Helmut Schlaad | Universitaet Potsdam (original) (raw)

Papers by Helmut Schlaad

Macromolecules, Jan 18, 2000

The addition of 1,1-diphenylethylene (DPE) and 1,1-bis(4-methylphenyl)ethylene (DTE) to hydrochlo... more The addition of 1,1-diphenylethylene (DPE) and 1,1-bis(4-methylphenyl)ethylene (DTE) to hydrochlorinated isobutylene (IB) n-mers, H-[IB] n-Cl (n ) 2, 3, 4, 36), in the presence of TiCl4, was investigated in hexane (Hex)/methyl chloride (MeCl) 60/40 (v/v) at -80°C using on-line visible spectroscopy. The apparent equilibrium constants of capping/decapping, Ke, and the apparent rate constants of capping, kcKi, have been determined. The Ke value was found to be similar for the capping reaction of all investigated IB n-mers with DPE, and they were about 10 times higher for DTE but independent of the chain length n. The value of kcKi increased with increasing n for the capping with both DPE and DTE: For n ) 3, 4, and 36, it was approximately three, four, and five times higher, respectively, than for n ) 2. The capping reaction of IB n-mers was approximately fifteen times faster with DTE than with DPE, which could be ascribed to a higher reactivity of DTE compared to DPE. The capping reaction was found to be first order in [diarylethylene] at [DPE] < 2 × 10 -2 M and at [DTE] < 3 × 10 -3 M. At higher than 3 ×10 -3 M DTE concentrations, the order in [DTE] was lower than unity, and the apparent initial rate of addition became independent of DTE concentration at [DTE] > 10 -1 M. The change in the reaction order from unity to zero was attributed to a change in the rate-determining step from addition of DTE to the H-[IB]n + cation to ionization of H-[IB]n-Cl. The rate constant of ionization, ki ) 6, 11, and 15 M -2 s -1 , could then be calculated for the hydrochlorinated IB 2-, 3-, and 36-mers, respectively. Comparison of these ki values with the corresponding kcKi values indicated that the observed increase of the apparent rate constant of capping with increasing chain length can be mainly ascribed to a similar increase in ki and Ki.

Langmuir, 2010

We report the first attachment of polymers with pendant vinyl groups to hydrogen-terminated silic... more We report the first attachment of polymers with pendant vinyl groups to hydrogen-terminated silicon(111) (Si(111)-H); 1,2-polybutadiene (M(w) = 3200-3500 g/mol) was attached to Si(111)-H under mild conditions at room temperature with visible light. We also report the partial functionalization, in solution, of 1,2-polybutadiene with various thiols using thiol-ene chemistry and the subsequent attachments of these compounds to Si(111)-H. The partially functionalized or unfunctionalized polybutadienes allow further functionalization at the surface through their unreacted carbon-carbon double bonds. We present this as a useful strategy for silicon surface modification. Surfaces were characterized with contact angle goniometry, spectroscopic ellipsometry, X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (ToF-SIMS), and atomic force microscopy (AFM).

Macromolecules, 2001

Metal chelates and coordination compounds play an extraordinary role in very diverse areas like t... more Metal chelates and coordination compounds play an extraordinary role in very diverse areas like the chemistry of living matter and biominerals, wastewater treatment, industrial-scale polymer synthesis, catalysis, and hydrometallurgy, to mention just a few. 1 Over the past three decades, macromolecular science has strongly been entering this field of organic-inorganic hybrid materials, aiming to combine potential applications of metal compounds with the special features of copolymers, namely the formation of nanometer-scale structured materials, the electrosteric stabilization of colloids, and good mechanical performance. Up to the present, a large number of coordination polymers with O-, S-, and N-containing ligands and polymer-metal complexes have been described. The majority of studies investigated homopolymers, random copolymers and resins which were mainly obtained from conventional free radical polymerization techniques. 1 However, radical reactions polymerize many monomers and tolerate most functional groups, but they often yield chemically disperse products which are not suited for accurate systematic studies on phase behavior and material properties. The synthesis of well-defined materials and block copolymers, on the other hand, requires advanced polymerization techniques (e.g., living/ controlled radical or ionic polymerization methods) 4,5 or polymer modification reactions starting from welldefined precursor polymers involving quantitative and side reaction-free conversion. We are focusing on amphiphilic block copolymers with bidentate -dicarbonyl moieties because of their strong affinity to multivalent cations and their expected interesting aggregation behavior. 2 Polymers with -dicarbonyl repeating units have so far been obtained from the free radical polymerization of (meth)acroylacetone, 7,8 ethylacrylolyl acetate, 8 and acetoacetoxyethyl (meth)acrylate 9 or by the controlled oxidation of poly(vinyl alcohol). 10 Procedures for a living and controlled synthesis of block copolymers from acetoacetyl-or ketalfunctional monomers have not been reported yet. We therefore employed this alternate route to prepare coordinating polymers with pendant -dicarbonyl ligands that involves the chemical modification of suitable precursor block copolymers. Considering established methods of synthetic organic chemistry, -dicarbonyl compounds can be obtained from (1) the transesterification of tert-butyl acetoacetate with alcohols (transacetoacetylation) 11 or (2) the Claisen acylation of esters with sodium acetonate. 12 Poly(2-hydroxyethyl methacrylate) and poly(2-hydroxyethyl ethylene), which can both be prepared via anionic polymerization of readily available monomers and subsequent modification, were therefore taken as the precursor segments for transacetoacetylation. Poly(tert-butyl methacrylate) was used for the modification via Claisen acylation because of its good tert-butoxide leaving groups.

