Polyimides preparation

Diacetone alcohol has been recently claimed as a solvent for polyimide preparation. According to the patent,107 ODA was dissolved in the solvent and then PMDA added to the solution. The patent claims good storage stability and easy removal of the solvent (boiling point 166°C). 

TABLE 1. Physical Properties of d-Polyimides Prepared by Condensing Pyromellitic Dianhydride with Deuterated o-Tolidine and then Heating to 200-300°C... 

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... 

Stability for use in optical interconnects. In the near future, optoelectronic integrated circuits and optoelectronic multichip modules will be produced. Materials with high thermal stability will thus become very important in providing compatibility with conventional 1C fabrication processes and in ensuring device reliability. Polyimides have excellent thermal stability so they are often used as electronic materials. Furuya et al. introduced polyimide as an optical interconnect material for the first time. Reuter et al. have applied polyimides to optical interconnects and have evaluated the fluorinated polyimides prepared from 6FDA and three diamines, ODA (3), 2,2-bis(3-aminophenyl) hexafluoropropane (3,3 -6F) (4), and 4,4 -6F (2), as optical waveguide materials. 

Figure 15.20. Schematic representation of refractive index ellipsoids of (a) polyimide prepared on isotropic substrates, and (b) uniaxially drawn polyimide.

Considerable research effort has been devoted in recent years to the use of chloral derivatives for the synthesis of linear heterocyclic polymers. Of these, the most common are aromatic polyimides [1-12], Many of these polymers have been synthesised from compounds like 4,4 -diaminobenzophenone, and other diamines, which, as demonstrated in the previous chapter, can be obtained from chloral. Polyimides prepared from these diamines were largely synthesised by the conventional two-step procedure [11, 12] involving mild reaction of the diamines with the bis(phthalic)anhydrides, isolation of poly(o-carboxy)amide (PCA) prepolymers, and then processing into products followed by thermal or chemical imidisation [13—16] (Scheme 3.1). Some properties of polyimides prepared from 4,4 -diaminobenzophenone are provided in Table 3.1. 

The thermal stability of polyimides prepared from l,l-dichloro-bis(3-amino-4-chlorophenyl)-ethylene is lower than that of polyimides prepared with other 3,3 -diamino-4,4 -dichloroarylenes, in particular 3,3 -diamino-4,4 -dichlorobenzophenone. This suggests a negative effect of 1,1-dichloroethylene groups on thermal stability in these polymers. Based on softening temperatures, the heat resistance of polyimides with different dianhydride residues decreases in the series ... 

The effect of aromatic diamine residues on the heat resistance of polyimides is less clear cut. It was only by comparing thermomechanical curves of polypyromellitimides obtained from 3,3-diamino-4,4 -dichlorodiphenylmethane, and l,l-dichloro-2,2-di(3-amino-4-chlorophenyl)-ethylene that the system containing the 1,1-dichloroethylene group was found to be less heat resistant. With polyimides prepared from other dianhydrides this rule holds true as well but is less distinct. 

Polyimides prepared from 3,3 -diamino-4,4 -dichloroarylenes, particularly those containing 1,1-dichloroethylene groups, are peculiar in that they are soluble in organic solvents. Polymers formed from... 

Viscosity of polyimides prepared by catalytic imidisation of PCA using a pyridine-acetic anhydride complex viscosity measured in trichloroethane (TCE)/phenol. 

Up to the decomposition temperature, polypyromelliteimide based on 3,5-diaminoanisole does not soften. The softening points of polyimides prepared from benzophenonetetracarboxylic and diphenyloxidetetracarboxylic acid dianhydrides are 300 and 310 °C, respectively, (Table 5.1). 

None of the polyimides synthesised dissolve in amide solvents, including NMP. Moreover, the polyimide prepared from 3,5-diaminoanisole and diphenyloxidetetracarboxylic acid dianhydride is soluble in OT-cresol and a mixed trichloroethane/phenol (3 1) solvent, whereas the polypyromelliteimide and polyimide based on benzophenonetetracarboxylic acid dianhydride do not dissolve in these phenolic solvents. 

The attempt to synthesise this polyimide in t77-cresol using high-temperature condensation was not very successful since, although the synthesis proceeded in a homogeneous system, the viscosity of the polymer solution in w-cresol was significantly lower than that of the corresponding polyimide prepared using the catalytic PCA-cyclisation process (Table 5.1). 

As can be seen from Table 5.3, the polyimides prepared demonstrate relatively low refractive indices (RI) and dielectric constants (e). This observation is in a good agreement with known results [21]. 

Comparison of these properties with the properties of the polyimides prepared on the basis of... 

Figure 5 represents the temperature dependence of inherent viscosity of the polyimide prepared by the polycondensation of salt monomer ODPMA for 1 h [27]. From the DSC and TG studies, the aromatic salt monomer was found to undergo polycondensation at the endothermic peak temperature of 220 °C. The polymerization at a temperature lower than 220 °C resulted in the polymer with low viscosity value. The inherent viscosity of the polymer increased with in-... 

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]. 

LARC TPI is a linear polyimide prepared with BTDA and 3,3 -diaminobenzo-phenone. The polyamide acid intermediate was used to prepare a semi-IPN with the PMR-15 reactants. After curing the blend exhibited a twofold Tg and an improved value of Glc (Table 8). 

The role of the miscibility of semi-IPN components on the mechanical properties has been discussed. The linear bisnadimide was a benzhydrol bisnadimide (Fig. 33). Three polyimides prepared from the same diamine and three different dianhydrides (Fig. 37) were used as linear components. The blends were cured up to 300 °C in a similar fashion to the bisnadimide alone. The results for the blend containing 20% by weight of linear polymers are summarized in Table 9. The non-miscible character of the components gives a phase segregation leading to the best toughness [121]. 

The semi-IPN concept has also been used in order to improve the high-temperature adhesive properties of a flexible polyimide. Polyimide prepared with isophthaloyldiphthalic anhydride and mefa-phenylenediamine presents good adhesive properties but is limited to 270 °C. By blending it with a bisnadimide... 

TABLE 1. d -Polyimides prepared from perdeuterated dianhydrides and diamines and physical properties of the corresponding polymer. 

The polyimides prepared with 6F dianhydride (Table II) were exceedingly soluble in the solvents studied. Solubility increased with incorporation of meta or ortho isomerism which serves to create more "kinks and dissymmetry in the polymer chains. The same trend was observed for ODPA-containing films (Table III) except to a lesser degree. Ortho isomerism appeared to have a greater effect on the solubility of ODPA films than did meta isomerism as had been noted previously. ( )... 

Soluble polyimide prepared by reaction of 4,4 -hexanuoroisopropylidene diphthalic anhydride (6F) with 3,5-diaminobenzoic acid. 

Recently St. Clairs [48] reported that polyimides prepared from a bis(ether anhydride) and p-phenylenediamine and benzidine were crystalline as shown below... 

Figure 1. Infrared spectra (KBr) of (A) polyimide prepared by photolysis of benzene sobitions of ii,N -hexarnethylenebistnaleirnide (B) polyimi prepared from benzene-maleic anhydride photoadauct (2) and 1,6-hexanediamine and (C) the N,N -bis(n-...

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