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Krzysztof Matyjaszewski

Publications and source records attributed to Krzysztof Matyjaszewski.

At least 19 recordsLinked to original sources
PubMed2007

Synthesis and in situ atomic force microscopy characterization of temperature-responsive hydrogels based on poly(2-(dimethylamino)ethyl methacrylate) prepared by atom transfer radical polymerization.

Well-defined copolymers of 2-(dimethylamino)ethyl methacrylate (DMAEMA) and benzophenone methacrylate (BPMA) with different compositions were synthesized via atom transfer radical polymerization. The molecular weights of these copolymers were Mn approximately 30 000 g/mol, while the BPMA content varied from 2.5 to 10 mol %. The copolymers with a low content of BPMA (2.5 and 5 mol %) exhibited a sharp thermal transition at 33-36 degrees C in aqueous solution. A hydrogel was immobilized and patterned on a silicon wafer via UV treatment of the spin-coated polymer layer using a photomask technique. The thermoresponsive behavior of the patterned polymer gel was quantitatively investigated by variable temperature in situ contact mode atomic force microscopy, which revealed the presence of two lower critical solution temperature regions. One region was between 25 and 30 degrees C, corresponding to the topmost layer of the hydrogel film, and the other region, around 40 degrees C, corresponded to the bulk of the hydrogel. Concurrent lateral force microscopy measurements revealed that, just above the transition temperature, the bulk region exhibited enhanced friction.

Free Radicals↗
PubMed2006

Highly active copper-based catalyst for atom transfer radical polymerization.

Atom transfer radical polymerization (ATRP) generally requires a catalyst/initiator molar ratio of 0.1 to 1 and catalyst/monomer molar ratio of 0.001 to 0.01 (i.e., catalyst concentration: 1000-10,000 ppm versus monomer). Herein, we report a new copper-based complex CuBr/N,N,N',N'-tetrakis(2-pyridylmethyl)ethylenediamine (TPEN) as a versatile and highly active catalyst for acrylic, methacrylic, and styrenic monomers. The catalyst mediated ATRP at a catalyst/initiator molar ratio of 0.005 and produced polymers with well-controlled molecular weights and low polydispersities. ATRP occurred even at a catalyst/initiator molar ratio as low as 0.001 with copper concentration in the produced polymers as low as 6-8 ppm (catalyst/monomer molar ratio = 10(-5)). The catalyst structures were studied by X-ray diffraction and NMR spectroscopy. The activator CuIBr/TPEN existed in solution as binuclear and mononuclear complexes in equilibrium but as a binuclear complex in its single crystals. The deactivator CuIIBr2/TPEN complex was mononuclear. High stability and appropriate KATRP (ATRP equilibrium constant) were found crucial for the catalyst working under high dilution or in coordinating solvents/monomers. This provides guidance for further design of highly active ATRP catalysts.

Journal Article↗
PubMed2006

Low polydispersity star polymers via cross-linking macromonomers by ATRP.

A new method for the synthesis of star polymers with high molecular weight and narrow molecular weight distribution (MWD) is presented. The star copolymers were prepared by atom transfer radical (co)polymerization (ATRP) of linear macromonomers with divinyl cross-linkers using low molar mass initiator. In contrast to prior "arm-first" procedures with macroinitiators, by using lower ratio of concentration of initiator to MM, the star polymers contained less initiating sites in the core, which decreased the extent of star-star coupling reactions and resulted in formation of star polymers with narrower MWD. Addition of more cross-linker and initiator during the reaction increased the star molecular weight and star yield while retaining the narrow MWD of the star polymer. For example, we synthesized a star polymer with molecular weight Mn = 466 000 g/mol and Mw/Mn < 1.2 in >98% yield.

Journal Article↗
PubMed2006

A scanning force microscopy study on the motion of single brush-like macromolecules on a silicon substrate induced by coadsorption of small molecules.

