Degradation of Polydienes Induced by Alkyllithium: Characterization and Reaction Mechanism

Abstract

The lithiation reaction is a key step in anionic graft polymerization of polydienes. However, we observed that polymer degradation occurs concurrently with the lithiation process. Herein, alkyllithium-induced degradation of polydienes was investigated, which showed that the alkyllithium/N,N,N′,N′tetramethylethylenediamine system causes polydiene degradation at room temperature or higher. The number-average molecular weight of rubber decreased from hundreds of thousands to thousands within a few minutes. This reaction occurred in polydienes such as polybutadiene, high-vinyl polybutadiene, polyisoprene, and natural rubber. The effects of the reaction time, temperature, butyllithium dosage, and alkyllithium species in this reaction were studied in detail. Furthermore, the structure of degradation products was characterized by gas chromatography mass spectrometry, gel permeation chromatography, Fourier transform infrared, 1 H nuclear magnetic resonance (NMR), 13 C NMR, two-dimensional heteronuclear single-quantum coherence NMR, and 2 H NMR spectroscopy. Thus, a possible reaction mechanism was proposed, which is described as a process whereby the allylic carbanion undergoes resonance and rearrangement, leading to cleavage of the C−C bond and generation of products with conjugated double bonds at the end group. In addition, the reaction mechanism was also supported by density functional theory calculations, which is revealed as an entropy-driven process.

Strong Hydrophobic and Ultraviolet Reflective Film from Fluorinated Polyisoprene with Microphase Separation via Thiol–Epoxy Click Chemistry

“…Thus, mercapto group anion as a strong nucleophile also attacks these ether linkage and reduces the molecular weight of original EIR. [ 40 ] In addition, since alkyllithium can bring about an obvious degradation of polydienes during anionic grafting modification or anionic polymerization, [ 41 ] Li + contained in the catalyst may also have a degradative effect on polyisoprene.…”

Precision Synthesis of Tunable Polyallenamers from “Masked” Precursors

“…Having prepared our precursor polymers, we next evaluated Skattebøl conditions to access the desired polyallenamers. As alkyl lithiums have recently been shown to react with allylic protons in polymer matrices, 29 we initially hypothesized that the olefins throughout 3 DP could hinder the Skattebøl rearrangement. To explore this, 3 55 was treated with MeLi (5 equiv) at −78 °C for 5 h, which yielded a tacky material (80% yield).…”

Characterization Techniques of Polymer Aging: From Beginning to End

“…Peak assignment and spectral analysis by NMR: (A) possible aging mechanism, 1 H and 13 C NMR spectra of polybutadiene during aging. Reproduced with permission from ref . Copyright 2021 American Chemical Society.…”

“…For example, Hua's group has studied the aging of polybutadiene by 1 H, 2 H, and 13 C NMR spectroscopy. 167 They speculated a possible aging mechanism of polybutadiene and suggested the formation of conjugated C=C end groups during aging (Figure 21A). The metalation reaction occurred for polybutadiene, generating carbanions 14 and 19 in the pathway 1 and 2.…”