Limitations of radical thiol-ene reactions for polymer-polymer conjugation

Koo, S. P. S., Stamenović, M. M., Arun Prasath, R., Inglis, A. J., Prez, F. E. D. U., Barner-Kowollik, C., Van Camp, W. I. M., & Junkers, T. (2010) Limitations of radical thiol-ene reactions for polymer-polymer conjugation. Journal of Polymer Science, Part A: Polymer Chemistry, 48(8).

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In this work, we report our findings on the use of radical thiol-ene chemistry for polymer-polymer conjugation. The manuscript combines the results from the Preparative Macromolecular Chemistry group from the Karlsruhe Institute of Technology (KIT) and the Polymer Chemistry Research group from Ghent University (UGent), which allowed for an investigation over a very broad range of reaction conditions. In particular, thermal and UV initiation methods for the radical thiol-ene process were compared. In the KIT group, the process was studied as a tool for the synthesis of star polymers by coupling multifunctional thiol core molecules with poly(n-butyl acrylate) macromonomers (MM), employing thermally decomposing initiators. The product purity and thus reaction efficiency was assessed via electrospray ionization mass spectrometry. Although the reactions with 10 or 5 equivalents of thiol with respect to macromonomer were successful, the coupling reaction with a one-to-one ratio of MM to thiol yielded only a fraction of the targeted product, besides a number of side products. A systematic parameter study such as a variation of the concentration and nature of the initiator and the influence of thiol-to-ene ratio was carried out. Further experiments with poly(styrene) and poly(isobornyl acrylate) containing a vinylic end group confirmed that thermal thiol-ene conjugation is far from quantitative in terms of achieving macromolecular star formation. In parallel, the UGent group has been focusing on photo-initiated thiol-ene chemistry for the synthesis of functional polymers on one hand and block copolymers consisting of poly(styrene) (PS) and poly (vinyl acetate) (PVAc) on the other hand. Various functionalization reactions showed an overall efficient thiol-ene process for conjugation reactions of polymers with low molecular weight compounds (∼90% coupling yield). However, while SEC and FT-IR analysis of the conjugated PS-PVAc products indicated qualitative evidence for a successful polymer-polymer conjugation, 1H NMR and elemental analysis revealed a low conjugation efficiency of about 23% for a thiol-to-ene ratio equal to one. Blank reactions using typical thiol-ene conditions indicated that bimolecular termination reactions occur as competitive side reactions explaining why a molecular weight increase is observed even though the thiol-ene reaction was not successful. The extensive study of both research groups indicates that radical thiol-ene chemistry should not be proposed as a straightforward conjugation tool for polymer-polymer conjugation reactions. Head-to-head coupling is a major reaction pathway, which interrupts the propagation cycle of the thiol-ene process. © 2010 Wiley Periodicals, Inc.

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ID Code: 99250
Item Type: Journal Article
Refereed: Yes
Additional Information: Cited By :136
Export Date: 5 September 2016
Correspondence Address: Prez, F. E. D. U.; Department of Organic Chemistry, Polymer Chemistry Research Group, Ghent University, Krijgslaan 281 (S4-bis), Ghent 9000, Belgium; email:
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Keywords: Block copolymers, Click chemistry, Electrospray ionization mass spectrometry (ESI-MS), Macromonomers, Mass spectrometry, Polymer-polymer conjugation, Star polymer synthesis, Thiol-ene, Electrospray ionization mass spectrometry, Star polymers, Thiol-enes, Chemical bonds, Computer crime, Copolymerization, Electrospray ionization, Functional groups, Functional polymers, Gel permeation chromatography, Group technology, Ionization, Macromolecules, Molecular weight, Particle detectors, Styrene, Synthesis (chemical), Polyvinyl acetates
DOI: 10.1002/pola.23933
ISSN: 0887624X
Divisions: Current > Schools > School of Chemistry, Physics & Mechanical Engineering
Current > Institutes > Institute for Future Environments
Current > QUT Faculties and Divisions > Science & Engineering Faculty
Deposited On: 22 Sep 2016 04:50
Last Modified: 07 Oct 2016 03:19

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