PolyAM chains

Also we have not considered the possibility of grafting on grafted polyAM chains. If this could happen efficiently, the graft layer should have grown much thicker. Relevant to this problem, grafting onto poly(ethylene-g-maleimide) was not observed in photoinduced graft polymerization of maleimide to polyethylene... 

Figure 5.11. (a) A polyamic salt which will spread at the air/water interface and form LB films. (b) A polyimide which can be produced as a multilayer by heating a multilayer of the polyamic salt and driving oif the long chains associated with the salt. 

Main Chain Polymers. Another system of dye attached polymers is a polyamic acid and a polyimide with a Tt-electron conjugation in the main chain. The Tt-electron conjugated system is not an intramolecular charge transfer system, unlike the azo and stilbene dye mentioned above. The polyamic acids (PAAs) were obtained through the reaction of a carboxylic acid anhydride and a diamine. A Tt-electron conjugated system exists in the diamine compound. These polyamic acids were soluble in conventional solvents and... 

The experimental procedures and x-ray photoemission results for the preparation of ultrathin (d = 1.1 nm) polyimide films on polycrystalline silver by co-condensation of PMDA and ODA are described elsewhere [5]. In that work our XPS results suggested that the polyimide chains bond to the silver surface via a carboxylate type bonding. This conclusion was derived from an analysis of the results obtained for the interaction of the monomers (PMDA and ODA) and of the resulting ultra-thin polyimide film. Due to the relatively larger thickness of the polyamic acid films as compared to the monomer adsorbate phases and the polyimide film, no conclusions were possible about the reaction of the polyamic acid with the silver substrate. 

The interaction of the polyimide chains via carboxylate type bonds is however clearly evident in spectra 7b for the cured polyimide film on polycrystalline silver. In addition to the characteristic vibrational modes of bulk polyimide we find two strong bands at 1600 cm 1 and 1440 cm 1 not present in the bulk spectra in the thick film (7c). These are interpreted as arising from the polyimide-silver carboxylate type interface bonding as discussed above for polyamic acid. The presence of both the asymmetric and symmetric V(C00 stretch could again be due to a preferential monodentate bonding configuration or to the polycrystalline nature of the substrate. 

The present method consists of three steps as illustrated in Scheme 1. In the first step, monolayer films of polyamic acid long chain alkyl-amine salts 4 at the air-water interface are prepared.(9) Unexpectedly, the polyamic acid 3 itself, which possess hydrophilic carboxyl functions in the polymer backbone, did not afford a stable monolayer at the air-water interface. Introduction of a hydrophobic long alkyl chain into 3 was performed by mixing polyamic acids and longchain alkylamines. Polyamic acid salts 4, thus obtained, afforded very stable monolayer films at the air-water interface. In the second step,(10) the polyamic acid salt monolayer films are successfully deposited on appropriate plates such as glass, quartz, or silicon wafer. Finally polyimide multilayer films are obtained by treatment of polyamic acid salt multilayer films on the plates with a mixture of acetic anhydride and pyridine. 

In the IR spectrum of polyimide films of 5a, the absorption-due to hydrocarbon group of the film disappeared, and new characteristic absorptions corresponding to the imide carbonyl groups appeared at 1780 and 1720 cm. This suggested that the cyclization of the polyamic acid salt to polyimide 5a proceeded almost completely with the removal of the long chain alkylamine. 

Hence, the theoretical calculations and the conclusions on the free unhindered motion about the oxygen bridges in the main chain of polyamic acid have been confirmed. 

A similar analysis of the shape of curves Y(Tlrj) for labeled polyamic acid and numberical calculations of the rotatory diffusion coefficients of its units show that the relaxation behavior of a chain is similar to that of a model chain with free internal rotations. This result is in agreement with the data on other conformational and hydrodynamic properties of PAA ° and with theoretical conformational... 

This paper shows the kinetic data for the imidization reaction of several polyamic acids and polyamic acid derivatives. An evaluation of the data with respect to polymer chain chemistry and acid substitution is given. 

The curing behavior of PMDA-ODA (Figure 1) has been analyzed previously The overall process is characterized by various physical and chemical steps Decomplexation of the complex formed between NMP and polyamic acid 2 3 6 plasticization of the material by the decomplexed NMP n 12 evaporation of the solvent cycloimidization accompanied by re-formation of anhydride and amine, a side reaction which leads to chain scission 2 vitrification caused by solvent evaporation and imidization and finally molecular ordering of the polyimide near and above the glass transition n 13 14. The particular features of all these processes are heating rate dependent (e.g. compare Figure l.a and l.b) 2 n. 

Comparison of Chain Dimensions. Knowledge of the intrinsic viscosities and molecular weights of a series of PMDA/DAPE polyamic acids allows estimation of the unperturbed chain dimensions. Comparison may then be made with the cured polyimide, with results obtained by other workers, and with calculated values. The expressions in the literature using values for [n] obtained in good solvents generally involve extrapolation of [t)]/M toM = 0, where excluded volume effects are presumed to be minimal (12-14). Although this method is not strictly valid, it is useful for comparison purposes when direct measurement of the dimensions is impractical. The data in Table I for the polyamic acid in distilled NMP and in the poorer mixed solvent NMP/dioxane yield (see Figure... 

For example, it is possible to prepare hyperbranched polyimides from 3,5-dimethoxyphenol and 4-nitrophthalonitrile in the presence of diphenyl(2,3-dihydro-2-thioxo-3-benzoxazolyl) phosphonate (DBOP) as a condensation agent at room temperature. Hyperbranched polyimide was obtained through thermal or chemical imidization of the precursor (polyamic acid) (Scheme 1.3) [19]. The obtained hyperbranched polyimide had a relatively great molecular mass (A/ ) of about 190000gmor but low inhinsic viscosity of 0.30 dLg . Therefore, it had a compact configuration and the lack of entanglement of polymer chains. The polymer obtained via chemical imidization was soluble in apiotic polar solvents such as tetrahydrofuran (THF), while the polymer from thermal imidization was insoluble in any solvents. 

In order to better understand miscibility in polyimide-based systems. Sun et al. (1991) prepared pairs of polyimide blends with different molecular structures by two ways, mixing of the polyamic acid precursors with subsequent imidization and direct solution mixing of the polyimides. Dynamic mechanical analysis (DMA) techniques showed that aU of the blends prepared in the two different ways were miscible, as evidenced by the existence of only one Tg for all of the blends. It was proposed that the miscibility of these polyimide/polyimide blends is a result of the strong intermolecular charge-transfer interaction between the chains of the blend components. 

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