Controlled/Living Cationic Polymerization of p-Methoxystyrene in Solution and Aqueous Dispersion Using Tris(pentafluorophenyl)borane as a Lewis Acid:  Acetonitrile Does the Job

Abstract

The living cationic polymerization of p-methoxystyrene using the 1-(4-methoxyphenyl)ethanol/B(C6F5)3 initiating system in solution and in aqueous dispersion is reported. Solution experiments first showed that the molar mass of the obtained polymers increases in direct proportion to the monomer conversion and the molar mass distribution stays narrow in the course of the polymerization (M w/M n ∼ 1.2). The living nature of the growing chains was confirmed by sequential monomer addition experiments, although matrix-assisted laser desorption ionization time-of-flight mass spectroscopy (MALDI-TOF-MS) revealed some hydroxyl elimination under monomer-starved conditions. Aqueous suspension polymerization of p-methoxystyrene using the same initiating system did not show a good control of molar masses, since after polymerization has proceeded at the interface up to critical DP, oligomers terminated by water penetrate inside the particles where they stop propagating. This limitation was leveled off for the first time by polymerizing p-methoxystyrene in an aqueous dispersion, i.e., in a mixture of H2O:CH3CN 3:2 (v/v). Under these conditions, the hydroxyl-terminated poly(p-methoxystyrene)s can be reactivated by B(C6F5)3 located inside the particles to reinitiate the polymerization; molar masses thus increase with conversion, up to 3000 g mol-1, and exhibit a narrow molar mass distribution (M w/M n ∼ 1.3) and an almost pure hydroxylated functionality.

Cationic polymerization of p-methylstyrene in selected ionic liquids and polymerization mechanism

“…The M w /M n invariably remained relatively broad throughout the reactions (M w /M n = 1.8-2.0). [69][70][71] The M n,NMR of the polymer sample (determined from the peak intensity ratio of the aromatic ring protons at δ 6.3-7.3 ppm to the initiating α-end protons at δ 1.0 ppm) was slightly larger than the GPC data. Fig.…”

Photoinitiated Cationic Polymerization of Mono and Divinyl Ethers in Aqueous Medium Using Ytterbium Triflate as Lewis Acid

“…Although there have been several reports [15,17,20] on cationic polymerization, this is the first report on light-induced cationic polymerization in the presence of large amount of water.…”

“…This indicates that acetonitrile enhances the dispersion of the monomer in water leading to successful transfer of the reactants and intermediates between these phases. [20] In the light of the role of iodonium salts in photoacid generation and previous reports, [7,15,24] a plausible reaction mechanism for the heterogeneous polymerization by the direct initiation is proposed in Scheme 2. According to this mechanism, photoinitiator is transferred from the aqueous to organic phase in the presence of acetonitrile.…”

Transapical repair of mitral valve paravalvular leakage using 3‐D transesophageal guidance

“…Moreover, we showed recently that R ‐OH/BF 3 ·OEt 2 initiating system indeed controls the styrene polymerization, but it is very sensitive to small changes in water contents and cannot be applied in aqueous dispersion due to the coinitiator decomposition 20. Quite recently, we reported a new initiating system, 1‐(4‐methoxyphenyl)ethanol ( 1 )/B(C 6 F 5 ) 3 , which polymerized p ‐methoxystyrene in a living fashion not only in the presence of excess of water to Lewis acid,21, 22 but also for the first time in aqueous dispersion 22. Most importantly, this initiating system was successfully applied for the synthesis of hydroxyl‐terminated polystyrenes with perfect functionality under aqueous suspension conditions 23…”

“…Considering the scarcity of data and general approaches to control the molecular weight and regioselectivity during the cationic polymerization of conjugated dienes, we are now concentrating our attention on this subject. Because CPD is highly reactive in cationic polymerization, as compared to common conjugated dienes (CPD is more reactive than p ‐methylstyrene but less reactive than p ‐methoxystyrene25), and because 1 /B(C 6 F 5 ) 3 initiating system effectively induced controlled/living cationic polymerization of p ‐methoxystyrene in the presence of water and aqueous media as well,22 we started our investigations with this monomer.…”