A Miktoarm Star Copolymer as a “Chameleon” Compatibilizer for Polymer Blends

A miktoarm star (μ-star) terpolymer bearing poly(ε-caprolactone) (PCL), polystyrene (PS), and poly(methyl methacrylate) (PMMA) arms is introduced as a general compatibilizer for both binary and ternary polymer blends. Atomic force microscopy of thin films and scanning electron microscopy of cryo-fractured bulk samples show that incorporation of 5 wt % μ-star terpolymer consistently reduces dispersed-domain size and stabilizes phase morphology relative to control blends. Correspondingly, mechanical testing shows that 5 wt % μ-star terpolymer significantly improves the properties of both binary (60/40 PCL/PS) and ternary (50/30/20 PCL/PS/PMMA) blends, with increases in elongation at break and overall toughness gains of 149 and 130%, respectively. Together, these results establish the μ-star terpolymer as a single, adaptable compatibilizer for compositionally distinct polymer blends, enabling simultaneous morphological control and mechanical enhancement.