Asymmetric Membranes from Amphiphilic ABC Triblock Copolymers

Abstract

We report the synthesis and characterization of a new kind of amphiphilic ABC triblock copolymers consisting of a hydrophilic(polyethylene oxide)- A block a hydrophobic poly(dimethyl siloxane)-B middle block and a hydrophilic-poly(2-methyl oxazoline)C block. For certain hydrophilic to hydrophobic block length ratios these polymers self-assemble into membrane-like super-structures and vesicles in aqueous media. Due to the inherent incompatibility of the two hydrophilic blocks they segregate to different sides of the underlying membranes thus leading to asymmetric block copolymer membranes. Moreover, depending on the relative lengths of the two hydrophilic blocks we are able to control which of them is oriented toward the inner and the outer surface of the vesicles. Different water-soluble polymers are inherently incompatible and undergo phase separation in aqueous media. Hence, membranes formed by ABC triblock copolymers(with water soluble blocks A and C and a hydrophobic middle block B)are asymmetric: one side is predominantly covered by the blocks A and the other by the blocks B. These systems offer not only a convenient way to modify the inner and outer surface of vesicles with different functional groups but represent also an asymmetric matrix for the directed insertion of membrane proteins.