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211.
Summary: A novel chitosan derivative with polysarcosine side chains, i.e., chitosan‐graft‐polysarcosine [chitosan‐graft‐poly(N‐methylglycine)], was synthesized by ring‐opening polymerization of sarcosine N‐carboxyanhydride (NCA) with chitosan as a macroinitiator in the presence of carboxylic acids in dimethyl sulfoxide at 27 °C. Degree of substitution ( ) for polysarcosine side chains introduced to chitosan was controlled successfully by the feed amount of the additive nicotinic acid ( = 0.21–0.71). Independent of control, degree of polymerization ( ) for polysarcosine side chains was controlled by adjusting feed ratios of NCA monomer to chitosan ( = 14–43). Kinetic analysis of the propagation of sarcosine NCA was conducted by measuring CO2 evolution. Apparent kp values decreased with increased feed amounts of nicotinic acid, supporting the theory that propagation of NCA in the presence of nicotinic acid proceeds via equilibrium between active amine and dormant ammonium species.
212.
Keigo Aoi Aki Motoda Masahiko Okada Toyoko Imae 《Macromolecular rapid communications》1997,18(10):945-952
Novel linear polymer/dendrimer block copolymers, poly(2-methyl-2-oxazoline)-block-poly(amido amine) dendrimers (water-soluble full-generation type 4 (G = 4.0 and 5.0) and amphiphilic half-generation type 5 (G = 3.5, 4.5, and 5.5)), were synthesized by divergent-growth dendrimer construction with ω-ethylenediamine-terminated poly(2-methyl-2-oxazoline), which was prepared by living ring-opening polymerization of 2-methyl-2-oxazoline. Assembly of the amphiphilic dendrimer-based block copolymer (G = 5.5) was investigated by surface tension measurements (critical micelle concentration, 0.49 wt.-%) and by small-angle neutron scattering analysis (spherical particles; assembled number, ca. 103). 相似文献
213.
Masahiko Okada Kouji Tachikawa Keigo Aoi 《Journal of polymer science. Part A, Polymer chemistry》1997,35(13):2729-2737
A series of polyesters were synthesized by the bulk polycondensations of the respective combinations of two difuranic diesters, i.e., bis(5-(methoxycarbonyl)-2-furyl)methane ( 4a ) and 1,1-bis(5-(methoxycarbonyl)-2-furyl)ethane ( 4b ), with two 1,4 : 3,6-dianhydrohexitols [1,4 : 3,6-dianhydro-D -glucitol ( 1 ) and 1,4 : 3,6-dianhydro-D -mannitol ( 2 )], four aliphatic diols, and three oligo(ethylene glycol)s. The polycondensations were carried out at 220–230°C in the presence of titanium isopropoxide as a catalyst, giving polyesters having number average molecular weight up to 2.4 × 104. These polyesters are soluble in a variety of solvents including chlorinated hydrocarbons, 1,4-dioxane, dimethyl sulfoxide, dimethylformamide, and sulfolane. Soil-burial tests along with enzymatic degradation experiments showed that these polyesters are potentially biodegradable. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 2729–2737, 1997 相似文献
214.
Poly(vinyl alcohol)-Congo Red (PVA-CR) complexes in aqueous solutions have a unique sol-gel transition behaviour. At an appropriate PVA concentration, a sol-gel-sol-gel type reentrant transition takes place with increasing CR concentration. The microscopic structure and Theological properties of these complexes were investigated by small-angle neutron scattering (SANS) and viscometry. 相似文献
215.
Keigo Okamoto Amato Igarashi Hiroaki Imoto Kensuke Naka 《Journal of polymer science. Part A, Polymer chemistry》2022,60(2):214-220
We recently reported a bifunctional methacrylate monomer having a side-opened cage-silsesquioxane as a scaffold. Although free-radical polymerization proceeded mainly through cyclopolymerization, cross-linking structures were included. In this work, we have optimized the reaction conditions for reversible addition-fragmentation chain transfer cyclopolymerization using 2-cyano-2-propyl dithiobenzoate. As a result, polymers with relatively low polydispersity indices were successfully obtained. After removal of dithiobenzoate end groups, the transparency was high (>98%) in the range of visible range (400–800 nm). The content of the unreacted dangling vinyl groups, which was controlled by monomer concentration, affected the thermal stability of the resulting polymers. In addition, the bifunctional cage-silsesquioxane monomer can be readily copolymerized with methyl methacrylate without cross-linking. 相似文献
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219.
Junyong Kang Yasunori Okano Keigo Hoshikawa Tsuguo Fukuda 《Journal of Crystal Growth》1994,140(3-4):435-438
A vertical gradient freeze apparatus was set up to investigate the influence of a vertical magnetc field on Te dopant segregation in InSb. Te-doped InSb crystals were grown in the presence and absence of an 80.0 kG magnetic field. The axial profile of the Te concentration in the crystal grown in the magnetic field was observed to be more uniform than that grown without magnetic field, which was attributed to the influence of the high magnetic field on Te dopant segregation by reducing convection in the melt. 相似文献
220.
The effect of heat treatment at temperatures above 300°C on the low temperature relaxation of poly(4,4′-oxydiphenylenepyromellitimide) (Kapton H-film) was studied by wide-line nuclear magnetic resonance (NMR), mechanical, and dielectric measurements. In the NMR line spectrum of the as-received film, a narrow component above ?60°C and a broad component which begins to narrow at about ?100°C were observed. It is proposed that the narrow component is associated with absorbed water, because it disappeared in the heat-treated film at 300°C in N2. On the other hand, the behavior of the broad component was not influenced by heating to 300°C in N2. Mechanical and dielectric loss peaks were observed at ?75°C (11 Hz) and ?65°C (1 kHz), respectively, in the as-received film. These loss peaks did not change in intensity with heating to 300°C in N2. It is proposed that the mechanical and dielectric loss peaks corresponding to the narrowing of the NMR broad component are associated with the local-mode motion of the diphenylether portion of the polypyromellitimide chain. It was found that crosslinks are formed by heating to 374°C in air through coupling of the diphenylether portions of the molecular chains. With the formation of crosslinks the dielectric loss peak shifted toward higher temperature and the intensity decreased through restriction of the local-mode motion of the diphenylether portion of the molecular chain. 相似文献