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Water-Soluble “Poly(propylene oxide)” by Random Copolymerization of Propylene Oxide with a Protected Glycidol Monomer

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journal contribution
posted on 10.04.2012, 00:00 by Martina Schömer, Holger Frey
Hydrophilic, functional poly­(propylene oxide) (PPO) copolymers were prepared by anionic random copolymerization of propylene oxide with the protected glycidyl derivative ethoxy ethyl glycidyl ether (EEGE). The monobenzyl-protected ethylene glycol initiator 2-(benzyloxy)­ethanol was used to initiate the polymerization because it allows for the introduction of hydroxyl groups at both ends of the polymer chain. Acidic deprotection permitted selective removal of the acetal protecting groups in the chain or alternatively orthogonal deprotection of the terminal hydroxyl group by catalytic hydrogenation. A series of narrowly distributed hydroxyl-functional PPO copolymers (Mw/Mn < 1.07–1.25 g mol–1) was obtained with varying composition between 2 and 75% glycerol units and molecular weights in the range of 3000 to 8000 g mol–1. Monomer consumption and compositional drift in monomer feed were studied via 1H NMR kinetics, revealing a slightly tapered structure, but confirmed a distribution of EEGE in the polar PPO-based copolymers. Cloud-point measurements showed temperature-dependent water solubility, with LCSTs in the range of 20 to 70 °C. The study demonstrates that an incorporation of 11% of the hydroxyl-functional, linear glycerol units suffices to obtain functional PPO copolymers that are water-soluble at room temperature.