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A method of non-aqueous capillary zone electrophoresis has been optimized for the characterization of five functionalized mixed-ligand iridium(III) polypyridyl complexes and four functionalized ruthenium(II) bis-terpyridine complexes. Their mobilities, the relation to their molar mass, and the capillary lifetime (measured in number of injections) have been determined

A variety of organocatalysts has been surveyed in the ring opening polymerization of trimethylene carbonate. Excellent control was found for several of these catalysts yielding well-defined polycarbonates with molecular weights up to 50,000 g mol(-1), polydispersities below 1.08, and high end-group fidelity. Melt or bulk polymerization was accomplished without loss of control of molecular weight or polydispersity, and random ester-carbonate bulk polymerizations were also demonstrated. Furthermore, by combining disparate polymerization techniques using bifunctional initiators, the mild polymerization conditions allow for the preparation of new block copolymers. Hydrogen-bond activation of monomer and initiator/propagating species is proposed as the underlying mechanism, which can be tuned to mitigate adverse side reactions.

Applications of analytical ultracentrifugation in the field of synthetic polymers have followed a clearly increasing trend in the past few years, concerning the variety of investigated samples, experimental approaches, and methods of data analysis. We report a characterization study of two metallo-supramolecular diblock copolymers with different block lengths and of a chain extended metallo-supramolecular polymer. The analysis of sedimentation velocity and sedimentation equilibrium profiles was discussed in detail and the results were compared to each other, to determine the molar mass distribution and the state of association in solution. A simple method for determining the average translational diffusion coefficients is proposed and discussed relative to other methods. The average values of the molar mass and sedimentation coefficient distributions, the average friction coefficients, and size information were obtained and discussed.

1,5,7-Triazabicyclo[4.4.0]dec-5-ene (TBD), N-methyl-TBD (MTBD), and 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) are effective organocatalysts for the ring-opening polymerization (ROP) of cyclic esters such as lactide (LA), δ-valerolactone (VL), and e-caprolactone (CL). TBD is shown to polymerize LA, VL, and CL in a fast and controlled manner, whereas MTBD and DBU polymerized LA and addition of a thiourea cocatalyst led to the ROP of VL and CL being achieved. Each of the catalysts produced polymers displaying high end group fidelity, good correlation between theoretical and observed molecular weight, and linear relationships between conversion and molecular weight. The enhanced activity of TBD relative to MTBD and DBU is attributed to its bifunctionality, enabling the simultaneous activation of both the cyclic ester monomer and the alcohol group of the initiator/propagating species. Temperature-dependent NMR studies generated individual association constants for MTBD with benzyl alcohol and thiourea with VL. ...

The structural flexibility and efficacy of thiourea−amine catalysts for the supramolecular activation and ring-opening polymerization (ROP) of lactide are described. The nature of the hydrogen bonding group and its strength as well as the steric congestion have been altered, leading to shorter polymerization times, better control, and pathways to influence the stereochemistry of the resulting polymer. The tolerance to functionality and the mild conditions of the ROP mechanism allow for block copolymer synthesis by combination of nitroxide-mediated polymerization as well as reversible addition fragmentation and chain transfer polymerization using dual-headed initiators. Tandem hydrogen bond activation to organocatalyze ROP of lactide is an effective, versatile means to generate polymers with predictable molecular weights, narrow polydispersities, control of microstructure and a variety of complex architectures and block copolymers.

An organocatalytic approach to living and condensation polymerization using N -heterocyclic carbenes as nucleophilic catalysts is detailed. The N -heterocyclic carbene catalyst platform is extremely versatile with the nature of the substituents having a pronounced effect upon catalyst stability and activity towards different substrates. Rapid screening of libraries of catalysts provided a basic understanding of catalyst structure (sterics, electronics, etc.) as it influences the polymerization rate, control, substrate and range of molecular weights. ROP from an immiscible ionic liquid (precatalyst reservoir) and a THF solution of monomer and initiator is presented as a simplified method of carbene formation. In situ activation of the ionic liquid generated a nucleophilic N -heterocyclic carbene, which migrates to the organic phase effecting ROP. Other simplified methods of generating carbene thermally from carbene adducts are also presented as polymerization catalysts.

A library of metallo-supramolecular block copolymers has been synthesized, and the micellization behavior of those copolymers in water has been studied. A series of amphiphilic block copolymers composed of poly(styrene) and poly(ethylene oxide) joined by a bis(terpyridine) ruthenium complex were prepared. The micelles formed from these copolymers were characterized by AFM and TEM. The results evidence that the classical scaling laws relating the micelle size to the size of the hydrophobic block are not valid for metallo-supramolecular copolymers. This different behavior is due to electrostatic repulsions between the charged and bulky metal-ligand complexes present at the core-corona interface. If those repulsions are screened by increasing the ionic strength during micelle formation, the classical behavior is observed.

Nanoporous thin polymer films have been produced by a simple two-step approach using metallo-supramolecular block copolymers as the starting materials. The first step is the self-assembly of the copolymer, yielding cylindrical microdomains oriented normal to the substrate. The second step involves the opening of the metal-ligand complex located at the junction of the two blocks by redox chemistry to release the minor block and create the pores (see Figure).

