The influence of stereochemistry of polar modifiers on the microstructure of polybutadiene and poly(styrene-co-butadiene) was evaluated for 2,2′-ditetrahydrofurylpropane (DTHFP). The meso and d,l diastereomers were isolated from commercial 50/50 mixtures through column chromatography and characterized by 1H-NMR and gas chromatography/mass spectrometry. The meso-DTHFP was found to be more active than d,l-DTHFP in incorporation of vinyl during anionic polymerization. To form a polymer with approximately 55% vinyl, twice the amount of d,l-DTHFP was required compared with using pure meso-DTHFP. The mechanism for this effect will be discussed.