Kinetics of ϵ‐caprolactone polymerization and formation of cyclic oligomers

Abstract

Abstract The kinetics of the anionic polymerization of ϵ‐caprolactone, including the kinetics of macrocyclization and the kinetics of macrocycles propagation in THF solution, initiated with (CH 3 ) 3 SiONa, were investigated. Rate constants of propagation ( k p( n ) ) and of back‐biting ( k d( n ) ) involving monomer and cyclic oligomers (macrocycles) with n = 2, 3, … monomeric units were determined for n ≤ 7. It was found that starting from the tetramer k d( n ) ∼ n −1,4±0,1 and k p( n ) ∼ n 0,7±0,15 (in Jacobson‐Stockmayer's theory k p( n ) ∼ n ). This discrepancy is explained in terms of “conformational hindrance”, increasing for small cycles with the increase of the ring size until a certain ring size is reached. This hindrance decreases the availability of some of the ester groups in the macrocyclics for attack of the growing species, lowering in this way the exponent in the dependence of k p( n ) on n from one to a lower value.