Polyimides containing ester

Sillion et al [47] prepared polyimides containing benzhydrol groups by using the reduction product of benzophenonetetracarboxylic acid dimethyl ester shown below. 

Poly(benzimidazoles) have become commercially important. Whereas polyimides contain two carboxyl groups per amine group, two amine groups are allowed to react with a carboxyl group in poly(benzimidazole) manufacture. Diphenyl esters are used as dicarboxyl compounds, since (a) the free acids decarboxylate under the reaction conditions (250°C at first, subsequently 400°C), (b) the acyl chlorides react too quickly, so that ring closure becomes difficult, and (c) with methyl esters, the amino groups become partially methylated. Moreover, eliminated phenol can easily be washed out. Typical materials are 3,3 -diaminobenzidine and diphenyl... 

They are generally dianhydrides containing ester groups. The polymerization scheme for these monomers to yield polyimides by reaction with diamines is depicted in Scheme (26). 

Polyimide esters, (IV), prepared Buchecker [3], containing a photoactive side chain were used as orientation layers for liquid crystals and in the construction of both unstructured and structured optical elements. 

Polyimides, and derivative copolymers such as poly(ester-imide)s have been known for decades but none were reported before 1987 to contain lyotropic or thermotropic mesophases, except certain copoly(esterimide)s with three or more monomers [6,7]. 

In 1994 Kricheldorf reviewed the field and showed that it was difficult to obtain LC-polyimides free of ester groups. Only three classes were then cited, with ether or amide supplementary linkages, which contained either aliphatic spacers in the main chain with a high tendency to form layer structures in the solid state, or a fully aromatic chain sufficiently substituted to stabilise the formation of nematic phases [41]. 

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. 

Hyperbranched polyimides can result due to the self-polycondensation reactions of AB2-, A2- and Bs-types. The preparation of hyperbranched polyimides involves chemical imidization of polyamic acid ester synthesized from AB2-monomers, which are carboxylic dianhydrides containing an ether bond and a diamine [6,19,76]. Polyamic acid in combination with a condensation agent is used because it is difficult to separate the synthesized polymer from AB2-type monomers. 

Common laminating resins used are phenolic and epoxy, although cyanate esters, polyimides, and other resins are used in specialty applications. The copper foil used is 99.5 percent pure and may contain some silver. Generally, electrodeposited foil is used rather than rolled copper, and the foil is usually treated to improve the adhesion of the laminating resin to the foil surface. 

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... 

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