Nanostructured polymer blends by addition of gradient copolymer during melt mixing: Effects of copolymer sequence distribution on morphology and crystallization behavior

Nanostructured blends of polystyrene and poly(ethylene oxide) (PEO) are produced via the addition of styrene/methyl methacrylate (S/MMA) gradient copolymer during conventional melt mixing, introducing dipole-dipole interactions between PEO and MMA repeat units. Upon addition of S/MMA gradient copolymer, stable PEO domains with diameters of $\sim $ 100 nm are formed in optimized cases. This results in PEO domains homogenously crystallizing at $\sim $ -20 C, well below the crystallization temperature of bulk PEO ($\sim $ 50 C). Additionally, nanostructured blends annealed at room temperature for 40 days resulted in no melting behavior upon heating, showing that the nanoconfined PEO domains remain in a rubbery state at room temperature, while bulk PEO typically remains in a crystalline state. This demonstrates that the blend properties can be easily tuned by adjusting the copolymer characteristics. This study is the first to lead to nanostructured polymer blends from non-reactive, simple melt mixing of two homopolymers and a compatibilizer.