Formation Of Block Copolymers Research Articles

Spontaneous onion shape vesicle formation and fusion of comb-like block copolymers studied by dissipative particle dynamics

The formation of an onion shape vesicle.

Photo-reversible bonding and cleavage of block copolymers

We introduce a synthetic avenue for the completely photoreversible formation of block copolymers based on anthracene chemistry.

Nanolithography of cylinder forming block copolymers via DSA for semiconductor manufacturing

To realize the full benefit of directed self-assembly (DSA), it is necessary to understand the interplay between the target structures and the process parameters.

Living Cationic Polymerization of Vinyl Ethers through a Photoinduced Radical Oxidation/Addition/Deactivation Sequence.

A new photoinitiating system for living cationic polymerization of vinyl ethers is reported. In the current approach, visible-light irradiation of dimanganese decacarbonyl (Mn2 (CO)10 ) in the presence of an alkyl bromide results in the formation of carbon-centered radicals. The photochemically generated radicals were then oxidized by diphenyliodonium ions to the corresponding cations. These cations can add vinyl ether monomers, which are then rapidly deactivated by the bromide anions to give α-halide functional end groups. Poly(vinyl ether) chains are then grown through successive photoinduced radical oxidation/addition/deactivation (PROAD) in a controlled manner. The living nature of the system is evaluated through kinetics studies and block copolymer formation.

Living Cationic Polymerization of Vinyl Ethers through a Photoinduced Radical Oxidation/Addition/Deactivation Sequence

AbstractA new photoinitiating system for living cationic polymerization of vinyl ethers is reported. In the current approach, visible‐light irradiation of dimanganese decacarbonyl (Mn2(CO)10) in the presence of an alkyl bromide results in the formation of carbon‐centered radicals. The photochemically generated radicals were then oxidized by diphenyliodonium ions to the corresponding cations. These cations can add vinyl ether monomers, which are then rapidly deactivated by the bromide anions to give α‐halide functional end groups. Poly(vinyl ether) chains are then grown through successive photoinduced radical oxidation/addition/deactivation (PROAD) in a controlled manner. The living nature of the system is evaluated through kinetics studies and block copolymer formation.

Leucine‐Based Block Copolymer Nano‐Objects via Polymerization‐Induced Self‐Assembly (PISA)

SummaryPolymerization‐induced self‐assembly (PISA) technique has been used to prepare leucine‐based block copolymer nano‐objects. A side‐chain leucine appending macromolecular chain transfer agent (macroCTA) has been employed for reversible addition‐fragmentation chain transfer (RAFT) mediated dispersion polymerization of benzyl methacrylate (BzMA) in methanol at 65 °C. 1H NMR spectroscopy reveals near quantitative monomer conversions (≥90%) and gel permeation chromatography (GPC) indicated well‐defined block copolymer formation. Morphological evolution has been observed from spherical micelle to fibre to vesicle with increase of the length of the solvophobic block keeping the stabilizer block length and monomer solid content constant.

Integration of a templated directed self-assembly-based hole shrink in a short loop via chain

The use of directed self-assembly (DSA) of cylinder forming block copolymers (BCP) for contact hole shrink applications has gained increased attention due to the dimensions that can be achieved with this materials. Recent work has focused on engineering the dimensions and surface energy of the templates to obtain straight profiles of the cylinders assembled in them. However, the impact of process optimization on defect formation is measured using scanning electron microscopy before and after transferring the BCP features to a hardmask, which provides limited information about the presence of defects or three-dimensional morphologies in the polymer structures. To identify the presence of single defects in arrays of various densities and sizes, we use Kelvin and chain structures available in the IMEC 28-nm node via chain electrical test vehicle, Everest, in combination with templated DSA. We tuned the surface energy and dimensions of the templates with the use of random copolymers and through the exposure conditions, respectively. Finally, the contact holes obtained with templated DSA of BCP were subsequently transferred into a relevant stack to apply advanced metallization processes and, ultimately, validated electrically.

