Polymeric glasses formed from linear poly(methyl methacrylate) (PMMA) chains in various molecular weights were exposed to chloroform vapor to study swelling and viscous flow mechanisms. In situ steady state fluorescence (SSF) experiments were performed to monitor the vapor uptake and viscous flow processes. Direct illumination of the disc shape films were performed to excite the pyrene (P) molecules embedded inside the PMMA films. Variation in P intensity, Ip, was monitored during swelling and viscous flow of the PMMA material exposed to chloroform vapor. It was observed that PMMA film swells like a crosslinked gel at early times by obeying the Li-Tanaka equation. At later times, i.e. longer than terminal relaxation times, tau(t), swollen PMMA material flows linearly with time. Swelling time constant, tau(c), terminal relaxation time, tau(t), and viscosity n of PMMA films during vapor uptake were measured and found to be strongly correlated with the molecular weight (M) of PMMA. The exponent of M for tau(t) and n were measured and found to be around 3.