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ABSTRACT We use self-consistent field theory to calculate the energy of defect formation in cylinder-forming diblock copolymers in laterally confining thin channels. We focus on two isolated defects, dislocations and disclinations and explore a wide range of polymer and channel characteristics. Our findings suggest appropriate conditions for the design of optimized graphoepitaxial processes, where defects are limited to very low concentrations. Using the string method, we also investigate the energy barriers and kinetic pathways of the transition from defective to perfect states. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40790. [ABSTRACT FROM AUTHOR]

We herein report a new facile strategy to ellipsoidal block copolymer nanoparticles that exhibit a pH-triggered anistropic swelling profile. In a first step, elongated particles with an axially stacked lamellae structure are selectively prepared by utilizing functional surfactants to control the phase separation of symmetric polystyrene- b-poly(2-vinylpyridine) (PS- b-P2VP) in dispersed droplets. In a second step, the dynamic shape change is realized by cross-linking the P2VP domains, thereby connecting glassy PS discs with pH-sensitive hydrogel actuators. [ABSTRACT FROM AUTHOR]

We report a facile strategy to synthesize amphiphilic gold (Au) nanoparticles functionalized with a multilayer, micelle-like structure consisting of a Au core, an inner hydroxylated polyisoprene (PIOH) layer, and an outer polystyrene shell (PS). Careful control of enthalpic interactions via a systematic variation of structural parameters, such as number of hydroxyl groups per ligand (NOH) and styrene repeating units (NPS) as well as areal chain density of ligands on the Au-core surface (Σ), enables precise control of the spatial distribution of these nanoparticles. This control was demonstrated in a lamellae-forming poly(styrene-b-2-vinylpyridine) (PS-b-P2VP) diblock copolymer matrix, where the favorable hydrogen-bonding interaction between hydroxyl groups in the PIOH inner shell and P2VP chains in the PS-b-P2VP diblock copolymer matrix, driving the nanoparticles to be segregated in P2VP domains, could be counter balanced by the enthalphic penalty of mixing of the PS outer brush with the P2VP domains. By varying NOH, NPS, and Σ, the nanoparticles could be positioned in the PS or P2VP domains or at the PS/P2VP interface. In addition, the effect of additives interfering with the hydrogen-bond formation between hydroxyl groups on Au nanoparticles and P2VP chains in a diblock copolymer matrix was investigated, and an interesting pea-pod-like segregation of Au nanoparticles in PS domains was observed. [ABSTRACT FROM AUTHOR]

Novel binuclear complexes, 4,4'-bis([N-(2,6-diisopropylphenyl)-2-(2,6-diisopropylphenylimino)propanamidato-k2-N,O-(trimethylphosphine)riickel(l l)]methyl)-1 , 1 `-biphenyl (2a) and 4,4'-bis((N-(2,6-diisopropylphenyl)-2-(2,6-diisopropylphenylimino)-4-methylpentamidato-k2-N, O-(trimethylphosphine)nickel(ll)]methyl)-1 ,1 `-biphenyl (2b), were synthesized by linking two nickel centers through a bis(benzyl) fragment. When activated with nickel bis(1 ,5-cyclooctadiene) (Ni(COD)2), 2a and 2b are capable of polymerizing ethylene in a quasi-living fashion, producing polymers with approximately twice the molecular weights relative to those obtained by using a structurally related mononuclear system. In addition, 2b/Ni(COD)2 was utilized to synthesize a series of pseudo-tnblock polyethylene (PE) macroinitiating copolymers, bearing atom-transfer radical polymerization (ATRP) initiators. Pseudo-pentablock copolymers were also prepared by taking advantage of a pressure-pulsing technique, wherein the ethylene pressure was increased from 100 to 500 psi in order to produce semicrystalline ethylene-rich end-blocks. Copolymers with elastomeric properties were synthesized by grafting n-butyl acrylate from the PE macroinitiators via ATRP. Examination using monotonic and step-cyclic stress-strain tests demonstrates that the materials exhibit large strains at break (1600-2000%) and excellent elastic recoveries at large strains (∼80%). That materials with such desirable properties could riot be attained using a mononuclear initiator demonstrates the clear advantage of growing the polymer via a telechelic mechanism. [ABSTRACT FROM AUTHOR]

