Anionic-mediated polymerizations

During the last 5 years, there have been several reports of multiblock copolymer brushes by the grafting-from method. The most common substrates are gold and silicon oxide layers but there have been reports of diblock brush formation on clay surfaces [37] and silicon-hydride surfaces [38]. Most of the newer reports have utilized ATRP [34,38-43] but there have been a couple of reports that utilized anionic polymerization [44, 45]. Zhao and co-workers [21,22] have used a combination of ATRP and nitroxide-mediated polymerization to prepare mixed poly(methyl methacrylate) (PMMA)Zpolystyrene (PS) brushes from a difunctional initiator. These Y-shaped brushes could be considered block copolymers that are surface immobilized at the block junction. 

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. 

Though a vast number of studies on the characteristics of neodymium-mediated polymerizations were performed to the present day, only a few studies focus on the influence of the anion of the Nd precursor. As already mentioned in Sect. 2.1.1.2 Wilson systematically varied the structure of carboxylates and studied the influence on hydrocarbon solubility and on polymerization activity [183]. The dependence of polymerization activity on various halogenated Nd-carboxylates Nd(OCOR)3 (R = CF3, CCI3, CHCI2, CH2C1, CH3) was the target of a study by Kobayashi et al. [ 177]. 

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... 

Besides the intense research activity in synthesizing new activators and catalyst precursors, as well as in studying activation processes for metallocene-and CGC-mediated polymerization, the Northwestern group has been particularly interested in the characterization of isolable, crystallographically charac-terizable metaiiocenium cation—anion pairs for studying the molecular basis of the polymerization catalysis. A significant effort has been devoted to understanding the nature of the metaiiocenium cation—anion interaction(s) and their consequences for polymerization characteristics. This section of the review focuses on the thermodynamic and kinetic aspects of... 

In the past decade, several new approaches for controlled NCA polymerization based on the classical primary amine initiation have been reported. In 2003, Dimitrov and Schlaad reported the controlled ( ammonium mediated ) polymerization of ZLL-NCA at elevated temperature using primary amine hydrochloride salts as initiators (Figure 4.3). The initiator reactivity most likely is due to the formation of a small amount of free amine by reversible dissociation of HCl. This equilibrium is strongly shifted toward the dormant amine hydrochloride species. Consequently, as soon as a free amine reacts with an NCA, the resulting adduct is immediately protonated and prevented from further reaction. The presence of protons in the system suppresses formation of unwanted NCA anions ( activated monomers ). The obtained polypeptide blocks exhibit a very narrow, close to a Poisson, molar-mass distribution. 

Ring-opening polymerization (ROP) has seen broad utility for synthesizing main-chain organometallic polymers. Initially reported by Rauchfuss [9], and thoroughly developed by Manners and coworkers [10], the transformation from 10 to 11 (Schane 1.4) has been optimized to include various conditions for polymerization such as thermal, anionic, photo, and metal-mediated polymerizations Both solution and solid-state polymerization have also been reported. Molecular weights on the order of 10 Da have been achieved and the ability to prepare monomers of varying functionahty has assisted... 

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). 

Boileau, Kaempf, Schue and coworkers have studied the cryptate mediated anionic addition polymerization of several systems including ethylene oxide [38], propylene sulfide [39-40], isobutylene sulfide [40], isoprene [38], methyl methacrylate [38], hexamethyl trisiloxane [40], e-caprolactone [41], styrene [38, 40, 41], ct-methylstyrene [41], 1,1-diphenylethylene [41] and /3-propiolactone [42]. The polymerization of the latter compound induced by dibenzo-18-crown-6 complexed sodium acetate has also been reported [43]. In general, it was found that the polymer-... 

The combination of living cationic polymerization and NCA polymerization has also been reported. Schlaad synthesized poly(2-isopropyl-2-oxazoline)-h-PBLG (16) based on an ammonium-mediated polymerization system. By adding an acid in the NCA polymerization, a primary amino (NH2)-propagating chain end could be transformed into an ammonium (NH3 ) chain end via equilibrium and this system suppresses the generation of the aminyl anion of an NCA monomer that causes byproducts via activated monomer mechanism (Scheme 13.2) (Dimitrov and Schlaad, 2003). 

In the second method, the alkoxyamine-ftmctionalized backbone is prepared by a chemical modification of a preformed polymer. Abbasian and Entezami prepared alkoxyamine-functionalized poly(vinyl chloride) (PVC) in a three-step procedure. PVC was first arylated with toluene by Friedel-Crafts acylation followed by a bromination step using N-bromosuccinimide. The bromine atom was finally reacted via nucleophilic substitution by the TEMPO hydro-xylamine anion. PVC-g-PS was finally obtained after TEMPO-mediated polymerization of styrene. A TEMPO-functionalized isotactic poly(l-butene) macroinitiator was synthesized by Jo et al. who used a rhodium-catalyzed activation of the alkane C-H bonds and subsequent transformations of the boronate ester group into an hydroxyl pendant group. This reactive moiety was then used to attach a TEMPO-based alkoxyamine bearing another hydroxy function by an ether linkage. A method to prepare PE-g-PS from a poly(ethylene-co-m,p--methylstyrene) obtained by metallocene-catalyzed polymerization was also reported. The macroalkoxya-mine was synthesized after bromination with N-bromosuccinimide followed by a nucleophilic reaction with the TEMPO hydroxylamine anion. 

---