Synthesis and solution properties of water-soluble hydrophilic-hydrophobic block copolymers

A series of water-soluble diblock copolymers containing 2-(dimethylamino)ethyl methacrylate and various alkyl methacrylates has been synthesized using group transfer polymerization. These hydrophilic-hydrophobic copolymers have been characterized with respect to chemical composition and molecular weight by NMR spectroscopy, elemental microanalyses, and gel permeation chromatography. Block copolymers containing methyl methacrylate as the hydrophobic component were water-soluble provided that the hydrophilic monomer content was greater than 60 mol % of the overall block copolymer. Quaternization of the DMAEMA block with methyl iodide was near-quantitative and considerably enhanced the water-solubility of the copolymers. NMR studies, surface tension measurements, and photon correlation spectroscopy all indicated that the PDMAEMA-b-MMA block copolymers form micelles in deionized water. However, in acidic solution (pH 2), copolymer micellization occurred only in the presence of added electrolyte. The block copolymer micelles initially increased in size on addition of added electrolyte at pH 9.5. Further electrolyte addition led to macroscopic precipitation.