Efficient thermo-base generators (TBGs) which can release an secondary alicyclic amine (e.g. 2,6-dimethylpiperidine; DMP) have been developed for low temperature solid-phase imidation of poly(amic acid) (PAA). Such latent thermo-sensitive catalysts promote thermal imidation of PAA film smoothly up to 200 degrees C, without the salt formation and storage instability of PAA solution.