Kapton polyimides chemical structure

Polyimide or its most common type Kapton HN (chemical structure shown in Fig. 14.4) is the most studied polymer, as it can be ablated with all common excimer laser wavelengths and pulse lengths (r). Most ablation models are based on Kapton, as its material properties are well characterized. 

Aromatic polyimides are well recognized to have excellent chemical stability, so they have found applications in extremely harsh and corrosive environments. For example, they are used as insulators in nuclear facilities and as thermal blankets on spacecraft where the materials may be exposed to high-energy radiation in the presence of oxygen. The best known of the commercial polyimides is Kapton, which is marketed by Du Pont. The chemical structure of Kapton is shown in Figure 1, along with that of Ultem, another commercial polyimide marketed by General Electric. 

Following high-energy radiolysis new chemical structures are formed in a polymer. Kapton and many of the other polyimides have been reported to undergo nett chain scission (77) on radiolysis. On the other hand, Ultem undergoes nett crosslinking (70), with a gel dose above 10 MGy. However, the nature of the crosslinks in Ultem has still not been unequivocally identified. 

During the past three decades, since the commercialization of Kapton polyimide, an impressive variety of polyimides have been synthesized [258, 259]. Polyimides possess outstanding key properties, such as thermooxidative stability [260], high mechanical strength [261], high modules, excellent electrical [262] and optical properties [263, 264], and superior chemical resistance [265]. Recently polyimides have also been applied as membranes for gas separation [266, 267]. Approximately 15 years ago the direct structuring or laser ablation of polyimides by excimer lasers was first described [73, 130]. 

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