Soluble aromatic polyimides

The recently reported value of q = 13 nm for a soluble aromatic polyimide containing entirely 77-catenations - exemplifies the differences that symmetry makes in terms of the persistence length. We did not obtain the persistence... 

Structural modifications to attain soluble aromatic polyimides have also been carried out by introducing bulky substituents, aryl or heterocyclic rings. One of the first references to this approach was made by Korschak and Rusanov, who synthesized soluble aromatic polyimides containing side phthalimide groups [85 ]. More recent work by Rusanov et al. has enriched this topic with new soluble polyimides containing pendent imide groups [86,87]. 

Fluorinated polyimides have achieved great importance as barrier materials during the last few years. Many experimental polyimides prepared from fluorine-containing monomers, mainly novel diamines, show an advantageous balance of permeability and selectivity for technical gases and vapours, which makes them very attractive for the fabrication of permselective membranes [119]. This is an application field showing very rapid expansion, where there exists a strong demand for new polymeric materials, and where soluble aromatic polyimides are considered as a real alternative [136-146]. 

Soluble Aromatic Polyimides for Film and Coating Applications... 

King, F. 1985. Synthesis and characterization of new soluble aromatic polyimides. Journal of Engineering Thermoplastics. 315. 

The molecular design of organo-soluble aromatic polyimides used in the optical applications has been focused on the issue to interrupt the electron conjugation along... 

We have investigated many macroscopic properties of the organo-soluble aromatic polyimide films and all of them exhibit anisotropic behaviors which are closely associated with the anisotropic structure in the films. One question still remains is whether we can find a common physics background to describe these properties. If we consider the fi-ee energy (or internal energy or energy) term, the first derivative of... 

In summary, we have briefly reviewed our understanding in the development of organo-soluble aromatic polyimides via molecular design and architecture control and the establishment of relationships between the anisotropic structure and properties in the films. These anisotropic structures and properties are also found to be film thickness and molecular weight dependent. In particular, the LOA behavior has led to a invention where these aromatic polyimide films can be used as UNB retardation compensators in LCDs to increase viewing angles. This technology initiated from our researches has been commercialized to produce compensators for wide applications in LCDs,... 

To investigate the additional effect of triphe-nylamine (TPA) moieties on >C(CF3)2 containing polyimides, Liou et al. [183] synthesized a series of novel organo-soluble aromatic polyimides bearing pendant methoxy-substituted TPA moieties. They also prepared the same polyimide series without the >C(Cp3)2 group to compare their physical properties. A synthetic scheme of the TPA containing polyimide series is shown in Scheme 3.19. All of the... 

Liou, G. S. et al. Preparation and properties of new soluble aromatic polyimides from 2,2 -bis(3,4-dicarboxyphenoxy) biphenyl dianhydride and aromatic diamines. J. Polym. Sci. Part A,Polym. Chem. 36(12), 2021-2027 (1998). 

Optical properties, of colorless polyimides, 277-279 Optical rotation, 490 Opto-electronic targets, 271-272 Organic phase-soluble aromatic polyesters, 77... 

Aromatic polyimides are synthesized by the reactions of dianhydrides with diamines, for example, the polymerization of pyromellitic anhydride with p-phenylenediamine to form poly(pyromeUitimido-l,4-phenylene) (XLV) [de Abajo, 1988, 1999 Hergenrother, 1987 Johnston et al., 1987 Maier, 2001]. Solubility considerations sometimes result in using the half acid-half ester of the dianhydride instead of the dianhydride. 

