Correlating the mechanical and surface properties with the composition of triblock copoly(2-oxazoline)s

Abstract

The elastic moduli, surface energies, and phase morphologies of poly(2-oxazoline) triblock copolymers were investigated and compared to the corresponding homopolymers and diblock copolymers, at a constant degree of polymerization. The elastic moduli of ABA triblock copolymers were bound by those of the respective AB diblock copolymers and A homopolymers. These results show that the elastic moduli of these copolymers – obtained by instrumented indentation – depended on the interplay between phase-separation, crystallization and hygroscopicity, and can be adjusted by tailoring the composition. The surface energy strongly depended on the presence of a poly(2-nonyl-2-oxazoline) block. If such a block was present, the surface energy was reduced due to segregation of nonyl side-chains to the surface. This segregation was promoted by annealing. The crystallization of nonyl side-chains at the surface promoted the development of surface texture and an increase in surface roughness, as demonstrated by atomic force microscopy topographic imaging.