Supramolecular Helix–Helix Block Copolymers

Two chemically distinct monotelechelic helical polymers were synthesized using anionic and reversible addition–fragmentation chain-transfer (RAFT) polymerizations. A chiral poly(isocyanide) block was obtained using a palladium–ethynyl complex modified with the N1,N3-bis(6-butyramidopyridin-2-yl)-5-hydroxyisophthalamide (Hamilton wedge) moiety as a catalyst employing anionic polymerization. A complementary barbiturate-functionalized chain-transfer agent was used to polymerize chiral N-(1-(naphthalen-2-yl)ethyl)methacrylamides by RAFT polymerization. The assembly into helix–helix supramolecular block copolymers in chloroform via hydrogen bonding was analyzed by 1H NMR spectroscopy, resulting in an average measured association constant of (9.5 ± 0.5) × 103 M–1. After block copolymer formation, the secondary structures of both helical polymers were maintained within the block copolymer, as evidenced by circular dichroism and infrared spectroscopies. Films were prepared from a 1:1 mixture of polymers in soluti...

Asymmetric Membranes from Two Chemically Distinct Triblock Terpolymers Blended during Standard Membrane Fabrication

Deviating from the traditional formation of block copolymer derived isoporous membranes from one block copolymer chemistry, here asymmetric membranes with isoporous surface structure are derived from two chemically distinct block copolymers blended during standard membrane fabrication. As a first proof of principle, the fabrication of asymmetric membranes is reported, which are blended from two chemically distinct triblock terpolymers, poly(isoprene-b-styrene-b-(4-vinyl)pyridine) (ISV) and poly(isoprene-b-styrene-b-(dimethylamino)ethyl methacrylate) (ISA), differing in the pH-responsive hydrophilic segment. Using block copolymer self-assembly and nonsolvent induced phase separation process, pure and blended membranes are prepared by varying weight ratios of ISV to ISA. Pure and blended membranes exhibit a thin, selective layer of pores above a macroporous substructure. Observed permeabilities at varying pH values of blended membranes depend on relative triblock terpolymer composition. These results open a new direction for membrane fabrication through the use of mixtures of chemically distinct block copolymers enabling the tailoring of membrane surface chemistries and functionalities.

RAFT-mediated emulsion polymerization of styrene with a thermoresponsive MacroCTA

Heterogeneous RAFT polymerization is an attractive ‘living’ radical polymerization technique to control not only the molecular weight distribution but also the particles size distribution. Here, we demonstrate the use of a thermoresponsive RAFT macro chain transfer agent (MacroCTA) to form seed particles for the chain extension of styrene to form block copolymer latex particles. By incorporating a few styrene units into the MacroCTA, the polymerizations become faster, producing both narrow particle size and molecular weight distributions. This is due to the ‘superswelling effect’, in which all the seed particles swell with monomer and nucleated at the same time. The resulting latex particles could then be transformed into a variety of nanostructures by cooling below the lower critical solution temperature of the thermoresponsive block in the presence of a plasticizer for polystyrene. The dominant structure was cylindrical worms with the observation of other structures including jelly fish and the rare disc. Cooling under ultrasound produced either vesicles or cauliflower structures. The work demonstrated that utilizing the ‘superswelling effect’, control over the rate, and molecular weight and particle size distributions could be obtained, providing design parameters to construct new nanostructures.

Near-Infrared Photoinduced Coupling Reactions Assisted by Upconversion Nanoparticles.

We introduce nitrile imine-mediated tetrazole-ene cycloadditions (NITEC) in the presence of upconversion nanoparticles (UCNPs) as a powerful covalent coupling tool. When a pyrene aryl tetrazole derivative (λabs, max =346 nm) and UCNPs are irradiated with near-infrared light at 974 nm, rapid conversion of the tetrazole into a reactive nitrile imine occurs. In the presence of an electron-deficient double bond, quantitative conversion into a pyrazoline cycloadduct is observed under ambient conditions. The combination of NITEC and UCNP technology is used for small-molecule cycloadditions, polymer end-group modification, and the formation of block copolymers from functional macromolecular precursors, constituting the first example of a NIR-induced cycloaddition. To show the potential for in vivo applications, through-tissue experiments with a biologically relevant biotin species were carried out. Quantitative cycloadditions and retention of the biological activity of the biotin units are possible at 974 nm irradiation.

