Number: 2002-023-1-400
Title: Critically evaluated propagation
rate coefficients for free-radical polymerizations: acrylic acid
alkyl esters
Task Group
Chairman: Robin
Hutchinson
Members: Sabine
Beuermann, Michael
Buback, Igor Lac�k,
Jean-Pierre Vairon,
Alex van Herk,
and R.G. Gilbert
Completion Date: 2004 - project completed
Objective:
Critical evaluation of propagation rate coefficients for free-radical
polymerization of alkyl acrylic acid esters with this kp
data being derived from pulsed-laser initiated polymerizations in
conjunction with polymer molecular weight analysis by size-exclusion
chromatography.
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publications and projects
Description:
First-principles modeling of free-radical polymerizations remains
an important objective for polymer science and industry, in order
to efficiently introduce process modifications and new products.
The lack of reliable rate coefficients remains a major impediment
in reaching this goal. For measurement of individual propagation
rate coefficients, kp, the IUPAC Working Party
on "Modeling of Polymerisation Kinetics and Processes" recommended
pulsed-laser initiated polymerization (PLP) in conjunction with
size-exclusion chromatography (SEC) as the method of choice. This
technique has been successfully used to determine reliable propagation
rate coefficients for several monomers. After having established
benchmark value data of kp for styrene and a series
of methacrylates in three previous publications of the IUPAC Working
Party (fourth manuscript in preparation), the intention of the present
project is to collate reliable kp data for alkyl
acrylates. The knowledge of kinetic data for these monomers is of
great importance, as they are frequently used in technical polymerizations,
e.g. in the coatings and adhesives industries.
Acrylate chain-growth kinetics have been
measured using PLP techniques, but only at low temperatures (<30
�C); it was found kp is 50 times greater than
that for methacrylates. Recent studies, while not questioning the
accuracy of these data, conclude that PLP-measured values could
not be used to effectively model polymerizing acrylate systems.
This discrepancy can be explained by invoking a more complex set
of mechanisms that include intramolecular hydrogen abstraction followed
by slower propagation of the resulting mid-chain radical or by chain
b-scission. Thus a goal of this present
effort is to discuss and clarify the conditions under which the
PLP-measured values may be effectively used in modeling studies.
Progress:
The project has resulted in the publication of a 5th paper in the
series of benchmark data sets of critically evaluated propagation
rate coefficients: "Critically
evaluated rate coefficients in free-radical polymerization - 5.
Propagation rate coefficients for butyl acrylates", J.M. Asua,
S..Beuermann, M. Buback, P. Castignolles, B. Charleux, R.G. Gilbert,
R.A. Hutchinson, J.R. Leiza, A.N. Nikitin, J.-P. Vairon, and A.M.
van Herk, Macromol. Chem. Phys. 205, 2151-2160 (2004).
> abstract
(MCP website)
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publications and projects
project completed
Last update: 18 March 2005