Effect of Sequence Distribution on Copolymer Interfacial Activity

Interfacial segregation of diblock, gradient, and random copolymers was measured using forward recoil spectrometry. The polymers were synthesized by a ring-opening metathesis polymerization, allowing a high degree of control over the sequence distribution. The norbornene-based monomers have reactivity ratios close to unity, which makes them ideal for facile tailoring of different gradient copolymer profiles. The copolymers form a good weakly segregating model system for which we can obtain an estimate of the interaction parameter χ. Mean-field theory was used to describe the interfacial segregation results and to relate the measured quantities to the detailed molecular structure of the interface. The diblock copolymer forms a monolayer at the interface and significantly reduces the interfacial tension, while the random copolymer forms an interfacial wetting layer. The gradient copolymer exhibits intermediate behavior, forming a monolayer with a larger interfacial width than that of the diblock copolymer.