The Nucleophilic, Phosphine-Catalyzed Thiol-ene Click Reaction and Convergent Star Synthesis With RAFT-Prepared Homopolymers
Document Type
Article
Publication Date
7-1-2009
Department
Polymers and High Performance Materials
Abstract
The synthesis of 3-arm star polymers from reversible addition-fragmentation chain transfer (RAFT)prepared precursor homopolymers in combination with thiol-ene click chemistry is described. Homopolymers of n-butyl acrylate and N,N-diethylacrylamide were prepared with 1-cyano-1-methylethyl dithiobenzoate and 2,2'-azobis(2-methylpropionitrile) yielding materials with polydispersity indices (M(W)/M(n)) <= 1.18 and controlled molecular weights as determined by a combination of NMR spectroscopy, size exclusion chromatography (SEC), and matrix assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS). Subsequent one-pot reaction of homopolymer, hexylamine (HexAM), dimethylphenylphosphine (DMPP), and trimethylolpropane triacrylate (TMPTA) results in cleavage of the thiocarbonylthiol end-group (by HexAM) of the homopolymer yielding a macromolecular thiol that undergoes DMPP-initiated thiol-Michael addition to TMPTA yielding 3-arm star polymers. The presence of DMPP is demonstrated to serve an important second role in effectively suppressing the presence of any polymeric disulfide as determined by SEC. Such phosphine-mediated thiol-ene reactions are shown to be extremely rapid, as verified by a combination of FTIR and NMR spectroscopies, with complete consumption of the C=C bonds occurring in a matter of min. MALDI-TOF MS and SEC were used to verify the formation of 3-arm stars. A broadening in the molecular weight distribution (M(W)/M(n) similar to 1.35) was observed by SEC that was attributed to the presence of residual homopolymer and possibly 2-arm stars formed from trimethylolpropane diacrylate impurity. Interestingly, the MALDI analysis also indicated the presence of 1- and 2-arm species most likely formed from the fragmentation of the parent 3-arm star during analysis. Finally, a control experiment verified that the consumption of C=C bonds does not occur via a radical pathway. (C) 2009 Elsevier Ltd. All rights reserved.
Publication Title
Polymer
Volume
50
Issue
14
First Page
3158
Last Page
3168
Recommended Citation
Chan, J. W.,
Yu, B.,
Hoyle, C. E.,
Lowe, A. B.
(2009). The Nucleophilic, Phosphine-Catalyzed Thiol-ene Click Reaction and Convergent Star Synthesis With RAFT-Prepared Homopolymers. Polymer, 50(14), 3158-3168.
Available at: https://aquila.usm.edu/fac_pubs/1314