Efficient Synthesis of Amine-Functional Diblock Copolymer Nanoparticles via RAFT Dispersion Polymerization of Benzyl Methacrylate in Alcoholic Media

Abstract

Benzyl methacrylate (BzMA) is polymerized via reversible addition–fragmentation chain transfer (RAFT) chemistry under alcoholic dispersion polymerization conditions in ethanol using a poly(2-(dimethylamino)ethyl methacrylate) (PDMA) chain transfer agent (CTA) at 70 °C. In principle, polymerization-induced self-assembly can lead to the formation of either spherical micelles, worm-like micelles, or vesicles, with the preferred morphology being dictated by the hydrophilic–hydrophobic balance of the PDMA–PBzMA diblock copolymer chains. Very high monomer conversions (>99%) are routinely obtained within 24 h as judged by 1H NMR studies. Moreover, THF GPC analyses confirmed that relatively low polydispersities (Mw/Mn < 1.30) are achieved, indicating reasonably good pseudoliving character. A detailed phase diagram was constructed using a PDMA31 macro-CTA by systematically varying both the target degree of polymerization of the PBzMA block and the total solids concentration of the reaction solution. This phase diagram can be used to reliably predict the synthesis conditions required to produce pure phases, rather than merely mixed phases (e.g., spheres plus worms or worms plus vesicles). Finally, these PDMA–PBzMA diblock copolymer nanoparticles remain colloidally stable when transferred from ethanol into water; aqueous electrophoresis studies confirmed that the particles acquire appreciable cationic character below pH 7 due to protonation of the PDMA stabilizer chains.