Diad tacticity of methyl methacrylate (MMA) sequences in thr copolymers of MMA and various acrylates and their crosslinked polymers was characterized by pyrolysis-gas chromatography (Py-GC) based on the relative peak intensities of the diastereomeric MMA tetramers in the pyrograms. The diad tacticity in the copolymers synthesized at a given temperature proved to be almost consistent with that; of corresponding MMA homopolymers (PMMA) prepared under the same conditions. Furthermore, the diad tacticity of PMMAs was also consistent with that of the corresponding crosslinked polymers. These results suggest that the tacticity of MMA sequences in the polymer chains would be dominated by polymerization temperature, independent of the copolymerization and crosslinking.