High‐Speed Living Polymerization of Polar Vinyl Monomers by Self‐Healing Silylium Catalysts

Abstract

This contribution describes the development and demonstration of the ambient-temperature, high-speed living polymerization of polar vinyl monomers (M) with a low silylium catalyst loading (≤ 0.05 mol % relative to M). The catalyst is generated in situ by protonation of a trialkylsilyl ketene acetal ((R)SKA) initiator (I) with a strong Brønsted acid. The living character of the polymerization system has been demonstrated by several key lines of evidence, including the observed linear growth of the chain length as a function of monomer conversion at a given [M]/[I] ratio, near-precise polymer number-average molecular weight (M(n), controlled by the [M]/[I] ratio) with narrow molecular weight distributions (MWD), absence of an induction period and chain-termination reactions (as revealed by kinetics), readily achievable chain extension, and the successful synthesis of well-defined block copolymers. Fundamental steps of activation, initiation, propagation, and catalyst "self-repair" involved in this living polymerization system have been elucidated, chiefly featuring a propagation "catalysis" cycle consisting of a rate-limiting C--C bond formation step and fast release of the silylium catalyst to the incoming monomer. Effects of acid activator, catalyst and monomer structure, and reaction temperature on polymerization characteristics have also been examined. Among the three strong acids incorporating a weakly coordinating borate or a chiral disulfonimide anion, the oxonium acid [H(Et(2)O)(2)](+)[B(C(6)F(5))(4)](-) is the most effective activator, which spontaneously delivers the most active R(3)Si(+), reaching a high catalyst turn-over frequency (TOF) of 6.0×10(3) h(-1) for methyl methacrylate polymerization by Me(3)Si(+) or an exceptionally high TOF of 2.4×10(5) h(-1) for n-butyl acrylate polymerization by iBu(3)Si(+), in addition to its high (>90 %) to quantitative efficiencies and a high degree of control over M(n) and MWD (1.07-1.12). An intriguing catalyst "self-repair" feature has also been demonstrated for the current living polymerization system.

N‐Heterocyclic Carbene‐Catalyzed Hydrosilylation of Styryl and Propargylic Alcohols with Dihydrosilanes

“…[8] From the perspective of this dual activation, the versatility offered by NHCs was attractive. The hydrosilylation would be the first step towards the organocatalyzed one-pot reduction of nonactivated carbon-carbon multiple bonds, whereas the tBuOK-catalyzed reaction is limited to some activated alkynes.…”

Enhanced Activation of Coordinated Dinitrogen with p‐Block Lewis Acids

“…[33] In the silyldiazenido complexes 16 and 17,t he NMR resonances of the 29 Si nucleus are shiftedt oh igh field, strongly suggesting that the positive chargei sn ot carried by the Si atom. [34] The actual electronic situation in the group 6c omplexes 14-17 remains debatable and calculations are under way to better appreciate it. This shouldallow detailed comparison with Szymczak's and Ashley's examples.…”

B(C6F5)3-catalyzed group transfer polymerization of alkyl methacrylates with dimethylphenylsilane through in situ formation of silyl ketene acetal by B(C6F5)3-catalyzed 1,4-hydrosilylation of methacrylate monomer

“…In addition, acid organocatalysts, such as triphenylmethyl tetrakis(pentafluorophenyl)borane, [18][19][20][21] (R)-3,3'-bis[3,5-bis(trifluoromethyl)phenyl]-1,1'-binaphthyl-2,2'-disulfonimide, 22 trifluoromethanesulfonimide, [23][24][25][26] N-(trimethylsilyl)triflylimide, 27,28 and 1-[bis(trifluoromethanesulfonyl)methyl]-2,3,4,5,6-pentafluorobenzene, 25,26 were suitable for the controlled/living unstable SKA. For the former issue, Taton et al reported that NHC was efficient for the synthesis of block copolymers composed of methacrylate and acrylate monomers, N,N-dimethylacrlamide, and methacrylonitrile.…”