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

Abstract

The 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

Investigation of 1,1‐diphenylethylene Oligomerization in the End‐Capping Reaction of Poly(styryl)lithium

“…[2] This behavior was observed in the addition of nBuLi to excess DPE that was followed by the reduction of volume during the reaction. [14] The rate of volume reduction was very slow after complete formation of the monoadduct.…”

“…The UV absorption peaks at l max of 440 nm for poly(diphenylalkyl)lithium chain-ends and 334 nm for poly(styryl)-lithium chain-ends were followed to determine the required time for complete reaction. [1,2,5] In the presence of excess DPE, the reaction is expected to proceed as reported by George and Evans [14] for the addition reaction of nBuLi to DPE, taking into account an additional equilibrium reaction for the incorporation of a second DPE unit onto the growing polymeric chain. Scheme 3 shows the proposed reaction for the end-capping of poly(styryl) lithium in the presence of a large excess of DPE.…”

“…The chemical resonances present in both spectra were identical and the proton resonance for the terminal methine proton was observed at d 3.6 ppm. [2] The observed integration ratios between the methyl protons of the initiator unit and the terminal methine proton at d3.6 ppm is 6.0/1.0 for the polymer end-capped in the presence of 16 mol-eq of DPE.…”

“…[1][2][3] In particular, the end-capping reaction of poly(styryl)lithium using a stoichiometric amount of DPE in benzene is a quantitative addition reaction that was completed after 6 hours. The UV absorption peaks at l max of 440 nm for poly(diphenylalkyl)lithium chain-ends and 334 nm for poly(styryl)-lithium chain-ends were followed to determine the required time for complete reaction.…”

“…[1][2][3] In particular, the addition of organolithium polymeric compounds to DPE and its derivatives (end-capping reaction) is a powerful method for the quantitative incorporation of various functional groups [1,4,5] (e.g., diphenol groups, [6] primary [7] and tertiary amine groups [8][9][10] and carboxyl group [11] ). The addition of organolithium polymers [e.g., poly(styryl)-lithium] to substituted DPE compounds is a quantitative living functionalization reaction due to the formation of an active diphenylalkyllithium chain-end.…”