J Am Chem Soc, 2002

Polybutadiene-block-poly(L-glutamate) copolymers were made by anionic polymerization and subseque... more Polybutadiene-block-poly(L-glutamate) copolymers were made by anionic polymerization and subsequent ring-opening polymerization of N-carboxyanhydrides and were characterized by NMR, IR, SEC, and circular dichroism. These polymers, when appropriately designed, form so-called &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;quot;polymersomes&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;quot; or &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;quot;peptosomes&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;quot;, vesicles composed of modified protein units. The size and structure of the vesicles are determined by dynamic light scattering, small-angle neutron scattering, and freeze-fracture electron microscopy. It is also shown that the size of the peptosomes does not depend on the pH; that is, the solvating peptide units can perform a helix-coil transition without serious changes of the vesicle morphology.

Macromolecules, Oct 1, 2001

Metal chelates and coordination compounds play an extraordinary role in very diverse areas like t... more Metal chelates and coordination compounds play an extraordinary role in very diverse areas like the chemistry of living matter and biominerals, wastewater treatment, industrial-scale polymer synthesis, catalysis, and hydrometallurgy, to mention just a few. 1 Over the past three decades, macromolecular science has strongly been entering this field of organic-inorganic hybrid materials, aiming to combine potential applications of metal compounds with the special features of copolymers, namely the formation of nanometer-scale structured materials, the electrosteric stabilization of colloids, and good mechanical performance. Up to the present, a large number of coordination polymers with O-, S-, and N-containing ligands and polymer-metal complexes have been described. The majority of studies investigated homopolymers, random copolymers and resins which were mainly obtained from conventional free radical polymerization techniques. 1 However, radical reactions polymerize many monomers and tolerate most functional groups, but they often yield chemically disperse products which are not suited for accurate systematic studies on phase behavior and material properties. The synthesis of well-defined materials and block copolymers, on the other hand, requires advanced polymerization techniques (e.g., living/ controlled radical or ionic polymerization methods) 4,5 or polymer modification reactions starting from welldefined precursor polymers involving quantitative and side reaction-free conversion. We are focusing on amphiphilic block copolymers with bidentate -dicarbonyl moieties because of their strong affinity to multivalent cations and their expected interesting aggregation behavior. 2 Polymers with -dicarbonyl repeating units have so far been obtained from the free radical polymerization of (meth)acroylacetone, 7,8 ethylacrylolyl acetate, 8 and acetoacetoxyethyl (meth)acrylate 9 or by the controlled oxidation of poly(vinyl alcohol). 10 Procedures for a living and controlled synthesis of block copolymers from acetoacetyl-or ketalfunctional monomers have not been reported yet. We therefore employed this alternate route to prepare coordinating polymers with pendant -dicarbonyl ligands that involves the chemical modification of suitable precursor block copolymers. Considering established methods of synthetic organic chemistry, -dicarbonyl compounds can be obtained from (1) the transesterification of tert-butyl acetoacetate with alcohols (transacetoacetylation) 11 or (2) the Claisen acylation of esters with sodium acetonate. 12 Poly(2-hydroxyethyl methacrylate) and poly(2-hydroxyethyl ethylene), which can both be prepared via anionic polymerization of readily available monomers and subsequent modification, were therefore taken as the precursor segments for transacetoacetylation. Poly(tert-butyl methacrylate) was used for the modification via Claisen acylation because of its good tert-butoxide leaving groups.

