Structural Transformations in Chemical Modification of the Surface of Polypyromellitimide Films

Electron microscopy data are used to investigate the formation of a submicron layer of a polyamido acid (PAAc) on the surface of polypyromellitimide (PI) film subjected to sequential treatment with aqueous alkali and acid solutions. To analyze the topology of distribution of PAAc macromolecule clusters on the surface of modified PI films, PAAc is decorated with silver chloride nanoparticles. The presence of ordering in the spatial distribution of the ensemble density of decorating nanoparticles is revealed. The degree of order is shown to vary nonmonotonically with the duration of alkaline hydrolysis of PI. This variation is explained by superposition of two processes: the formation of PAAc clusters as a result of a topochemical reaction in the macromolecular PI chains and random cluster-cluster aggregation. The formation of PAAc clusters is centered around periodically alternating microdomains, i.e., dense aggregates of PI molecules. Conditions leading to the formation of the ordered cluster PAAc structure upon modification of PI surface are identified.