Polyamic acids derived from

Whang and Wu [3] have described the liquid crystalline state of polyimide precursors and shown that certain polyamic acids derived from pyromellitic anhydride exhibit lyotropic behaviour. Liquid crystal phases have also been observed by Wenzel et al. [4] in polyimides derived from pyromellitic anhydride and 2,5-di-n-alkoxy-1,4-phenyl ene diisocyanate. Dezern [5] has disclosed a synthesis for linear polyamide-imides derived from benzophenone dianhydride but the occurrence or otherwise of mesophases is not mentioned. 

A polyamle acid derived from an amine component comprising a 2-cyano-1,4-phenylene diamine and a family of diaryl ketones is claimed. The polyamic aeids are useful in formation of polyimides, also claimed, and for the optieal alignment of liquid crystals and the manufacture of liquid crystal optical elements, also claimed. 

In general polyimides derived from BTDA + p,p -DABP yielded rather poor quality, very brittle films which were due in part to the low viscosity of the resulting polyamic acid solution. 

Table 1 lists some of the metal compounds employed and the results obtained when attempts were made to cast films of the resulting metal ion filled polyimide derived from BTDA + m,m -DABP. Brittle films were produced in most cases regardless of whether the added metal ion was hydrated or anhydrous. The relatively low viscosities of the resulting polyamic acid-metal ion solutions no doubt accounted for this. Addition of AlCl3 6H20 or any simple aluminium salt to the polyamic acid produced immediately a rubbery material that could not be cast into a film. 

Further work in this area is underway employing polyamic acid systems which are known to produce higher viscosity solutions (e.g. polyimides derived from 4,4 -oxydianiline and either BTDA or pyromellitic dianhydride). This is being carried out in the belief that higher viscosity solutions will give rise to higher quality, less brittle films and will, thereby, enable a broader spectrum of metal systems to be studied regarding the adhesive and electrical conductance properties of metal ion filled polyimides. 

The experimental procedures and x-ray photoemission results for the preparation of ultrathin (d = 1.1 nm) polyimide films on polycrystalline silver by co-condensation of PMDA and ODA are described elsewhere [5]. In that work our XPS results suggested that the polyimide chains bond to the silver surface via a carboxylate type bonding. This conclusion was derived from an analysis of the results obtained for the interaction of the monomers (PMDA and ODA) and of the resulting ultra-thin polyimide film. Due to the relatively larger thickness of the polyamic acid films as compared to the monomer adsorbate phases and the polyimide film, no conclusions were possible about the reaction of the polyamic acid with the silver substrate. 

Starting materials and solvents were purchased from Aldrich Chemical Co. acetonitrile (ACN), N,N-dimethylformamide (DMF), and N-methyl-2-pyrrolidone (NMP) were obtained anhydrous in Sure/Seal bottles and used as received. The polyamic acid of PMDA-ODA (2545 Pyralin) was supplied by DuPont. The soluble polyimide XU-218, derived from 3,3, 4,4 -benzophenone tetracarboxylic dianhydride (BTDA) and diamino-1,1,3-trimethyl-3-phenylindan isomers (DAPI) was purchased from Ciba-Geigy Corp. The acetylene terminated imide oligomer powder (Thermid MC-600) derived from BTDA, aminophenylacetylene, and 1,3-bis (2-aminophenoxy) benzene (APB) was obtained from National Starch and Chemical Company. Kapton Type II (PMDA-ODA) films were obtained from DuPont Co., Apical polyimide films were obtained from Allied Corp., and Upilex Type-S and Type-R polyimide films derived from 3,3, 4,4 -biphenyl tetracarboxylic dianhydride (BPDA) plus p-phenylenediamine (PDA) and ODA, respectively were obtained from ICI Americas Inc. 

The organic dielectrics known as polyimides have been studied extensively by a variety of bulk characterizational techniques as a perusal of the literature will illustrate. Little has been published on their surface properties. X-ray photoelectron spectroscopy (ESCA) has been extremely useful for polymer characterization (, 7, ), In a previous paper ( ), we have reported the ESCA spectra of structurally different polyimides derived from both commercially available polyamic acid resins (DuPont s PI5878, PI2525, PI2550), and from laboratory synthesized polyamic acid resins. 

Aliphatic diamines react with a diester-diacid derived from a dianhydride to form an ammonium salt which can be polymerized, usually in the melt, to a polyamic acid. Further heat converts the polyamic acid to the polyimide... 

Formation of the Polyamic Acid Ester Derived From the para-di-r-butyl Ester of Pyromellitic Acid and PDA in NMP. 

