Architecturally-Induced Tricontinuous Cubic Morphology in Compositionally Symmetric Miktoarm Starblock Copolymers

We report the synthesis and morphological characterization of a miktoarm block copolymer architecture: (PS α M −PI M ) n −(PS M −PI α M ) n, where M ∼ 20 000, n = 1, 2, and the arm asymmetry parameter α = 1, 2, or 4 (α is the ratio of the outer block molecular weight to that of the inner block). These block copolymers are symmetric in overall composition and exhibit n - and α-dependent microdomain morphologies. Alternating lamellae are observed for linear tetrablocks ( n = 1), α = 1, 2, 4, and for inverse starblock ( n = 2), α = 1, 2. An architecturally-induced morphological transition from lamellae to a tricontinuous cubic structure is observed with n = 2 and α = 4. The formation of the tricontinuous cubic microdomain structure in this compositionally symmetric system is thought to relieve the overcrowding of the four peripheral PS−PI junctions by providing a curved intermaterial dividing surface with a triply periodic microdomain structure, allowing some bridging by the interior blocks of the miktoarm star.