Polymer complexes of a basic polymer, poly(N-methyl-4-piperidinyl methacrylate) (PMPMA), with a weak acidic polymer poly(p-vinylphenol) (PVPh), and strong acidic polymers such as poly(acrylic acid) (PAA), poly(methacrylic acid) (PMAA), poly(styrenesulfonic acid) (PSSA), and poly(vinylphosphonic acid) (PVPA), have been prepared by mixing ethanol/H2O (1:1) solutions of the respective components. The complexes were examined by Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and differential scanning calorimetry. Both the FTIR and XPS studies showed the existence of piperidinium ions in the complexes of PMPMA with PAA, PMAA, PVPA, and PSSA, indicating that the interactions in these complexes are ionic in nature. However, the N-methyl groups prevent the piperidine nitrogen atoms from interaction with PVPh and hence the carbonyl groups of PMPMA interact with the hydroxyl groups of PVPh by hydrogen bonding. From the XPS studies, the number of protonated piperidine atoms was found to correlate with the acid strength of the polyacid.