Scanning force microscopy was applied to visualise the motion of single poly(butanoate-ethylmethacrylate)-graft-poly(n-butyl acrylate) molecules on silicon and SrTiO(3) substrates. Macromolecular mobility was induced by cyclic exposure of the wafers with the adsorbed brush-like macromolecules to water and alcohol vapours. Exposure to saturated alcohol vapour induced collapse of the adsorbed individual polymer chains while exposure to saturated water vapour promoted their extension. The characteristic times of both conformational changes were long enough that it was possible to visualise step-by-step the morphology transformation in situ by means of an environment-controlled scanning force microscope. Several successive collapse-decollapse cycles were recorded, and small diffusive shifts of the macromolecular position on the substrate were detected after each cycle. Manipulating and visualising single polymer molecules in situ and real time on a silicon substrate opens up new possibilities for the controlled structure formation in ultrathin polymer films. As shown on the sample of a faceted SrTiO(3) wafer, upon extension the brush-like molecules can crawl or extend along nanoscopic surface structures. Silicon can be structured both topographically and chemically at dimensions comparable to those of single polymer molecules with a variety of fabrication techniques ranging from well established conventional silicon micro- nano- machining to new tools constantly developed as dip-pen and nanoimprint lithography.

Journal Article↗
PubMed2006

Diminishing catalyst concentration in atom transfer radical polymerization with reducing agents.

The concept of initiators for continuous activator regeneration (ICAR) in atom transfer radical polymerization (ATRP) is introduced, whereby a constant source of organic free radicals works to regenerate the Cu(I) activator, which is otherwise consumed in termination reactions when used at very low concentrations. With this technique, controlled synthesis of polystyrene and poly(methyl methacrylate) (Mw/Mn < 1.2) can be implemented with catalyst concentrations between 10 and 50 ppm, where its removal or recycling would be unwarranted for many applications. Additionally, various organic reducing agents (derivatives of hydrazine and phenol) are used to continuously regenerate the Cu(I) activator in activators regenerated by electron transfer (ARGET) ATRP. Controlled polymer synthesis of acrylates (Mw/Mn < 1.2) is realized with catalyst concentrations as low as 50 ppm. The rational selection of suitable Cu complexing ligands {tris[2-(dimethylamino)ethyl]amine (Me6TREN) and tris[(2-pyridyl)methyl]amine (TPMA)} is discussed in regards to specific side reactions in each technique (i.e., complex dissociation, acid evolution, and reducing agent complexation). Additionally, mechanistic studies and kinetic modeling are used to optimize each system. The performance of the selected catalysts/reducing agents in homo and block (co)polymerizations is evaluated.

Catalysis↗
PubMed2006

Development of an ab initio emulsion atom transfer radical polymerization: from microemulsion to emulsion.

Atom transfer radical polymerization (ATRP) has been successfully extended to an ab initio emulsion system using a "two-step" procedure, in which the final emulsion polymerization system was formed by adding monomer to an ongoing microemulsion ATRP. The newly developed AGET (activators generated by electron transfer) initiation technique was employed in the first stage of this ab initio ATRP. It allows using oxidatively stable Cu(II) species that is reduced in situ by ascorbic acid. The surfactant concentration in the final emulsion system was efficiently decreased to approximately 2 wt % (approximately 10 wt % vs monomer) by decreasing the catalyst concentration and changing the ratio of the monomer added at the microemulsion stage to the monomer added during the second stage. This two-step procedure avoids the necessity of transporting catalysts through the aqueous media during polymerization, resulting in a controlled emulsion polymerization, as evidenced by a linear first-order kinetic plot and formation of a polymer with a relatively narrow molecular weight distribution (Mw/Mn = 1.2-1.4). The polymerization typically reached 70-90% monomer conversion in 5-6 h. The resulting polymer had high chain-end functionality and was successfully chain extended to form in situ block copolymers by adding the second monomer to an ongoing emulsion polymerization. The stable latex from the ab initio emulsion ATRP had a particle size approximately 120 +/- 10 nm.

Emulsions↗
PubMed2006

Inverse miniemulsion ATRP: a new method for synthesis and functionalization of well-defined water-soluble/cross-linked polymeric particles.

