Thermoplastic imide structure

Introduced by GE Plastics in 1982, polyetherimide (PEI) is an amorphous thermoplastic offering outstanding high heat resistance and strength. The high heat resistance and heat stability are attributable to its imide structure. PEI also has resistance to a broad range of chemicals, and is inherently flame resistant with low smoke emission. A major component of PEI is bisphenol A, which is also produced by GE Plastics, mainly for use in polycarbonates. 

Chemical structure of LaRC-TPI (Linear Aromatic Condensation-Thermoplastic Imide) (Bell and Stump 1976)... 

POLYAMIDE-IMIDE RESINS. An injection-moldable, high-performance engineering thermoplastic, polyamide-imide is the condensation polymer of tnmellitic anhydride and various aromatic diamines with the general structure ... 

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. 

Commercial polyetherimide (PEI Ultem , GEC) is an amorphous, high performance thermoplastic with its repeat unit structure containing both the rigid aromatic imide units and the somewhat more flexible aromatic ether units. 

The polyester-imides constitute a class of modified polyimide. These are typified by the structure shown in Figure 4.23. Polyether-imides form yet another class of modified polyimide. These are high-performance amorphous thermoplastics based on regular repeating ether and imide linkages. The aromatic imide units provide stiffness, while the ether linkages allow for good melt-flow characteristics and processability. 

Polyether-imides are noncrystalline polymers made up of alternating aromatic ether and imide imits. The molecular structure has rigidity, strength, and impact resistance in fabricated parts over a wide range of temperatures. PEI is one of the strongest thermoplasts even without reinforcement. 

Figure 22.18 Examples of aromatic polyether, -ketone and -imide by SPC which are structurally analogous with engineering thermoplastics.

This means that water molecules evolve within the adhesive layer and must be removed to avoid the formation of large voided areas. To circumvent this drawback, research was focused on the synthesis of fully cyclised heterocyclic polymers, which are intrinsically thermoplastic, even though the Tg can be extremely high. Polyphenylquinoxalines, poly(isoimides), and poly(ether-imides) have been extensively studied to prepare structural adhesive films and pastes. 

Polyetherimide (PEI) is an engineering thermoplastic with the structural formula shown in Figure 8.2. The PEIs are alternating aromatic ether and imide... 

Further improvements in the chemistry of polyimides during the last years have been directed towards novel, linear species that are soluble in workable organic solvents or melt-processable while fully imidized. Thus, changes had to be introduced in the chemical structure to adapt the behaviour and performance of these specialty polymers to the demands of the new technologies. As a consequence, a new generation of condensation polyimides has appeared, the so-called thermoplastic polyimides. 

M.B. Saeed, Mao-Sheng Zhan (2006) Effects of monomer structure and imidization degree on mechanical properties and viscoelastic behavior of thermoplastic polyimide films. European Polymer Journal. 42 1844-1854. 

For the purpose of discussing mesophase formation in polymers it is conveiuent to partition the polymers into two categories and introduce abbreviations that refer to these categories. Polymerized liquid crystals, here abbreviated PLCs, are derived from known, low molecular weight monomer liquid crystals (MLCs) that contain polymerizable functionality (e.g. vinyl units). We designate liquid-crystalline polymers (LCPs) to be semiflexible, linear polymers that are structurally related to conventional engineering thermoplastics, i.e. polymers derived from poly(ester)s, poly(amide)s, poly(imide)s, etc. We will examine the attributes of polymerized liquid crystals first, stressing the similarities between their properties and those of MLCs. 

Polyamide imides, PAI, were first developed at DuPont in 1955. In the early 1960s they became commercially available from Standard Oil of Indiana (Amoco now Solvay Advanced Polymers) under the Torlon trade name [52]. PAIs are prepared from trimellitic anhydride chloride and various aromatic diamines such as ODA and methylene dianiline, MDA [53]. PAIs are amorphous thermoplastics that offer T s around 275 °C. Structures are shown in Fig. 1.30. PAIs offer long-lasting performance in severe service environments and a distinct combination... 

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