Synthesis of polyolefin‐block‐polystyrene through sequential coordination and anionic polymerizations

ABSTRACTTwo representative bulk polymers, polyolefin (PO) and polystyrene (PS), were molecularly connected to form PO‐block‐PS by sequentially performing coordination and anionic polymerizations in one pot. Ethylene/1‐octene copolymerization was performed using a typical ansa‐metallocene catalyst, rac‐[Me2Si(2‐methylindenyl)]2ZrCl2, in the presence of (benzyl)2zinc to grow PO‐chains at the Zn site. Anionic styrene polymerization was subsequently performed using nBuLi·(tmeda) (tmeda, N,N,N′,N′‐tetramethylethylenediamine) initiator to consecutively grow PS‐chains at the Zn site. The composition and the molecular weight of the PO‐blocks were controllable depending on the feed amounts of 1‐octene and (benzyl)2zinc (1‐octene fraction: ∼20, ∼40 wt %; PO‐Mw, 77,000–174,000) and the PS‐block size was also controlled (PS‐Mn, ∼21,000) with the complete conversion of the styrene monomer. Formation of block copolymers was evident in the GPC curves, TEM images, and strain‐stress curves. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 3110–3118

Understanding the Formation of Linear Olefin Block Copolymers with Dynamic Monte Carlo Simulation

Chain‐shuttling polymerization with dual catalysts has introduced a new class of polyolefins called olefin block copolymers (OBCs). A dynamic Monte Carlo model to describe the kinetics of chain‐shuttling copolymerization in a semi‐batch reactor is developed, and used it to study how the microstructure of OBCs with different numbers of blocks per chain evolves during polymerization. The model also describes how chain‐shuttling rate constants and concentration of chain‐shuttling agent affect populations of OBCs with different numbers of blocks per chain. These model predictions are useful to make OBCs with precisely designed microstructures.image

A Light-Activated Reaction Manifold.

We introduce an efficient reaction manifold where the rate of a thermally induced ligation can be controlled by a photonic field via two competing reaction channels. The effectiveness of the reaction manifold is evidenced by following the transformations of macromolecular chain termini via high-resolution mass spectrometry and subsequently by selective block copolymer formation. The light-controlled reaction manifold consists of a so-called o-quinodimethane species, a photocaged diene, that reacts in the presence of light with suitable enes in a Diels-Alder reaction and undergoes a transformation into imines with amines in the absence of light. The chemical selectivity of the manifold is controlled by the amount of ene present in the reaction and can be adjusted from 100% imine formation (0% photo product) to 5% imine formation (95% photo product). The reported light-controlled reaction manifold is highly attractive because a simple external field is used to switch the selectivity of specific reaction channels.

Structure Formation of Metallopolymer-Grafted Block Copolymers

Microphase separation drives the structure formation in block copolymers. Here, functional metallopolymer-grafted diblock copolymers consisting of polystyrene-block-polyisoprene (PS-b-PI) as polymer backbone featuring low molar mass polyferrocenyldimethylsilane (PFS) and polyvinylferrocene (PVFc) are synthesized via an iterative anionic grafting-to polymerization strategy. PS-b-PI block copolymers having about 30 mol % 1,2-polyisoprene moieties are subjected to platinum-catalyzed hydrosilylation reaction for the introduction of chlorosilane groups. The Si–Cl moieties are shown to efficiently react with the active metallopolymers yielding block-selective metallopolymer-grafted copolymers with 34 vol % PVFc and 43 vol % PFS as evidenced by 1H NMR spectroscopy as well as size exclusion chromatography. The microphase separation of the functional metallopolymer-grafted block copolymers is evidenced via TEM measurements revealing fascinating morphologies. The structure formation of the PVFc-grafted block copoly...

Atom Transfer Radical Polymerization of Functionalized Vinyl Monomers Using Perylene as a Visible Light Photocatalyst.

A standardized technique for atom transfer radical polymerization of vinyl monomers using perylene as a visible-light photocatalyst is presented. The procedure is performed under an inert atmosphere using air- and water-exclusion techniques. The outcome of the polymerization is affected by the ratios of monomer, initiator, and catalyst used as well as the reaction concentration, solvent, and nature of the light source. Temporal control over the polymerization can be exercised by turning the visible light source off and on. Low dispersities of the resultant polymers as well as the ability to chain-extend to form block copolymers suggest control over the polymerization, while chain end-group analysis provides evidence supporting an atom-transfer radical polymerization mechanism.

