We followed the surface imide ring hydrolysis of fully imidized polyimide films by aqueous base solutions using Rutherford backscattering spectrometry. The hydrolysis reaction was studied using several different polyimide films including spuncast and thermally imidized PMDA-ODA, Kapton-H, and Upilex-S films. The boundary between the modified layer at the surface and the underlying film is a sharp front behind which the conversion of the polyimide into poly(amic acid) is complete and ahead of which there is almost no hydrolysis. The modified layer grows linearly with the time it is exposed to the basic solution. The growth velocity increased strongly with increases in the temperature of the basic solution. Under the reasonable hypothesis that the growth of the modified layer is controlled by the kinetics of the hydrolysis of the imide ring at the interface, we extract an activation energy for this process in Kapton-H films of 60 kJ/mol as compared to 68 kJ/mol for Upilex-S. Using forward recoil spectrometry, we studied the amount of interpenetration when a second layer of deuterium-labeled poly(amic acid) was spun-cast onto the surface-modified PMDA/ODA film. We determined that the interface between the spun-cast layer and the base layer is broader when the modification depth is greater. The fracture energy of such an interface, as measured with a T-peel test, rises rapidly as a function of modification depth and saturates at a value ∼20 times the value for an interface formed from PMDA/ODA polyimide with an unmodified surface.

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Dynamic secondary ion mass spectrometry (SIMS), nuclear reaction analysis, and neutron reflectometry were used to profile polyimide-polyimide interfaces. For interfaces between two layers of poly(4,4′-oxydiphenylene-pyromellitimide) (PMDA-ODA) polyimide it was determined that the interfacial fracture energy Gc and the interfacial width depended primarily upon the imide fraction, f, of the base layer. For f <0.9, there was a sharp interface between the deuterium-labeled poly(amic acid ethyl ester) (dPAE) and the base layer with a long low volume fraction tail of dPAE penetrating into the base layer. The volume fraction of the penetrant was limited by the imide fraction of the base layer and approached zero for f > 0.9. The PMDA-ODA/PMDA-ODA interface formed with a fully imidized base layer was ∼30 Å in width, whereas that formed when f ) 0.9 was ∼80 Å in width. The interface formed during the spin-casting process did not broaden significantly after annealing at 400°C. We also investigated the interface between a more flexible thermoplastic polyimide poly(4,4′-oxydiphenylene-oxydiphthalimide) (ODPA-ODA) and a fully imidized PMDA-ODA layer. The shape of the ODPA-ODA/PMDA-ODA interface was found to depend upon annealing temperature. Unannealed samples and samples annealed at 350°C could be fit with an error function, and the interfacial width was ∼50 Å. Samples annealed at 400 and 450°C were best fit by a fairly sharp interfacial profile with ODPA-ODA tails proceeding into the PMDA-ODA layer. The volume fraction of the ODPA-ODA in the PMDA-ODA depended upon the annealing temperature Tann. The Gc of the ODPA-ODA/PMDA-ODA interface appears limited by the solubility of ODPA-ODA in PMDA-ODA.

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