Three molecular imprinted polymers (MIPs) were prepared with different amounts of crosslinker (ethylene glycol dimethacrylate) in methacrylic acid functional monomer. Positron lifetime spectroscopy has been used to study the variation in free volume cavities (nanosize pores) in these MIPs of different monomer-crosslinker ratio. The changes in free volume cavities after the template molecule 4-chlorophenol extracted from the polymer matrix were measured. The results indicate that the optimum monomer-crosslinker ratio for this MIP is 1:5. The free volume distribution derived from CONTIN program further reveals the presence and absence of template molecules in the system. The Fourier transform infrared spectra results have been used to compliment this through the absence of stretching frequencies at 648 cm−1 and 825 cm−1 of C[BOND]Cl suggesting the successful extraction of the template from the MIPs. Scanning electron microscope (SEM) scans indicate the grains are of heterogeneous shape and size in agreement with earlier studies. POLYM. ENG. SCI., 54:667–674, 2014. © 2013 Society of Plastics Engineers