Chain-Length-Dependent Termination in Acrylate Radical Polymerization Studied via Pulsed-Laser-Initiated RAFT Polymerization

Michael Buback; Pascal Hesse; Tanja Junkers; Thomas Theis; Philipp Vana

doi:10.1071/CH07236

RESEARCH ARTICLE

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Chain-Length-Dependent Termination in Acrylate Radical Polymerization Studied via Pulsed-Laser-Initiated RAFT Polymerization

Michael Buback ^A ^D , Pascal Hesse ^A , Tanja Junkers ^A ^B , Thomas Theis ^A ^C and Philipp Vana ^A ^D

+ Author Affiliations

- Author Affiliations

^A Institut für Physikalische Chemie, Georg-August-Universität Göttingen, Tammannstrasse 6, D-37077 Göttingen, Germany.

^B Present address: Centre for Advanced Macromolecular Design, School of Chemical Sciences and Engineering, The University of New South Wales, Sydney NSW 2052, Australia.

^C Present address: Department of Chemistry, University of California, Berkeley, CA 94720-1460, USA.

^D Corresponding authors. Email: mbuback@gwdg.de; pvana@uni-goettingen.de

Australian Journal of Chemistry 60(10) 779-787 https://doi.org/10.1071/CH07236
Submitted: 11 July 2007 Accepted: 4 September 2007 Published: 1 October 2007

Abstract

The chain-length dependence of the termination rate coefficient, k_t, in methyl acrylate (MA) and dodecyl acrylate (DA) radical polymerization has been determined via the single pulse pulsed-laser polymerization near-infrared reversible addition–fragmentation chain transfer (SP-PLP-NIR-RAFT) technique. Polymerization is induced by a laser SP and the resulting decay in monomer concentration, c_M, is monitored via NIR spectroscopy with a time resolution of microseconds. A RAFT agent ensures the correlation of radical chain length and monomer-to-polymer conversion. The obtained rate coefficients for termination of two radicals of approximately the same chain length, i, are represented by power-law expressions, k_t(i,i) ∝ i^–α. For both monomers, composite model behaviour of k_t(i,i) showing two distinct chain length regimes is observed. The exponent α_s referring to short chain lengths is close to unity, whereas the exponent α_l, which characterizes the chain-length dependency of large radicals, is slightly above the theoretical value for coiled chain-end radicals. The crossover chain length, i_c, which separates the two regions, decreases from MA (i_c = 30) to DA (i_c = 20). The results for MA and DA are consistent with earlier data reported for butyl acrylate. There appears to be a correlation of α_s and i_c with chain flexibility.

Acknowledgements

Financial support by the Deutsche Forschungsgemeinschaft within the frame of the European Graduate School ‘Microstructural Control in Free-Radical Polymerization’ (GRK 585) and the Graduate School ‘Spectroscopy and Dynamics of Molecular Coils and Aggregates’ (GRK 782) is gratefully acknowledged. P. H. is grateful to the Fonds der Chemischen Industrie for receiving a fellowship.

References

Chain-Length-Dependent Termination in Acrylate Radical Polymerization Studied via Pulsed-Laser-Initiated RAFT Polymerization

Abstract

Acknowledgements

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