Hydroxyl-terminated Polystyrene Research Articles

Lithography-Free Route to Hierarchical Structuring of High-χ Block Copolymers on a Gradient Patterned Surface.

A chemically defined patterned surface was created via a combined process of controlled evaporative self-assembly of concentric polymer stripes and the selective surface modification of polymer brush. The former process involved physical adsorption of poly (methyl methacrylate) (PMMA) segments into silicon oxide surface, thus forming ultrathin PMMA stripes, whereas the latter process was based on the brush treatment of silicon native oxide surface using a hydroxyl-terminated polystyrene (PS-OH). The resulting alternating PMMA- and PS-rich stripes provided energetically favorable regions for self-assembly of high polystyrene-block-polydimethylsiloxane (PS-b-PDMS) in a simple and facile manner, dispensing the need for conventional lithography techniques. Subsequently, deep reactive ion etching and oxygen plasma treatment enabled the transition of the PDMS blocks into oxidized groove-shaped nanostructures.

Effect of Ink Molecular Weights and Annealing Conditions on Molecular Transfer Printing

The molecular transfer printing (MTP) technique has been invented to fabricate chemical patterns with high fidelity using homopolymer inks. In this work, we systematically studied the effects of the molecular weights of homopolymer inks and transfer conditions on the MTP process. We explored a large range of molecular weights (∼3.5−56 kg·mol−1) of hydroxyl-terminated polystyrene (PS-OH) and hydroxyl-terminated poly(methyl methacrylate) (PMMA-OH) in the MTP process, and found that the resulting chemical patterns on replicas from all five blends were functional and able to direct the assembly of films of the same blends. The transfer temperature and the film annealing sequences had an impact on the MTP process. MTP was sensitive to the transfer temperature and could only be performed within a certain temperature range, i.e. higher than the glass transition temperature (Tg) of copolymers and lower than the rearrangement temperature of the assembled domains. Pre-organization of the blend films was also necessary for MTP since the preferential wetting of PMMA domains at the replica surface might result in the formation of a PMMA wetting layer to prevent the presentation of underlying chemical patterns to the replica surface.

Enhanced self-assembly of block copolymers by surface modification of a guiding template

The formation of highly ordered patterns of block copolymers (BCPs) with high χ is important for next-generation lithography applications. We demonstrate here a surface-engineering methodology to enhance the self-assembly of poly(styrene-b-dimethylsiloxane) (PS-b-PDMS) BCPs with high χ by employing a hydroxyl-terminated polystyrene (PS-OH) brush. By precisely controlling the molecular weight (MW) and weight percent of PS-OH, well-ordered sub-20-nm BCP patterns were obtained over a large area in a short annealing time (<10 min) with the use of guiding templates. We systemically analyzed how the PS-OH brush affects the self-assembly kinetics of BCPs with various MWs and volume fractions. Moreover, the transmission electron microscopy (TEM) results strongly support that the PS-modulated surface plays an important role in the ordering of BCP patterns. We also achieved well-aligned 12 nm line and 18 nm dot patterns within 3 min by means of binary solvent vapor annealing at a moderate temperature under the optimum PS-OH brush conditions. These results provide a new platform for effective engineering and manipulation of the self-assembly of other BCPs for advanced BCP nanotechnologies. A facile and practical surface-engineering methodology to enhance the self-assembly of PS-b-PDMS BCPs with high χ by precisely controlling the molecular weight and weight percent of PS brushes. Highly ordered sub-20-nm BCP patterns were successfully obtained in a few minutes under the optimum PS brush condition.

Anisotropic and Interconnected Nanoporous Materials from Randomly End-Linked Copolymer Networks

Microphase separation within randomly end-linked copolymer networks (RECNs) provides access to disordered bicontinuous morphologies over a wide composition range of the constituent network strands. Here, we rely on end-linking of telechelic hydroxyl-terminated polystyrene (PS) and poly(d,l-lactide) (PLA) chains of equal molecular weight, with a tetrafunctional isocyanate cross-linker in a good solvent for both strands, followed by solvent removal to induce microphase separation, and finally etching of the PLA phase to yield nanoporous materials. Transmission electron microscopy (TEM) tomographic reconstructed 3D images along with gravimetric measurements and small-angle X-ray scattering (SAXS) indicate the formation of highly interconnected structures over a range of ∼40–70 vol % of PLA, while N2 adsorption measurements indicate narrowly distributed pore sizes that can be tuned by varying the strand molecular weights. Stretching of the PS/PLA copolymer networks above the glass transition temperatures of b...

Superhydrophobic coatings with improved mechanical robustness based on polymer brushes

Abstract Superhydrophobic surfaces show great promise for applications that range from self-cleaning windows to anti-icing air-crafts. Practical applications require development of methods and materials for one-step fabrication of such coatings with sufficient mechanical robustness on large surface areas at low costs. Spray-coating of nanoparticles functionalized with low energy molecules can meet all these requirements except the challenges associated with the mechanical robustness of the coatings. Here, we demonstrate that the mechanical robustness of the spray-coated films can be improved by engineering the polymer matrix. Hydroxyl-terminated polystyrene (PS-OH) serves as a matrix for dispersing silica nanoparticles (12 nm) functionalized with fluorinated silanes. Hydroxyl ends of the PS-OH facilitate chemical and physical interactions with the underlying substrate, through grafting of polymer chains to form brushes and by presenting hydrophilic groups, respectively. The fabricated films showed a high level of surface roughness with water contact angles (θ) greater than 170°. The coatings retained their superhydrophobic behavior (θ > 150° and sliding angle

