Synthesis and solution properties of dimethylsiloxane-2-(dimethylamino)ethyl methacrylate block copolymers

A series of novel well-defined dimethylsiloxane-2-(dimethylamino)ethyl meth acrylate diblock and triblock copolymers mere synthesized in various solven ts at or above ambient temperature. This was achieved by the oxyanion-initi ated polymerization of 2-(dimethylamino)ethyl methacrylate (DMA) using eith er monofunctional or bifunctional low molecular weight poly(dimethylsiloxan e) (PDMS) as macroinitiators. Provided that the terminal hydroxyl groups of the PDMS macroinitiators are carefully titrated to the corresponding potas sium alcoholates, reasonably good control over the DMA chain length was ach ieved. H-1 NMR characterization of these DMS-DMA diblock copolymers proved unexpectedly problematic since micellization generally occurred even in sol vents such as CDCl3 or d(8)-toluene, which are good solvents for both DMS a nd DMA homopolymers. Electron microscopy and dynamic light scattering studi es confirmed the formation of spherical, polydisperse micelles of 200 nm. P resumably micellization is driven by a demixing term: the PDMS block prefer s to be less solvated in order to avoid interacting with the DMA residues. Reliable block compositions were eventually obtained by NMR analysis of dil ute solutions of the diblock copolymers in 3:1 d(8)-IPA-D2O mixtures. These DMS-DMA diblock copolymers were highly surface active, particularly at pH 9 where the degree of protonation of the DMA. block was low. Dynamic light scattering studies indicated micellization in aqueous solution, as expected .