Poly chemical imidization

The chemical imidization of poly(amic alkyl esters) was only reported very recently [59], although reports in the literature claim chemical imidization with a traditional acetic anhydride/pyridine mixture [87]. The chemical imidization of poly(amic alkyl esters) is based on the observation that PMDA/ODA based poly(amic ethyl ester) samples, when formulated at low concentrations for size exclusion chromatography, precipitated upon standing overnight [88]. Distillation of the NMP from phosphorus pentoxide to remove low levels of methyl-amine, a known impurity in this particular solvent, eliminated this unusual behavior. The precipitated polymer had significant levels of imidization as evidenced by IR. Apparently, organic bases, such as alkyl amines, were able to catalyze the conversion of amic alkyl esters to the corresponding imide. 

Hedrick JC, Arnold CA, Zumbrum MA, Ward TC, McGrath JE (1990) Poly(arylene ether ketone)/poly(aryl imide) homo- and polydimethylsiloxane segmented copolymer blends influence of chemical structure on miscibility and physical property behavior. 35th International SAMPE Symposium, pp 82-96... 

As a final example of the use of proton NMR invoking spin diffusion to study miscibility of polymer blends, the use of CRAMPS to remove proton dipolar coupling in a blend of an aromatic poly(ether-imid) (PEI), and a poly(aryl-ether-ketone) (PEEK), with detection of the magnetization of the C in the blend under high resolution conditions is cited [51]. Here, detailed information on the chemical composition of the phases present, as inferred from high resolution NMR of C, is linked to typical sizes of domains as reflected in spin diffusion of proton magnetization. 

Figure 10.12 shows the and NMR spectra of poly(ether-imide)/ poly(aryl ether ketone) (PEI/PAEK) obtained from the chemical-shift selective Goldman-Shen experiment with (the righthand side) and without (the lefthand side) detection [108]. The signals from the aliphatic protons of PEI at 2 ppm are resolved from the aromatic protons of PEI and... 

The solubility of the polyimide dictates, to a large extent, the synthetic route employed for the copolymerization. The ODPA/FDA and 3FDA/PMDA polyimides are soluble in the fully imidized form and can be prepared via the poly(amic-ac-id) precursor and subsequently imidized either chemically or thermally. The PMDA/ODA and FDA/PMDA polyimides, on the other hand, are not soluble in the imidized form. Consequently, the poly(amic alkyl ester) precursors to these polymers were used followed by thermal imidization [44]. For comparison purposes, 3FDA/PMDA-based copolymers were prepared via both routes. The synthesis of the poly(amic acid) involved the addition of solid PMDA to a solution of the styrene oligomer and diamine to yield the corresponding poly(amic acids) (Scheme 8). The polymerizations were performed in NMP at room temperature for 24 h at a solids content of -10% (w/v). Chemical imidization of the po-ly(amic-acid) solutions was carried out in situ by reaction with excess acetic anhydride and pyridine at 100 °C for 6-8 h. The copolymers were subjected to repeated toluene rinses in order to remove any unreacted styrene homopolymer. 

Solderable wires are used in telecommunications and the construction of analytical instruments, but they are becoming more and more common in small motors and dry-type transformers. The special characteristic of solderable wire enamels is the direct soldering. When the enameled wire is dipped in a solder bath at temperatures above 350 °C the coating melts and leaves the bare copper wire, avoiding the need for elaborate mechanical or chemical removal of the enamel. This characteristic achieved in solderable poly(ester-imide) by a special polymer composition and in polyurethane based wire enamels is due to the thermally reversible splitting of the polyurethane group. Nevertheless, good thermal stability is necessary and product temperature indexes >155 are required. For temperature indexes of 130, simply polyurethane wire enamels were used. 

Sterilizability is of essential importance when the pol5mier is used in medical applications. Steam sterilization is preferred over chemical sterilization and radiation sterilization. Steam sterilization consists of a treatment of the membrane with superheated steam of >110°C for 30 min. Steam sterilizable membranes include poly(ether imide), PES and poly-(vinylidene fluoride). 

Figure 5. Polar order stability as determined by thermal ramping (rate 37minute) laser frequency fundamental 1.047 //m. (a) film prepared from the poly(amic acid) PAA-5 heated to a maximum temperature of 280°C in the corona field (b) chemically imidized film of PI-5 poled at 310°C (corona field).