A new methodology for the synthesis and functionalization of nanometer-sized colloidal particles consisting of well-defined, water-soluble, functional polymers with narrow molecular weight distribution (M(w)/M(n) < 1.3) was developed, utilizing atom transfer radical polymerization (ATRP) of water-soluble monomers in an inverse miniemulsion. The optional introduction of a disulfide-functionalized cross-linker allowed for the synthesis of cross-linked (bio)degradable nanogels. Dynamic light scattering (DLS) and atomic force microscopy (AFM) measurements indicated that these particles possessed excellent colloidal stability. ATRP in inverse miniemulsion led to materials with several desirable features. The colloidal particles preserved a high degree of halogen chain-end functionality, which enabled further functionalization. Cross-linked nanogels with a uniformly cross-linked network were prepared. They were degraded to individual polymeric chains with relatively narrow molecular weight distribution (M(w)/M(n) < 1.5) in a reducing environment. Higher colloidal stability, higher swelling ratios, and better controlled degradability indicated that the nanogels prepared by ATRP were superior to their corresponding counterparts prepared by conventional free radical polymerization (RP) in inverse miniemulsion.

Journal Article↗
PubMed2006

Adsorption-induced scission of carbon-carbon bonds.

Covalent carbon-carbon bonds are hard to break. Their strength is evident in the hardness of diamonds and tensile strength of polymeric fibres; on the single-molecule level, it manifests itself in the need for forces of several nanonewtons to extend and mechanically rupture one bond. Such forces have been generated using extensional flow, ultrasonic irradiation, receding meniscus and by directly stretching a single molecule with nanoprobes. Here we show that simple adsorption of brush-like macromolecules with long side chains on a substrate can induce not only conformational deformations, but also spontaneous rupture of covalent bonds in the macromolecular backbone. We attribute this behaviour to the fact that the attractive interaction between the side chains and the substrate is maximized by the spreading of the side chains, which in turn induces tension along the polymer backbone. Provided the side-chain densities and substrate interaction are sufficiently high, the tension generated will be strong enough to rupture covalent carbon-carbon bonds. We expect similar adsorption-induced backbone scission to occur for all macromolecules with highly branched architectures, such as brushes and dendrimers. This behaviour needs to be considered when designing surface-targeted macromolecules of this type-either to avoid undesired degradation, or to ensure rupture at predetermined macromolecular sites.

Journal Article↗
PubMed2006

Determination of equilibrium constants for atom transfer radical polymerization.

Atom transfer radical polymerization (ATRP) equilibrium constants (K(ATRP)) were determined using modified Fischer's equations for the persistent radical effect. The original Fischer's equations could be used only for low conversion of Cu(I) to X-Cu(II) and consequently for relatively low values of K(ATRP). At higher conversion to X-Cu(II) (>10%) and for larger values of K(ATRP) (>10(-)(7)), modified equations that take into account the changes in catalyst and initiator concentrations should be used. The validity of new equations was confirmed by detailed kinetic simulations. UV-vis spectrometric and GC measurements were used to follow the evolution of X-Cu(II) species and the initiator concentration, respectively, and to successfully determine values of K(ATRP) for several catalysts and alkyl halides. The effect of structure on reactivities of ATRP components is presented.

Journal Article↗
PubMed2006

Flow-enhanced epitaxial ordering of brush-like macromolecules on graphite.

Long-range orientational order in monolayers of brush-like macromolecules was achieved during spreading of a polymer melt on the surface of highly oriented pyrolytic graphite. The combination of wetting-induced flow and epitaxial adsorption of poly(n-butylacrylate) side chains on graphite led to the formation of large domains of uniaxially oriented rodlike molecules. The domain size varied from ca. 1 to 10 microm which is noticeably larger than the submicrometer-sized mosaic domains typically observed upon adsorption from solution. The increase in the degree of order is attributed to the flow-enhanced diffusion of the macromolecules within spreading monolayers which facilitates the epitaxial alignment of the large macromolecules. The diffusion coefficient was shown to increase linearly with the spreading rate. Even though the ordering occurred during flow, no correlation was observed between the molecular orientation and the flow direction. Thus, the role of the flow was not to induce the molecular orientation but to facilitate the intrinsic ordering process. This finding can inspire and lead to new strategies for constructing large scale ordered structures on surfaces.