A series of bis(phenoxyketimine)titanium dichloride complexes were synthesized and evaluated as catalysts for living, isoselective propylene polymerization upon activation with methylaluminoxane (MAO). Catalysts bearing phenoxyketimine ligands with different substituents at the ortho and para positions of the phenolate ring and substituents at the ketimine carbon were investigated. The identity of the ketimine substituent had the largest effect on the activity and isoselectivity of propylene polymerization. Complex 12/MAO promoted the living, isoselective polymerization of propylene ([m4] = 0.73, α = 0.94). This catalyst system was used for the synthesis of a number of block copolymers featuring isotactic polypropylene semicrystalline blocks and poly(ethylene-copropylene) amorphous blocks. Several triblock samples with varying block lengths, a pentablock, and a heptablock copolymer were synthesized. Mechanical testing has revealed that each is elastomeric with elongations at break between ~790-1000%. [ABSTRACT FROM AUTHOR]

We report the creation of highly asymmetric lamellar structures with a well-designed miktoarm star block copolymer of the S(IS')3 type, where S and S' are polystyrenes of different lengths and I is poly(isoprene). The domain spacing can be tuned continuously from 37 nm to over 300 nm when the miktoarm star block copolymer is blended with suitable molecular weight polystyrene homopolymers. Beyond the unbinding transition of the lamellar phase, extremely asymmetric lamellar structures were obtained with up to 97 wt % polystyrene, remarkably leaving the poly(isoprene) layers intact at only 3 wt %! [ABSTRACT FROM AUTHOR]

A regioregular (RR) donor–acceptor conjugated copolymerbased on cyclopenta[2,1-b:3,4-b′]dithiophene(CDT) and pyridal[2,1,3]thiadiazole (PT) structural units was preparedby using polymerization reactions involving reactants specificallydesigned to avoid random orientation of the asymmetric PT heterocycle along the copolymer backbone.Compared to its regioirregular (RI) counterpart, the RR polymer exhibitsa 2 orders of magnitude increase in hole mobility from 0.005 to 0.6cm2V–1s–1. To probethe reason for this difference in mobility, we examined the crystallinestructure and its orientation in thin films of both copolymers asa function of depth via grazing incidence wide-angle X-ray scattering(GIWAXS). In the RI film, the π–π stacking directionof the crystallites is mainly perpendicular to the substrate normal(edge-on orientation) while in the RR film the crystallites adopta mixed π–π stacking orientation in the centerof the film as well as near the interface between the polymer andthe dielectric layer. These results demonstrate that control of backboneregularity is another important design criterion to consider in thesynthesis and optimization of new conjugated copolymers with asymmetricstructural units. [ABSTRACT FROM AUTHOR]

π-Conjugated, narrow band gap copolymers containing pyridal[2,1,3]thiadiazole (PT) were synthesized via starting materials that prevent random incorporation of the PT heterocycles relative to the backbone vector. Two regioregular structures could be obtained: in one the PTs are oriented in the same direction, and in the other the orientation of the PTs alternates every other repeat unit. Compared to their regiorandom counterparts, the regioregular polymers exhibit a 2 orders of magnitude increase of the hole mobilites, from 0.005 to 0.6 cm2 V-1 s-1, as determined by field-effect transistor measurements. [ABSTRACT FROM AUTHOR]

The manufacture of smaller, faster, more efficient microelectronic components is a major scientific and technological challenge, driven in part by a constant need for smaller lithographically defined features and patterns. Traditional self-assembling approaches based on block copolymer lithography spontaneously yield nanometer-sized hexagonal structures, but these features are not consistent with the industry-standard rectilinear coordinate system. We present a modular and hierarchical self-assembly strategy, combining supramolecular assembly of hydrogen-bonding units with controlled phase separation of diblock copolymers, for the generation of nanoscale square patterns. These square arrays will enable simplified addressability and circuit interconnection in integrated circuit manufacturing and nanotechnology. [ABSTRACT FROM AUTHOR]