Polystyrene-poly Methyl Methacrylate Block Research Articles

Synthesis of Block Copolymer Particles by One-Pot, Two-Step Dispersion Reversible Chain Transfer Catalyzed Polymerization (Dispersion RTCP) in Supercritical Carbon Dioxide

Direct synthesis of micrometer-sized, poly(methyl methacrylate)-block-polystyrene (PMMA-b-PS) particles by one-pot, two-step dispersion reversible chain transfer catalyzed polymerization (dispersion RTCP) with nitrogen catalyst was successfully demonstrated in supercritical carbon dioxide (scCO2). The molecular weight distribution was clearly shifted to higher molecular weight side compared to that of PMMA-I prepared in the first step, indicating the successful synthesis of the block copolymer. This was supported by thin-layer chromatographic result. The blocking efficiency, which was obtained from the two number-distribution curves of molecular weight measured from gel permeation chromatography with dual detectors (refractive index and ultraviolet), was 87%.

Nanostructured Thin Films of Moderately Functionalized PMMA-b-PS.

A library of poly(methyl methacrylate)-block-polystyrene (PMMA-b-PS) block copolymers (BCPs) bearing small amounts (<10 mol%) of functional comonomer in either one or both blocks is investigated for their phase separation behavior in bulk and in thin films. Particularly, functionalities typically involved in modern postpolymerization modifications are considered, e.g., azide, pentafluorophenyl, furfuryl. Small-angle X-ray scattering and atomic force microscopy are employed to determine the characteristic dimensional features of lamellae-forming BCPs, which differ essentially in the functional groups. It is shown that the presence of the reactive moieties does not perturb the ability to phase separate in bulk, yet has an impact on the dimensions of the domains. Using a classic two-step procedure involving surface neutralization with a statistical PMMA-co-PS copolymer, it is observed that some functional copolymers are not able to form homogeneous thin films. Solvent stability and crosslinking ability of the films are then briefly assessed as a first step to establishing the functional films as nanoresolved molecular immobilization platform with feature sizes of 20 nm and below.

In Situ Synthesis of Coil–Coil Diblock Copolymer Nanotubes and Tubular Ag/Polymer Nanocomposites by RAFT Dispersion Polymerization in Poly(ethylene glycol)

Hollow polymeric nanotubes have the potential to be employed as advanced nanomaterials in a variety of applications; however, their synthesis from the assembly of coil–coil diblock copolymers (DBCPs) has typically been limited. Herein, we report a novel method for synthesis of coil–coil DBCP nanotubes by implementing RAFT dispersion polymerization in low molecular weight poly(ethylene glycol) (PEG). This method for the in situ synthesis of coil–coil DBCP nanotubes is particularly versatile and can be achieved with a range of block copolymers including poly(N-isopropylacrylamide)-block-polystyrene (PNIPAM-b-PS), poly(4-vinylpyridine)-block-polystyrene (P4VP-b-PS), and poly(methyl methacrylate)-block-polystyrene (PMMA-b-PS). Using this approach, several interesting coil–coil DBCP tubular morphologies are observed, including single-wall nanotubes, multiwall nanotubes, and porous nanotubes. Furthermore, RAFT dispersion polymerization conducted in the presence of Ag nanoparticles can be used to yield complex t...

Facile synthesis of block copolymers from a cinnamate derivative by combination of AGET ATRP and click chemistry

An azido- and bromo-containing compound derived from naturally occurring ethyl cinnamate was used successfully to prepare block copolymers by a combination of ‘activator generated by electron transfer atom transfer radical polymerization’ (AGET ATRP) and Huisgen “click” reactions in emulsion. First, azido-end poly(methyl methacrylate) and alkyne-end polystyrene were prepared under AGET ATRP conditions, then, poly(methyl methacrylate) block polystyrene (PMMA-b-PS) diblock copolymer was formed by Huisgen 1,3-dipolar cycloaddition. Finally, polystyrene block poly(methyl methacrylate) block polystyrene (PS-b-PMMA-b-PS) triblock copolymer was synthesized via simultaneous AGET ATRP and click reactions, catalyzed by the same copper-based catalyst. The polymers were characterized by 1H nuclear magnetic resonance (NMR) spectroscopy and gel permeation chromatography (GPC), which confirmed the successful synthesis of the corresponding polymers.

Conformation and structural changes of diblock copolymers with octopus-like micelle formation in the presence of external stimuli

External stimuli such as vapours and electric fields can be used to manipulate the formation of AB-diblock copolymers on surfaces. We study the conformational variation of PS-b-PMMA (polystyrene-block-poly(methyl methacrylate)), PS and PMMA adsorbed on mica and their response to saturated water or chloroform atmospheres. Using specimens with only partial polymer coverage, new unanticipated effects were observed. Water vapour, a non-solvent for all three polymers, was found to cause high surface mobility. In contrast, chloroform vapour (a solvent for all three polymers) proved to be less efficient. Furthermore, the influence of an additional applied electric field was investigated. A dc field oriented parallel to the sample surface induces the formation of polymer islands which assemble into wormlike chains. Moreover, PS-b-PMMA forms octopus-like micelles (OLMs) on mica. Under the external stimuli mentioned above, the wormlike formations of OLMs are able to align in the direction of the external electric field. In the absence of an electric field, the OLMs disaggregate and exhibit phase separated structures under chloroform vapour.

