Number: 2000-028-1-400
Title: Critically evaluated termination rate coefficients for
free-radical polymerization. 1. Current status, evaluation of experimental
methods, data for styrene and methyl methacrylate
Task Group
Chairman: Greg Russell
Members: Sabine
Beuermann, Michael Buback,
Mark Egorov, Robert
Gilbert, Robin Hutchinson,
Vladimir Kaminsky,
Oskar Friedrich Olaj,
Philipp Vana, and Gerhard
Zifferer
(added in 2003) Christopher
Barner-Kowollik, Takeshi
Fukuda, Atsushi
Goto, Bunichiro Yamada,
Per Zetterlund,
Graeme Moad and Hans
Heuts.
Objective:
To begin the task of providing critically evaluated ("benchmark") values
of termination rate coefficients for free-radical polymerization.
Description:
Free-radical polymerization (FRP) has always been a scientifically and
commercially important field. This importance is set to increase even
further due to recent advances such as the development of "controlled
radical polymerization". Hence it is of great benefit for both science
and industry to be able to model the kinetics of FRP systems. Such modeling
is dependent on the availability of reliable values of rate coefficients.
Unfortunately FRP systems have proven to be difficult subjects for investigations
aimed at determining accurate rate coefficients. However recently the
IUPAC Working Party on "Modeling of Polymerization Kinetics and Processes"
has made considerable progress in delivering critically evaluated propagation
rate coefficients, kp, for FRP systems.
> See Related
Publications
But the situation is not so well developed for termination rate coefficients,
kt, which are equally as fundamental and important
as kp. Therefore there is great necessity for the
progress made with regard to kp to be matched on the
termination front. It is the aim of this project to make such progress.
To do this there is first of all the need to make workers aware of the
subtleties involved in studying and describing the termination reaction.
Secondly there needs to be carried out an evaluation of methods for
determining kt, and for agreement to be arrived at
regarding the strengths and weaknesses of each method. Finally, we will
apply our conclusions to data from the initial stages of bulk polymerizations
of styrene and methyl methacrylate, two otherwise well characterized
systems, so as to come up with critically evaluated kt
for these systems.
Progress:
The first of our three objectives was realised in the form of the
following publication:
"Critically evaluated termination rate coefficients for free-radical
polymerization", M. Buback, M. Egorov, V. Kaminsky, O.F.Olaj,
G.T. Russell, P. Vana, G. Zifferer, Macromol. Chem. Phys. 203,
2570-2582 (2002)
> abstract
(MCP website)
Since then there have been two specific gatherings of taskgroup members:
(1) On 20 August 2002, during the 224th ACS meeting in Boston; (2) On
17 November 2003, at the Institute of Physical Chemistry, University
of Göttingen. These discussions facilitated the meeting of the
second of our three objectives through the following publication:
"Critically evaluated termination rate coefficients for free-radical
polymerization: experimental methods", C. Barner-Kowollik, M.
Buback, M. Egorov, T. Fukuda, A. Goto, O.F. Olaj, G.T. Russell, P.
Vana, B. Yamada and P.B. Zetterlund, Prog. Polym. Sci. 2005,
in press
The third and final task of establishing and documenting benchmark
termination rate coefficients for styrene and methyl methacrylate bulk
polymerizations was initiate in July 2004, and it is anticipated that
this task will be completed by Hans Heuts, Michael Buback and Greg Russell,
acting on information provided by most other taskgroup members, over
the middle months of 2005.