Polyimide chemical structures

The incorporation of fluorine into polyimide chemical structures affects many properties, and can impart superior performance to different properties simultaneously. Because of the great potential for dramatic advances in performance in many areas, fluorine-containing polyimides have been widely synthesized and studied. 

SCHEME 3.17 Chemical structures of polyimide materials used as hosts for NPD doping. 

Structural steels, tellurium in, 24 425 Structure(s), see also Chain structure Chemical structures Cocontinuous structures Controlled structure Crystal structure Molecular structure Morphology Phase structure of carbon fibers, 26 737-739 detersive systems for, 8 413t HDPE, 20 157-162 LLDPE, 20 182-184, 203-205 polyesterether elastomer, 20 72-73 polyester fiber, 20 21 polyether antibiotics, 20 137-139 polyimide, 20 276-278 polymer, 20 395-405 protein, 20 449 PTT, 20 68t... 

Principally, one commercially available sulfonated diamine (4,4 -diamino-2,2 -biphenyl disulfonic acid) has been used to synthesize sulfonated polyimides. In addition to the commercially available diamine, several novel sulfonated diamines incorporating flexible or kinked structures have been prepared in Okamoto s lab. " The chemical structures and names of all five diamines are shown in Figure 23. 

The chemical structures of thermosets are generally much more diverse than the commodity thermoplastics. The most common types of thermosets are the phenol-formaldehydes (PF), urea-formaldehydes (UF), melamine-formaldehydes (MF), epoxies (EP), polyurethanes (PU), and polyimides (PI). Appendix 2 shows the chemical structure of these important thermosetting polymers. 

Transient Tms have been observed in other systems (i.e. polyimides) and appear to be due to synthetic conditions coupled with chemical structure. Under the same synthetic conditions, polymers of certain chemical structures form transient crystalline phases whereas others do not For example, when the polyamide acid from the reaction of 3,3, 4,4 -benzophenonetetracarboxylic di-... 

The most important application for bismaleimide resin is multilayer boards. The development in this area requires resins with low dielectric constants. It is well documented in the literature that fluorine containing linear polyimides show lower dielectric constants vis a vis their non-fluorinated counterparts. Recently, Hitachi Research Laboratory, Japan, reported the thermal and dielectric behaviour of fluorine-containing bismaleimides (29). The chemical structures of the fluorinated BMIs investigated are provided in Fig. 6. The non-fluorinated four aromatic rings containing BMI, 4,4 -bis(p-maleimidophenoxyphenyl) propane, was tested in comparison. 

One resin based on the BTDA/ODA backbone and 2-aminobiphenylene as an endcapper was thought to be such a resin (126). High quality laminates could be fabricated, but the Tg of the crosslinked polymer was lower than expected and therefore thermal oxidative stability was poor. The chemical structure of this thermosetting polyimide is given in Fig. 42. 

The idea of synthesizing imide oligomers which carry acetylenic terminations appeared attractive because homopolymerization through acetylenic endgroups occurs without any volatile evolution and provides materials with good properties. Landis et. al (8,9) published the synthesis of such acetylene terminated imide oligomers from benzophenone tetracarboxylic anhydride, aromatic diamine and 3-ethynylaniline via the classical route. As usual, the amide acid is formed as an intermediate which, after chemical cyclodehydration, provides the polymide. Since ethynyl-terminated polyimide is used as a matrix resin for fiber composites, processing is possible via the amide acid, which is soluble in acetone, or via the fully imidized prepolymer, which is soluble in NMP. The chemical structure of the fully imidized ethynyl-terminated polyimide is provided in Fig. 44. 

As in all thermosetting polyimides, the diamine and the tetracarboxylic dianhydride employed to build the backbone can be varied. Alteration of the diamine, tetraacid or both, allow the modification of the polyimide s melting point and solubility. Of interest to the end user is the influence of chemical structure on the melting transition of the prepolymer and the Tg of the fully cured product. Lowering the uncured Tg means increasing flow and, in most... 

The key to acetylene terminated polyimides is the availability of the end-capper which carries the acetylene group. Hergenrother (130) published a series of ATI resins based on 4-ethynylphthalic anhydride as endcapping agent. This approach first requires the synthesis of an amine-terminated amide acid prepolymer, by reacting 1 mole of tetracarboxylic dianhydride with 2 moles of diamine, which subsequently is endcapped with 4-ethynylphthalic anhydride. The imide oligomer is finally obtained via chemical cyclodehydration. The properties of the ATI resin prepared via this route are not too different from those prepared from 3-ethynylaniline as an endcapper. When l,3-bis(3-aminophenox)benzene was used as diamine, the prepolymer is completely soluble in DMAc or NMP at room temperature, whereas 4,4 -methylene dianiline and 4,4 -oxydianiline based ATIs were only partially soluble. The chemical structure of ATIs based on 4-ethynylphthalic anhydride endcapper is shown in Fig. 45. 