Three-dimensional mesoporous structures fabricated by independent stacking ofself-assembled films on suspended membranes

We report an original iterative method for fabricating three-dimensional mesoporous structuresby independently stacking multiple self-assembled block copolymer films supported bySi membranes. A first layer is formed on the substrate by a self-assembled PS-b-PMMA (polystyrene-block-poly(methyl methacrylate)) film. A porous,permeable Si membrane deposited on top of the first block copolymer filmprovides mechanical support, preventing pattern collapse during the wetdeveloping used to selectively remove the PMMA component of the PS-b-PMMA film. A second, dense Si membrane is deposited to seal the porous membrane,resulting in an impermeable coating suspended atop the self-assembled mesoporouspolystyrene structures. The process can then be iterated using the sealed membrane as thenew substrate to support a subsequent self-assembled block copolymer film. This multilayerapproach provides a flexible three-dimensional fabrication technique where, in each layer,pattern morphology, domain orientation and degree of ordering can be designedindependently. Furthermore, the process is compatible with electron-beam directedassembly, used to achieve regular patterns with feature density multiplication at any levelin the stack.

Formation of periodic nanoring arrays on self-assembled PS-b-PMMA film under rapid solvent-annealing

Periodic nanoring arrays are prepared by self-assembled poly styrene-block-polymethylmethacrylate (PS-b-PMMA) diblock copolymer under rapid solvent-annealing. The dimension of the nanorings can be modified by controlling the solvent-annealing time.

Polystyrene-Polymethylmethacrylate Block Copolymers for Lithographically Assisted Bottom-Up Assembly of Nanostructures

Polystyrene-polymethylmethacrylate (PS-PMMA) block copolymers are well known to exhibit microphase separation to form a series of regular structures with local periodic arrangements of the blocks. By developing films of PS-PMMA within topographically patterned silicon (100) substrates (with photolithographically defined rectangular channels of depth 60 nm and widths 166 – 433 nm) these irregular arrangements form highly periodic structures where the features are parallel to the side walls of the channels. However, the use of silicon substrates leads to problems in processing of these films. PS-PMMA does not wet the surface, and this results in island formation on flat substrates. On channel etched substrates this phenomena ensures that the thickness of the films is irregular and poorly defined alignment is seen. Detailed considerations of this polymer system suggest that feature sizes below 25 nm are not realisable. The results suggest other copolymer systems should be studied.

In situ and time-resolved ultra small-angle neutron scattering observation on growing poly(methyl methacrylate)-block-polystyrene via reversible addition–fragmentation chain transfer living radical polymerization

Reversible addition–fragmentation chain transfer (RAFT) living radical polymerization of poly(methyl methacrylate)-block-polystyrene (PMMA-b-PS) was investigated by a combined method of gel permeation chromatography (GPC) and in situ and time-resolved ultra small-angle neutron scattering (tr-USANS) measurements. GPC enables us to examine a growing single molecule as a function of polymerization time, with respect to monomer conversion, molecular weight (Mn) and polydispersity index (Mw/Mn) of PMMA-b-PS. On the other hand, tr-USANS, observing in meso-length scales from nm to µm, reveals polymerization-induced molecular self-assembly, such as microphase separation by PMMA-b-PS or macrophase separation between PMMA-b-PS and homo-polystyrene (by-product). By combining these two experimental methods, we elucidated that RAFT living polymerization was retarded by micro- and macrophase separations.

Poly(methyl methacrylate)-block-polystyrene and polystyrene-block-poly(n-butyl acrylate) as compatibilizers in PMMA/PnBA blends

Abstract The influence of the addition of poly(methyl methacrylate)-blockpolystyrene (PMMA-b-PS) and PS-b-poly(n-butyl acrylate) (PS-b-PnBA) diblock copolymers on the structure and the mechanical properties of PMMA/PnBA polymer blends was investigated. In binary polymer blends of PMMA and PS, and PS and PnBA, and in the ternary system the corresponding diblock copolymers caused a significantly higher distribution of the dispersed phase and an appreciable narrowing of the particle size distribution as shown by scanning force microscopy using the pulsed force mode technique. Transmission electron microscopy images proved that in the ternary system the two diblock copolymers formed no own separate phase but are arranged as a ring layer at the interface between the two homopolymers PMMA and PnBA. Charpy tests demonstrated that the impact strength of the ternary blends is increased by the two diblock copolymers even at low amounts of the latter. The influence on mechanical properties like Young’s modulus, yield stress, and tensile strength at break was less marked as strainstress measurements showed. The major effect seems to be exerted on the elongation at break.

“Living” Radical Polymerization of Styrene Using Diphenylmethane Diisocyanate-Based Polyurethane Iniferter

Polyurethane iniferter, synthesized from diphenylmethane diisocy-anate and 1,1,2,2-tetraphenyl-1,2-ethanediol, was used to polymerize styrene. The increase of number-average molecular weight of the polystyrene while increasing both conversion and polymerization time prove that the polymerization of styrene using polyurethane iniferter is through a “living” radical mechanism. Postpolymerization of polystyrene in the presence of styrene and methyl methacrylate yielded high molecular weight polystyrene and polystyrene-polymethyl methacrylate block copolymers respectively.

Note: Selectivity and Permeability of Microporous Block Copolymer Membranes

Abstract : A selective solvent was used to develop a uniform microporous structure in a polystyrene-polymethylmethacrylate block copolymer. Pore diameters in the range of 200-500 angstroms were produced. Gas permeation measurements demonstrated a dramatic, five order of magnitude, increase in permeability coefficient associated with the throughgoing microporous structure. These high-flux membranes retained some selectivity for certain gas pairs as expected for transport based on Knudsen diffusion in the porous materials.... Microporous membranes, Gas separations, Knudsen diffusion, Block copolymers.