The copolyimides were synthesized via the poly(amic acid)s followed by chemical imidization (Scheme 1). They are soluble in solvents such as THF, chloroform, NMP, tetrachloroethane, DMF and DMSO. The polymer with a relatively low chromophore loading level possesses poorer solubility in THF and chloroform. 

Aromatic poly(amide-imide) (PAI) has an outstanding resistance not only to the thermal operations but also mechanical, electrical, and chemical operations. Although the properties of PAI are inferior to those of aromatic polyimide (PI), which is one of the most heat-resistant polymers, PAI has been widely utilized as a high performance heat resistant polymer as well as PI, because PAI is superior to PI in its workability in industry. ... 

The choice of the membrane depends on several factors chemical and thermal resistance to the process conditions, sharp separation, wettability of the membrane, tendency to adsorb hydrophobic materials and resistance to cleaning. The most common polymeric materials are PTFE, PVDF, PP, PS, CA/CN, CTA, PE, polycarbonate, polyester, poly ether imide and nylon 6. Of these, only PTFE, PVDF and PP have excellent to good chemical stabiHty. Even though hydrophilic CA/CN and CTA membranes have limited chemical stabiHty, they are best suited for treating high fouling feeds using tubular membranes. 

For TLCPs [-OOC-c )-OOC-c )-COO-c )-COO-R-]m [67], when R is line spacer, Ea was found to be similar to those of polyesters such as PET and PBT, and Ea decreases with increasing numbers of methylene groups in R. Li et al. [84-86] have reported some kinetic data of the X7G analogues, Veetra A with 58/42 molar ratio of pHBA/2,6-HNA, and Ekonol fiber with the same chemical structure units as Xydar. Kinetic data were also used to support the related conclusion about the thermal degradation behavior of the blends of Veetra A950 with Nylon 6 [61] and Veetra B950 with poly(ether imide), etc. [62]. 

S. Rajesh, P. Maheswari, S. Senthilkumar, A. Jayalakshmi, D. Mohan, Preparation and characterisation of poly (amide-imide) incorporated cellulose acetate membranes for polymer enhanced ultrafiltration of metal ions. Chemical Engineering Journal 171 (1) (2011)33 4. 

S. Takahashi, D.R. Paul, Gas permeation in poly (ether imide) nanocomposite membranes based on surface-treated silica. Part 1 without chemical coupling to matrix. Polymer 47 (2006) 7519-7534. 

In the second step, polyamic acid is cyclo-dehy-drated at elevated temperatures (thermal imidization) or in the presence of a cyclizing agent (chemical imidization). Advantages of this method over one-step polymerization are the use of less toxic solvents and direct processing of soluble polyamic acids to form the final polyimide products in the form of films or fibers by thermal imidization. However, the storage instability of polyamic acid intermediates and the control of thermal imidization are still important issues [28]. A detail description of the thermal and chemical imidization of poly(amic acid) is given below. 

Poly(amic acid)s can also be chemically imidized. This is accomplished by using chemical dehydrating agents combined with basic catalysts [36]. Various reagents have been employed, including... 

Scheme 3.20 Chemical structure of the synthesized poly(ether imide)s, series I.

Scheme 3.21 Chemical structure of poly(ether imide) series II, III, IV, V, VI, and VII.

Poly(amide imide) precursors have excellent mechanical properties after imidization, at tenq)eratures up to 260 °C. It was first synthesized in the 60 s as a material for hi tenq)erature wire enamel (2). This high performance thermoplastic was developed fi-om research done by James Stephens of Amoco Chemicals (see Ref 3). It became available as an injection molding resin in 1976. These materials were first applied to make bum-in electrical pin connectors. At present the usage has spread into the aerospace, transportation, chemical processing and electronics industries. 

Figure II - 31. Tne chemical structure of a polyimide (PI) and a poly(ether imide) (PEI).

Figure 13 Chemical formula of General Electric Ultem 1000 thermoplastic poly (ether-imide) 26 with a macromolecular backbone comprising two oxygen bridges and one methylethylidene linking unit between the aromatic rings.

Figure 36 Chemical formulae of fluorinated thermoplastic poly(ether-isoimides) 52 and 54, and poly(ether-imides) 53 and 55 used to prepare heat-resistant, flexible...

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