Table 13.1. Chemical Structures of Dianhydrides from Polyimides Where One or Both Monomer Components Are Fluorinated...

Fluorinated polyimides have been made with a broad range of chemical structures and possess an equally wide range of properties. Their value as low-dielectric, hydrophobic, and thermally stable materials is now well established in industry, and work continues to try to further understand underlying principles of structure-property relationships. 

Shimadzu, A., Miyazaki,T., Maeda, M. and Ikeda, K. (2000) Relationship between the chemical structure and the solubility diffusivity and permselectivity of propylene and propane in 6-FDA-based polyimides. Journal of Polymer Science Part B-Polymer Physics, 38, 2525. 

Not only do the chemical structure and the molecular weight affect the processability but also the method of synthesis, in particular the imidation step. Thermally imidized polyimides are always less tractable than solution imidized polyimides. That is because thermally imidized polyimides can undergo cross-linking, and because thermal treatment (about 300 °C) favour chains packing and provide higher molecular order than that achievable by solution imidation. Therefore, solution imidation is always preferable when thermoplastic polyimides are to be developed. 

With regards to crystallinity, aromatic polyimides are recognized as semirigid polymers that can crystallize in many instances, and, in fact, crystallinity has been reported for many polyimides. They can spontaneously crystallize when the chemical structure and the synthesis method are favourable, or they can develop crystallinity after an appropriate thermal treatment [65,66,74,75]. 

Figure 1. Chemical structure of a polyimide (PI) unit cell (top), phthalimide (pim) and methyl-phthalimide (mpim) (bottom, left), and the model systems NH(CH0)2 and NCH3(CHO)2 (bottom, right).

Figure 1. Chemical structure of PMDA/ODA polyimide (PI) monomer unit, benzene (BE), phthalimide (PIM), benzene-phthalimide (BPIM), methyl-phthalimide (MPIM), and malonamid (MAM).

The surface chemical structure of several thin polyimide films formed by curing of polyamic acid resins was studied using X-ray photoelectron spectroscopy (ESCA or XPS). The surface modifications of one of the polymer systems after exposure to KOH, after exposure to temperature and humidity, after exposure to boiling water, and after exposure to O2 and 02/CF plasmas were also evaluated. The results showed imide bond formation for all cured polyimide systems. It was found that (a) K on the surface of the polyamic acid alters the "normal" imidization process, (b) cured polyimide surfaces are not invarient after T H and boiling water exposures, and (c) extensive modifications of cured polyimide surfaces occur after exposures to plasma environments. Very complex surfaces for these polymer films were illustrated by the C Is, 0 Is, N Is and F Is line characteristics. 

The chemical structure of the polyimide polymers (named PI-1 and PI-2) studied by Sekkat et al. is shown in Figure 12.12. They prepared the polymer samples by spin-casting onto glass substrates. PTl was cast from a cyclohexanone solution and PI-2 from 1,1,2,2- tetrachloroethane. The Tg values of PI-1 and PI-2 were determined to be 350°C and 252 C, respectively, by scanning calorimetry method. The thicknesses of the PI-1 and PI-2 films were, respectively, approximately 0.72 im and 0.14 im, and their respective optical densities were approximately 0.79 and 0.3 at 543.5 nm. Details of the preparation and characterization of the samples can be found in References 3 and 20. In their EFISH experiment, a typical corona poling technique was used to pole the samples, with a dc electric field about 2-3 MV/cm across a 1-2 lm thick polymer film. They used the SHG output from the EFISH experiment to in situ monitor the photochemical change in the third-order susceptibility of the PI-1 and PI-2 polymers. 

Fig. 7 Chemical structures of some sulfonated polymers and a polyimide (A) sulfonated polyetheretherketone, PEEK, PSE (B) sulfonated polyphenylenesulfide, PPS (C) sulfonated polysulfone (D) poly(4,4 -biphenol) (4,4 -dichlorodiphenyl sulfone), BPSH-XX (XX is mol% of disulfdonated units) (E) sulfonated polybenzimidazole, PBI (F) polyimide.

Three kinds of aromatic poly(amic acid)s that contain acetylene groups in the main chain were cured in air at temperatures up to 400 °C to give intermolecular crosslinked polyimides. The crosslink reactions occurred at the internal acetylene units and the chemical structures thus generated have been investigated by high resolution solid-state CPMAS NMR. ... 

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