Journal Article↗
PubMed2005

Oil-in-water emulsions stabilized by highly charged polyelectrolyte-grafted silica nanoparticles.

Fully sulfonated poly(styrenesulfonate) brushes were grown from the surface of colloidal silica particles and used to prepare stable trichloroethylene-in-water and heptane-in-water Pickering emulsions. These particles were highly charged and colloidally stable in water but could not be dispersed in trichloroethylene or heptane. Both two-phase (emulsion plus neat water) and three-phase (emulsion separating neat oil and water phases) systems were observed, with water-continuous emulsion phases in all cases. Emulsion phases containing as much as 83% (v/v) oil were stable for over six months. Poly(styrenesulfonate)-grafted particles were very efficient emulsifiers; stable emulsion phases were prepared when using as little as 0.04 wt% particles. The emulsifying effectiveness of the poly(styrenesulfonate)-grafted silica particles can be attributed to the hydrophobicity of the vinylic polymer backbone that makes this highly charged polyelectrolyte unusually surface active at the oil/water interface.

Journal Article↗
PubMed2005

Self-assembly of pODMA-b-ptBA-b-pODMA triblock copolymers in bulk and on surfaces. A quantitative SAXS/AFM comparison.

The phase state of a series of poly(n-octadecyl methacrylate)-b-poly(tert-butyl acrylate)-b-poly(n-octadecyl methacrylate) (pODMA-b-ptBA-b-pODMA) triblock copolymers, synthesized through atom transfer radical polymerization, has been investigated in bulk and on surfaces using small-angle X-ray scattering and atomic force microscopy, respectively. The mean-field theory was employed to construct the bulk phase diagram. Excellent agreement was found between the bulk and surface morphologies as well as for the domain spacing (domain spacing scaled as d approximately equal to N(0.64)), suggesting that the strong polymer-polymer interactions in bulk are also the dominant interactions on surfaces.

Journal Article↗
PubMed2005

Molecular visualization of conformation-triggered flow instability.

A new type of flow fingering instability was observed in monolayer-thick polymer films as they spread on a solid substrate. Tracing the movement of individual molecules by atomic force microscopy enabled us to follow the development of the flow instability on the molecular level and to understand the underlying physical mechanism. The fingering instability was observed to be triggered by conformational changes of brushlike macromolecules in response to the pressure gradient driving the flow.

Journal Article↗
PubMed2005

Synthesis of mesoporous carbons using ordered and disordered mesoporous silica templates and polyacrylonitrile as carbon precursor.

Mesoporous carbons were synthesized from polyacrylonitrile (PAN) using ordered and disordered mesoporous silica templates and were characterized using transmission electron microscopy (TEM), powder X-ray diffraction, nitrogen adsorption, and thermogravimetry. The pores of the silica templates were infiltrated with carbon precursor (PAN) via polymerization of acrylonitrile from initiation sites chemically bonded to the silica surface. This polymerization method is expected to allow for a uniform filling of the template with PAN and to minimize the introduction of nontemplated PAN, thus mitigating the formation of nontemplated carbon. PAN was stabilized by heating to 573 K under air and carbonized under N2 at 1073 K. The resulting carbons exhibited high total pore volumes (1.5-1.8 cm3 g(-1)), with a primary contribution of the mesopore volume and with relatively low microporosity. The carbons synthesized using mesoporous templates with a 2-dimensional hexagonal structure (SBA-15 silica) and a face-centered cubic structure (FDU-1 silica) exhibited narrow pore size distributions (PSDs), whereas the carbon synthesized using disordered silica gel template had broader PSD. TEM showed that the SBA-15-templated carbon was composed of arrays of long, straight, or curved nanorods aligned in 2-D hexagonal arrays. The carbon replica of FDU-1 silica appeared to be composed of ordered arrays of spheres. XRD provided evidence of some degree of ordering of graphene sheets in the carbon frameworks. Elemental analysis showed that the carbons contain an appreciable amount of nitrogen. The use of our novel infiltration method and PAN as a carbon precursor allowed us to obtain ordered mesoporous carbons (OMCs) with (i) very high mesopore volume, (ii) low microporosity, (iii) low secondary mesoporosity, (iv) large pore diameter (8-12 nm), and (v) semi-graphitic framework, which represent a desirable combination of features that has not been realized before for OMCs.

