Volume 47 Issue 1, January 2015

Half-metallocene complexes of the type CpM(L^L)X₂ (L^L=chelating ligands) offer the advantage of catalyst modification: by changing one cyclopentadienyl ligand of metallocene complexes to other ligands such as three-, four-, five-, six- and seven-membered chelates, bidentate and tridentate coordination, and monoanionic, dianionic and trianionic system, steric and/or electronic modification of the coordination environment is much flexible. The structural uniqueness of the metal complexes and the effects of the chelate ring sizes on their productivity and activation processes of the metal complexes with cocatalysts are highlighted.

This review focuses on the development of donor–acceptor semiconducting polymers using electron-deficient π-building units, such as thiazolo[5,4 -d]thiazole, benzo[1,2-d:4,5-d′]bisthiazole, naphtho[1,2-c:5,6-c′]bis[1,2,5]thiadiazole and thieno[3,2-b]thiophene-2,5-dione. All of the polymers form crystalline structures in thin films and possess deep highest occupied molecular orbital energy levels; consequently, the polymers demonstrate high charge carrier mobilities with high air stability. Several key parameters were identified that must be taken into account when designing high-performance polymers: the symmetry of the building units, backbone shape, and delocalization of the π-electrons along the backbone.

We investigated the initial photooxidation mechanism leading to reactive radical formation of polythiophene derivatives by focusing on the differences in the photochemical behaviors of photounstable poly(3-hexylthiophene) (P3HT) and photostable poly(3-octyloxythiophene) (P3OOT). Electron spin resonance measurements revealed that the [P3HT]⁺· (formed by oxygen doping) decayed, whereas no change was observed in the photostable [P3OOT]⁺· after light irradiation. Furthermore, the absorption decrease of the [P3HT]⁺· was suppressed by superoxide dismutase. Therefore, the oxygen dopant is superoxide, which might also initiate the oxidation of P3HT.

Germylenes (1a and 1b) reacted with p-quinoneimine (2) to give copolymers (3a and 3b) having a tetravalent germanium unit and a p-aminophenol unit, alternatively. The copolymerization took place at 0°C smoothly without added catalyst or initiator. 1 acted as a reductant monomer whereas 2 as an oxidant monomer (oxidation-reduction alternating copolymerization). Soluble copolymers were obtained in very high yields, having high molecular weight. ESR spectroscopic studies of the reaction suggested a structure of stable germyl radical and a biradical copolymerization mechanism.

Three-dimensional structural analyses of huge spherulites of poly(oxyethylene) (PEG) using X-ray computerized tomography (CT) in blends of PEG and amorphous poly(d,l-lactic acid) are reported for the first time. Slit-shaped cracks that were straight or curved were clearly observed using X-ray CT. Furthermore, they appeared to form a set of spokes, presenting a signature of a huge spherulite. Several aspects that are representative of an axialite structure are presented, and they are in good agreement with the intuitively proposed structural model for axialite long ago, although the size scale is much larger in our study.

Network structure of syndiotactic-polystyrene (sPS) or syndiotactic-poly(styrene-co-4-R-styrene) (St/RSt) -organic solvents gels has been quantitatively studied by means of a scanning microscopic light scattering (SMILS). The SMILS analysis cleared that most of the gels showed relaxation peaks derived from small mesh size ~0.6–1.8 nm and large cluster structure ~1000–6000 nm, and a gel formation model was proposed based on the analysis. Interaction between R groups (R=OH, antracenecarbonyl) affected the network structure of the gels.

An end-grafted flexible diblock copolymer exists a critical adsorption point T_c from a desorbed state to an adsorbed state. The finite-size scaling law is adopted to determine T_c and the crossover exponent φ. The non-adsorbed block B weakens the adsorption of the adsorbed block A. Then the effective influence of the B block is reduced with increase in the length of the A block but it is independent of the length at T_c.

Fluorescence probe methods were applied to investigate micelle formation of poly(N-isopropylacrylamide) (PNIPA) with surfactant, sodium n-dodecyl sulfate (SDS) or n-dodecyltrimethylammonium chloride (DTAC), in aqueous solutions. Two PNIPA samples, one having a hydrophobic chain-end group (M sample) and the other having a negatively charged hydrophilic chain-end group (R sample), were used to investigate the effects of the chain-end group on the micelle formation. It is found that the microenvironmental polarity in the formed micelles depends on the kinds of chain-end group and surfactant.

Poly(methyl methacrylate) surface was fluorinated by simply immersing into 3-(perfluoro-7-methyloctyl)-1,2-epoxypropene, followed by heat treating at 120 °C. The contact angle of water for fluorinated PMMA increased to 111° after the treating. This value corresponds to the surface free energy of 10 mJ m⁻², which is much lower than that (18 mJ m⁻²) of polytetrafluoroethylene. The fluorinated PMMA showed low albumin adsorption. When materials come into contact with blood, protein will rapidly adsorb onto the surfaces, which plays a trigger of clotting. However, protein adsorption was reduced on this very hydrophobic surface.

Poly(2-(methacryloyloxy)ethyl phosphorylcholine)-block-poly(cholesteryl 6-methacryloyloxyhexanoate) (PMPC₈₂-b-PChM_n) with different PChM block lengths was prepared via controlled/living radical polymerization. To prepare the aqueous solution, the diblock copolymer was dissolved in an organic solvent and then subject to dialyze against pure water. These diblock copolymers formed spherical and rod-like micelles in water depending on the composition of cholesteryl (Chol) group in the polymer. The morphology of the polymer aggregates could be controlled from spherical to rod-like micelles with increasing amount of Chol groups in the polymer.