Hi,
PDMS is generally soluble in non polar solvents like toluene, hexane, heptane etc. If your other polymer layer is insoluble in one of these solvents then you can use these solvents to dissolve PDMS without affecting the other layer.
Concentrated sulphuric acid (98%) also etches the cured PDMS very quickly (except chemically modified, e.g. irradiated, parts -> this makes possible to use PDMS as a negative resist material in lithography). Dilute sulphuric acid does not etch PDMS away. If concentrated sulfuric acid does not damage your polymer, you can use this method to remove your cured PDMS layer selectively.
KOH and NaOH solutions etch only the chemically modified (irradiated) parts of PDMS -> positive resist material in lithograpy
30 wt% KOH + 20 wt% IPA+50 wt% DI water solution at 70 °C temperature etches away the cured PDMS (even if PDMS is chemically modified/degraded by e.g. radiation).
More detailed info (etch rates, etc.) in my two latest papers:
S.Z. Szilasi, C. Cserháti, Selective etching of PDMS: Etching technique for application as a positive tone resist, Applied Surface Science 457 (2018) 662–669
S.Z. Szilasi, L. Juhasz, Selective etching of PDMS: Etching as a negative tone resist, Applied Surface Science 447 (2018) 697–703
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