Living free-radical polymerisation

Star microgels have also been produced using a living linear polymer as the arms of the microgel structure, which were prepared first. The living polymer was then reacted with a divinyl cross-linker to form a star microgel consisting of a central core and surrounded by linear polymeric arms. Experimental details are reported elsewhere [8]. 

---

Figure 5 Comparison of conventional free-radical polymerisation, controlled living free-radical polymerisation and the middle ground of statistical I pragmatic modification...

Figure 7 Schematic representation of non-linear architectures, (a) and (c) are star and branched structures, respectively, that may he available by statisticallpragmatic modification of free-radical polymerisation, (b) and (d) are controlled analogues which could be made by living free-radical polymerisation...

Living Free Radical Polymerisations in Aqueous Media... 

A rapidly emerging and blossoming area in radical chemistry is living free radical polymerisation. Notwithstanding their enormous importance, radical polymerisations in general are not within the scope of this book nevertheless,... 

Several methods have been reported for the synthesis of microgel particles, these include emulsion polymerisation (EP) [5, 6], inverse EP [7], living free-radical polymerisation [8,9] and synthesis by radiation [10,11]. 

Quinn JF, Bamer L, Davis TP, Thang SH, Rizzardo E Living free radical polymerisation under a constant source of gamma Radiation—an example of reversible addition-fragmentation chain transfer or reversible termination Macromol Rapid Commun 23 717-721, 2002. 

One of the issues that concern liquid feedstock cracking operations is a higher rate of fouling. This is not only a consequence of heavier coke forming precursors, but also as a consequence of long lived free radicals which act as agents for the formation of a polymer (often referred to as pop-corn polymer) in the primary fractionator and downstream units. For instance, free radicals based on styrene or indene have sufficiently long half-lives to pass from the pyrolysis section into the primary fractionator. These can concentrate in this unit and produce polymer (free radical polymerisation) when sufficient amounts of suitable olefins are present, in particular styrene itself and di-olefins such as cyclo-pentadiene or butadiene. 

In typical free radical polymerisation, polydispersity is above 2 and as high as 20. In anionic polymerisation, the absence of termination due to a living polymerisation, may cause very narrow molecular weight distribution with polydispersities as low as 1.06. 

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. 

Proportion of living chains in a classical free-radical polymerisation [radicals]... 

Materials that are constructed from organic polymers such as polyethylene, polystyrene, polyisoprene (natural rubber and a synthetic elastomer) and poly(vinyl chloride) are common features of our daily lives. Most of these and related organic polymers are generated from acyclic precursors by free radical, anionic, cationic or organometallic polymerisation processes or by condensation reactions. Cyclic precursors are rarely used for the production of organic polymers. 

Free radical polymerizations are generally not living polymerizations that is, growing macroradicals are terminated after a time, and, so, do not individually remain in existence till 100% conversion is achieved. An exception appears to be the solutions of methacrylic esters in phosphoric acid induced to polymerise by y rays. Some biradical polymerizations are also living systems. 

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... 

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. 

---