A supramolecular AB diblock copolymer has been prepared by the sequential self-assembly of terpyridine end-functionalized polymer blocks by using Ru(III)/Ru(II) chemistry. By this synthetic strategy a hydrophobic poly(ferrocenylsilane) (PFS) was attached to a hydrophilic poly(ethylene oxide) (PEO) block to give an amphiphilic metallo-supramolecular diblock copolymer (PEO/PFS block ratio 6:1). This compound was used to form micelles in water that were characterized by a combination of dynamic and static light scattering, transmission electron microscopy, and atomic force microscopy. These complementary techniques showed that the copolymers investigated form rod-like micelles in water; the micelles have a constant diameter but are rather polydisperse in length, and light scattering measurements indicate that they are flexible. Crystallization of the PFS in these micelles was observed by differential scanning calorimetry, and is thought to be the key behind the formation of rod-like structures. The cylindrical micelles can be cleaved into smaller rods whenever the temperature of the solution is increased or they are exposed to ultrasound.

Micelles prepared from amphiphilic block copolymers in which a poly(styrene) segment is connected to a poly(ethylene oxide) block via a bis-(2,2':6',2"-terpyridine-ruthenium) complex have been intensely studied. In most cases, the micelle populations were found to be strongly heterogeneous in size because of massive micelle/ micelle aggregation. In the study reported in this article we tried to improve the homogeneity of the micelle population. The variant preparation procedure developed, which is described here, was used to prepare two "protomer"-type micelles: PS20-[Ru]PEO70 and PS20-[Ru]-PEO375. The dropwise addition of water to a solution of the compounds in dimethylformamide was replaced by the controlled addition of water by a syringe pump. The resulting micelles were characterized by sedimentation velocity and sedimentation equilibrium analyses in an analytical ultracentrifuge and by transmission electron microscopy of negatively stained samples. Sedimentation analysis showed virtually unimodal size distributions, in contrast to the findings on micelles prepared previously. PS20-[Ru]PEO70 micelles were found to have an average molar mass of 318,000 g/mol (corresponding to 53 protomers per micelle, which is distinctly less than after micelle preparation by the standard method) and an average hydrodynamic diameter (d(h)) of 18 nm. For PS20-[Ru]-PEO375 micelles, the corresponding values were M = 603,000 g/mol (31 protomers per micelle) and dh = 34 nm. The latter particles were found to be identical to the "equilibrium" micelles prepared in pure water. Both micelle types had a very narrow molar mass distribution but a much broader distribution of s values and thus of hydrodynamic diameters. This indicates a conformational heterogeneity that is stable on the time scale of sedimentation velocity analysis. The findings from electron microscopy were in disagreement with those from the sedimentation analysis both in average micelle diameter and in the width of the distributions, apparently because of imperfections in the staining procedure. The preparation procedure described also may be useful in micelle formation from other types of protomers. (C) 2004 Wiley Periodicals, Inc.

The formation of asymmetric bis-complexes, based on terpyridine ligands and ruthenium ions, is described as a powerful tool for the self-assembly of polymer blocks end-functionalized with terpyridine units. This is illustrated in this contribution for the synthesis of amphiphilic metallo-supramolecular block copolymers, which are further used to produce aqueous micelles. Finally, the reversibility of the supramolecular bond opens new avenues for the preparation and manipulation of these nano-objects. [on SciFinder (R)]

A metallo-supramol. ABC triblock copolymer contg. a bis(2,2':6',2''-terpyridine)ruthenium(II) complex as a supramol. connection between the constituting polystyrene-block-poly(2-vinylpyridine) diblock and poly(ethylene oxide) block (PS32-b-P2VP13-[Ru]-PEO70) was prepd. The copolymer was further utilized to prep. aq. micelles consisting of a PS core, a pH-sensitive P2VP shell, and a PEO corona. The micelles were characterized by a combination of dynamic light scattering, TEM, and at. force microscopy. Spherical micelles and a minor fraction of bigger aggregates were obsd. by these three independent techniques. The pH sensitivity of the P2VP shell was demonstrated and the reversibility of the metallo-supramol. complex was studied utilizing a strong competitive ligand. The bis(2,2':6',2''-terpyridine)ruthenium(II) connection was stable, and the integrity of the triblock copolymer was kept in the aq. environment even at extreme pH values. This complex is opened whenever a large excess of a strong competitive ligand was added, allowing the release of PEO coronal chains; the metal complex was then re-formed, even using a different metal ion. This last feature will be used in the near future as a tool to manipulate or to chem. modify nano-objects such as micelles. These micelles attractive for encapsulation and/or release of active species

[reaction: see text] An organocatalytic route to narrowly dispersed poly(carbosiloxanes) of predictable molecular weight and end group fidelity is described. N-Heterocyclic carbenes (NHC) and 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) catalyze the ring opening of cyclic carbosiloxanes. The pK(b) of the catalyst is important in preventing adverse transetherification reactions and obtaining well-defined polymers. Mechanistic studies indicate that hydrogen bonding to TBD or the NHC activates alcohols or silanols for ring-opening reactions.

