Thiol ene chemistry

In spite of the large number of grafted and side functionalized polysilox-anes commercially available and the variety of modification techniques available [25,50] (hydrosilylation, thiol-ene chemistry, halogen substitution, polycondensation), only a few of them have been used as in situ-formed graft copolymer compatibilizers. 

The concept of copolymerizing with a functional comonomer that is soluble in the continuous phase can virtually be extended to any vinyl functional monomer, provided that under such conditions the copolymerization parameters will allow a copolymerization to occur. The functionalities available using hydrophobic monomers with functional monomers in direct miniemulsions are summarized in Table 15.1. Latexes with a double functionality were prepared via a free-radical polymerization of divinylbenzene in miniemulsion [49, 50] after polymerization, the remaining vinyl bond might be reacted with a thiol-functionalized PEG via the thiol-ene chemistry [49]. 

Like the 1,3-dipolar Huisgen cycloaddition reaction between azides and acetylenes, thiol-ene chemistry is more than a century old, with the first thiol-alkene addition reaction having been reported by Posner in 1905 [19]. The first thiol-ene... 

A review of click chemistry and its application to material synthesis would not be complete without a discussion of the network-forming abilities of CuAAC and fhiol-ene coupling reactions. In particular, thiol-ene chemistry has been well established in the field, and has been used extensively in network formation for over... 

Kade, M., Burke, D.J., Hawker, C. The power of thiol-ene chemistry. Journal of Polymer Science Part A 48, 743-750 (2010)... 

Figure 11 Synthesis of PI macroinitiators via thiol-ene chemistry. Reproduced from Wang, G. Fan, X. Huang, J. J. Polym. Sci., Part A Polym. Chem. 2010, 48, 3797. =...

Other interesting structures belonging to this family of monomers were also synthesised by thiol-ene chemistry and by using ricinoleic acid (see Chapter 6). 

Lucas, P. Fleury, E. Estur, J.-F. Lapinte, V. Robin, J.-J., Peroxide-Grafted PDMS Hydrosilylation Reaction and Thiol-Ene Chemistry as an Alternative Pathway. Macromol. Chem. Phys. 2009, 210,1933-1941. 

PAU 12] Pauloehrl T., Delaittre G., Bastmeyer M. et al, Ambient temperature polymer modification by in situ phototriggereddeprotection and thiol-ene chemistry . Polymer Chemistry, vol. 3, pp. 1740-1749, 2012. 

In perhaps the most elegant example to date of the use of thiol-ene chemistry for macromolecular synthesis. Hawker and colleagues prepared up to fourth-generation dendrimers... 

In a further, and more comprehensive investigation into radical-based thiol-ene chemistry. Hawker and colleagues prepared a series of polymers with either single or multiple alkene functionality and clicked on a variety of commercially available mercaptans under both photoinitiation (with trace amounts of DMPA) and thermal initiation (in the presence of radical initiator 2,2 -azobis(2-methylpropionitrile)) (Campos et al, 2008). In aU cases studied, the photoinitiated thiol-ene reactions (all performed at ambient temperature) could be made to proceed to completion in times ranging from 30 min to 2h. 

An alternative and convenient approach that is also highly versatile is the use of polymers prepared via RAFT polymerization as precursors to thiol-capped polymers. RAFT polymerization is the most versatile controlled radical polymerization method in terms of the wide variety of monomers that may be used. As such, the combination of this technology with thiol-ene chemistry offers, arguably, the greatest accessibility to synthetic functional materials. 

Hoyle, C.E., Lee, T.Y., and Roper, T. (2004) Thiol-enes chemistry of the past with promise for the future. Journal of Polymer Science Part a-Polymer Chemistry, 42,5301. 

Below, first a brief summary of the state-of-the-art for more traditional design of dendrimers is given, after which we focus on the use of the CuAAC, Diels-Alder cycloaddition reactions and thiol-ene chemistry for the preparation of these dendritic structures. 

In contrast to the CuAAC reaction, the combination of thiol-ene chemistry with a traditional esterification reaction allowed for an efficient synthesis of dendrimers without the use of a metal catalyst. Moreover, as thiol-ene click can occur in the absence of solvent under benign reaction conditions, this reaction seems to be quite a promising alternative. 

Van Der Ende, A. et al. (2009) Tailored polyester nanoparticles post-modification with dendritic transporter and targeting units via reductive amination and thiol-ene chemistry. Soft Matter, 5,1417-1425. 

---