Controlled radical polymerization of 2‐hydroxyethyl methacrylate with a hydrophilic ruthenium complex and the synthesis of amphiphilic random and block copolymers with methyl methacrylate

Abstract

A hydrophilic ruthenium complex with ionic phosphine ligands {1: RuCl2[P(3‐C6H4SO3Na)(C6H5)2]2} induced controlled radical polymerization of 2‐hydroxyethyl methacrylate (HEMA) in methanol under homogeneous conditions; the initiator was a chloride (R‐Cl) such as CHCl2COPh. The number‐average molecular weights of poly(HEMA) increased in direct proportion to monomer conversion, and the molecular weight distributions were relatively narrow (Mw/Mn = 1.4–1.7). A similar living radical polymerization was possible with (MMA)2‐Cl [(CH3)2C(CO2CH3)CH2C(CH3)(CO2CH3)Cl] as an initiator coupled with amine additives such as n‐Bu3N. In a similar homogeneous system in methanol, methyl methacrylate (MMA) could also be polymerized in living fashion with the R‐Cl/1 initiating system. Especially for such hydrophobic polymers, the water‐soluble ruthenium catalyst was readily removed from the polymers by simple washing with an aqueous dilute acid. This system can be applied to the direct synthesis of amphiphilic random and block copolymers of HEMA and MMA. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2055–2065, 2002

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“…As expected for any living polymerization, each of the product polymers carries an initiator fragment (the isobutyrate in the example) at the α end, and we have indeed shown that end‐functionalized polymers can be synthesized with our RuCl 2 (PPh 3 ) 3 ‐based systems coupled with functionalized initiators [Scheme (B)] 21. The key to the synthesis is that the ruthenium(II) catalyst is robust toward polar functional groups, such as amines, alcohols, and amides, in the initiator and at the α end of the products 21, 22…”

Metal‐catalyzed living radical polymerization: discovery and developments

“…Another modification was directed to give a hydrophilic nature to ruthenium complexes ( 7 and 8 ),26,27 which is better suited for hydrophilic monomers, polymerization in aqueous media, and catalyst removal. This topic will be described later in this review.…”

“…We thus developed a variety of metal catalysts for living‐radical polymerization of various monomers, which now include methacrylates,9,12,13,16,20 acrylates,16,31 styrenes,12,16,29 acrylamides,32,41 vinyl acetate,33 olefins,34 and monomers with polar functional groups26,42 (Figure 5).…”

“…Even the iron catalyst ( 10 ) worked in water without loss of activity and controllability 49. A modified ruthenium catalyst with hydrophilic ligands such as 7 and 8 gave further improvements in compatibility with the hydrophilic monomers and also in the polymerization in polar solvents such as methanol 26,27…”

Aqueous metal-catalyzed living radical polymerization: highly active water-assisted catalysis

“…25 This rendered previous controlled radical polymerizations of HEMA, reliable only in alcohols or mixed solvents with water. 26,27 In contrast, the catalytic system with PPh 2 (pPhOH) allowed a controlled aqueous polymerization of HEMA (Figure 7). The polymerization proceeded smoothly, without insoluble or crosslinked products, and the polymers showed narrow MWDs (reaching M w /M n ¼1.28 at a higher conversion).…”