Effect of junction point functionality on the lamellar spacing of symmetric (PS)_n(PI)_n miktoarm star block copolymers

To probe the effect of junction point functionality in miktoarm star block copolymer architecture on chain conformation and morphology, a series of A_nB_n miktoarm star copolymers where A arms are PS blocks and B arms are PI blocks were investigated. The overall series including a diblock and the star block copolymers can be represented by A_nB_n where n = 1, 2, 4, and 16. These materials were produced by synthesizing a single batch of living PS arms and a single batch of living PI arms and then linking them together with chlorosilane coupling agents of different functionality. Thus, all PS arms are identical and all PI arms are identical across the entire series of materials. All stars in the series have equal numbers of PS and PI arms, and the volume fractions of all the samples in the series (nearly 0.50 PS by volume) are identical within experimental error. All the materials were found, via small-angle X-ray scattering and transmission electron microscopy, to form lamellar morphologies. A significant increase in lamellar spacing with increasing junction point functionality (n) was found in this series of materials and can be attributed to molecular crowding near the junction point.