Synthesis and characterization of amphiphilic diblock copolymers of 2-(1-imidazolyl)ethyl methacrylate and styrene

Abstract

Six amphiphilic diblock copolymers based on the hydrophilic monomer 2-(1-imidazolyl)ethyl methacrylate (ImEMA) and the hydrophobic monomer styrene (Sty) were prepared by sequential reversible addition–fragmentation chain transfer (RAFT) polymerization. RAFT polymerization was performed via the use of 4-cyano-4-(dodecylsulfanylthiocarbonylsulfanyl)pentanoic acid (CDP) as the chain transfer agent and glacial acetic acid as the solvent. Amphiphilic diblock copolymers with a range of compositions were prepared, with ImEMA first blocks of constant (nominal) degree of polymerization (DP) equal to 100, and Sty second blocks of a DP between 18 and 482, having ImEMA contents between 15 and 80 mol%, as measured by ¹H NMR spectroscopy in CDCl₃. Only the Sty-rich (≥51 mol%) diblock copolymers were fully soluble in the solvent for gel permeation chromatography (GPC), tetrahydrofuran; GPC analysis of these copolymers indicated molecular weights in the range of 15 to 34 kDa, and molecular weight dispersities ranging from 1.1 to 1.6. At room temperature, the side-group of the ImEMA units was stable in an acidic environment but hydrolyzed slowly under alkaline conditions. In bulk neutral samples, the ImEMA side-group was thermally stable up to ∼250 °C. Finally, dynamic light scattering and polarized light microscopy indicated that the Sty-rich diblock copolymers formed spherical micelles in chloroform, whereas all diblock copolymers formed anisotropic nanophases in water.