1,5,7-Triazabicyclo[4.4.0]dec-5-ene (TBD) is an effective organocatalyst for acyl transfer as well as the ring-opening polymerization of cyclic esters. Its high activity is attributed to its ability to simultaneously activate both esters and alcohols, as demonstrated in a model reaction. This unique mechanism makes TBD a remarkably simple example of a bifunctional catalyst. The simplicity of the reaction conditions, the ready commercial availability of the catalyst, and its high activity provide an accessible methodology to allow future studies of tailor-made polyesters.

The focus of the presented research lies on the synthesis of novel charged iridium(III) compounds with potential applications in light-emitting electrochemical cells. The design involves iridium(III)-based materials with polymer side-chains leading to linear light-emitting polymer arrangements.To study the electro-optical properties of such light-emitting polymers conventional and combinatorial deposition methods are used. Straightforward screening approaches are introduced. The combinatorial efforts engage the processing via inkjet printing and the screening of the optical properties using plate reader technologies based on steady state UV-vis and fluorescence. Furthermore, the morphological properties are investigated using optical interferometry and atomic force microscopy (AFM). Overall it can be shown that novel materials can be deposited revealing high-quality thin films, which allow the screening of electro-optical features using combinatorial methods. Some initial local current density studies by AFM have also been performed to characterize the current injection and transport properties of the novel materials.

In aqueous solutions, amphiphilic block copolymers in which a polystyrene (PS) segment is connected to a poly(ethylene oxide) (PEO) block via a bis(2,2':6',2"-terpyridine ruthenium) complex can form micelles. Such micelles of the protomer type PS20-[Ru]-PEO70, according to the preparation procedure representing frozen micelles, were studied by sedimentation velocity and sedimentation equilibrium analysis in an analytical ultracentrifuge and by transmission electron microscopy, with different techniques applied for the sample preparation. The particles obtained were surprisingly multifarious in size. In ultracentrifugation experiments performed at relatively low salt concentrations, the distributions of the sedimentation coefficient s(20,w) showed a pronounced peak at 9.6 S and a broad, only partly separated second peak around 14 S. The molar mass of the particles at the peak was around 430,000 g/mol, corresponding to an aggregation number of approximately 85. The average hydrodynamic diameter of the particles in the peak fraction was approximately 13 run. In electron micrographs of negatively stained samples, spheres of diameters between 10 and 25 nm were the most abundant particles, but larger ones with a wide size range were also visible. The latter particles apparently were composed of smaller ones. The data from both sedimentation analysis and electron microscopy showed that (1) the studied compound formed primary micelles of diameters around 20 nm and (2) the primary micelles had a tendency toward aggregation. (C) 2003 Wiley Periodicals, Inc.

Diblock copolymers of poly(styrene) and poly(ethylene oxide) were prepared utilizing a bisterpyridine ruthenium complex as non-covalent interaction for the connection of the two blocks. Apart from the synthesis and characterization of four metallo-supramolecular block copolymers, first studies on the thermal properties of the block copolymers have been performed. A complex crystallization behavior was observed and is described in a qualitative fashion. The influence of the metal complex on the thermal stability of the metallo-supramolecular block copolymers remains a question for further investigation.

1,5,7-Triazabicyclo[4.4.0]dec-5-ene (TBD) is an effective organocatalyst for acyl transfer as well as the ring-opening polymerization of cyclic esters. Its high activity is attributed to its ability to simultaneously activate both esters and alcohols, as demonstrated in a model reaction. This unique mechanism makes TBD a remarkably simple example of a bifunctional catalyst. The simplicity of the reaction conditions, the ready commercial availability of the catalyst, and its high activity provide an accessible methodology to allow future studies of tailor-made polyesters.

A versatile, metal-free, organocatalytic approach to the living ring-opening polymerization of lactide using a bifunctional thiourea-tertiary amine catalyst is described. Mild and highly selective polymerization conditions produced poly(lactides) with predictable molecular weights and extremely narrow polydispersities ( approximately 1.05), characteristic of a living polymerization. The extraordinary selectivity of this catalyst system for polymerization relative to transesterification is remarkably unusual. The low polydispersities and exceptional control observed are a consequence of selective transesterification of lactide relative to the open chain esters. Presumably, the ring strain of lactide provides both a driving force for the polymerization and a kinetic preference for polymerization relative to transesterification with catalyst. We postulate that the initiating/propagating alcohol is activated by acid-base interaction with the tertiary amine moiety and the carbonyl of the lactide monomer is simultaneously activated by hydrogen bonding to the thiourea moiety of the catalyst.

Extended core discotic molecules self-assemble in water by different secondary interactions to give well-defined, helical columns in which the chirality of one chiral molecule is transferred to on average 12 achiral molecules.

New sterically encumbered N-heterocyclic carbene catalysts were synthesized and used to polymerize rac-lactide to give highly isotactic polylactide or meso-lactide to give heterotactic polylactide.