Adducts of Polymeric Organolithiums with 1,1‐Diphenylethylene. Rates of Formation and Crossover to Styrene and Diene Monomers

Abstract

AbstractThe addition reactions of 1,1‐diphenylethylene (DPE) to polymeric organolithium (PLi) compounds and the crossover reactions of the resulting polymeric 1,1‐diphenylalkyllithiums with styrene, isoprene and butadiene monomers have been investigated and optimized. The addition of poly(styryl)lithium (PSLi) to one unit of DPE at 25 °C is complete in 6 and 8 h in benzene and cyclohexane, respectively. After 3 d at 25 °C, the extent of end‐capping with DPE was only 9% for poly(butadienyl)lithium and 15% for poly(isoprenyl)lithium. Addition of THF ([THF]/[PLi] = 15–40) promotes quantitative addition of poly(dienyl)lithiums to DPE within 1–4 hours at 25 °C. Crossover reactions of polymeric 1,1‐diphenylalkyllithiums (growth out) to styrene monomers are slow relative to crossover reactions to diene monomers. Crossover to diene monomers is complete within approximately 2 min at 25 °C and leads to well‐defined, narrow molecular weight distribution block copolymers ($\overline M _{\rm w} /\overline M _{\rm n}$ = 1.01 with $\overline M _{\rm n}$ (out, calc) > 2 900 g · mol−1). Crossover to styrene monomers requires 12 h and leads to broad molecular weight distributions ($\overline M _{\rm w} /\overline M _{\rm n}$ > 1.1) and inefficient crossover if $\overline M _{\rm n}$ (out; calc) < 7 000 g · mol−1 and the chain end concentration is ≤ 10−3 M. Crossover to the styrene monomer is favored by low temperatures (5 °C), high chain end concentrations, and higher molecular weights of the growing block. magnified image