Polyimides from isomeric

Another approach to the synthesis of polyimides from chloral derivatives involves the use of dianhydrides of isomeric tetracarboxylic acids containing central carbonyl or 1,1-dichloroethylene groups and two ether bonds as the starting electrophilic compounds [31-33] (Scheme 3.8). 

V.L. Bell, B.L. Stump, H. Gager, Polyimide structure-property relationships. II. Polymers from isomeric diamines, J. Polym. Sci., Part A Polym. Chem. 14 (9) (1976) 2275-2291. 

Diesters of Tetracarboxylic Acids with Diamines. Dianhydrides react with alcohols at a moderate temperature, producing the tetracarboxyhc acid diesters. Ben2ophenonetetracarboxyhc acid diester (BTTA diester) is obtained from B I DA as a mixture of three positional isomers. Partiy because it is an isomeric mixture, the diester of BTTA is soluble in methanol at high concentrations. A state-of-the-art thermoset polyimide,... 

Among these systems, polyimide with azobenzene chromophores in the backbone was first studied by Agolini and Gay in 1970 [30]. They reported 0.5% contraction of the polymer film at 200 °C taking place under ultraviolet irr liation. No correlation, however, was reported between the degree of isomerization and film contraction. At the high temperature they studied, the cis isomer content in the photo-stationary state would be very low, because a rapid thermal reverse reaction from the cis to the trans form should occur. Thus, the isomerization is not the sole origin of the contraction of the system. 

This new zeolite-catalyzed ring-shift isomerization could provide a new route to anthracene and its derivatives [Song, 1996], which are valuable chemicals in demand, from phenanthrene, which is rich in liquids from coal. Selective partial hydrogenation of phenanthrene would be needed as the first step. Possible applications of sym-OHAn include the manufacturing of anthracene (for dyestuffs and fine chemicals), anthraquinone (pulping agent), and pyromellitic dianhydride (the monomer for polyimides such as Du Pont s Kapton) [Song and Schol rt, 1993]. Fundamental research is needed to clarify the mechanisms and reaction pathways. 

A series of 15 wt % isomeric polyimide precursor resin solutions was prepared by the National Aeronautics and Space Administration Langley Research Center. The polymerization procedure has been described previously (2,3). The poly(amic-acid) resin solutions were made from 3,3, 4,4 -benzophenonetetracarboxylic acid dianhydride (BTDA), 4,4 -oxydiphthalic anhydride (ODPA), diaminobenzophenone (DABP), and methylenedianiline (MDA) monomers. 

Isomerization polymerization is feasible with lactams containing a carboxylic group capable of interacting with the lactam amide function it affords macromolecules whose repeating units derive from isomers of the original monomers. Tlius, the polymers obtained eu e polyimides rather than polyamides. 

A photomechanical effect involves a reversible contraction and expansion of an oriented rubbery film after irradiation, based on the change in the dimension of chromophores embedded in the polymer networks. This effect was first described, by Agolini and Gay [5], for a partly crystalline polyimide [see structure (2)] with azo-aromatic chromophores in the backbone. They reported a contraction of the polymer film at 200°C of 0.5% by UV irradiation, which in principle could cause isomerization of azobenzene chromophores from the trans- to cw-form. A correlation between the isomerization and the film contraction was not obtained. At this high temperature, however, the content of cw-isomer in the photostationary state is believed to be very low because of rapid back-reaction from the cis- to trans-form. At the same time, the rapid thermal reaction made it difficult to measure any correlation between the contraction and the isomerization. It seems that the isomerization may not be the sole origin of the contraction of this system. 

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