Physical Chemistry Chemical Physics, Jun 4, 2004

Co-micellisation of the di-block copolymer polybutadiene-poly(ethylene oxide) (Bb-EO) with the an... more Co-micellisation of the di-block copolymer polybutadiene-poly(ethylene oxide) (Bb-EO) with the anionic surfactant sodium dodecylsulfate (SDS) was investigated in aqueous solution using different scattering methods and cryo-transmission electron microscopy. In dilute aqueous ...

Advan Polym Sci, 2010

An experimental study is presented on the hierarchical assembly of α-helical block copolymers pol... more An experimental study is presented on the hierarchical assembly of α-helical block copolymers polystyrene-poly(γ-benzyl-L-glutamate) into anisotropic ordered structures. We transformed thin solid films into solutions through exposure to solvent vapor and studied the nucleation and growth of ordered threedimensional structures in such solutions, with emphasis on the dependence of these processes on supersaturation with respect to the solubility limit. Interestingly, polymer solubility could be significantly influenced via variation of humidity in the surrounding gas phase. It is concluded that the interfacial tension between the ordered structures and the solution increased with humidity. The same effect was observed for other protic non-solvents in the surrounding gas phase and is attributed to a complexation of poly(γ-benzyl-L-glutamate) by protic non-solvent molecules (via hydrogen-bonding interactions). This change of polymer solubility was demonstrated to be reversible by addition or removal of small amounts of protic non-solvent in the surrounding gas phase. At a constant polymer concentration, ordered ellipsoidal structures could be dissolved by removing water or methanol present in the solution. Such structures formed once again when water or methanol was reintroduced via the vapor phase.

J Colloid Interface Sci, 2011

Association of tannic acid (TA) with structurally isomeric poly(N-isopropylacrylamide) (PNIPAM) a... more Association of tannic acid (TA) with structurally isomeric poly(N-isopropylacrylamide) (PNIPAM) and poly(2-isopropyl-2-oxazoline) (PIPOX) has been examined at surfaces to understand the effect of different molecular arrangements in a polymer repeating unit of structural isomers on the construction and pH-stability of hydrogen-bonded multilayers. Films were fabricated using layer-by-layer (LbL) technique through hydrogen-bonding interactions primarily between carbonyl groups of neutral polymers and hydroxyl groups of TA molecules at pH 2. PIPOX and TA formed thinner and more stable films in the pH scale with a critical dissolution pH of 9 when compared to films of PNIPAM and TA with a critical pH of 8. The differences in the thickness and pH-stability were due to different conformational behavior of PNIPAM and PIPOX in water which affects the accessibility of carbonyl groups for participation in the hydrogen bonding and the number of binding sites between the polymer pairs. Addition of electrostatic interactions by introducing amino groups only at the PIPOX chain end shifted the critical dissolution pH to higher values and resulted in gradual dissolution of the films in a wide pH range of 9–12. Such films hold promise for use in biomedical field due to biocompatibility and lower critical solution temperature (LCST) behavior at near physiological temperature of PNIPAM and PIPOX together with the pH-response of the hydrogen-bonded films.LbL films of a polyacid and PIPOX or PNIPAM, two structural isomers, showed difference in pH-stability. Addition of electrostatic interactions only at the chain end shifted the critical dissolution pH to higher values.► Structurally isomeric hydrogen accepting neutral polymers behaved differently within LbL films. ► Different arrangement of atoms in isomeric polymers resulted in different film thickness and pH-stability of multilayers. ► pH-stability of hydrogen-bonded films can be enhanced by functionalizing only the chain end of the hydrogen accepting polymer.

