Atom transfer radical polymerisation ATRP

Abstract Over the past decade significant advances have been made in the fields of polymerisation, oligomerisation and telomerisation with metal-NHC catalysts. Complexes from across the transition series, as well as lanthanide examples, have been employed as catalysts for these reactions. Recent developments in the use of metal-NHC complexes in a-olefin polymerisation and oligomerisation, CO/olefm copolymerisation, atom-transfer radical polymerisation (ATRP) and diene telomerisation are discnssed in subsequent sections. 

There are a number of reports of NHC complexes of mid-late transition metals being used as catalysts for atom transfer radical polymerisation (ATRP) of acrylates and styrene. Grubbs reported Fe(II) complexes of a simple monodentate carbene. 

TEMPO combines with the radical chain and keeps the concentration of the growing radical chain low, such that the recombination of radicals is suppressed. This type of radical polymerisation is called Atom Transfer Radical Polymerisation (ATRP). It has the properties of a living polymerisation, as the molecular weight increases steadily with time and one can make block polymers this way by adding different monomers sequentially. 

Atom Transfer Radical Polymerisation (ATRP) was discovered independently by Wang and Matyjaszewski, and Sawamoto s group in 1995. Since then, this field has become a hot topic in synthetic polymer chemistry, with over 1000 papers published worldwide and more than 100 patent applications filed to date. ATRP is based on Kharasch chemistry overall it involves the insertion of vinyl monomers between the R-X bond of an alkyl halide-based initiator. At any given time in the reaction, most of the polymer chains are capped with halogen atoms (Cl or Br), and are therefore dormant and do not propagate see Figure 1. 

The Cu(II)/Cu(I) redox system added as bromide has recently been used to prepare well-defined polymers (controlled molecular weight, reduced poly-dispersity, terminal functionalities). One of the most successful methods to make well-defined polymers is atom transfer radical polymerisation (ATRP)18 ... 

Polymer brushes are polymers tethered to a surface via one end. The connection to the surface can be covalent or non-covalent, and the brushes can be made via grafting to or grafting from the surface. In the past few years, there has been considerable interest in the growth of polymer brushes via surface-initiated polymerisations from (patterned) initiator-functionalised SAMs.62,63 For example, we have recently shown that surface confined Atom Transfer Radical Polymerisations (ATRP) in aqueous solvents leads to rapid and controlled... 

Nitroxide-mediated CRP has been investigated for use in emulsion polymerisation systems, but with mixed the results. " Atom transfer radical polymerisation (ATRP) offers greater scope than nitroxide-mediated CRP in that it is less discriminating in terms of the monomers that can be used. However, there are few reports of work on adapting ATRP to heterogeneous systems. " Given the established requirements for control of these polymerisations, both nitroxide-mediated CRP and ATRP suffer from problems brought about by... 

A corresponding principle applies to controlled radical polymerisation performed in quite a number of modes such as nitroxide-mediated polymerisation (NMP), atom transfer radical polymerisation (ATRP), reversible addition fragmentation chain transfer (RAFT) or catalytic chain transfer (CCT) reactions. All of these variants of controlled radical polymerisation lead to well-defined architectures with the particular advantage that a much larger number of monomers are suitable and the reaction conditions are much less demanding than those of living ionic polymerisation reactions. 

The copolymer with PMMA 229 (Scheme 104), however, had to be made in a step-wise grafting onto procedme, as the initiator for the atom transfer radical polymerisation (ATRP) of methyl methacrylate was not stable under Yamamoto reaction conditions. 

Many publications dealing with the free-radical homo/copolymerisation of saturated fatty acid acrylates and methacrylates appeared between 2001 and 2011, particularly using living systems such as atom transfer radical polymerisation (ATRP) [91-112]. Monomers were prepared, for example, by the reaction of acrylic and methacrylic acid chlorides with fatty alcohols of different chain length, as shown in Scheme 4.23 in the case of methacrylates (which also includes their ATRP conditions). A very... 

In recent years, transition metal mediated free radical processes have gained in importance. In particular the Kharasch addition to olefins such as atom transfer radical addition (ATRA) and atom transfer radical cyclisation (ATRC) and its extension to olefin polymerisation known as atom transfer radical polymerisation (ATRP) have been reported with a wide range of metal catalysts. 

Although free radical polymerisation is most common, other types of polymerisations have been carried out in emulsion polymerisation, including reversible addition-fragmentation transfer (RAFT) (131), atom transfer radical polymerisation (ATRP) (76, 222), and stable free radical polymerisation (SFRP) (77). 

The silane-diffusion techniques developed by Chaudhury and Whitesides, and Elwing et alP have been used to generate gradients of grafting sites on silica surfaces. These grafting sites were used to either initiate the polymerisation of various monomers by atom transfer radical polymerisation (ATRP), a grafting-from technique, - or were used to attach PEG chains by the... 

Simal, F., Demonceau, A., Noels, A.F., Kharasch addition and controlled atom transfer radical polymerisation (ATRP) of vinyl monomers catalysed by Grubbs ruthenium-carbene complexes. Tetrahedron Lett. 1999, 40 5689-5693. 

The key to successful polymerisation from the protein in solution was the use of sacrificial polymerisation initiators on an added insoluble resin. With the resin present the P(NIPAM) polymers grew in a controlled fashion from the protein although the polydispersity (PDI) was quite high compared to other polymers grown by atom-transfer radical polymerisation (ATRP). Nevertheless, this paper demonstrated the principle of growing polymers from biomolecule surfaces and this technique has much to offer for... 

With the rapid expansion in controlled radical polymerisation chemistry, for example, atom-transfer radical-polymerisation (ATRP) [47], it is clear that combinations with the inorganic polyphosphazene backbone, and its many unique properties, can add extra dimensions and multiply the opportunity for new hybrid materials. As the inorganic component in such polymers is low, often below 5%, the resultant polymers often possess the solution, chemical and biological properties of the attached organic component and can, in effect, be viewed as highly branched versions on an inorganic (potentially degradable) backbone. 

Instead of functionalising the polymer blocks after formation, the polymers can also be synthesised directly from the linker. A peptide sequence with the desired enzyme sensitivity can be modified on one end with an atom transfer radical polymerisation (ATRP) initiator and used to grow the first polymer block in a living polymerisation. Once complete, the second terminus of the peptide can be similarly modified and used to initiate the polymerisation of the second polymer block (de Graaf et al, 2012). 

Although ROMP or ADMET reactions hold a prominent position among polymerisation processes initiated by NHC-Ru complexes, other catalytic paths leading to macromolecular products were also investigated. The activity of compounds 30 and other similar monometallic [(NHQRuCl2(p-cymene)] complexes was tested in the atom transfer radical polymerisation (ATRP) of vinyl monomers by Delaude and Demonceau, along with 32. These complexes led to the controlled polymerisation of methyl methacrylate at 85 °C (Equation (7.8)). Attempts to polymerise n-butyl acrylate and styrene turned out to be more challenging, because of difficulties to control the acrylate polymerisation and of competition with the self-metathesis of styrene. 

Functionalised PO as block and graft copolymers used as compatibilisers or to increase interactions with other materials are prepared by free radical grafting (the simplest method), metallocene-catalysed copolymerisation of olefins with functional monomers, or anionic polymerisation (silane-containing PO). They are also produced by controlled/living polymerisation techniques such as nitroxide-mediated controlled radical polymerisation, atom transfer radical polymerisation (ATRP), and reversible addition-fragmentation chain transfer (RAFT). 

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