Polyamide-imide formation

The polyimides and polyamide-imides are produced by condensation reactions which give off volatile low-molecular-weight by-products. The polybismalemimides may however be produced by rearrangement polymerization with no formation of by-products. The starting materials in this case are the bismaleimides, which are synthesized by the reaction of maleic anhydride with diamines (Figure 4.21). 

A correlation between matrix changes and formation of certain degradation products has also been found for polyamide 6.6 [53]. Especially the amount of cyclic imides increased during thermo-oxidation, of which... 

Thermal degradation of polyoxymethylene and polyacetals results in the formation of formaldehyde, which is furthermore catalyzed by oxidation of formaldehyde to formic acid. In addition to antioxidants and acid scavengers, formaldehyde scavengers are used in polyacetal formulations. Formaldehyde scavengers of choice are nitrogen compounds, for example, melamine derivatives such as benzoguanamine, urea derivatives such as allantoin, hydrazides, imides, and polyamide. 

The chemistry taking place in the swollen polyamide 6 (PA-6) granules is given in Fig. 13.2. Most probably, at elevated temperatures the obtained amic acid is partially converted into the ring-closed imide with formation of a water molecule [80]. 

Although polyimides can have an open-chain structure, cyclic polyimides have found more use because they are more thermally stable than open-chain polyimides. The polyether-imide prepared from pyromellitic dianhydride and 4,4 -diaminodiphenyl ether has found use in high temperature coatings, adhesives, and structural plastics. The reaction involves rapid formation of the polyamide, called polyamic acid, followed by a high-temperature ring closure step. 

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