Physical Review E, Aug 1, 2003

Micelles of the diblock copolymer poly(butadiene)-poly(ethyleneoxide) (B40-b-EO62) and mixed mice... more Micelles of the diblock copolymer poly(butadiene)-poly(ethyleneoxide) (B40-b-EO62) and mixed micelles of this polymer with the cationic surfactant dodecyltrimethylammonium bromide (C12TAB) were investigated using static and dynamic light scattering and small-angle neutron scattering. It is shown that the surfactant induces a major structural change from large mainly rodlike aggregates to smaller spherical mixed micelles. The rodlike assemblies found in the absence of surfactant have a contour length L of ca. 500 nm and a diameter d ≈30 nm. The spherical mixed micelles obtained upon addition of C12TAB possess a hydrodynamic radius of 15 nm and still contain several polymer molecules. The results of the scattering experiments are consistent with observations of the aggregates by cryogenic transmission electron microscopy.

Biomimetic organic-inorganic composite materials were fabricated via one-step self-organization o... more Biomimetic organic-inorganic composite materials were fabricated via one-step self-organization on three hierarchical levels. The organic component was a polyoxazoline with pendent cholesteryl and carboxyl (N-Boc-protected amino acid) side chains that was able to form a chiral nematic lyotropic phase and bind to positively charged inorganic faces of Laponite. The Laponite particles formed a mesocrystalline arrangement within the liquid-crystal (LC) polymer phase upon shearing a viscous dispersion of Laponite nanoparticles and LC polymer in DMF. Complementary analytical and mechanical characterization techniques (AUC, POM, TEM, SEM, SAXS, μCT, and nanoindentation) covering the millimeter, micrometer, and nanometer length scales reveal the hierarchical structures and properties of the composite materials consisting of different ratios of Laponite nanoparticles and liquid-crystalline polymer.

J Am Chem Soc, 2007

The interaction between poly(L-glutamic acid) (PLE) and calcite crystals was studied with AFM-bas... more The interaction between poly(L-glutamic acid) (PLE) and calcite crystals was studied with AFM-based single molecule force spectroscopy. Block copolymers of poly(ethylene oxide) (PEO) and PLE were synthesized and covalently attached to the tip of an AFM cantilever. In desorption measurements the molecules were allowed to adsorb on the calcite crystal faces and afterward successively desorbed. The corresponding desorption forces were detected with high precision, showing for example a force transition between the two blocks. Because of its importance in the crystallization process in biominerals, the PLE-calcite interaction was investigated as a function of the pH as well as the calcium concentration of the aqueous solution. The sensitivity of the technique was underlined by resolving different interaction forces for calcite (104) and calcite (100).

Polymer Journal, Nov 1, 1996

Colloid and Polymer Science, 2009

The self-assembly of polystyrene-block-poly(L-lysine) (PS-PLLys) copolymers with different block ... more The self-assembly of polystyrene-block-poly(L-lysine) (PS-PLLys) copolymers with different block lengths has been studied in toluene. The obtained spherical micelles proved to be sensitive to size variation by addition of acids or bases. This was studied by following the effect of the addition of pyridine to the organic solutions using light and neutron scattering techniques. It is shown that pyridine induces a shrinking of the polystyrene chains in the micelle shell region decreasing the aggregates-solvent interface. Oppositely, the addition of benzoic acid leads to a swelling of copolymer micelles proportional to the molar fraction of polypeptide. This fact suggests a selective permeability of PS-PLLys micelles and the possibility to encapsulate organic compounds in toluene depending on their chemical nature.

Anticancer research

The presence of lymph node metastases relevantly and significantly impairs disease-specific survi... more The presence of lymph node metastases relevantly and significantly impairs disease-specific survival in patients suffering from squamous cell carcinoma of the upper aerodigestive tract. In a VX2 animal tumor model, we present an interstitial translymphatic therapeutic approach using cisdiaminedichloro-platinum(II) (CDDP) conjugated to a poly(ethylene oxide)-block-poly(lysine) (PEO-b-PLys) block copolymer tracking systems for the successful treatment of lymph node metastases. Most effective was the application of a high cargo-load CDDP tracking system (48 wt.% CDDP) curing 90% of the animals and causing only minor local side-effects. Systems containing 1 or 10 wt.% of CDDP were less effective but still cured 50% of the animals. Moreover, the administration of 1 or 10 wt.% of CDDP consistently limited tumor growth to the draining lymph nodes (50%) and prevented systemic distribution of the metastasis even with 1 wt.% CDDP load. The systems contained 0.25-0.003 mg/kg per body weight CDDP compared to 1 ml/kg per body weight as usually used for intravenous administration. This approach encourages further and more detailed research of a CDDP-based interstitial translymphatic administration of chemotherapy for lymphogenic metastasizing carcinomas in different body regions.