The classical synthetic pathway to prepare polyimides consists of a two-step scheme in which the first step involves polymerization of a soluble and thus processable poly(amic acid) intermediate, followed by a second dehydration step of this prepolymer to yield the final polyimide. This preparative pathway is representative of most of the early aromatic polyimide work and remains the most practical and widely utilized method of polyimide preparation to date. As illustrated in Scheme 4, this approach is based on the reaction of a suitable diamine with a dianhydride in a polar, aprotic solvent such as dimethyl sulfoxide (DMSO), dimethylacetamide (DMAc), dimethylformamide (DMF), or AT-methylpyrrolidone (NMP), generally at ambient temperature, to yield a poly(amic acid). The poly(amic acid) is then cyclized either thermally or chemically in a subsequent step to produce the desired polyimide. This second step will be discussed in more detail in the imidization characteristics section. More specifically, step 1 in the classical two-step synthesis of polyimides... 

PFMB can be used to prepare aromatic polyimides that display solubility in ketone, ether, and polar aprotic solvents. This unusual solubility can be utilized in die facile preparation of thin films that display anisotropy in their structures and properties. The anisotropy in the optical properties of the films makes them promising candidates for use as compensation layers in liquid-crystal displays. Their low dielectric constants and CTEs in combination with their outstanding thennal and thermooxidative stabilities make diem candidates for dielectric layers in microelectronics applications. 

Trinitrotoluene (TNT)-based aromatic diamines are used for the preparation of substituted polyimides. Interest in substituted polyimides is very understandable due to the known poor tractability of unsubstimted aromatic polyimides [1—4], As is known, the introduction of methoxy substituents to macromolecules of polyimides enhances their solubility in organic solvents [5]. One of the simplest TNT derivatives, 3,5-diaminoanisole, is used for the preparation of methoxy-substituted polyimides [6]. 

Aromatic polyimides are most useful super engineering plastics which exhibit excellent thermal, electrical, and mechanical properties, and have been used widely in aerospace, electronics, and other industries over the past three decades [ 1 -4]. Aromatic polyimides are generally prepared through a two-step procedure by the ring-opening polyaddition of aromatic diamines to aromatic tet-racarboxylic dianhydrides in NMP (or DMAc) solution giving soluble polyamic acids, followed by thermal cyclodehydration (Eq. 1) [1-5]. 

This review article deals with aromatic polyimides that are processable from the melt or soluble in organic solvents. Conventional aromatic polyimides represent the most important family of heat resistant polymers, but they cannot be processed in the melt, and their application in the state of soluble intermediates always involves a hazardous step of cyclodehydration and elimination of a non-volatile polar solvent. A major effort has therefore been devoted to the development of novel soluble and/or melt-processable aromatic polyimides that can be applied in the state of full imidation. The structural factors conducive to better solubility and tractability are discussed, and representative examples of monomers showing favourable structural elements have been gathered and listed with the chemical criteria. Experimental and commercial aromatic polyimides are studied and evaluated by their solubility, transition temperatures and thermal resistance. An example is also given of the methods of computational chemistry applied to the study and design of polyimides with improved processability. 

Fortunately, aromatic polyimides could be used as materials because they can be prepared through a multistep process, being applicable in the state of soluble polymeric intermediate. Nevertheless, the transformation into polyimides at the moment of application is an approach far from being optimal in most cases, and it can be said that, for many years, aromatic homopolyimides could be successfully applied only in the form of films or coatings [2,3]. 

As mentioned before, the first generation of fully aromatic homopolyimides, could be used in a few applications because they had to be applied in the form of soluble polyamic acids, and this limited the materials to be transformed almost exclusively into films or coatings [2,10]. They all had to be synthesized by a two-step method, as exemplified for an aromatic polyimide from pyromellitic dianhydride in Scheme 1. The method involves the synthesis of a soluble polyamic acid, which, after shaping, can be converted to the related polyimide by a thermal or a chemical treatment. Abundant literature is available on the methods and the mechanisms involved in the synthesis of these polymers [3,4,11-13]. 

Table 3 shows the Tg values and solubility of some selected polyimides among those prepared from monomers of Tables 1 and 2. The combination of non-pla-nar dianhydrides and non-planar, raefa-oriented aromatic diamines containing flexible linkages provides the structural elements needed for solubility and melt processability. Some aromatic polyimides marketed as thermoplastic materials are based on these statements [9,57-60]. 

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