Four‐Phase Morphologies in Blends of ABC and BAC Triblock Terpolymers

Abstract

considerably more complex compared to diblock copolymers due to an increased number of variables. Thus, the morphology of linear ABC triblock terpolymers is controlled mainly by three interaction parameters (χ AB , χ AC , χ BC ,) and two independent volume fractions (f A , f B , f C = 1 -f A -f B ), as well as the block sequence. Among the morphologies are lamellae, lamellae with spheres or cylinders, knitting pattern, spheres on sphere, alternating and core-shell double gyroids, cylinder in cylinder, undulated/perforated cylinder in cylinder, cylinder at cylinder, spheres on cylinder, helices on cylinder. [12][13][14][15][16][17][18] The helices on cylinder represents a special case in between these morphologies. On the one hand, it is rare because it can be achieved only in a rather narrow composition window, but what is even more peculiar, it is the self-assembly of a nonchiral block copolymer into a chiral structure. [19] In order to develop functional materials with special electrical, optical, or magnetic properties, multiblock copolymers are promising, because of their capability to self-assemble into complex ordered morphologies, with symmetries like crystalline structures known from low molecular weight inorganic salts. [20] Lee et al. [21,22] were the first to identify a Frank-Kasper σ phase, which is a large tetragonal unit cell with P4 2 /mnm symmetry and 30 spheres, [23,24] in linear block copolymers. From then on numerous studies about novel sphere-forming morphologies in AB diblock [25][26][27] copolymers and ABAC tetrablock terpolymers [28] have been published. Especially linear ABAC tetrablock terpolymers are promising for the investigation of new structures. [29] Chanpuriya et al. [30] have presented nine different spherical phases for tetrablock terpolymers.Controlling the morphology for a given block copolymer by changing the volume fractions of the corresponding blocks implies the synthesis of one block copolymer for each morphology. There are other, more readily available methods to achieve different morphologies starting from one block copolymer. One method implicates chemical postmodification, like complexation or hydrogenation. Bronstein et al. [31] have modified the polybutadiene block (PB) of a polystyreneblock-polybutadiene-block-poly(methyl methacrylate) (SBM) triblock terpolymer by complexation with transition metal complexes, like Fe-complex and Pd-complex. They were able to observe a change from a lamellar morphology before modification to a cylindrical or gyroid morphology after the Blends It is investigated how binary blends of two asymmetric triblock terpolymers with the same type of monomers but different block sequences (ABC, BAC) and different block lengths lead to three new ABAC tetrablock terpolymer like morphologies. This study ascribes the formation of four microphases to a parallel chain orientation during the blend process. Because of the resultant spatial superposition, the B-blocks of both block copolymers can mix into each other as well as both C-blocks, whereas bot...

Morphological Control Over Three‐ and Four‐Phase Superstructures in Blends of Asymmetric ABC and BAC Triblock Terpolymers

“…In a previous work, we have studied the structure formation of nine binary mixtures with different amounts of asymmetric I 37 S 42 M 21 95 (ISM 95 ) and S 26 I 07 M 67 171 (SIM 171 ), from now on referred to as “series A.” To investigate binary mixtures of asymmetric SIM und ISM triblock terpolymers in more detail, nine new blends with the same SIM 171 but another I 12 S 58 M 30 318 (ISM 318 ) were prepared, hereinafter referred to as “series B.” The ISM 318 used for the new series B, differs in two essential points from the one used in our earlier work: the molecular weight and the PI to PS ratio. As we will see, the variation of these parameters will have a massive impact on the resulting blend morphologies.…”

“…So far, we have seen the results for consecutive blends of I 12 S 58 M 30 318 and S 26 I 07 M 67 171 (series B). Now, we want to compare them with results from our previous work where blends of I 37 S 42 M 21 95 and S 26 I 07 M 67 171 with the same blend ratios were analyzed (series A). Therefore, the results of both works are schematically presented in Figure .…”

“…The number average molecular weight of the copolymers was determined by gel permeation chromatography (GPC) and 1 H nuclear magnetic resonance spectroscopy ( 1 H NMR), as described before . Nuclear magnetic resonance spectra of the copolymers were recorded on a Bruker Avance II 400 MHz (Bruker BioSpin GmbH, Karlsruhe, Germany) at 300 K using CDCl 3 as solvent and tetramethylsilane as internal standard.…”

“…The microphases of the copolymer blends were investigated by SAXS and TEM investigations, as described before . Therefore, polymer films were cast from chloroform by slow evaporation over a period of 4 weeks in a chloroform atmosphere.…”

Self‐Assembly of Multiblock Copolymers

“…Bulk phases of ABAC tetrablock terpolymers can also be accessed via blending of ABC and BAC triblock terpolymers . PS‐ b ‐PI‐ b ‐PMMA and PI‐ b ‐PS‐ b ‐PMMA were dissolved and mixed in defined molar ratios (90/10–10/90 wt %) before film casting.…”