Macromolecules, Jan 18, 2000

The addition of 1,1-diphenylethylene (DPE) and 1,1-bis(4-methylphenyl)ethylene (DTE) to hydrochlo... more The addition of 1,1-diphenylethylene (DPE) and 1,1-bis(4-methylphenyl)ethylene (DTE) to hydrochlorinated isobutylene (IB) n-mers, H-[IB] n-Cl (n ) 2, 3, 4, 36), in the presence of TiCl4, was investigated in hexane (Hex)/methyl chloride (MeCl) 60/40 (v/v) at -80°C using on-line visible spectroscopy. The apparent equilibrium constants of capping/decapping, Ke, and the apparent rate constants of capping, kcKi, have been determined. The Ke value was found to be similar for the capping reaction of all investigated IB n-mers with DPE, and they were about 10 times higher for DTE but independent of the chain length n. The value of kcKi increased with increasing n for the capping with both DPE and DTE: For n ) 3, 4, and 36, it was approximately three, four, and five times higher, respectively, than for n ) 2. The capping reaction of IB n-mers was approximately fifteen times faster with DTE than with DPE, which could be ascribed to a higher reactivity of DTE compared to DPE. The capping reaction was found to be first order in [diarylethylene] at [DPE] < 2 × 10 -2 M and at [DTE] < 3 × 10 -3 M. At higher than 3 ×10 -3 M DTE concentrations, the order in [DTE] was lower than unity, and the apparent initial rate of addition became independent of DTE concentration at [DTE] > 10 -1 M. The change in the reaction order from unity to zero was attributed to a change in the rate-determining step from addition of DTE to the H-[IB]n + cation to ionization of H-[IB]n-Cl. The rate constant of ionization, ki ) 6, 11, and 15 M -2 s -1 , could then be calculated for the hydrochlorinated IB 2-, 3-, and 36-mers, respectively. Comparison of these ki values with the corresponding kcKi values indicated that the observed increase of the apparent rate constant of capping with increasing chain length can be mainly ascribed to a similar increase in ki and Ki.

Langmuir, 2010

We report the first attachment of polymers with pendant vinyl groups to hydrogen-terminated silic... more We report the first attachment of polymers with pendant vinyl groups to hydrogen-terminated silicon(111) (Si(111)-H); 1,2-polybutadiene (M(w) = 3200-3500 g/mol) was attached to Si(111)-H under mild conditions at room temperature with visible light. We also report the partial functionalization, in solution, of 1,2-polybutadiene with various thiols using thiol-ene chemistry and the subsequent attachments of these compounds to Si(111)-H. The partially functionalized or unfunctionalized polybutadienes allow further functionalization at the surface through their unreacted carbon-carbon double bonds. We present this as a useful strategy for silicon surface modification. Surfaces were characterized with contact angle goniometry, spectroscopic ellipsometry, X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (ToF-SIMS), and atomic force microscopy (AFM).

Macromolecules, 2001

Metal chelates and coordination compounds play an extraordinary role in very diverse areas like t... more Metal chelates and coordination compounds play an extraordinary role in very diverse areas like the chemistry of living matter and biominerals, wastewater treatment, industrial-scale polymer synthesis, catalysis, and hydrometallurgy, to mention just a few. 1 Over the past three decades, macromolecular science has strongly been entering this field of organic-inorganic hybrid materials, aiming to combine potential applications of metal compounds with the special features of copolymers, namely the formation of nanometer-scale structured materials, the electrosteric stabilization of colloids, and good mechanical performance. Up to the present, a large number of coordination polymers with O-, S-, and N-containing ligands and polymer-metal complexes have been described. The majority of studies investigated homopolymers, random copolymers and resins which were mainly obtained from conventional free radical polymerization techniques. 1 However, radical reactions polymerize many monomers and tolerate most functional groups, but they often yield chemically disperse products which are not suited for accurate systematic studies on phase behavior and material properties. The synthesis of well-defined materials and block copolymers, on the other hand, requires advanced polymerization techniques (e.g., living/ controlled radical or ionic polymerization methods) 4,5 or polymer modification reactions starting from welldefined precursor polymers involving quantitative and side reaction-free conversion. We are focusing on amphiphilic block copolymers with bidentate -dicarbonyl moieties because of their strong affinity to multivalent cations and their expected interesting aggregation behavior. 2 Polymers with -dicarbonyl repeating units have so far been obtained from the free radical polymerization of (meth)acroylacetone, 7,8 ethylacrylolyl acetate, 8 and acetoacetoxyethyl (meth)acrylate 9 or by the controlled oxidation of poly(vinyl alcohol). 10 Procedures for a living and controlled synthesis of block copolymers from acetoacetyl-or ketalfunctional monomers have not been reported yet. We therefore employed this alternate route to prepare coordinating polymers with pendant -dicarbonyl ligands that involves the chemical modification of suitable precursor block copolymers. Considering established methods of synthetic organic chemistry, -dicarbonyl compounds can be obtained from (1) the transesterification of tert-butyl acetoacetate with alcohols (transacetoacetylation) 11 or (2) the Claisen acylation of esters with sodium acetonate. 12 Poly(2-hydroxyethyl methacrylate) and poly(2-hydroxyethyl ethylene), which can both be prepared via anionic polymerization of readily available monomers and subsequent modification, were therefore taken as the precursor segments for transacetoacetylation. Poly(tert-butyl methacrylate) was used for the modification via Claisen acylation because of its good tert-butoxide leaving groups.

