Polyimides imidization

The reactions of primary amines and maleic anhydride yield amic acids that can be dehydrated to imides, polyimides (qv), or isoimides depending on the reaction conditions (35—37). However, these products require multistep processes. Pathways with favorable economics are difficult to achieve. Amines and pyridines decompose maleic anhydride, often ia a violent reaction. Carbon dioxide [124-38-9] is a typical end product for this exothermic reaction (38). 

Imides - Polyimides (PI) have been conventionally prepared by the chemical or thermal cyclodehydration of polyamic acids formed from the solution reaction of aromatic tetracarboxylic dianhydrides and aromatic diamines. The early PI were insoluble and relatively intractable. The polyamic acid was the processable intermediate. However, the polyamic acid precursor has two major shortcomings, hydrolytic instability and the evolution of volatiles during the thermal conversion to PI. In addition, residual solvent was left in adhesive tapes and prepregs to obtain tack, drape and flow. During the fabrication of components, the evolution of volatiles caused processing problems and led to porosity in the part. As work progressed on PI, other synthetic routes were investigated (e.g. reaction of esters of aromatic tetracarboxylic acids with diamines... 

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. 

ZONE 7 polyamide-imide, polyimide ZONE 8 plastics now being developed us ... 

Special considerations trace metals such as Co, Cu, Ni radically reduce thermal stability some carbon fibers cause degradation due to the surface impurities some types of glass reduce stability of poly imide polyimide is used as modifier of PEEK/carbon fiber composite " ... 

This requirement has been met with soluble, pre-imidized polyimides. It has been found that secondary amines react quite readily with such polyimides in polar solvents such as N-methylpyrrolidinone or dimethylacetamide The reaction was done initially with morpholine for a series of available pre-imidized polymers (see Table I). The reaction was easily followed by infra-red spectroscopy (IR) (see Figure 2), the imide carbonyl absorptions at 1780 and 1723 cm 1 being replaced by amide carbonyls at 1645 cm1. In addition, the aliphatic C-H absorptions at 2880 cm 1 were noted. 

The cured or fully imidized polyimide, unlike the poly(amic acid), is insoluble and infusible with high thermooxidative stability and good electrical-insulation properties. Thermoplastic polyimides that can be melt processed at high temperatures or cast in solution are now also available. Through an appropriate choice of the aromatic diamine, phenyl or alkyl pendant groups or main-chain aromatic polyether linkages can be introduced into the polymer. The resulting polyimides are soluble in relatively nonpolar solvents. 

Tbflon urethane surface overcoat overcoat overcoat Polyester overcoat imide polyimide silicon... 

Overcoat Overcoat Overcoat Polyester Overcoat imide Polyimide Silicon... 

Volume resistivities are listed in Table 5.2. They range from as low as 2 ohm.cm for epoxy resins to as high as 16-18 ohm.cm for high-density polyethylene, polyether ether ketone, polystyrene, polymethylpentene, polyethylene terephthalate, polyarylates, polyphenylene oxide, polyamide imide, polyimides, polyurethane, polytetrafluoro-ethylene, perfluoroalkoxy ethylene, fluorinated ethylene-propylene copolymer, ultra-high-molecular-weight polyethylene, polysulfones, and polyethersulfones. 

Polyimide fiber is made from an aromatic heterocyclic polymer, and P84 is the brand name of the polyimides manufactured by Evonik Fibers with a trilobal fiber cross section (Fig. 2.25). P84 is a fully imidized polyimide derived from aromatic dianhydrides and aromatic diisocyanates and has a glass transition temperature of 315°C. The fibers start to carbonize at temperatures beyond 370°C. Due to the aromatic structure, the polymer and fibers are inherently nonflammable. An FOl of 38% can be measured. P84 can be used for temperatures up to 260°C, depending on the environment [71]. Typical properties of P84 are introduced in Table 2.67. 

Acrylic Polyacrylate Polymethyl methaorylate Polydihydroxymethyl qrclohexyl terephthalate Polyamide imide Polyimides... 

The polymers used to manufacture the film or tape adhesives are either thermoplastic materials including acrylic, polyester, and fully imidized polyimides or thermosetting resins based on epoxy and polyimide chemistries. The tapes are often made with partially cured (B-staged) epoxies similar to those used in the fabrication of the PCBs. Some commercially available films are also... 

The most commonly used polymer precursors for carbon membranes have been reported to be polyimides, polyfurfuryl alcohol, phenol formaldehyde resins and cellulose. Their common characteristic is that they do not melt during pyrolysis at high temperature, which keeps their original shape and structure during the thermal heating and decomposition process. In this sense, the commercially available Matrimid and Kapton are the fully imidized polyimides with high values. They do not abruptly change their... 

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