Major Progress in Catalysts for Living Cationic Polymerization of Isobutyl Vinyl Ether: Effectiveness of a Variety of Conventional Metal Halides

Abstract

Cationic polymerization of isobutyl vinyl ether (IBVE) was examined using a variety of metal halides. In the presence of an appropriate added base, ester or ether, the living polymerization of IBVE proceeded for almost all Lewis acids (MCl n ; M: Fe, Ga, Sn, In, Zn, Al, Hf, Zr, Bi, Ti, Si, Ge, Sb) used in conjunction with an IBVE-HCl adduct in toluene at 0°C. The difference in the polymerization activity of these Lewis acids was significant. As examples, polymerization with some acids, such as FeCl 3 , proceeded in the order of seconds, whereas it took more than a few weeks with others such as SiCl 4 and GeCl 4 . The difference in activity is based on the strength of the interaction between the Lewis acid and the propagating end chloride anion and/or the basic carbonyl (or ether) oxygen atom of the added base, that is, the chlorophilic or oxophilic nature of each metal halide is a decisive factor. In addition, a suitable combination of a Lewis acid and an additive was indispensable for living polymerization. With metal pentachlorides, NbCl 5 and TaCl 5 , addition of a salt (nBu 4 NCl) resulted in superior control of the reaction over that for addition of a base. Lewis acids for living cationic polymerization of vinyl ether were categorized into groups depending on the preferences for these additives.

Cationic polymerization of isobutyl vinyl ether using alcohols both as cationogen and catalyst‐modifying reagent: Effect of Lewis acids and alcohols on living nature

“…Such uncontrolled portion can be produced despite the low activity of the catalyst, as in the case of polymerization using SiCl 4 or SbCl 3 without additives in conjunction with IBVEHCl. 8 In addition, the surplus diol may have induced undesired reactions such as coupling, that is, reactions (termination and/or transfer) of the two hydroxy groups with the propagating chains. With SnCl 4 , polymers with larger M n values and broad MWDs were obtained with amounts of ethylene glycol both equal to and twice that of the catalyst, although the reactions still proceeded very smoothly (entries 5 and 6).…”

“…The order of the relative oxophilicity estimated from the results is as follows: NbCl 5 > ZrCl 4 > SnCl 4 . 8,9 The polymerization behaviors using alcohols may become one of the meaningful index for the nature of Lewis acids. It should also be pointed out that the differences in chloro-and oxophilicities of the metal catalysts observed in this study are derived as relative scales based on the chloro-and oxophilicities of the carbocation.…”

“…Our group recently demonstrated that, in addition to the conventional metal chlorides, a variety of metal chlorides can induce living cationic polymerization of vinyl ether (VE) in conjunction with a VE-HCl adduct or methanol as a cationogen. 8,9 When combined with suitable types of metal chlorides, methanol in the methanol-initiated system not only works as a cationogen producing propagating chains, 10 but also as a donor of an alkoxy group to the catalysts (Scheme 1). 9 Such alcoholinitiated systems produce alkoxy-modified catalysts in situ.…”

Lewis acid‐specific polymerization behaviors in living cationic polymerization of vinyl ether with a malonate group

“…The interaction strength between equivalent amounts of a metal halide and ethyl acetate had been previously investigated by 13 C NMR spectroscopy and it was found to decrease in the following order: TiCl 4 > EtAlCl 2 > SnCl 4 > ZnCl 2 . 25 Thus, TiCl 4 and Et 1.5 AlCl 1.5 are more likely to interact strongly with malonic diester groups than ZnCl 2 , FeCl 3 , or SnCl 4 . Strong interactions of TiCl 4 and Et 1.5 AlCl 1.5 with diester groups cause the chain transfer (or termination) reaction through the mechanism illustrated in Scheme 1.…”

“…24 The chelating ability of the malonate pendant of VOEM may be trouble in cationic polymerization with a metal halide, because the chelation would cause a catalyst to be deactivated. Since the base-assisting living system has been realized using a series of Lewis acids, 25 we used several Lewis acids to investigate the effect of pendant malonate groups on the polymerization behavior.…”