J Am Chem Soc, 2002

Polybutadiene-block-poly(L-glutamate) copolymers were made by anionic polymerization and subseque... more Polybutadiene-block-poly(L-glutamate) copolymers were made by anionic polymerization and subsequent ring-opening polymerization of N-carboxyanhydrides and were characterized by NMR, IR, SEC, and circular dichroism. These polymers, when appropriately designed, form so-called &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;quot;polymersomes&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;quot; or &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;quot;peptosomes&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;quot;, vesicles composed of modified protein units. The size and structure of the vesicles are determined by dynamic light scattering, small-angle neutron scattering, and freeze-fracture electron microscopy. It is also shown that the size of the peptosomes does not depend on the pH; that is, the solvating peptide units can perform a helix-coil transition without serious changes of the vesicle morphology.

Macromolecules, Oct 1, 2001

Metal chelates and coordination compounds play an extraordinary role in very diverse areas like t... more Metal chelates and coordination compounds play an extraordinary role in very diverse areas like the chemistry of living matter and biominerals, wastewater treatment, industrial-scale polymer synthesis, catalysis, and hydrometallurgy, to mention just a few. 1 Over the past three decades, macromolecular science has strongly been entering this field of organic-inorganic hybrid materials, aiming to combine potential applications of metal compounds with the special features of copolymers, namely the formation of nanometer-scale structured materials, the electrosteric stabilization of colloids, and good mechanical performance. Up to the present, a large number of coordination polymers with O-, S-, and N-containing ligands and polymer-metal complexes have been described. The majority of studies investigated homopolymers, random copolymers and resins which were mainly obtained from conventional free radical polymerization techniques. 1 However, radical reactions polymerize many monomers and tolerate most functional groups, but they often yield chemically disperse products which are not suited for accurate systematic studies on phase behavior and material properties. The synthesis of well-defined materials and block copolymers, on the other hand, requires advanced polymerization techniques (e.g., living/ controlled radical or ionic polymerization methods) 4,5 or polymer modification reactions starting from welldefined precursor polymers involving quantitative and side reaction-free conversion. We are focusing on amphiphilic block copolymers with bidentate -dicarbonyl moieties because of their strong affinity to multivalent cations and their expected interesting aggregation behavior. 2 Polymers with -dicarbonyl repeating units have so far been obtained from the free radical polymerization of (meth)acroylacetone, 7,8 ethylacrylolyl acetate, 8 and acetoacetoxyethyl (meth)acrylate 9 or by the controlled oxidation of poly(vinyl alcohol). 10 Procedures for a living and controlled synthesis of block copolymers from acetoacetyl-or ketalfunctional monomers have not been reported yet. We therefore employed this alternate route to prepare coordinating polymers with pendant -dicarbonyl ligands that involves the chemical modification of suitable precursor block copolymers. Considering established methods of synthetic organic chemistry, -dicarbonyl compounds can be obtained from (1) the transesterification of tert-butyl acetoacetate with alcohols (transacetoacetylation) 11 or (2) the Claisen acylation of esters with sodium acetonate. 12 Poly(2-hydroxyethyl methacrylate) and poly(2-hydroxyethyl ethylene), which can both be prepared via anionic polymerization of readily available monomers and subsequent modification, were therefore taken as the precursor segments for transacetoacetylation. Poly(tert-butyl methacrylate) was used for the modification via Claisen acylation because of its good tert-butoxide leaving groups.

