A real-time monitoring of excimer emission fluorescence probe di(I-pyrenemethyl)ether (DiPyM) was used for study swelling interpenetrating polymer network (IPN) consisting of polyethylene/poly(styrene-co-butylmethacrylate) (PE/P(S-co-BMA)) and containing different network density. DiPyM was introduced into IPN during polymerisation or was penetrated into blocks from toluene solution. The effect of solvent quality for swelling of IPN and density of IPN network was also studied. From steady-state measurements of monomer and excimer emission ratio (I-e/I-m), no difference was found between rate of swelling IPN with 0.5, 1 and 3 mol% of cross-linker. The rate of IPN swelling seems to be rather high. Some differences was found at real-time monitoring of excimer emission (lambda(em) = 495 nm) of DiPyM measured during desorption of DiPyM from swelled IPN blocks. At higher content of cross-linker, a slower rate of DiPyM desorption from IPN matrix was observed.