Structure–property relationships for film‐forming copoly(amide imide)s

Thin films of copoly(amide imide)s (coPAIs) from dichloro‐dianhydride of trimellitimide‐N‐acetic acid and mixtures of diphenylmethane diamine (DPA) and cardo 9,9′‐bis‐phenylfluorene diamine (CDA) cast from solutions in dimethylacetamide (DMAA) were characterized by wide‐angle and small‐angle X‐ray scattering (WAXS and SAXS), dynamic mechanical thermal analysis (DMTA) (temperature interval: 293–703 K, frequency range: 1–100 Hz), and thermogravimetric analysis (TGA) (nitrogen flux, temperature interval: 303–973 K). The mean interchain spacings (WAXS) smoothly increased with the CDA/DPA molar ratio from 0.55 nm for CDA/DPA = 0/1 up to 0.60 nm for CDA/DPA = 1/0. The smooth patterns of the SAXS curves for all coPAIs were explained by the smearing‐out of electron density differences between densely‐packed and loosely‐packed microregions of coPAIs due to the wide dispersion of their sizes. The step‐like patterns of the TGA traces in the temperature intervals below and above 600 K were associated with successive weight losses due to the evaporation of residual water and of DMAA, and to the thermal degradation of diamine and dianhydride chain fragments, respectively. As could be inferred from the TGA data, the loosely‐packed regions comprise about 25–35% of the total volume of studied coPAIs. The mechanical relaxations observed in all coPAIs at T_β < T_α′ < T_α (DMA) were attributed to the onset of non‐cooperative segment motion in loosely‐packed regions, of cooperative segment motion in loosely‐packed regions, and of cooperative segment motion in densely‐packed regions, respectively. At constant frequency, the sub‐glass relaxations were roughly composition‐independent, while chain‐stiffening effect was assumed to be responsible for the smooth increase of T_α′ and T_α, as well as of the corresponding apparent activation energies with the CDA/DPA ratio. Copyright © 2003 John Wiley & Sons, Ltd.     

Molecular description of the collapse of hydrophobic polymer chains in water

We propose a self-consistent molecular theory of conformational properties of flexible polymers in solution. It is applied to the collapse of a hydrophobic polymer chain in water, and can be readily generalized to any polymer-solvent system (e.g., copolymers with high complexity). We stress the potential of this method for a variety of problems, such as protein folding.     

Calix[4]arene methylenebisphosphonic acids as calf intestine alkaline phosphatase inhibitors

Calix[4]arenes bearing one or two methylenebisphosphonic acid fragments were prepared via addition of diethylphosphite to the parent calix[4]arene aldehydes. The resulting compounds displayed stronger inhibition of calf intestine alkaline phosphatase than simple methylenebisphosphonic or 4-hydroxyphenyl methylenebisphosphonic acids. The action of these phosphorylated calix[4]arenes is concordant with partial mixed-type inhibition. The inhibition constants Ki and Ki' for the calix[4]arene bis(methylenebisphosphonic) acid in Tris-HCl buffer at pH 9 are 0.38 microM and 2.8 microM respectively. The replacement of the phosphoric acid moieties on the macrocycle with diethylphosphonates results in a sharp decrease of its inhibitory action. Preorganizing phosphonic acid fragments using a calixarene platform therefore provides a promising approach for the design of efficient alkaline phosphatase inhibitors.     

BaIrIn4 and Ba2Ir4In13: two In-rich polar intermetallic structures with different augmented prismatic environments about the cations

