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Electronic excitation in anionic polymerization of butadiene: Nonempirical calculations of reaction complexes
Author(s) -
Kalninsh K. K.,
Podolsky A. F.
Publication year - 2002
Publication title -
international journal of quantum chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.484
H-Index - 105
eISSN - 1097-461X
pISSN - 0020-7608
DOI - 10.1002/qua.10213
Subject(s) - chemistry , excited state , polymerization , molecule , ab initio , triplet state , photochemistry , monomer , computational chemistry , polymer , atomic physics , physics , organic chemistry
A new mechanism of anionic polymerization of butadiene is proposed. In the elementary chemical act, the “living” polymer–monomer complex is excited into the low‐lying triplet state. This state has the character of charge (electron) and cation (Li + or Na + ) transfer from the terminal unit of the active center to the monomer molecule. In the framework of this concept, the probability of chemical bond formation is determined by spin density on radical centers of reagent molecules. Semiempirical and ab initio 6‐31G** quantum‐chemical calculations showed stable interaction between components of the complex in the ground electronic state (9–11 kcal/mol) and low energy levels of triplet excited states (<14 kcal/mol). This new approach is shown to be useful in the analysis of polymerization kinetics and the microstructure of polybutadiene depending on the cation type and the ion pair state. The mechanism of cis‐trans isomerization in the terminal unit of the living polymer consists in concerted rotation about the C β C γ bond and the migration of Li between C α and C γ atoms. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002