Radical/cation transformation polymerization and its application to the preparation of block copolymers

Abstract

p-Methoxystyrene (MOS), butyl vinyl ether (BVE), and Nvinylcarbazole (VCZ) were polymerized in high yield by azohitiators such as 2, 2'-azodiisobutyronitrile (AIBN) in the presence of electron acceptors such as Phg+PF6-. An electron paramagnetic resonance (ESR) study of the model radicals of the propagating radical showed the transformation of the radical to the corresponding cation in the presence of the electron acceptors. In the case of BVE, the polymer formation was caused by cationic species produced by the transformation of the initiating radical. The polymerizations of MOS and VCZ were ascribed to the transformation of the growing radical to the corresponding cation during the propagation step which was classified as the radicaUcation transformation polymerization. Block copolymers of MOS/cyclohexene oxide (1,2-epoxycyclohexane) (CHO) and VWCHO were effectively prepared by the radicaUcation transformation polymerization of the appropriate monomers in the presence of AIBN, electron acceptor and CHO. The formation of block copolymers was characterized by turbidimetry, thin-layer chromatography, and solubility tests.

In-Situ Direct Mechanistic Transformation from RAFT to Living Cationic Polymerization for (Meth)acrylate−Vinyl Ether Block Copolymers

“…Along with the slight monomer consumptions, the M n values slightly increased while retaining narrow MWDs (M n = 4400, M w /M n =1. 16).…”

“…A similar strategy was also employed for the simultaneous copolymerization of methyl methacrylate and n -butyl vinyl ether in the presence of both AIBN and Ph 2 I + PF 6 − . Kamachi et al also used the Ph 2 I + PF 6 − -induced in-situ transformation for the simultaneous polymerization of p -methoxystyrene or N -vinylcarbazole and cyclohexene oxide (CHO), in which the oxidation of the electron-rich radical species derived from the electron-donating vinyl monomer by the salt was confirmed by ESR study. − However, the well-defined synthesis of the block copolymers was difficult by these methods principally because they were based on the conventional radical polymerization that cannot control the chain length of the polymer. The transformation reaction based on such salts was recently applied for living or controlled radical polymerization of styrenes and methyl methacrylate (MMA) followed by living cationic ring-opening polymerization of CHO and THF, in which the dormant carbon−halogen terminal or the resulting radical species was irreversibly oxidized into the carbocationic species for the ring-opening polymerization. − The covalent or dormant carbon−halogen terminal obtained by the transition-metal-catalyzed living radical polymerization or atom transfer radical polymerization (ATRP) of MMA was further transformed into another dormant carbon−halogen terminal, which can be activated by a Lewis acid, by the addition of styrenic monomers, − and was changed into the living cationic polymerization of isobutene (IB) to give multiblock copolymers consisting of MMA−St−IB segments. , …”

“…13 Kamachi et al also used the Ph 2 I þ PF 6 --induced in-situ transformation for the simultaneous polymerization of p-methoxystyrene or N-vinylcarbazole and cyclohexene oxide (CHO), in which the oxidation of the electron-rich radical species derived from the electron-donating vinyl monomer by the salt was confirmed by ESR study. [14][15][16][17] However, the well-defined synthesis of the block copolymers was difficult by these methods principally because they were based on the conventional radical polymerization that cannot control the chain length of the polymer. The transformation reaction based on such salts was recently applied for living or controlled radical polymerization of styrenes and methyl methacrylate (MMA) followed by living cationic ring-opening polymerization of CHO and THF, in which the dormant carbon-halogen terminal or the resulting radical species was irreversibly oxidized into the carbocationic species for the ring-opening polymerization.…”

“…21,22 Another route to the block copolymers via radical and cationic polymerizations is based on transformation from cationic to radical polymerization, where the chain end of the living cationic ring-opening polymerization of THF or living cationic polymerization of IB has been indirectly converted into another chain end effective for living radical polymerization. [15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31] The dormant carbon-halogen terminal obtained by living cationic polymerization of St or β-pinene was also directly used for the ATRP of St, methyl acrylate (MA), or MMA to result in their block copolymers. 32,33 Irrespective of various block copolymers via radical/cationic or cationic/radical transformations, almost no well-defined synthesis of block copolymers of vinyl ether and (meth)acrylic monomers has been reported so far except for an indirect method.…”

Synthesis and characterization of cyclohexene oxide functional poly(ε‐caprolactone) macromonomers and their use in photoinitiated cationic homo‐ and copolymerization

“…These polymers were also used13 in so‐called free radical promoted cationic polymerization to yield block copolymers of structurally different monomers such as cyclohexene oxide (CHO) and ε‐caprolactone (CL). There are many reports on the use of photoinitiated cationic polymerization for the preparation of block copolymers 14–20. However, corresponding graft copolymerization via similar photoinduced process has hardly been studied 21.…”