Open AccessKinetics and mechanisms in carbocationic polymerization: The quest for true rate constants
Author(s) -
Puskas Judit E.,
Chan Sam W. P.,
McAuley Kimberley B.,
Shaikh Sohel,
Kaszas Gabor
Publication year - 2005
Publication title -
journal of polymer science part a: polymer chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.768
H-Index - 152
eISSN - 1099-0518
pISSN - 0887-624X
DOI - 10.1002/pola.21011
Subject(s) - chemistry , polymerization , reaction rate constant , taft equation , kinetics , thermodynamics , activation energy , reaction mechanism , kinetic energy , cationic polymerization , polymer chemistry , stereochemistry , polymer , organic chemistry , physics , catalysis , quantum mechanics , substituent
Abstract This article is a critical analysis of kinetic dataavailable on carbocationic polymerizations. A survey of published propagation rate constant ( k p ) data revealed several orders of magnitude differences. In this article, an explanation of this apparent discrepancy is offered with a case study involving the carbocationic polymerization of 2,4,6‐trimethylstyrene (TMS). With the polymerization mechanism originally proposed for this system, k p = 1.35 × 10 4 L mol −1 s −1 was extracted from experimental data with the Predici polyreaction package. The alternative mechanism yielded k p = 1.01 × 10 7 L mol −1 s −1 , close to that predicted by Mayr's Linear Free Energy Relationship (LFER). We propose that true rate constants can only be obtained from direct competition experiments or from kinetic interpretation based on independently proven mechanisms. The second part of this review discusses critical analysis of the temperature and concentration dependence of various living IB systems. Comparison of the temperature dependence in systems initiated with 2‐ chloro‐2,4, 4‐ trimethylpentane (TMPCl)/TiCl 4 from various laboratories yielded of Δ H ∼−25 and −34.5 kJ/mol for high and low TMPCl/TiCl 4 ratios, respectively. Aromatic (cumyl‐type) initiators show Δ H ∼ −40 kJ/mol, whereas H 2 O/TiCl 4 in the presence of the strong electron‐ pair donor dimethylacetamide gave Δ H = −12 kJ/mol. The significant differences indicate different underlying mechanisms with complex elementary reactions. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5394–5413, 2005