- Chain-length dependence in controlled/living radical polymerizations: physical manifestation and Monte Carlo simulation of reversible transfer agents. SW Prescott. Macromolecules, 36(25), 9608–9621, 2003.
Abstract:
A Monte Carlo model is used to show that chain-length dependent termination
plays an important role in free-radical polymerization systems containing
reversible transfer agents (RTAs) such as RAFT agents and alkyl halides.
As dormant chains are activated through the reversible transfer reaction,
the chain-length of the active species changes. By changing the length
of the propagating radical, the RTA changes the behavior of the entire
system, through the chain-length dependent termination reaction.
The amount of polymer that may be produced before two radicals terminate
is studied as a function of system parameters such as the transfer
constant of the RTA, the concentration of the RTA, and the length
of the dormant chains by modeling RTA-mediated polymerization, with
emphasis on emulsion polymerizations. High transfer constant RTAs
and short dormant chains exhibit significantly shorter radical lifetimes
and hence have a slower overall rate of polymerization (seen as a
lower average number of radicals per particle) than systems without
RTA. Conversely, long dormant chains may lead to an extension of
radical lifetimes and an increase in the number of radicals per particle.
These effects are due to the change in the chain length of the polymeric
radical because of transfer to dormant species, such that significant
amounts of short-short termination are seen at low conversions and
long-long termination is required at high conversions. This work
also suggests several experimental techniques, including the use
of oligomeric adducts to the RTA, that may offer solutions to the
known problems of RTA systems in bulk, solution, and particularly
emulsion polymerization.
Last edited: Friday September 10, 2010
Copyright © 1996-2014 Stuart Prescott