Suguru Motokucho

The effect of cross-linking density and dangling chains on surface molecular mobility of network polyurethanes

Chemically cross-linked polyurethanes (PUs) were synthesized with two different cross-linking densities and dangling chain concentrations to understand the difference between the molecular mobility of the bulk and free surface based on dynamic viscoelastic properties, lateral force microscopy (LFM) and scanning viscoelasticity microscopy (SVM) measurements. The PUs were synthesized from poly(oxypropylene) triol (PPT; Mn = 3000) and tolylene-2,4-diisocyanate (TDI) with a formulation ratio (= [NCO]/[OH]) of 0.85 and 1.20. The former PU has a lightly cross-linked structure with dangling chains, and the latter one has a densely cross-linked structure with allophanate groups and without dangling chains. The α-relaxation process, associated with glass transition of the PPT chains for the bulk and surface, was observed for both PUs in dynamic viscoelastic properties and lateral force microscopy measurements, respectively. The temperature region, at which the α-relaxation process was observed, for the surface was lower and broader in comparison with bulk and the trend was more obvious for the PU with dangling chains. These results can be explained well with the existence of dangling chains and their segregation at the top surface because of lower conformational entropy.

A relationship between electrical conductivity and photodegradation in styrene-butadiene copolymer/multi-wall carbon nanotube composite

An effect of photodegradation on electrical conductivity of a styrene-butadiene copolymer (SBR)/multiwall carbon nanotube (MWNT) composite was studied with a TiO2/polyethylene oxide/methyl linoleate paint photocatalyst under UV and/or visible light irradiation. An oxidative etching of impurities on the MWNT surface was caused by the UV or visible light irradiation, leading to an increase of quality of MWNT. On the other hand, the photocatalyst addition caused the degradation of MWNT structure. A relationship between the electrical conductivity and MWNT content showed that the MWNT dispersity in a SBR was superior to that in a polystyrene (PS). In addition, the PS addition to SBR matrix caused MWNT aggregation. The electrical conductivity decrease of the MWNT composite was due to electrical percolation structure loss caused by the photocatalyst under the visible light irradiation, and its rate depended on the MWNT dispersity. The PS molecular weight change behavior with the photocatalyst was consistent with the electrical conductivity one of the SBR/MWNT. The photocatalyst ability was estimated from the electrical conductivity of the SBR/MWNT.

Chain and mirophase-separated structures of ultrathin polyurethane films

Measurements are presented how chain and microphase-separated structures of ultrathin polyurethane (PU) films are controlled by the thickness. The film thickness is varied by a solution concentration for spin coating. The systems are PUs prepared from commercial raw materials. Fourier-transform infrared spectroscopic measurement revealed that the degree of hydrogen bonding among hard segment chains decreased and increased with decreasing film thickness for strong and weak microphase separation systems, respectively. The microphase-separated structure, which is formed from hard segment domains and a surrounding soft segment matrix, were observed by atomic force microscopy. The size of hard segment domains decreased with decreasing film thickness, and possibility of specific orientation of the hard segment chains was exhibited for both systems. These results are due to decreasing space for the formation of the microphase-separated structure.

Synthesis and activity characteristics of visible light responsive polymer photocatalyst system with a styrene block copolymer containing TiO2 gel

A polymer photocatalyst system was synthesized using a poly(styrene-block-acrylic acid) (PS-b-PAA) containing TiO2 gel without calcination, and its activity characteristics were assessed with methylene blue (MB) photodegradation test in water under visible light irradiation. The initial photodegradation activity was controllable by the polymer chain length and PAA/PS molar ratio. The longer polymer chain length provoked the activity decrease by macromolecular crowding effect. The lower molar ratio did an increase in the photocatalytic surface area by generation of a large number of anatase TiO2 crystal nuclei, leading to the activity increase. The copper phthalocyanine (CuPc) loading remarkably improved the activity. A higher active site was formed on the interface and showed good recycling performance.

Molecular mobility of soft segment of polyurethane elastomers under elongation

In this study, we investigated molecular mobility of a soft segment in the poly(oxypropylene) glycol (PPG), 4,4′‐diphenylmethane diisocyanate (MDI) and 1,4‐butane diol (BD)‐based polyurethane elastomers (PUE) with and without elongation by dynamic viscoelastic property measurement and pulse nuclear magnetic resonance (NMR) measurement. The peak position of the loss tangent (tand) curves shifted to the lower temperature region with increasing elongation. In the pulse NMR measurement, the long spin‐spin relaxation time (T2) component appeared at −18.0(e = 0) and −26.0 °C(e = 1.5), respectively, with increasing temperature. Since this temperature seems to be related to the glass transition temperature (Tg) of the soft segment in the PUE, it is likely to consider that the Tg decreased with increasing strain. These results might be attributed that the size of cooperative motion during the glass transition decrease due to the orientation of the soft segment, and the soft segment phase approach to a pure phase o...