Isobutyl vinyl ether living polymer

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. 

The first synthesis of star polymers with a microgel core was reported by Sa-wamoto et al. for poly(isobutyl vinyl ether) (poly(IBVE)) [3,4]. In the first step, living cationic polymerization of IBVE was carried out with the HI/ZnI2 initiating system in toluene at -40 °C. Subsequent coupling of the living ends was performed with the various divinyl ethers 1-4. 

A large variety of AB- and ABA-type block copolymers have been prepared from vinyl ethers via sequential living cationic polymerizations. For example, as shown in Scheme 2 (A), isobutyl vinyl ether (IBVE) is first polymerized with the HI/ZnI2 or HCl/ZnCl2 initiating system, and from the resulting living polymer, the second monomer, 2-acetoxyethyl vinyl... 

The synthesis, starting from a bifunctional initiator followed by quenching the double-headed living ends, gives homotelechelic polymers (method B). Carboxylate-capped telechelic poly(isobutyl vinyl ether) has been obtained in this way [82], where the adduct of a bifunctional vinyl ether with trifluoroacetic acid is the initiator, and the quencher is the malonate anion. For method C, a bifunctional trimethylsilyl enol ether, CH2=C[OSi(CH3)3]C6H4OCH2CH20C6H4[(CH3)3SiO]C=CH2, is a useful terminator (chain coupler) for vinyl ethers [142,147] and a-methyl-styrene [159] (see also Section VI.B.4). 

Combination of a living ionic polymerization and a metal-catalyzed radical polymerization also leads to comb polymers, where both the molecular weights of the arm and main-chain polymers are well controlled. PMMA with poly(vinyl ether) arm polymers of controlled molecular weights (C-l) were prepared by the copper-catalyzed radical polymerization of methacrylate-capped macromonomers carrying a poly-(isobutyl vinyl ether), which were obtained by living cationic polymerization with a methacryloxy-capped end-functionalized initiator.428 Comb polymers with... 

S. Kwon, H. Chun, and S. Mah, Photo-induced living cationic polymerization of isobutyl vinyl ether in the presence of various combinations of halides of diphenyliodonium and zinc salts in methylene chloride. Fibers Polymers, 2004, 5(4), 253-258. 

S. Kwon, et al., Living cationic polymerization of isobutyl vinyl ether (II) Photoinduced living cationic polymerization in a mixed solvent of toluene and diethyl ether. J. Appl. Polym. Sci. 2006, 101(6), 3581-3586. 

M.U. Kahveci, M.A. Tasdelen, and Y. Yagci, Photochemically initiated free radical promoted living cationic polymerization of isobutyl vinyl ether. Polymer 2007, 48(8), 2199-2202. 

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). 

In 1975 we found that a long-lived propagating species forms in the polymerization of p-methoxystyrene (pMOS) initiated with iodine in nonpolar media Subsequently, similar results were obtained for the isobutyl vinyl ether (IBVE)/iodine system These monomers have strongly electron-donating substituents that stabilize the propagating carbocations derived from them, so that they are likely to form living polymers. 

Fig. 14. M versus conversion relationships for poly(isobutyl vinyl ether) obtained with HI/I2 in n-hexane at —15 °C [M]o = 0.38 mole/1 [Hilo = [T lo- [Hilo (mmole/1) (A) 1.2 (A) 2.0 (O) 5.0 ( ) 7.6. The straight lines indicate Ae M values calculated for living polymers (M = 100.2 [ML .a/IHl]o)...

In the presence of zinc chloride (as an activator), for example, diphenyl phosphate (as an initiator) rapidly and quantitatively polymerizes isobutyl vinyl ether (IBVE) in toluene at 0 C. As shown in Figure 1, the of the produced polymers is directly proportional to monomer conversion and in good agreement with the calculated value based on the feed molar ratio of IBVE to the initiator (one polymer chain per phosphate). On addition of a second feed of IBVE at the end of the polymerization, polymer molecular weight further increases with conversion, while the polymers invariably exhibit very narrow MWDs (M /Mj < 1.1). All these data show that the diphenyl phosphate/ ZnCl2 initiating system induces living polymerization of IBVE. 

---