Living Cationic Polymerization of Vinyl Monomers by Organoaluminum Halides V. Polymerization of Isobutyl Vinyl Ether with EtAlCl2 in the Presence of 2,6-Dimethylpyridine and Related Amines

Abstract

ABSTRACT:In the presence of 2,6-dimethylpyridine as an added base, living cationic polymerization of isobutyl vinyl ether was achieved in n-hexane at O to +40°C with the 1-(isobutoxy)ethyl acetate (3)/ethylaluminum dichloride [CH3CH(OiBu)-OCOCH3/EtAICl2] initiating system. A low concentration of the pyridine, 4 times that of the cationogen 3 ( or the active end), was sufficient for the living process. Without the added amine, the polymerization was almost instantaneous and nonliving. The use of triethylamine and less hindered pyridines (pyridine, 2-methylpyridine, and 2,4-dimethylpyridine), in place of the 2,6-dimethyl derivative, failed to induce living polymerization but instead resulted in chain termination. In contrast, highly crowded 2,3-dit-butylpyridine could not affect the polymerization by 3/EtAICl2 at all. It is proposed that 2,6-dimethylpyridine stabilizes the otherwise unstable growing carbocation via a nucleophilic interaction to endow it with livingness. The effects of the pyridine structures showed not the basicity but the steric crowding around the nitrogen to play a critical role in the nucleophilic stabilization of the growing cation.

Living cationic polymerization of isobutyl vinyl ether using a variety of metal oxides as heterogeneous catalysts: Robust, reusable, and environmentally benign initiating systems

“…Complex formation with a Lewis acid catalyst40–42 and interaction with a carbocation43 are also reported as additional roles of DTBP in some studies, although others claim there is no proof of this 44, 45. In polymerization of IBVE with IBVE–AcOH/EtAlCl 2 initiating systems,46 a large amount (1.0 M) of DTBP has little effect on the rate and control of the reaction, which indicates that DTBP cannot interact with the propagating species derived from IBVE. In addition, adventitious water does not initiate the polymerization using metal oxides, although it may induce undesired reactions such as chain transfer.…”

Living cationic polymerization of vinyl ethers in the presence of a strong base: Poisonous or helpful?

“…Cationic polymerization of IBVE was investigated in the presence of DMA. It was previously reported that strong bases such as amides or amines were the possible terminating agents or inhibitors for the cationic polymerization through electrostatic interactions with growing carbocations or Lewis acids 2(b), 4(a), 15, 17. To investigate the effect of DMA on the polymerization behavior, cationic polymerization of IBVE was examined using EtAlCl 2 or SnCl 4 in the presence of DMA in toluene at 0 °C ([IBVE] 0 = 0.76 M, [IBVE‐HCl] 0 = 4.0 mM, [Lewis acid] 0 = 5.0 mM).…”

“…In this article, cationic polymerization of an alkyl vinyl ether using various Lewis acids, including Et x AlCl 3− x and SnCl 4 , in the presence of an amide or an amine was examined. Such strong bases have rarely been used for the polymerization of vinyl ethers 10, 15. Therefore, polymerization with a strong base was compared to the conventional counterpart with a weak base, specifically focusing on the scope of adaptable Lewis acids and the relationship between basicity and the optimum amount of added bases.…”

Molecular engineering of side-chain liquid crystalline polymers by living polymerizations

“…Since most cationic polymerizations involve an equilibrium between covalent adducts and ionic species, the equilibrium can be shifted from free ions to dormant covalent species by adding a salt with a common counteranion. 104 Alternatively, the carbenium ions can be deactivated with nucleophiles, such as phosphines, 105 hindered arnines, 106 dialkyl sulfides, 107…”