Star copolymers have attracted significant interest due to their different characteristics compared with diblock copolymers, including higher critical micelle concentration, lower viscosity, unique spatial shape, or morphologies. Development of synthetic skills such as anionic polymerization and controlled radical polymerization have made it possible to make diverse architectures of polymers. Depending on the molecular architecture of the copolymer, numerous morphologies are possible, for instance, Archimedean tiling patterns and cylindrical microdomains at symmetric volume fraction for miktoarm star copolymers as well as asymmetric lamellar microdomains for star-shaped copolymers, which have not been reported for linear block copolymers. In this review, we focus on morphologies and microphase separations of miktoarm (A m B n and ABC miktoarm) star copolymers and starshaped [(A-b-B) n ] copolymers with nonlinear architecture.

wileyonlinelibrary.comspeed, and simplicity of the process. [1][2][3][4][5] Although vertical orientation of lamellar and cylindrical nanodomains of block copolymers on a substrate is desirable, parallel orientation is usually obtained in a thin fi lm because of different affi nity between two block segments in a block copolymer toward the substrate and/or air. To induce vertical orientation, diverse preor post-treatments to neutralize the preferential affi nity have been introduced in the literature, for instance, solvent vapor annealing, [6][7][8][9] surface neutralization by random copolymer brush treatment, [10][11][12] blend system, [ 13 ] graphoepitaxy, [ 14,15 ] temperature gradient, [ 16,17 ] electric fi eld [ 18,19 ] or top coating. [20][21][22] Among them, solvent vapor annealing is one of the most powerful post-treatment methods for developing vertical orientation of block copolymer nanodomains. However, this method is diffi cult to apply for industrial applications owing to the use of solvents and the dewetting problem. To avoid using solvent, thermal annealing of block copolymer thin fi lms would be the most promising platform for commercialization of DSA due to easy and large scale process. However, to induce vertically oriented nanodomains, neutralization of a substrate by various surface modifi cations, for instance, functionalization with random copolymers, introducing rough substrates, employing graphene fi lms or nanoparticle monolayers, [ 11,13,[23][24][25] is still needed to tune interfacial interactions between a substrate and each block of the block copolymer. Therefore, a simple and cost-effective DSA process that does not require above-mentioned neutralization methods and solvent vapor annealing is demanded for the fabrication of vertically oriented nanodomains to compete with conventional top-down lithography.Kramer and co-workers [ 26 ] investigated the effect of block copolymer chain architecture on the orientation of nanodomains in relatively thick fi lms (600-800 nm) using poly(cyclohexylethylene)-block -poly(ethylene) (PCHE-b -PE) block copolymers. They found that PCHE-b -PE-b -PCHE triblock copolymer showed perpendicularly oriented nanodomains by introducing lower surface energy block as the midblock, whereas PCHE-b -PE diblock copolymer exhibited parallel Vertical Orientation of Nanodomains on Versatile Substrates through Self-Neutralization Induced by Star-Shaped Block CopolymersSangshin Jang , Kyuseong Lee , Hong Chul Moon , Jongheon Kwak , Jicheol Park , Gumhye Jeon , Won Bo Lee , and

We have introduced a facile synthetic route for well-defined [poly(3-dodecylthiophene)] 2 poly(methyl methacrylate) miktoarm star copolymer (P3DDT 2 PMMA) by using a click reaction. For this purpose, PMMA with two ethynyl groups (PMMA-(≡) 2 ) and ω-azidopropyl-P3DDT were synthesized. We found that the use of alkyl linker (here, propyl group) between P3DDT and azido group is very essential to minimize the steric hindrance arising from bulky side group in P3DDT during the click reaction. When we employed a slightly excess amount of the ω-azidopropyl-P3DDT, we obtained a well-defined P3DDT 2 PMMA with a narrow molecular weight distribution (polydispersity index <1.20) after selective removal of the unreacted ω-azidopropyl-P3DDT in a crude product by using column chromatography. We also investigated self-assembled structure of P3DDT 2 PMMA by small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). P3DDT 2 PMMA with weight fraction of P3DDT block (w P3DDT ) of 0.33 had lamellar microdomains, while a linear diblock copolymer (P3DDT-b-PMMA) with w P3DDT = 0.37 showed cylindrical microdomains. Also, P3DDT 2 PMMA with w P3DDT = 0.59 showed the HEX cylindrical microdomains of PMMA in the P3DDT matrix, whereas P3DDT-b-PMMA with w P3DDT = 0.56 exhibited lamellar microdomains. More interestingly, P3DDT 2 PMMA with w P3DDT of 0.76 showed hexagonally packed PMMA cylinders in the P3DDT matrix at molten state, and this morphology was maintained even after crystallization of the P3DDT block. This behavior is quite different from linear P3DDT-b-PMMA diblock with the same weight fraction of P3DDT because the latter shows fibril structures after P3DDT crystallization. These results imply that controlling the molecular architecture is an effective way to tune the morphology of P3AT-containing block copolymers. ■ INTRODUCTIONRegioregular poly(3-alkylthiophene) (P3AT) is one of the most attractive semicrystalline polymers due to its high charge carrier mobility and good solubility in organic solvents. 1−3 To achieve high performance organic electronic devices, one challenge is fabrication of P3AT nanostructures with nanometer length scale. 4,5 For this purpose, various block copolymers consisting of P3AT and coil blocks have been synthesized 6−15 because of their self-assembly ability to form periodic nanostructures. 16−18 However, most poly(3-hexylthiophene) (P3HT)-containing block copolymers usually exhibit only fibril morphology due to strong rod/rod interaction of P3HT. 18−22 In the rod−coil block copolymer system, the phase behavior is determined by the competition between rod/rod interaction (μ) of rod block and the segregation power (governed by the Flory's segmental interaction parameter χ) between rod and coil blocks. 23−25 These two factors are adjusted by varying the composition of each block or tuning the crystallinity of the rod moiety. Some research groups used P3AT with longer (or bulkier) alkyl side chain than P3HT to depress the crystallization of the rod block. Ho et al. 26 reported various na...

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