Phase Diagram, Ordering Kinetics, and Molecular Dynamics of Conformationally Symmetric Poly(styrene- b -β-farnesene) Diblock Copolymers

High Resolution Image Download MS PowerPoint Slide A large set of polystyrene- b -polyfarnesene (PS–PF) diblock copolymers were synthesized over the composition range f PF ∈ [0.127–0.905] and with molar masses M n ∈ [10–161] kg·mol –1 aiming at constructing a pertinent phase diagram. PS–PF is the most conformationally symmetric diblock copolymer system investigated so far. The phase diagram was dominated by classical phases (lamellar (LAM), hexagonally packed cylinders (HPC)/cylinders (CYL), and spheres in a bcc lattice (SPH)) with vertical phase boundaries resulting in the absence of order-to-order transitions. A bicontinuous morphology (BIC) resembling the double gyroid (DG) ( Ia 3̅ d ) was restricted over a narrow composition range ( f PF ∼ 0.71), whereas the Frank–Kasper phases were completely absent. The interaction parameter, χ, determined from nearly symmetric copolymers within the Fredrickson–Helfand theory was found to be stronger than in the structurally similar PS–PI. The domain spacing scaled as d ∼ N 0.75 for 20 ≤ χ Ν ≤ 200. The viscoelastic response based on the van Gurp–Palmen plots revealed the presence of two characteristic plateaus: one related to the structural relaxation of the nanodomains (domain plateau) and the second to the chain entanglements (rubbery plateau). By combining small-angle X-ray scattering (SAXS) and rheology, we could show that the information on the nanodomain length scale is registered in the viscoelastic response of the system. The ordering kinetics was employed in extracting the equilibrium order-to-disorder transition temperature, T ODT 0 . The kinetics is shown to be affected by the conformational symmetry, as predicted. Furthermore, the combination of the ordering kinetics with an independent study of the molecular dynamics revealed that relaxation of all molecular processes is a necessary first step prior to the ordering process.