Acrylic Resins↗
PubMed2005

Long-range ordered thin films of block copolymers prepared by zone-casting and their thermal conversion into ordered nanostructured carbon.

Large-scale alignment of lamellae in thin films of diblock copolymers containing polyacrylonitrile and poly(n-butyl acrylate) was achieved by casting copolymer solution on a silicon substrate moved away at a constant speed from the casting nozzle (zone-casting). Grazing incidence small-angle X-ray scattering revealed that the lamellae, which were perpendicular to the substrate, were also aligned over macroscopic scale in the direction perpendicular to the casting direction. Such long-range ordered block copolymer films were then converted by pyrolysis into nanostructured carbons, with excellent preservation of lamellar morphology and orientation.

Acrylates↗
PubMed2005

Preparation of homopolymers and block copolymers in miniemulsion by ATRP using activators generated by electron transfer (AGET).

A new initiating/catalytic system for atom transfer radical polymerization (ATRP) is reported. This system starts with alkyl halides as initiators and transition metal complexes in their oxidatively stable state (e.g., Cu(II)Br2/ligand) as catalysts. The activators are generated by electron transfer (AGET) without involvement of initiating organic radicals. AGET ATRP has a significant advantage over simultaneous reverse and normal initiation (SR&NI) ATRP, because it provides a simple route for synthesizing pure polymers with complex architectures such as star copolymers, block copolymers, etc. Furthermore, AGET ATRP can be also successfully carried out in miniemulsion. Homopolymers and pure block copolymers were successfully synthesized via ATRP in miniemulsion using AGET ATRP. The final products were analyzed via two-dimensional chromatography, which combines high performance liquid chromatography (HPLC) and gel permeation chromatography (GPC). The resulting chromatograms showed that pure linear block copolymers and star block copolymers were prepared without the presence of any homopolymers.

Journal Article↗
PubMed2005

On the shape of bottle-brush macromolecules: systematic variation of architectural parameters.

We measured the form factor of bottle-brush macromolecules under good solvent conditions with small-angle neutron scattering and static light scattering. The systems under investigation are brushes, synthesized via the grafting-from route, built from a poly(alkyl methacrylate) backbone to which poly(n-butyl acrylate) side chains are densely grafted. The aim of our work is to study how the systematic variation of structural parameters such as the side chain length and backbone length change the conformation of the polymer brushes in solution. All spectra can be consistently described by a model, considering the bottle-brush polymers as flexible rods with internal density fluctuations. Parameters discussed are (1) the contour length per main chain monomer l(b), (2) the fractal dimension of the side chains Ds, as well as (3) the fractal dimension D, and (4) the Kuhn length lambdak of the overall brush. l(b)=0.253+/-0.008 nm is found to be independent of the side chain length and equal to the value found for the bare main chain, indicating a strongly stretched conformation for the backbone due to the presence of the side chains. The fractal dimension of the side chains is determined to be Ds=1.75+/-0.07 which is very close to the value of 10.588 approximately 1.70 expected for a three-dimensional self-avoiding random walk (3D-SAW) under good solvent conditions. On larger length scales the overall brush appears to be a 3D-SAW itself (D=1.64+/-0.08) with a Kuhn-step length of lambdak=70+/-4 nm. The value is independent of the side chain length and 46 times larger than the Kuhn length of the bare backbone (lambdak=1.8+/-0.2 nm). The ratio of Kuhn length to brush diameter lambda(k)d>or=20 determines whether lyotropic behavior can be expected or not. Since longer side chains do not lead to more persistent structures, lambda(k)d decreases from 8 to 4 with increasing side chain length and lyotropic behavior becomes unlikely.

Journal Article↗