Systematic functionalization of porous coordination polymers (PCPs), [Cu-2(L)(2)(ted)](n) (where L = dicarboxylates and ted = triethylenediamine), by introducing various substituents onto the component organic ligand, L, was performed to regulate the radical polymerization of methyl methacrylate (MMA) in the nanochannels. The effect of the substituent groups on stereoregularity of the resulting poly(methyl methacrylate) (PMMA) was observed, where the tacticity of the PMMA strongly depended on the number and position of the substituent. In particular, polymerization of MMA in [Cu-2(2,5-dimethoxyterephthalate)(2)(ted)](n) gave PMMA with high isotactic and heterotactic triad fractions, which is one of the most effective systems for changing the tacticity of PMMA in radical polymerization. To understand the mechanism of this drastic stereoregularity change, a variety of experimental and theoretical analyses, such as IR, N-2 adsorption, a statics study, and molecular dynamics (MD) calculations, were performed. Accurate MD calculations were helpful to determine the most plausible structures of [Cu-2(L)(2)(ted)](n) and revealed that the specific channel shape of [Cu-2(2,5-dimethoxyterephthalate)(2)(ted)](n) induces the large tacticity change of the resulting PMMA.