A heavily branched poly(methyl methacrylate) (PMMA) has been prepared by free radical solution copolymerization of methyl methacrylate (MMA) with ethylene glycol dimethacrylate (EGDMA) in the presence of dodecanethiol (DDT) to inhibit network formation. A molar feed ratio MMA/EGDMA/DDT of 100/15/13 was employed. These conditions allow a high conversion to fully soluble branched products, and the evolution of molar mass and intrinsic viscosity was monitored by subjecting extracted samples of polymerization mixture to rapid triple detection size exclusion chromatographic (SEC) analysis using a PL-PMC device. These data showed that the global molar mass increased with reaction time, but the corresponding viscosity rise was far lower than would expected for linear macromolecules, hence demonstrating the formation of an increasingly densely branched architecture. H-1 NMR spectral and elemental S analysis of the finally isolated branched PMMA showed the composition to be in reasonable agreement with the molar feed ratio MMA/EGDMA/DDT and that similar to 95% of the incorporated EGDMA was present as doubly reacted branched segments. High-resolution SEC analysis of the finally isolated material confirmed the branched nature of the product across the whole of its molar mass range and that branching increases as the molar mass of individual macromolecules increases.