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Cationoid living polymerisations
Author(s) -
Plesch Peter H.
Publication year - 1992
Publication title -
makromolekulare chemie. macromolecular symposia
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.257
H-Index - 76
eISSN - 1521-3900
pISSN - 0258-0322
DOI - 10.1002/masy.19920600104
Subject(s) - cationic polymerization , chemistry , polymer chemistry , reactivity (psychology) , trifluoromethanesulfonate , monomer , polymer , reagent , acceptor , transition metal , organic chemistry , catalysis , medicine , alternative medicine , physics , pathology , condensed matter physics
The cationoid living polymerisations have many of the characteristics of pseudo‐cationic (φ‐cat) polymerisations and none of those of cationic polymerisations. In contrast to the φ‐cat polymerisations by protonic acids, which are transfer‐dominated, those giving living polymerisations are propagated by esters which are part of a donor‐acceptor complex involving a “third reagent”. There are three types: The first is exemplified by an ester which is activated by a metal halide, e.g. HMI (from monomer M + HI) + ZnBr 2 , or oligoisobutyl acetate + BCl 3 . The second type is exemplified by a polymer triflate complexed by a dialkyl sulphide. The reagents which change the reactivity of the ester are termed “modifiers”. The acceptors, e.g. ZnBr 2 , which co‐ordinate to a donor group on the polymer, are positive modifiers (or activators). The donors, such as R 2 S, which coordinate onto an acceptor group at the end of the polymer, e.g. the acidic β‐H, are negative modifiers (or moderators). The propagation by both types of modified ester probably involves a 6‐centred cyclic transition state. The same applies to a third type of φ‐cat propagation, in which a polymeric ester reacts with a D‐A complex formed from M + I 2 . The formation of unwanted non‐living polymers of high DP and/or broad DPD, together with those resulting from living polymerisations, happens because the metal halides used in these reactions not only form the φ‐cat propagating centres, but also react with ionogenic impurities to initiate concurrent, short‐lived cationic polymerisations. These parasitic reactions can be suppressed by an excess of base, e.g. an ester or halide ions, which scavenge protons and carbenium ions. This phenomenon indicates that, whatever else is propagating the living polymerisations, it is unlikely to be carbenium ions. The kinetic equations for the living polymerisations, developed here, make it possible to calculate propagation rate‐constants from rate and DP data; such calculations are shown for a variety of published results.