In-situ steady-state fluorescence (SSF) measurements were performed for studying diffusion processes of pyrene end-capped polystyrene (Py-PSt) in gels formed by free radical cross-linking copolymerization (FCC) of styrene (St) and ethylene glycol dimethacrylate (EGDM) in toluene solutions. The pyrene end-capped polystyrene was prepared by atom transfer radical polymerization (ATRP). The process involves the synthesis of I-pyrenylmethyl 2-bromopropanoate (PMBP) and further use in the ATRP of St in conjunction with CuBr/2,2'-bipyridine (bpy) as the catalyst. Pyrene end-capped polymers with low polydispersities (PDI < 1.2) were obtained and characterized by GPC, H-1 NMR, and fluorescence spectroscopy. Gels were prepared at 70 +/- 2 degreesC for various EGDM contents. After the drying of these gels, diffusion experiments were performed in toluene solution of Py-PSt in various molecular weights at room temperature in real time by monitoring of pyrene fluorescence intensity. During these experiments, it was observed that pyrene emission intensities increased due to trapping of Py-PSt chains into the gel as the diffusion time is increased. The Li-Tanaka equation was employed to produce the diffusion parameters. Diffusion time constants, tau(c), of Py-PSt chains were found to be increased as the cross-linker density of the gels and molecular weight of Py-PSt chains increased. It was observed that collective diffusion coefficient, D-c, decreased by increasing molecular weight M-n by obeying the D-c approximate to M-1 law.