Neutral wetting brush layers for block copolymer thin films using homopolymer blends processed at high temperatures

Binary homopolymer blends of two hydroxyl-terminated polystyrene (PS-OH) and polymethylmethacrylate (PMMA-OH) homopolymers (Mn ∼ 16000 g mol−1) were grafted on SiO2 substrates by high-temperature (T > 150 °C), short-time (t < 600 s) thermal treatments. The resulting brush layer was tested to screen preferential interactions of the SiO2 substrate with the different symmetric and asymmetric PS-b-PMMA block copolymers deposited on top of the grafted molecules. By properly adjusting the blend composition and the processing parameters, an efficient surface neutralization path was identified, enabling the formation, in the block copolymer film, of homogeneous textures of lamellae or cylinders perpendicularly oriented with respect to the substrate. A critical interplay between the phase segregation of the homopolymer blends and their grafting process on the SiO2 was observed. In fact, the polar SiO2 is preferential for the PMMA-rich phase that forms a homogeneous layer on the substrate, while the PS-rich phase is located at the polymer-air interface. During the thermal treatment, phase segregation and grafting proceed simultaneously. Complete wetting of the PS rich phase on the PMMA rich phase leads to the formation of a PS/PMMA bilayer. In this case, the progressive diffusion of PS chains toward the polymer-SiO2 interface during the thermal treatment allows tuning of the brush layer composition.

Polystyrene as a brush layer for directed self-assembly of block co-polymers

Block co-polymer (BCP) lithography is becoming an established technique for patterning beyond optical lithography limitations. It is based on combining the intrinsic property of block co-polymers to phase separate at the molecular scale with the capabilities of conventional top-down lithographic methods for patterning surfaces. Guiding the self-assembly of block co-polymers by surface chemical modification is one of the most used processes to drive the self-assembly in a convenient way. It consists on using lithography and oxygen plasma to create different wettability regions on a polymer brush grafted on the surface. However, the optimal conditions for obtaining a good guiding pattern in chemical surface modification are difficult to find since the ultimate mechanism that causes the guiding is not completely known. We present an investigation about the use of hydroxyl-terminated polystyrene (PS-OH) as a single polymer brush layer for multiple patterning directed self-assembly DSA of PS/PMMA block co-polymers. We achieve pattern multiplication with density increase factors up to x12 and we demonstrate pattern transfer to silicon.

Synthesis of star-shaped polymers by coupling reaction between multifunctional core and terminal functionalized polymers

Star-shaped polymers that consist of well-defined polystyrene (PS) arms were successfully synthesized in high yield by coupling reaction between multifunctional core molecules and hydroxyl-terminated PS in the presence of 1, 3-dicyclohexylcarbodiimide and 4-(dimethylamino) pyridine at room temperature. Several systems were investigated: (1) Pyromellitic dianhydride (PMDA) and hydroxyl-terminated PS (PS-OH) with narrow molecular weight distribution, which was prepared by atom transfer radical polymerization (ATRP) of St with 2-hydroxyethyl bromoisobutylate (HEBiB) as initiator. (2) PMDA and PS-OH prepared by conventional free radical polymerization, with 2-mercaptoethanol as chain transfer agent. (3) Narrow molecular weight distributed alternating copolymer of maleic anhydride (MA) and styrene (St), which was obtained via reversible addition fragmentation chain transfer polymerization (RAFT) process, and PS-OH obtained by ATRP. The formation of star-shaped PSs was confirmed by proton nuclear magnetic resonance (1H NMR) and gel permeation chromatography (GPC).

Determination of acid and hydroxyl end-groups in endfunctionalized polystyrenes using 19F NMR

Abstract Carboxyl-terminated polystyrene was esterified with 2,2,2-trifluoroethanol using a carbodiimide-mediated room temperature reaction, and hydroxyl-terminated polystyrene was fluoro-derivatized with trifluoroacetic anhydride. The soformed fluorine-containing esters were then quantitatively determined with 19F NMR, using α,α,α-trifluorotoluene as secondary standard. This provides a technique for the reliable determination of carboxylic acid and hydroxyl groups in small samples of polymers.

Preparation and end-linking of hydroxyl-terminated polystyrene star macromolecules

Preparation and end-linking of hydroxyl-terminated polystyrene star macromolecules

Preparation and end-linking of hydroxyl-terminated polystyrene star macromolecules

An up-scale synthesis of 3-arm hydroxyl-terminated polystyrene (PS) star polymers is reported. Subsequent end-linking of these hydroxyl-terminated star polymers with 2,4-toluene diisocyanate gave branched polymers. The extent of reacted groups was measured by UV spectroscopy. The quenched samples were characterized by static-dynamic light scattering. The experimental gel point (critical hydroxyl conversion, pOH, cr = 0.65) is shifted significantly from the theoretically predicted gel point (pOH,cr = 0.50), indicating extensive ring formation during the end-linking process. Analysis of the shrinking factors (gh, gs) and the molar mass dependencies of the radii of gyration Rg, hydrodynamic radii Rh, and the second osmotic virial coefficient A2 gave qualitative agreement with crosslinking theories. The deviations are discussed to arise from the large non-uniformity in the size distribution and from a cross-over of mean field to percolation behavior, as was previously found from the quantitative analysis of molar mass distributions.

SYNTHESIS OF HYDROXYL-TERMINATED POLYSTYRENE

SYNTHESIS OF HYDROXYL-TERMINATED POLYSTYRENE