Living polymerization cationic, added base

Classic Living Cationic Polymerization with Added Base. 195... 

However, in the presence of a suitable Lewis base the polymerization becomes living, due to the nucleophihc stabilization of the growing cation generated by the added base. (3) Initiator, strong Lewis acid and onium salt as additive The previous method cannot be easily applied in polar media. In this case the living cationic polymerization is promoted by the addition of salts with nucleophihc anions, such as ammonium and phosphonium derivatives. 

As illustrated earlier, the inherent problem in controlled cationic polymerizations is the instability of the macrocarbocations. However, living polymerizations can be realized by stabilizing the growing carbenium ions with a suitable nucleophilic counterion (Be), 9-19, or an added Lewis base (X) containing a weakly nucleu-cleophilic counteranion (Be), 9-20 [7]. That is ... 

In this study, the authors investigate the living cationic polymerization of polar monomers in the presence of added bases to prepare living polymers of various properties and shapes. Based on the results, various types of amphiphilic copolymers are designed, and the stimuli-induced self-association of the products, such as thermosensitive physical gelation, is characterized. 

Living cationic polymerization in the presence of added bases (X). Scheme 2.24... 

A. Living Cationic Polymerization in the Presence of Added Bases and Synthesis of Various Functional Polymers... 

As shown in Scheme 2.27, POEVE and PNIPAM have similar structures with both hydrophilic and hydrophobic parts in each monomer unit. Quite recently, our group examined another possibility for thermosensitive phase separation random copolymers of hydrophilic and hydrophobic monomers.Although random copolymers have been investigated previously, the achieved phase separation was broad, with hysteresis and low turbidity. By living cationic polymerization in the presence of added bases, our group successfully prepared random copolymers of IBVE and HOVE, both of which are typical hydrophobic and hydrophilic monomers, and which are not thermosensitive themselves. At low temperature, the polymers were soluble in water, but when the temperature was increased to a critical point, the transparent solution became opaque. The phase separation was quite sensitive (Scheme 2.27(a)) and the temperature of phase separation was governed by the monomer feed ratio. 

Aoshima, S. and Kobayashi, E. (1995) Living cationic polymerization of vinyl ethers in the presence of added bases recent advances. Makromol. Chem. Makromol. Symp., 95,91-102. 

Living cationic polymerization has led to precision synthesis of functionalized polymers from species such as vinyl ethers, isobutene, and styrene derivatives [215]. Among those, vinyl ether polymers allow a wide choice of functional groups, which, along with the possibility of precision synthesis, has led to the development of a variety of stimuli-responsive polymers with well-defined structures [216]. This chapter describes our recent study on the synthesis and stimuli-responsive behavior of various poly(vinyl ether)s obtained by living cationic polymerization in the presence of an added base. 

It was reported that the rate of living cationic polymerization of IBVE with Al-based initiating systems was enhanced if the basicity of an added base was reduced. Thus, a weaker base was examined in the polymerization using SnCU and FeCU. An alternative weaker base, ethyl chloroacetate, realized very fast polymerization with SnCU in toluene at -78 °C, being completed within 2 s (determined using a high-resolution digital video camera).Moreover, FeCU induced faster polymerization with 1,3-dioxolane, a weaker base than 1,4-dioxane, which was completed in 2-3 s in toluene at 0 °C. ° In both cases, product polymers had very narrow MWD (Mw/Mn< 1.1), irrespective of the monomer conversion. 

Table 1 Living cationic polymerization of St derivatives using EtAICl2/SnCU with added base ...

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