Polymerization, anionic nitroxide-mediated radical

There are fewer reports on the preparation of block copolymers via the combination of anionic polymerization with nitroxide-mediated syntheses [132,133]. As shown in Scheme 3.30, the reaction product of sodium with 4-hydroxyl-TEMPO initiated the anionic polymerization of ethylene oxide at 60 °C in THF solution. After treatment with methanol, TEMPO-terminated PEO was obtained, and then used in the nitroxide-mediated radical polymerization of St at 120 °C resulting in block copolymers of type CLB-17 [133]. Another method is the transformation of anionic polymerization into nitroxide-mediated radical polymerization. A poly(butadienyl)lithium solution in... 

For SCVP of styrenic inimers, the mechanism includes cationic (14 [18], 19 [29]), atom transfer radical (15 [22, 27]), nitroxide-mediated radical (16 [21]), anionic (20 [19]), photo-initiated radical (17 [2], 18 [52-55]), and ruthenium-catalyzed coordinative (21 [56]) polymerization systems. Another example in-... 

One of the limitations of anionic polymerization with respect to preparation of block copolymers is the rather limited range of monomers that can be polymerized anionically to form polymers with well-defined stmctures. One solution to this problem is to utilize anionic polymerization to form a well-defined polymer that is functionalized with an end group that can be used to initiate polymerization via another polymerization method, for example, controlled free-radical polymerization. One such functional group is the aminoxy group which can be used to initiate nitroxide-mediated radical polymerization (NMP). °° PSLi has been reacted with 4-methoxy-2,2,6,6-tetramethylpiperidin-1-oxyl (MTEMPO), a stable nitroxide free radical, in THF at -78 °C as shown in eqn [30]. The mechanism of this functionalization was presumed to occur... 

ATRP, atom transfer radical polymerization AROP, anionic ring-opening polymerization NMRP, nitroxide-mediated free radical polymerization RAFT, reversible addition-fragmentation chain transfer. 

Various synthetic techniques have been used to obtain homopolymers and copolymers with defined chemical compositions and low polydispersity (1) living anionic or cationic polymerization [26,27], (2) controlled ring-opening polymerization (CROP) [28], and (3) controlled radical polymerization (CRP), which includes (a) atom transfer radical polymerization, (b) reversible addition-fragmentation chain transfer polymerization (RAFT), and (c) nitroxide mediated radical polymerization (NMP) [29-31]. 

Hawker et al. 2001 Hawker and Wooley 2005). Recent developments in living radical polymerization allow the preparation of structurally well-defined block copolymers with low polydispersity. These polymerization methods include atom transfer free radical polymerization (Coessens et al. 2001), nitroxide-mediated polymerization (Hawker et al. 2001), and reversible addition fragmentation chain transfer polymerization (Chiefari et al. 1998). In addition to their ease of use, these approaches are generally more tolerant of various functionalities than anionic polymerization. However, direct polymerization of functional monomers is still problematic because of changes in the polymerization parameters upon monomer modification. As an alternative, functionalities can be incorporated into well-defined polymer backbones after polymerization by coupling a side chain modifier with tethered reactive sites (Shenhar et al. 2004 Carroll et al. 2005 Malkoch et al. 2005). The modification step requires a clean (i.e., free from side products) and quantitative reaction so that each site has the desired chemical structures. Otherwise it affords poor reproducibility of performance between different batches. 

Nitroxide-Mediated Controlled Radical Polymerization (NMCRP) was first discovered by Solomon et al., who patented their discovery in 1985 [205]. This opened up new pathways in the field of free-radical polymerization. Polymer architectures, which were the domain of the anionic polymer chemist, became accessible to the free-radical polymer chemist. However, it was not until the work of Georges et al. [206] was published in 1993, that the world of polymer chemistry became aware of the possibihties of this new class of free-radical polymerization. This was the beginning of what is today one of the leading topics in free-radical polymer chemistry Controlled or Living Free Radical Polymerization. This initiated the search for new Controlled or Living Free Radical Polymerization techniques, and soon afterwards other methods (which will be discussed later) were developed. 

Since polystyrene is one of the oldest commercial polymers with over 9 million tonnes/yr of sales, there have been thousands of patents issued covering all aspects of its manufacture and property enhancement. The styrene monomer readily polymerizes to polystyrene either thermally or with free-radical initiators (see Chapter 6 on free-radical polymerization and Chapter 8 on nitroxide-mediated polymerization). Commercial processes for the manufacture of polystyrene are described in Chapter 3 while process modelling and optimization of styrene polymerization is examined in Chapter 5. Styrene also can be polymerized via anionic and Ziegler-Natta chemistries using organometallic initiators. Using free radical and anionic polymerization chemistries, the... 

It is obvious from the above discussion that under the correct conditions and with the appropriate mediating nitroxide free radical, living polymerization conditions can be achieved. On the basis of this realization, numerous groups have demonstrated that the degree of structural control normally associated with more traditional living processes, such as anionic procedures, can be equally applied to nitroxide-mediated living free radical polymerizations. 

Similarly to the poly(acrylamide)s and poly(vinyl amide)s, POEGMA can be prepared by free radical polymerization, CRP and anionic polymerization, whereby the latter two methods result in well-defined polymer structures with defined end-groups. Even though CRP of OEGMA can be performed by ATRP and RAFT polymerization (Becer et al, 2008 Lutz and Hoth, 2006a), the methacrylate obstructs OEGMA homopolymeriza-tion by nitroxide mediated polymerization. This can, however, be overcome by copolymerization with a minor amount of styrenic comonomer that enables good control over the polymerization (Charleux et al., 2005 Lessard et al., 2012). 

---