Physical Chemistry Chemical Physics, Jun 4, 2004

Co-micellisation of the di-block copolymer polybutadiene-poly(ethylene oxide) (Bb-EO) with the an... more Co-micellisation of the di-block copolymer polybutadiene-poly(ethylene oxide) (Bb-EO) with the anionic surfactant sodium dodecylsulfate (SDS) was investigated in aqueous solution using different scattering methods and cryo-transmission electron microscopy. In dilute aqueous ...

Advan Polym Sci, 2010

An experimental study is presented on the hierarchical assembly of α-helical block copolymers pol... more An experimental study is presented on the hierarchical assembly of α-helical block copolymers polystyrene-poly(γ-benzyl-L-glutamate) into anisotropic ordered structures. We transformed thin solid films into solutions through exposure to solvent vapor and studied the nucleation and growth of ordered threedimensional structures in such solutions, with emphasis on the dependence of these processes on supersaturation with respect to the solubility limit. Interestingly, polymer solubility could be significantly influenced via variation of humidity in the surrounding gas phase. It is concluded that the interfacial tension between the ordered structures and the solution increased with humidity. The same effect was observed for other protic non-solvents in the surrounding gas phase and is attributed to a complexation of poly(γ-benzyl-L-glutamate) by protic non-solvent molecules (via hydrogen-bonding interactions). This change of polymer solubility was demonstrated to be reversible by addition or removal of small amounts of protic non-solvent in the surrounding gas phase. At a constant polymer concentration, ordered ellipsoidal structures could be dissolved by removing water or methanol present in the solution. Such structures formed once again when water or methanol was reintroduced via the vapor phase.

J Colloid Interface Sci, 2011

Association of tannic acid (TA) with structurally isomeric poly(N-isopropylacrylamide) (PNIPAM) a... more Association of tannic acid (TA) with structurally isomeric poly(N-isopropylacrylamide) (PNIPAM) and poly(2-isopropyl-2-oxazoline) (PIPOX) has been examined at surfaces to understand the effect of different molecular arrangements in a polymer repeating unit of structural isomers on the construction and pH-stability of hydrogen-bonded multilayers. Films were fabricated using layer-by-layer (LbL) technique through hydrogen-bonding interactions primarily between carbonyl groups of neutral polymers and hydroxyl groups of TA molecules at pH 2. PIPOX and TA formed thinner and more stable films in the pH scale with a critical dissolution pH of 9 when compared to films of PNIPAM and TA with a critical pH of 8. The differences in the thickness and pH-stability were due to different conformational behavior of PNIPAM and PIPOX in water which affects the accessibility of carbonyl groups for participation in the hydrogen bonding and the number of binding sites between the polymer pairs. Addition of electrostatic interactions by introducing amino groups only at the PIPOX chain end shifted the critical dissolution pH to higher values and resulted in gradual dissolution of the films in a wide pH range of 9–12. Such films hold promise for use in biomedical field due to biocompatibility and lower critical solution temperature (LCST) behavior at near physiological temperature of PNIPAM and PIPOX together with the pH-response of the hydrogen-bonded films.LbL films of a polyacid and PIPOX or PNIPAM, two structural isomers, showed difference in pH-stability. Addition of electrostatic interactions only at the chain end shifted the critical dissolution pH to higher values.► Structurally isomeric hydrogen accepting neutral polymers behaved differently within LbL films. ► Different arrangement of atoms in isomeric polymers resulted in different film thickness and pH-stability of multilayers. ► pH-stability of hydrogen-bonded films can be enhanced by functionalizing only the chain end of the hydrogen accepting polymer.

Physical Review E, Aug 1, 2003

Micelles of the diblock copolymer poly(butadiene)-poly(ethyleneoxide) (B40-b-EO62) and mixed mice... more Micelles of the diblock copolymer poly(butadiene)-poly(ethyleneoxide) (B40-b-EO62) and mixed micelles of this polymer with the cationic surfactant dodecyltrimethylammonium bromide (C12TAB) were investigated using static and dynamic light scattering and small-angle neutron scattering. It is shown that the surfactant induces a major structural change from large mainly rodlike aggregates to smaller spherical mixed micelles. The rodlike assemblies found in the absence of surfactant have a contour length L of ca. 500 nm and a diameter d ≈30 nm. The spherical mixed micelles obtained upon addition of C12TAB possess a hydrodynamic radius of 15 nm and still contain several polymer molecules. The results of the scattering experiments are consistent with observations of the aggregates by cryogenic transmission electron microscopy.

