A New Insight into the Mechanism of 1,3‐Dienes Cationic Polymerization I: Polymerization of 1,3‐Pentadiene with ^tBuCl/TiCl₄ Initiating System: Kinetic and Mechanistic Study

Abstract

The cationic polymerization of 1,3-pentadiene using a tert -butyl chloride ( t BuCl)/TiCl 4 initiating system in CH 2 Cl 2 at different reaction conditions is reported. It is shown that the reaction rate increases with the increase of the t BuCl/TiCl 4 molar ratio, while the molecular weight distribution becomes narrower. Well-defi ned oligo(1,3-pentadiene)s (M n ≤ 3500 g mol − 1 ; M w /M n ≤ 3.0) are obtained at high t BuCl/TiCl 4 molar ratio (340) and low temperature (-78 °C). 1 H and 13 C NMR spectroscopy studies reveal the presence of tert -butyl head and -CH 2 -Cl end groups. The number-average functionalities ( F n s) at the α -and ω -ends are calculated to be F n ( t Bu) > 1 and F n (Cl) < 1, respectively. The general mechanism of 1,3-pentadiene polymerization is proposed.

The Structure of Cationic Polyisoprene: Branching versus Cyclization

“…Based on these data we can conclude that six‐membered cyclic structures are absent in a polymer chain of cationic polyisoprene. This observation is fully consistent with the earlier reported absence of six‐membered cyclic structures in a polymer chain of cationic poly(1,3‐pentadiene) . Based on the above‐mentioned results we can unambiguously conclude that reduced unsaturation of polyisoprene synthesized via cationic mechanism is not a result of intramolecular cyclization and other processes are responsible for the decrease of unsaturation of a polymer chain.…”

“…The formation of branched structures occurs through “grafting onto” mechanism via interaction of growing macrocations with double bond of the polymer chain with creation of branched point. The “grafting from” mechanism, which is consistent with the chain growth from branched macrocations as macroinitiators, can also operate under these conditions . The formation of branched polyisoprene during cationic polymerization of isoprene was confirmed in our earlier work .…”

“…According to some authors, this feature is connected with the occurrence of intramolecular cyclization with the formation of six‐membered cyclic structures. Others proposed another explanation of the observed reduced unsaturation, which is consistent with the formation of branched macromolecules due to the intensive chain transfer to polymer …”

“…According to work, the chlorine‐containing end groups are formed in the course of chain transfer to tert ‐butyl chloride. Taking into account that the concentration of t BuCl is very high ([ t BuCl] = 4.5 m ; [C 5 H 8 ] = 4.0 m ) and, therefore, almost does not change in the course of polymerization, the linearity of lg(F n (Cl)) versus lg(DP n ) dependence (Figure , line 2) indicates that chain transfer to tert ‐butyl chloride occurs with the constant rate independently on molecular weight of synthesized polymers.…”

Comprehensive structural characterization of polyisoprene synthesized via cationic mechanism

“…It should be noted that above‐mentioned signals of carbon atoms belong only to unsaturated part of polymer chain. According to the following works, the spectral signals belonging to carbon atoms at the branching points of polyisoprene chain are located under the pedestal line of 13 C NMR spectrum, and, therefore, were not characterized by NMR spectroscopy up to date. Besides, it was recently shown that six‐membered cyclic structures are totally absent in polyisoprene obtained by cationic polymerization of isoprene with t BuCl/TiCl 4 initiating system .…”