Living radical polymerisation

Control of the molar mass and MMD using LRP has important implications on the mechanical properties of the final polymer, making these techniques highly attractive for industrial applications. 

Reversible termination requires the deactivation of active polymeric radicals through termination reactions to form dormant polymer chains, and activation of dormant polymer chains to form active chains with, for example, heat, light or a redox reaction. The width of the MMD (as qualitatively described by the polydispersity index, PDI) is controlled by 

2 Synthesis of block copolymers and more complex architectures 

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Sawamoto, M. and Kamigaito, M. (1999) Living radical polymerisation, in Synthesis of Polymers, ed. Schliiter, A.-D. (Wiley-VCH, Weinheim) p. 163. 

Controlled/living radical polymerisation (CRP) is currently a fast developing area in polymer synthesis and it allows preparation of many advanced polymeric materials, including thermoplastic elastomers, surfactants, gels, coatings, biomaterials, materials for electronics and many others. 

K. Matyjaszewski (Ed.), Controlled/Living Radical Polymerisation, American Chemical Society, Washington, DC, 2000. 

A significant development of the last decade involving radicals and oiganometallic complexes is the living radical polymerisation. In a common radical polymerisation (see Atkins, page 910, 5th Ed.) the molecular weight... 

Compared to other living radical polymerisation techniques, ATRP offers two important advantages. Firstly, the synthesis of well-defined macro-initiators is facile and allows the preparation of a range of new diblock copolymers. Secondly, the presence of water (or methanol) has a remarkable accelerating effect on the... 

ATRP is a powerful synthetic tool for the synthesis of low molecular weight (Dp < 100-200), controlled-structure hydrophilic block copolymers. Compared to other living radical polymerisation chemistries such as RAFT, ATRP offers two advantages (1) facile synthesis of a range of well-defined macro-initiators for the preparation of novel diblock copolymers (2) much more rapid polymerisations under mild conditions in the presence of water. In many cases these new copolymers have tuneable surface activity (i.e. they are stimuli-responsive) and exhibit reversible micellisation behaviour. Unique materials such as new schizo-... 

Coelho and co-workers have recently reported another use of water in living polymerisation in the synthesis of a block copolymer [poly(vinyl chloride)-b-poly(/z-butyl acrylate)-b-poly(vinyl chloride)].3 The new material was synthesised by single electron transfer/degenerative chain transfer-mediated living radical polymerisation (SET-DTLRP) in two steps. 

Monteiro MJ, Charleux B. Living radical polymerisation in emulsion and miniemulsion. In van Herk A, editor. Chemistry and Technology of Emulsion Polymerisation. Oxford Blackwell Publishing 2005. pill. 

Bon SAF, Carmichael AJ, Haddleton DM, Seddon KR. 2000. Copper(I) mediated living radical polymerisation in an ionic liquid. Chem Commun 74 1237-1238. 

Fig. 5 Visible light-induced living radical polymerisation mediated by organo-cobalt porphyrins. Reproduced from ref. 169 with permission from The Royal Society of Chemistry.

The successful application of living radical polymerisations will be dependent on whether they can be used to produce materials with unique properties in an economical and acceptable manufacturing process. A... 

The adducts of ARs with organic free radicals have attracted considerable attention because of their potential utility as free radical initiators, and because of the important role of reversible dissociation of adducts of IV in living radical polymerisation. 

By the same method of living radical polymerisation, a series of block copolymers of poly(ethylene oxide-styrene) with narrow polydispersity were synthesised by the following two-step approach [96]. Initially, living anionic polymerisation of ethylene oxide with sodium-4-oxy-2,2,6,6-tetramethyl-l-piperidinoxyl as initiator yields polyethylene oxide with ARs at the chain end ... 

Lecolley, F., Tao, L., Mantovani, G., etal. (2005) A new approach to bioconjugates for proteins and peptides (pegylation) utilising living radical polymerisation, Chimica Oggi - Chemistry Today, 23, 45-51. 

This means that composition of the chain and chain length is determined in seconds. Terminated chains, in principle, do not take part in further reactions (except when transfer to polymer events occur. Section 2.3). The final chemical composition distribution and molecular mass distribution is determined by the accumulation of rapidly produced dead chains (chains without an active centre). In free radical polymerisation, the active centre is a free radical. In controlled or living radical polymerisation (Section 2.5) the radical is protected against termination and continues to grow during the complete reaction time. 

A further discussion of the living radical polymerisation techniques and its application in heterogeneous polymerisation techniques can be found in Chapter 5. 

Figure 5.7 Examples of alkoxyamines used as unimolecular initiator in nitroxide-mediated living radical polymerisation.

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