Living cationic polymerization of vinyl ethers

The observation in 1949 (4) that isobutyl vinyl ether (IBVE) can be polymerized with stereoregularity ushered in the stereochemical study of polymers, eventually leading to the development of stereoregular polypropylene. In fact, vinyl ethers were key monomers in the early polymer Hterature. Eor example, ethyl vinyl ether (EVE) was first polymerized in the presence of iodine in 1878 and the overall polymerization was systematically studied during the 1920s (5). There has been much academic interest in living cationic polymerization of vinyl ethers and in the unusual compatibiUty of poly(MVE) with polystyrene. 

A very interesting variant of this kind of initiation, leading to living cationic polymerizations of vinyl ethers, is the dissociation [233]... 

In a series of papers (see for example, ref. 250), Higashimura and Sawamo-to have described the living cationic polymerization of vinyl ethers at low... 

Figure 20 Protonic acid/Lewis acid (HB/MtX ) initiating systems for living cationic polymerizations of vinyl ethers. See Section V.A.l for references.

For these initiating systems, externally added nucleophiles are necessary to induce controlled/living cationic polymerizations of vinyl ethers [36,64]. Table 2 A lists nucleophiles (Lewis bases) that are effective for such purposes and includes esters (carboxylates and carbonates) [100,101,130-133], ethers (linear and cyclic) [102-104,137-140], methyl-pyridines [140], and phosphines [21,141]. CF3S03H-initiated polymerizations, sulfides are also effective [37,38,134,135]. 

Almost all of the initiating systems discussed in this section can be applied to the living cationic polymerizations of vinyl ethers that carry a variety of functional pendant groups, in a general form [42,43,65,66,180] ... 

A class of end-functionalized polymers with polymerizable terminal groups are generally called macromonomers. By both functional initiator and terminator methods, a variety of macromonomers have been synthesized in living cationic polymerization of vinyl ethers, styrenes, and isobutene, as summarized in Table 3 [16,31,147,149-151,155,158-171]. Some of these macromonomers are used in the synthesis of graft polymers (Section VI.C). 

As summarized in Chapter 4, Section V.E.l, a variety of multifunctional initiators are currently available for the living cationic polymerizations of vinyl ethers [83,188,189], alkoxystyrenes [149,190], and isobutene [191-201], and up to tetraarmed polymers with controlled arm lengths are prepared by the use of these initiating systems. Scheme 9 exemplifies such a synthesis for vinyl ethers [188]. The details for the design of these initiating systems are found in Chapter 4. 

Such a synthesis is feasible in living cationic polymerization of vinyl ethers [208], For bifunctional vinyl ethers (20), a series of compounds are examined (Scheme 11), among which 20a turned out the best, probably due to the appropriate rigidity and length of the spacer. By adjusting reaction... 

A key to the success of the living cationic polymerization of vinyl ethers is the stabilization of the unstable carbocations via suitable nucleophilic counterion. There are two ways to stabilize the carbocations (1) generation of suitable nucleophilic counterion resulted from the initiator and the catalyst, and (2) addition of nucleophilic agents to the polymerization media. In the first way, Bronsted acids such as hydrogen iodide are employed as the initiators, while Lewis acids such as zinc iodide are employed as the catalysts (Scheme 11.41) [140-143],... 

M. Kamigaito, M. Sawamoto, and T. Higashimura, Living cationic polymerization of vinyl ethers by electophile lewis acid initiating systems. 6. Living cationic polymerization of isobutyl vinyl ether by RCOOH/lewis acid initiating systems effects of carboxylate ions and lewis acid activators. Macromolecules 1991, 24(14), 3988-3992. 

All previously discussed examples of living cationic polymerization of vinyl ethers were based on homogeneous polymerization media. In 2007, Oashima and coworkers demonstrated the living polymerization of isobutyl vinyl ether in the presence of iron(III) oxide as heterogeneous catalyst and ethyl acetate or dioxane as base [58]. The major advantage of this heterogeneous catalytic system is the easy removal of the metal oxide catalyst. In addition, it was demonstrated that the iron(III) oxide could be reused for at least five times without a decrease in activity. 

Sugihara S, Matsuzono S-i, Sakai H, Ahe M, Aoshima S. Syntheses of amphiphilic block copolymers by living cationic polymerization of vinyl ethers and their selective solvent-induced physical gelation. J Polym Sci A 2001 39 3190-3197. 

Controlled/Living Cationic Polymerization of Vinyl Ethers Based on Cation Stabilization Using Flow Microreactor Systems [100]... 

Living cationic polymerization of vinyl ethers initiated by an SnCU/RCl catalytic system can be carried out in a continuous microflow system, which consists of a mutilamination micromixer M (channel width = 40 pm, IMM) and a microtube reactor R (Figure 14.1). A solution of a monomer and RCI is mixed with a solution of SnCU using the micromixer at —78 °C and the resulting mixture was allowed to react in the microtube reactor at the same temperature. For example, isobutyl vinyl ether (IBVE) was polymerized using functionalized initiators to obtain end-functionalized polymers of narrow molecular weight distribution (Mw/M < 1.2) (Scheme 14.4). 

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. 

In this paper, the living radical polymerization of N-isopropylacrylamide (NIPAM) and the living cationic polymerization of vinyl ethers having oxyethylene groups are outlined (Fig. 1), as they constitute a new wave of the... 

Similar results have been obtained by combining the living cationic polymerization of vinyl ethers and the ROP of thietane. In this case, the thietane acts as growing species stabilizer for the vinyl ether polymerization by reversible formation of an a-alkoxy-thietanium ion. This ion can, however, also be attacked at an endocyclic methylene by another thietane molecule leading to an alkyl-thietanium ion. This ion is incapable of reacting with a vinyl ether but is the active species for the thietane polymerization. Also in this case the end product is a star-shaped segmented polymer. 

To obtain telechelic polymers—that are, those carrying a same reactive molecular group at each of their ends—the most direct method is to use bifunctional initiators. Examples of such initiators can be found for all living chain addition polymerizations the example shown below illustrates the bifunctional initiation of living cationic polymerization of vinyl ethers ... 

Table 12. Two systems for living cationic polymerization of vinyl ethers ...

---