The requirement of a controllable level of charged groups having been met, attention turned to the elimination of the amine modifier. In order to obtain the desirable properties of the polyimide, it was important that the modification be readily eliminated. At the outset, there was an indication in the literature that this would in fact be the case. In 1970, Delvigs and co-workers (I 3) reported the diethylamide derivative of a polyamic acid as an alternative precursor to polyimides. They provided IR evidence that the amine was eliminated thermally to form a polyimide indistinguishable from that obtained from the polyamic acid. In the present work, the elimination of 1-methylpiperazine was followed by thermogravimetric analysis (TGA), IR, and size exclusion chromatography (SEC). 

Some of the problems seen with the commercially available polyimides such as limited shelf life,gelation and high ionic contamination are traceable to the raw materials themselves. A zone refining technique has been perfected for use with organic materials and these precursors have been used to synthesize ultrapure polyamic acids for IC device applications. The key feature of the synthesis is the use of solid ingots of the dianhydrides. Materials prepared by this technique show low metallic impurities and have been shown to be excellent film formers for a variety of applications. In particular a polyimide derived from PMDA-ODA has been used to passivate magnetic bubble devices. IR techniques coupled with electrical measurements have been used to optimize the cure conditions and a simple resist process has been defined to passivate these devices. Device performance compares well with conventional inorganic insulators. 

The desired polyimide derivatives were prepared by condensation polymerization as shown in Scheme 1. The initial polyamic acids (PAA 1-4) could be spun onto a substrate and cured by ramping the temperature to 260 C. For those examples where X=(CF3)2C, the polyimide derivatives were soluble in organic solvents. These materials were usually spun in the preimidized form. The improved thermal stability of the arylamino substituted chromophores tethered to the polyimide backbone is obvious from the DSC analysis. The onset decomposition temperature measured by DSC of the aryl substituted polymer PI-2b is almost 40°C hi er than that of Pl-lb (Td = 376 vs 338T). Likewise, this stabilizing effect is apparent variable temperature, UV-visible spectroscopic studies of the polymer films. In this case, the absorbance at the max of the chromophore was monitored versus time at a variety of temperatures (18), While the absorbance of PI-2b (Amax 498 nm) was little changed after one hour at 275°C, that of Pl-lb (Amax 474 nm) decreased by almost 30%. In each case, the heating was conducted under an inert atmosphere. Studies such as these are the origin of the data shown in the last column of Table I. 

Both the PAA-5 and the imidized form could be oriented by electrode poling. The former was poled by ramping the temperature slowly from 150-280°C (2 ). The decay of the orientated samples while heating at 37minute is shown in Figure 5. The lower orientational stability of the sample derived fi om the polyamic acid relative to the polyimide itself is believed to result from the lower cure temperature used for the former. Extrapolation of the decay curve from PI-5 poled at 300°C intersects the temperature axis aroimd 360°C which is close to the measured polymer Tg (i.e., 350°C). 

We report on the positive alkali-developable photosensitive polyimides based on an alkali-soluble polyimide precursor as a base polymer and diazonaphthoquinone (DNQ) sensitizer to improve process stability and sensitivity. Polyamic acid ester with pendant carboxylic acid (PAE-COOH) showed good dissolution behavior in aqueous alkali developer. The dissolution rate of PAE-COOH was controlled by the content of pendant carboxylic acid. It was found that a photosensitive system composed of butyl ester of PAE-COOH and a DNQ compound can avoid the residue at the edge of hole patterns (footing) after development, while that of methyl ester of PAE-COOH showed the residue. A DNQ compound containing sulfonamide derived from diaminodiphenylether renders improved sensitivity compared with DNQ compounds derived from phenol derivatives. 

Figure 7 sensitivity curves for photosensitive materials composed of polyamic butylester containing pendant carboxylic acid and a DNQ compound derived from tetrahydroxybenzophenone (O) and that from diaminodiphenylether ( ). 

Both negative and positive tone aqueous developable materials have been introduced. Negative tone materials have been derived from tbe covalent-type polyamic ester precursors through the use of additives that enhance solubility of the unexposed film in aqueous developers (53). Positive tone materials are based on either polyamic ester precursors containing carboxylic acid (54) or phenolic oxygen substituents (55,56) or on aromatic poly(ortho-hydroxyamides) as precursors to polybenzoxazoles (57,58), a class of high temperature stable, heterocyclic polymers with thermal and mechanical film properties similar to polyimides (Fig. 18). In both approaches, the acid-base reaction of the phenolic or carboxylic... 

First we needed to trace down if wholly aromatic polyimides existed that could be baked at lower temperatures. In the patent literature, the most used solvents to dissolve polyamic acids were cresols. By using certain cresol derivatives it was possible to form soluble polyimides from polyamic acids, and soluble polyimides were thus obtained and introduced to several LCD manufacturers that use these materials up to today. As a result (it will be regarded as obvious by now), the production of a prototype LCD, let alone the mass production of LCDs, would not have been possible without the disinfectant-like smell of cresol. The concept and the application to use soluble polyimide materials for low-temperature bakeable alignment films was not by mistake, but their research and development hit a big waU. 

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