The title phases were synthesized via high-temperature reactions of the elements in welded Ta tubes and characterized by single-crystal X-ray diffraction methods and band calculations. BaIrIn4 adopts the LaCoAl4-type structure: Pmma, Z = 2, a = 8.642(2), b = 4.396(1), and c = 7.906(2) A. Ba2Ir4In13 exhibits a new structure type: Cmc2(1), Z = 4, a = 4.4856(9), b = 29.052(6), and c = 13.687(3) A. BaIrIn4 is constructed from a single basic unit, a Ba-centered pentagonal prism of indium on which two adjacent and the opposed rectangular faces are capped by In and Ir, respectively. The three capping atoms are coplanar with Ba and represent the only augmentation of the pentagonal prism. The relatively large proportions of Ba:Ir, In, and of In:Ir lead to the condensation of homoatomic pentagonal prisms into zigzag chains through the sharing of the two uncapped faces. The cation proportion is much lower in Ba2Ir4In13, and Ba atoms are surrounded by a more anionic Ir/In network without any condensation between prisms. This and the greater Ir proportion lead to a network of formal augmented pentagonal Ba@Ir5In15 and hexagonal Ba@Ir7In15 prisms with overall 5-10-5 and 6-10-6 arrangements of parallel planar rings, respectively, although most Ir is not well bound to the prisms. The latter prism, with alternating Ir/In atoms in the basal faces, is novel for Ae-T-In phases (Ae = alkaline-earth metal, T = Co, Rh, Ir). Band structure calculation results (linear-muffin-tin-orbital method in the atomic sphere approximation) emphasize the greater overlap populations (approximately strengths) of the Ir-In bonds and confirm expectations that both compounds are metallic. The Ir 5d bands are narrower and lie higher in energy than those for Au in analogous phases.     

SrAu4In4 and Sr4Au9In13: polar intermetallic structures with cations in augmented hexagonal prismatic environments

The title compounds were synthesized via high-temperature reactions of the elements in welded Ta tubes and characterized by single-crystal X-ray diffraction analyses and band structure calculations. SrAu(3.76(2))In(4.24) crystallizes in the YCo5In3 structure type with two of eight network sites occupied by mixtures of Au and In: Pnma, Z = 4, a = 13.946(7), b = 4.458(2), c = 12.921(6) A. Its phase breadth appears to be small. Sr4Au9In 13 exhibits a new structure type, P_6 m2, Z = 1, a = 12.701(2), c = 4.4350(9) A. The Sr atoms in both compounds center hexagonal prisms of nominally alternating In and Au atoms and also have nine augmenting (outer) Au + In atoms around their waists so as to define 21-vertex Sr@Au9M4In8 (M = Au/In) and Sr@Au9In12 polyhedra, respectively. The relatively larger Sr content in the second phase also leads to condensation of some of the ideal building units into trefoil-like cages with edge-shared six-member rings. One overall driving force for the formation of these structures can be viewed as the need for each Sr cation to have as many close neighbors as possible in the more anionic Au-In network. The results also depend on the cation size as well as on the flexibility of the anionic network and an efficient intercluster condensation mode as all clusters are shared. Band structure calculations (LMTO-ASA) emphasize the greater strengths (overlap populations) of the Au-In bonds and confirm expectations that both compounds are metallic.     

Poly(ethylene imine)-controlled calcium phosphate mineralization

The current paper shows that poly(ethylene imine) (PEI) is an efficient template for the fabrication of spherical calcium phosphate (CaP)/polymer hybrid particles at pH values above 8. The polymer forms spherical entities, which contain one or a few CaP particles with diameters of ca. 6 nm. The samples contain up to 20 wt % polymer, which appears to be wrapped around the small CaP particles. The particles form via a mineralization-trapping pathway, where at the beginning of the precipitation small CaP particles form. Further particle growth is then prevented by precipitation of the PEI onto these particles at pH values of ca. 8. Stabilization of the particles is provided by the re-protonation of the PEI, which is adsorbed on the CaP particles, during the remainder of the mineralization process. At low pH, much larger particles form. They most likely grow via heterogeneous nucleation and growth on existing, polymer-modified CaP surfaces.     

Predicting the Morphology of Metallo‐Supramolecular Block Copolymers with Bulky Counter Ions

Summary: The phase behavior of metallo‐supramolecular block copolymers with bulky counter ions is theoretically studied within the framework of a mean‐field dynamic density functional theory and compared with recent experiments on a polystyrene–poly(ethylene oxide) metallo‐supramolecular diblock copolymer, PS₂₀‐[Ru]‐PEO₇₀, with tetraphenylborate counter ions. The copolymer is modeled as a triblock polyelectrolyte, in which the metal complex is treated as the polyelectrolyte block. The topology and kinetics of the formation of the observed three‐domain lamellar morphology in which the polyelectrolyte blocks and bulky counter ions are located together to form electroneutral complexes, are in good agreement with experimental results. In addition, the model predicts the existence of core–shell morphologies. The agreement with and variations from the experimental phase diagram are discussed in detail.

Morphological transformations in a metallo‐supramolecular block copolymer with bulky counter ions upon increasing the temperature.