Synthesis and aqueous solution properties of near-monodisperse tertiary amine methacrylate homopolymers and diblock copolymers

Abstract

Group transfer polymerisation (GTP) of four tertiary amine methacrylates, 2-(dimethylamino)ethyl methacrylate (DMA), 2-(diethylamino)ethyl methacrylate (DEA), 2-(diisopropylamino)ethyl methacrylate (DPA) and 2-(N-morpholino)ethyl methacrylate (MEMA) produced a series of near-monodisperse homopolymers (Mw/Mn<1.15). Molecular weights were controlled by varying the monomer/initiator ratio. The DMA and MEMA homopolymers were both water-soluble at 20°C in acidic or neutral media. Inverse temperature solubility behaviour was observed at higher temperatures, with cloud-points ranging from 32 to 53°C at pH 8. The Cloud-points decreased monotonically with increasing degrees of polymerisation, as expected. The MEMA homopolymers were particularly sensitive to the added electrolyte, with ‘salting out’ occurring at 20°C on addition of 0.2–0.3 M Na2SO4. The more hydrophobic DEA and DPA homopolymers were both insoluble at 20°C and neutral pH but readily dissolved as cationic polyelectrolytes in acidic media due to protonation of the tertiary amine residues. In addition, DMA was block copolymerized in turn with each of the other three tertiary amine methacrylate comonomers. These diblock copolymers could be dissolved molecularly without co-solvents in aqueous media at 20°C, with micellization occurring reversibly on judicious adjustment of the solution pH, temperature or electrolyte concentration. In all three cases, stable block copolymer micelles were formed with DMA coronas and hydrodynamic diameters of 20–60 nm.