Amphiphilic block copolymers: Self-assembly, phase behavior and new applications in biology, materials science and polymer synthesis

The polyoxyalkylene triblock copolymers, which contain polyoxyethylene (E), polyoxypropylene (P) or polyoxybutylene (B) blocks, tend to form micellar structures in aqueous solution with the hydrophobic blocks (P or B) form compact micellar cores and the hydrophilic blocks (E) form extended micellar shells. The micellization process can be characterized by static and dynamic light scattering. The micelle formation (e.g., cmc, association number and thermodynamic parameters) is temperature-dependent, entropy-driven and is determined mainly by the hydrophobic blocks. The hydrophilic blocks determine the micellar sizes and the intermicellar interactions. Two kinds of block copolymers can form mixed micelles in aqueous solution, while the one with the lower cmc value determines the micelle formation.; Empirical expressions are presented to quantitatively estimate the cloud-point temperature of dilute BEB and PEP triblock copolymer solutions. Small-angle X-ray scattering (SAXS) technique was used to determine the temperatureconcentration binary phase diagram of the E₄₅B₁₄E₄₅/water system and the E₄₅B₁₄E₄₅/E₉₉P ₆₉E₉₉/water ternary phase diagram at room temperature. The addition of CdCl₂ to copolymer/water gel-like systems can induce microphase separation, with the formation of salt-copolymer complexes, due to the coordination property of Cd2+ ions.; New applications of block copolymers have been explored in several different areas. The sieving ability and viscosity-adjustable property of the gel-like structures can be used for separating DNA fragments in capillary electrophoresis. The B ₁₀E₂₇₁B₁₀/B₆E₄₆E ₆ mixture in 1X TBE buffer is very good for separating double stranded DNA fragments. The mixture of E₁₄₅B₂₆E₁₄₅ and E₉₉P₆₉E₉₉ in sequencing buffer shows strong potential for single stranded DNA sequencing analysis. The ordered micellar packing in the gel-like region can be used as a matrix for synthesizing inorganic materials with nano-scale modifications. MoO₃ nano-particles with 6.0 nm empty holes inside are synthesized in the presence of a E ₄₅B₁₄E₄₅/water gel-like system and can be characterized by SAXS and wideangle X-ray diffraction. The MoO₃ particles formed bcc packing with a distorted crystal lattice. Finally, the block copolymers can be used as dispersants for microemulsion polymerization. The combination of static and dynamic light scattering is very suitable for monitoring the polymerization process.