Instantaneous Directional Growth of Block Copolymer Nanowires During Heterogeneous Radical Polymerization (HRP)

Polymeric nanowires that consist of ultrahigh molecular weight block copolymers were instantaneously prepared via one-step surfactant-free heterogeneous radical polymerization (HRP). Under heterogeneous reaction and initiator-starvation conditions, the sequential copolymerization of hydrophilic and hydrophobic monomers facilitates the formation of amphiphilic ultrahigh molecular weight block copolymers, which instantaneously assemble to polymeric nanowires. As polymerization progresses, initially formed nanoparticles exhibit the directional growth due to localized repulsive forces of hydrophilic blocks and confinement of the hydrophobic blocks that adopt favorable high aspect ratio nanowire morphologies. Using one-step synthetic approach that requires only four ingredients (water as a solvent, two polymerizable monomers (one hydrophilic and one hydrophobic), and water-soluble initiator), block copolymer nanowires ∼70 nm in diameter and hundreds of microns in length are instantaneously grown. For example, when 2-(N,N-dimethylamino)ethyl methacrylate (DMAEMA) and styrene (St) were copolymerized, high aspect ratio nanowires consist of ultrahigh (>10(6) g/mol) molecular weight pDMAEMA-b-St block copolymers and the presence of temperature responsive pDMAEMA blocks facilitates nanowire diameter changes as a function of temperature. These morphologies may serve as structural components of the higher order biological constructs at micro and larger length scales, ranging from single strand nanowires to engineered biomolecular networks capable of responding to diverse and transient environmental signals, and capable of dimensional changes triggered by external stimuli.

Block Copolymerization of Lactide and an Epoxide Facilitated by a Redox Switchable Iron‐Based Catalyst

AbstractA cationic iron(III) complex was active for the polymerization of various epoxides, whereas the analogous neutral iron(II) complex was inactive. Cyclohexene oxide polymerization could be “switched off” upon in situ reduction of the iron(III) catalyst and “switched on” upon in situ oxidation, which is orthogonal to what was observed previously for lactide polymerization. Conducting copolymerization reactions in the presence of both monomers resulted in block copolymers whose identity can be controlled by the oxidation state of the catalyst: selective lactide polymerization was observed in the iron(II) oxidation state and selective epoxide polymerization was observed in the iron(III) oxidation state. Evidence for the formation of block copolymers was obtained from solubility differences, GPC, and DOSY‐NMR studies.

Block Copolymerization of Lactide and an Epoxide Facilitated by a Redox Switchable Iron-Based Catalyst.

A cationic iron(III) complex was active for the polymerization of various epoxides, whereas the analogous neutral iron(II) complex was inactive. Cyclohexene oxide polymerization could be "switched off" upon in situ reduction of the iron(III) catalyst and "switched on" upon in situ oxidation, which is orthogonal to what was observed previously for lactide polymerization. Conducting copolymerization reactions in the presence of both monomers resulted in block copolymers whose identity can be controlled by the oxidation state of the catalyst: selective lactide polymerization was observed in the iron(II) oxidation state and selective epoxide polymerization was observed in the iron(III) oxidation state. Evidence for the formation of block copolymers was obtained from solubility differences, GPC, and DOSY-NMR studies.

Solvothermal Vapor Annealing of Lamellar Poly(styrene)-block-poly(d,l-lactide) Block Copolymer Thin Films for Directed Self-Assembly Application.

Solvothermal vapor annealing (STVA) was employed to induce microphase separation in a lamellar forming block copolymer (BCP) thin film containing a readily degradable block. Directed self-assembly of poly(styrene)-block-poly(d,l-lactide) (PS-b-PLA) BCP films using topographically patterned silicon nitride was demonstrated with alignment over macroscopic areas. Interestingly, we observed lamellar patterns aligned parallel as well as perpendicular (perpendicular microdomains to substrate in both cases) to the topography of the graphoepitaxial guiding patterns. PS-b-PLA BCP microphase separated with a high degree of order in an atmosphere of tetrahydrofuran (THF) at an elevated vapor pressure (at approximately 40-60 °C). Grazing incidence small-angle X-ray scattering (GISAXS) measurements of PS-b-PLA films reveal the through-film uniformity of perpendicular microdomains after STVA. Perpendicular lamellar orientation was observed on both hydrophilic and relatively hydrophobic surfaces with a domain spacing (L0) of ∼32.5 nm. The rapid removal of the PLA microdomains is demonstrated using a mild basic solution for the development of a well-defined PS mask template. GISAXS data reveal the through-film uniformity is retained following wet etching. The experimental results in this article demonstrate highly oriented PS-b-PLA microdomains after a short annealing period and facile PLA removal to form porous on-chip etch masks for nanolithography application.