Biomimetic organic-inorganic composite materials were fabricated via one-step self-organization o... more Biomimetic organic-inorganic composite materials were fabricated via one-step self-organization on three hierarchical levels. The organic component was a polyoxazoline with pendent cholesteryl and carboxyl (N-Boc-protected amino acid) side chains that was able to form a chiral nematic lyotropic phase and bind to positively charged inorganic faces of Laponite. The Laponite particles formed a mesocrystalline arrangement within the liquid-crystal (LC) polymer phase upon shearing a viscous dispersion of Laponite nanoparticles and LC polymer in DMF. Complementary analytical and mechanical characterization techniques (AUC, POM, TEM, SEM, SAXS, μCT, and nanoindentation) covering the millimeter, micrometer, and nanometer length scales reveal the hierarchical structures and properties of the composite materials consisting of different ratios of Laponite nanoparticles and liquid-crystalline polymer.

J Am Chem Soc, 2007

The interaction between poly(L-glutamic acid) (PLE) and calcite crystals was studied with AFM-bas... more The interaction between poly(L-glutamic acid) (PLE) and calcite crystals was studied with AFM-based single molecule force spectroscopy. Block copolymers of poly(ethylene oxide) (PEO) and PLE were synthesized and covalently attached to the tip of an AFM cantilever. In desorption measurements the molecules were allowed to adsorb on the calcite crystal faces and afterward successively desorbed. The corresponding desorption forces were detected with high precision, showing for example a force transition between the two blocks. Because of its importance in the crystallization process in biominerals, the PLE-calcite interaction was investigated as a function of the pH as well as the calcium concentration of the aqueous solution. The sensitivity of the technique was underlined by resolving different interaction forces for calcite (104) and calcite (100).

Polymer Journal, Nov 1, 1996

Colloid and Polymer Science, 2009

The self-assembly of polystyrene-block-poly(L-lysine) (PS-PLLys) copolymers with different block ... more The self-assembly of polystyrene-block-poly(L-lysine) (PS-PLLys) copolymers with different block lengths has been studied in toluene. The obtained spherical micelles proved to be sensitive to size variation by addition of acids or bases. This was studied by following the effect of the addition of pyridine to the organic solutions using light and neutron scattering techniques. It is shown that pyridine induces a shrinking of the polystyrene chains in the micelle shell region decreasing the aggregates-solvent interface. Oppositely, the addition of benzoic acid leads to a swelling of copolymer micelles proportional to the molar fraction of polypeptide. This fact suggests a selective permeability of PS-PLLys micelles and the possibility to encapsulate organic compounds in toluene depending on their chemical nature.

Anticancer research

The presence of lymph node metastases relevantly and significantly impairs disease-specific survi... more The presence of lymph node metastases relevantly and significantly impairs disease-specific survival in patients suffering from squamous cell carcinoma of the upper aerodigestive tract. In a VX2 animal tumor model, we present an interstitial translymphatic therapeutic approach using cisdiaminedichloro-platinum(II) (CDDP) conjugated to a poly(ethylene oxide)-block-poly(lysine) (PEO-b-PLys) block copolymer tracking systems for the successful treatment of lymph node metastases. Most effective was the application of a high cargo-load CDDP tracking system (48 wt.% CDDP) curing 90% of the animals and causing only minor local side-effects. Systems containing 1 or 10 wt.% of CDDP were less effective but still cured 50% of the animals. Moreover, the administration of 1 or 10 wt.% of CDDP consistently limited tumor growth to the draining lymph nodes (50%) and prevented systemic distribution of the metastasis even with 1 wt.% CDDP load. The systems contained 0.25-0.003 mg/kg per body weight CDDP compared to 1 ml/kg per body weight as usually used for intravenous administration. This approach encourages further and more detailed research of a CDDP-based interstitial translymphatic administration of chemotherapy for lymphogenic metastasizing carcinomas in different body regions.