Time-resolved momentum distributions of positron-electron annihilation photons were investigated for various polymers by means of-positron age-momentum correlation (AMOC) spectroscopy. The momentum distribution exclusively associated with orthopositronium (o-Ps) pick-off annihilation is found to be clement-specific and call sensitively probe different light atoms such as C, O, F. and Si that constitute the surface of nanometer-sized free volumes. It is demonstrated that the chemical environment around free volumes in polymers for practical use call be probed by positron annihilation AMOC spectroscopy.