, BPDA, and PMDA) were reacted with a diamine (BisAPAF) via azeotropic imidization under same conditions. FTIR analysis confirmed the formation of aromatic polyimides and all but one polyimide (HPI-BPDA) were found to be completely soluble in common solvents. The obtained molecular weights were between 16,000 and 32,000?g/mol, glass transition temperatures were between 250?°C and 275?°C, degradation temperatures were above 550?°C, and the d-spacing values were around 5?Å. These properties are promising and can be beneficial for various applications such as thin films and membranes.     

Imidization and interdiffusion of poly(amic ethyl ester) precursors of PMDA/3,4′-ODA

Para-, meta-, and mixed isomeric poly(amic ethyl ester) precursors of the polyimide based on pyromellitic dianhydride (PMDA) and 3,4′-oxydianiline (3,4′-ODA) were synthesized. The intrinsic viscosity of each of the isomers was measured in an NMP solution and found to be less than corresponding isomers derived from PMDA and 4,4′-oxydianiline (4,4′-ODA) precursors with comparable molecular weight. The imidization and solvent retention were measured as a function of imidization temperatures, T_i using forward recoil spectrometry (FRES). For samples cast from a single solvent, either N-methyl pyrrolidone (NMP) or dimethyl sulfoxide (DMSO), no difference was observed in the temperature-dependent imidization behavior between the isomers. In all cases the imide fraction f increased as T_i increased, and reached a value of unity, i.e., full conversion at 400°C. At the same T_i, samples cast from DMSO showed a slightly higher f than samples cast from NMP. FRES and time of flight FRES (TOF-FRES) were used to measure the interdiffusion distance, w, of deuterium-labeled tracers into nondeuterated base layers of the polyimide of PMDA/3,4′-ODA treated at various T_i. The primary determinant of w for all isomers was T_i, and the particular isomer used as either the base or the tracer molecule did not seem to affect w. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 2247–2258, 1998