Anionic polymerization with alkaline-earth counterion. I. Preparation and characterization of dicarbanionic oligostyrylbarium and -strontium in tetrahydrofuran

Dicarbanionic oligostyrylbarium or -strontium, PS⁼Ba⁺⁺ and PS⁼Sr⁺⁺, were prepared by reacting styrene with finely divided barium or strontium in THF or THP. The effects of reaction temperature, monomer, and metal concentration were described. Difunctionality of these living oligomers is confirmed from calculated and observed molecular weight data and also from conductivity measurements. λ_max of carbanions is found to vary with DP . At 25°C it decreases from 368 nm for dimers to 359 nm for DP > 10. As observed for monocarbanionic polystyrylbarium (PS^?)₂Ba⁺⁺, λ_max of PS⁼Ba⁺⁺ of high DP decreases with temperature, while λ_max of PS⁼Ba⁺⁺ of low DP increases with decreasing temperature. At ?100°C the difference between the two extreme values is about 30 nm. Similar results are obtained with PS⁼Sr⁺⁺. Such unusual spectral properties are interpreted, on the basis of excitation molecular theory, in terms of ring structures for the living oligomers.