Star-shaped block copolymers. III. Surface and interfacial properties

Surface and interfacial activities of A(B)₂ star-shaped block copolymers, where B is a polyoxirane block and A a polydiene or polyvinyl block, have been measured at 20°C. The surface tension of organic solvents is only slightly lowered by these copolymers, whereas a significant surface activity is noted in water. Interfacial tensions are dependent on both the nature of the organic solvent (aliphatic or aromatic hydrocarbons) and the molecular parameters of the copolymers; 50% polyoxirane seems to be the composition of maximum surface activity. The role played by the molecular architecture A-B or A(B)₂] of the copolymers is demonstrated. The same limiting interfacial tension is obtained on increasing the concentration of diblock A-B] or star-shaped block A(B)₂] copolymer. The limiting value is, however, attained at significantly lower concentration with the star-shaped copolymers. Their ability to fill the interface is accordingly higher.