Precursors of polyimides

In the case of the synthesis of polyimide, the polymerization solvent used for polyamic acid (a precursor of polyimide) is usually dimethyl acetoamide (DMAC). We found that clay ion-exchanged dodecyl ammonium ions could be homogeneously dispersed in DMAC. A solution of this organophilic clay and DMAC was added to a DMAC solution of polyamic acid. The film was cast from a homogeneous mixture of clay and polyamic acid, and was heated at 300 °C to achieve the desired polyimide clay nanocomposite film. Its permeability to water decreased to 50% upon addition of 2.0 wt% clay [13]. It was confirmed that its permeability to carbon dioxide also decreased by half [14]. 

Figure 15 Synthesis of oligoimide 31 precursor of polyimide 32 by thermal polycondensation of self-condensable monomers 30a and 30b carrying amine and ort/to-acid-ester groups on the same molecule.

Polyamlc Acid [(from poly(amide-acid)] A polymer containing both amide and acid groups. The aromatic varieties are precursors of Polyimides. 

Choi and Lee prepared poly(benzoxazole-co-pyrrolone) copolymers in various compositions from their precursors of polyimides containing both... 

Polycondensations by means od DBOP or TPP also proved useful for the preparation of hb polymides which served as precursors of polyimides [47-49] ((a) Formula 11.6) or polybnezoxazole)s (from (b) or (c) in Formula 11.6 [50-54]. For the best polyimide a DB of 0.48 and a Mw of 188 kDa were determined (by SEC-MALLS). Polycondensations of di or multifunctional aromatic amines and carboxylic acids in the melt are usually not successful, because the high temperatures (>300 °C) are needed to keep the reaction products in the molten state to cause partial decarboxylation. However, in the case of monomer (c). Formula 11.5, polycondensation at 235 °C proved successful, and a Mw of 74 kDa with a PD of 2.6 was achieved [54]. 

Methods of preparation of the laminates depend on the partieular grade of polyimide resin used but in one process the polyimide precursor is dissolved in acetone and this solution is used to impregnate the glass or carbon fibre and thus produce a pre-preg . The pre-preg is dried and then pre-cured at about 200°C for about 3 hours. This operation reduces the volatile content and also modifies the flow properties to make them more suitable for the subsequent... 

Photosensitive functions are in many cases also heat sensitive, so the preparation of photosensitive polyimides needs smooth conditions for the condensations and imidization reactions. Some chemical reactants, which can be used for polyamide preparation, have been patented for the synthesis of polyimides and polyimide precursors. For example, chemical imidization takes place at room temperature by using phosphonic derivative of a thiabenzothiazoline.102 A mixture of N -hydroxybenzotriazole and dicyclohexylcarbodiimide allows the room temperature condensation of diacid di(photosensitive) ester with a diamine.103 Dimethyl-2-chloro-imidazolinium chloride (Fig. 5.25) has been patented for the cyclization of a maleamic acid in toluene at 90°C.104 The chemistry of imidazolide has been recently investigated for the synthesis of polyimide precursor.105 As shown in Fig. 5.26, a secondary amine reacts with a dianhydride giving meta- and para-diamide diacid. The carbonyldiimidazole... 

Shobha, H. K., Sankarapandian, M., Glass, T. E. and McGrath, J. E. 2000. Sulfonated aromatic diamines as precursors for polyimides for proton exchange membranes. Abstracts of Papers of the Americttn Chemical Society 220 11278-11278. 

The solution behavior of poly(amic acids) was until recently, probably the least understood aspect of the soluble polyimide precursor. However, the advent of sophisticated laser light scattering and size exclusion chromatography instrumentation has allowed elucidation of the solution behavior of poly(amic adds). In the early days of polyimide chemistry, when most molecular weight characterization was based on viscosity determinations, a decrease in viscosity was associated with molecular weight degradation [15, 28, 29]. Upon combination of the two monomers an increase in the viscosity to the stoichiometric equivalence point is observed, followed by a decrease in the solution viscosity as a... 

Polyimides. In situ co-deposition of metal salts such as Co(II), or LiCl into a polyimide precursor from 3,3, 4,4 -tetracarboxybenzophenone dianhydride and 4,4 -diaminobenzophenone with subsequent thermal curing offers surface-conductive polyimide film [43]. By similar procedures, Taylor et al. prepared a series of polyimides modified with Pd, Pt, Ag, Au, Cu, Sn, Ti and magnetic-Fe [44, 45, 46]. 

The reaction sequence for the synthesis of polyimides is shown in Scheme I. The imide ring is formed via a thermally initiated condensation reaction from a polyamic acid, a soluble precursor polymer synthesized from... 

In addition to the polymer and facilitated transport membranes, novel materials are being proposed and investigated to achieve membranes with economically attractive properties. Carbon molecular sieve (CMS) membranes prepared by pyrolysis of polyimides displayed much better performance for olefin/paraffin separation than the precursor membranes [39, 46, 47]. Results obtained with CMS membranes indicated properties well beyond the upper-bond trade-off curve, as shown in Figure 7.8. Nonetheless, this class of materials is very expensive to fabricate at the present time. An easy, reliable, and more economical way to form asymmetric CMS hollow fibers needs to be addressed from a practical viewpoint. 

Structural modifications were envisioned early to overcome these limitations. A first improvement was outlined by preparing copolymers, which were soluble in the state of full imidation, mainly poly(ester-imide)s and poly(amide-imide)s [2,4, 5]. As an alternative to these conventional copolymers, addition polyimides were developed in the 1970s as a new class of thermosetting materials. Thus, bismaleimides, bisnadimides, and end-capped thermocurable polyimides were successfully developed and marketed [6,7]. These resins were the precursors of the modern PMR (polymeric monomer reactants) formulations [8]. 

Takeichi, T., Eguchi, Y., Kaburagi, Y., Hishiyama, Y., Inagaki, M. (1999) Carbonization and graphitization of BDPA/PDA polyimide films effect of structure of polyimide precursor, Carbon 37(4), 569-575. 

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