Frustrated Microparticle Morphologies of a Semicrystalline Triblock Terpolymer in 3D Soft Confinement

Self-assembly of block copolymers (BCPs) in three-dimensional (3D) confinement of emulsion droplets has emerged as a versatile route for the formation of functional micro- and nanoparticles. While the self-assembly of amorphous coil-coil BCPs is fairly well documented, less is known about the behavior of crystalline-coil BCPs. Here, we demonstrate that confining a linear ABC triblock terpolymer with a crystallizable middle block in oil-in-water (O/W) emulsions results in a range of microparticles with frustrated inner structure originating from the conflict between crystallization and curved interfaces. Polystyrene-block-polyethylene-block-poly(methyl methacrylate) (PS-b-PE-b-PMMA, S₃₂E₃₆M₃₂⁹³) in toluene droplets was subjected to different preparation protocols. If evaporation was performed well above the bulk crystallization temperature of the PE block (T_evap > T_c), S₃₂E₃₆M₃₂⁹³ first microphase-separated into microparticles with lamella morphology followed by crystallization into a variety of frustrated morphologies (e.g., bud-like, double staircase, spherocone). By evaporating at significantly lower temperatures that allow the PE block to crystallize from solution (T_evap < T_c), S₃₂E₃₆M₃₂⁹³ underwent crystallization-driven self-assembly into patchy crystalline-core micelles, followed by confinement assembly into lenticular microparticles with compartmentalized hexagonal cylinder lattices. The frequency of these frustrated morphologies depends on polymer concentration and the evaporation protocol. These results provide a preliminary understanding of the morphological behavior of semicrystalline block copolymers in 3D soft confinement and may provide alternative routes to structure multicompartment microparticles from a broader range of polymer properties.