Hardened cement paste (HCP) specimens were prepared with hydration times of 1, 3, 7, 28, and 180 days. Specimens were oven dried and subsequently impregnated with methyl methacrylate, tert-butylstyrene, polyethylene glycol, and an epoxy resin system via a vacuum–pressure technique. Internal friction (Q−1) of in situ polymerized specimens was measured over the temperature range from 100° to 500°K. Results indicate that the internal friction spectra of polymer-impregnated specimens closely parallels the internal friction spectra of the bulk polymers used for impregnation. Magnitudes of the internal friction peaks in the impregnated specimens were found to be less than that expected on the basis of volume fraction of polymer present. These results are attributed to hindered motion at the cement/polymer interface.