Controlled-radical Polymerisation Techniques

RAFT polymerisation is controlled radical polymerisation technique that is highly versatile and can be used with a wide range of monomers [38]. In RAFT polymerisation, a chain-transfer agent, typically a thiocarbonyl compound such as a xanthate, dithioester or thiocarbamate, is used in conjunction with a free-radical initiator to control the polymerisation (Figure 2.10). RAFT polymerisation has been... 

The present chapter reviews recent developments (work published in 1997 and later) in the synthesis of model block copolymers with a primary focus on ionic polymerisations. During this period controlled radical polymerisation techniques have attracted considerable interest and are emerging as a new method providing the synthesis of model polymers and copolymers. It is not the purpose of this chapter to cover this development since ionic methods still allow for better control of the polymers synthesised. Radical polymerization methods are the subject of Chapter 3. The question of how important differences in the widths of the molar mass distributions are has prompted the inclusion of a section on the MMD of model block copolymers. 

The controlled polymerisation of higher alkyl methacrylates and stearyl methacrylate has also been successfully achieved by the bulk atom transfer radical polymerisation technique at ambient temperature in the presence of CuCl/PMDETA/tricaprylyl methyl ammonium chloride (Aliquatw336)... 

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). 

The book is focusing on emulsion polymerisation in combination with both conventional and controlled radical polymerisation. Except for miniemulsion polymerisation, more exotic techniques, such as inverse emulsion polymerisation, microemulsion polymerisation and dispersion polymerisation are not covered. Chapter 1 gives a historic overview of the understanding of emulsion polymerisation, while also focusing on the solution of the... 

Polybutadiene was first prepared in the early years of the 20th century by such methods as sodium-catalysed polymerisation of butadiene. However, the polymers produced by these methods and also by the later free-radical emulsion polymerisation techniques did not possess the properties which made them desirable rubbers. With the development of the Ziegler-Natta catalyst systems in the 1950s, it was possible to produce polymers with a controlled stereo regularity, some of which had useful properties as elastomers. 

Taking a more radical approach to controlling morphology, studies have demonstrated the production of what are called polymer brushes on conducting substrates. These polymers are grown vertically from the substrate using a surface-initiated polymerisation technique (Snaith et al, 2005) and a layer of acceptor... 

It is always convenient to control the heat evolved during polymerisation and this is achieved when the reaction takes place in a solvent. It is possible to control the heat transfer by solution, suspension and emulsion polymerisations [5]. A short discussion of emulsion polymerisation will be given next. In this polymerisation technique, the initiator must be soluble in water. A common initiator for this purpose is persulfate-ferrous initiator which yields a radical sulfate anion through the reaction shown in Reaction 6.9. 

Although anionic polymerisation remains an important technique today for the preparation of block copolymers and other controlled polymer architecture, recent developments in controlled free-radical polymerisation has presented an alternative approach which may complement this methodology. 

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... 

Georges and co-workers [41] reported the first controlled polymerisation using the NMP technique. The stable free radical 2,2,6,6-tetramethyl-l-piperidynyl-N-oxy (TEMPO) was initially used, with a thermal radical initiator, for the polymerisation of styrene. NMP polymerisations usnally require higher polymerisation temperatures, and it was not possible to polymerise acrylates in the presence of excess TEMPO in the early systems, due to the very low propagation rate. The radical polymerisation... 

The ionic nature of the radicals generated, by whatever technique, can contribute to the stabilisation of latex particles. Soapless emulsion polymerisations can be carried out usiag potassium persulfate as initiator (62). It is often important to control pH with buffets dutiag soapless emulsion p olymerisation. 

---