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991.
992.
993.
Degree of crosslinking and mechanical properties of crosslinked poly(vinyl alcohol) beads for use in solid-phase organic synthesis 总被引:1,自引:0,他引:1
The limited swellability in polar media of the commonly used polystyrene/divinylbenzene (PS-DVB) support materials for solid-phase organic synthesis has led to the development of novel, highly swellable hydrophilic gels designed for use in aqueous or polar media. Poly(vinyl alcohol) beads crosslinked with epichlorohydrin (PVA-EP) were prepared by a two-step inverse-suspension polymerization method. While it is known that the morphology of the resulting beads can be controlled by the ratio of EP versus PVA as well as by the pre-crosslinking time, the actual degree of crosslinking of the beads and their mechanical properties remain unknown. It is therefore the purpose of this study to evaluate the actual degree of crosslinking of beads prepared with different quantities of crosslinker in the feed by spectroscopic (Raman, nuclear magnetic resonance) and chemical (functional group loading) methods. The mechanical properties of these swollen PVA-EP beads will be evaluated by single-bead unconfined compression in solvents such as water, N,N-dimethylformamide (DMF), and tetrahydrofuran (THF) and compared to model PS-DVB beads commonly used for solid phase synthesis. 相似文献
994.
报道了以磷钨钼杂多酸掺杂聚苯胺为催化剂,通过丁醛和乙二醇反应合成了丁醛乙二醇缩醛。系统考察了醛醇物质的量比、催化剂用量以及反应时间诸因素对产品收率的影响。确定适宜的工艺条件为n(丁醛)∶n(乙二醇)=1∶1.5,催化剂的质量为反应物料总质量的0.8%,反应时间1.0 h。在此反应条件下,丁醛乙二醇缩醛的收率可达71.1%。 相似文献
995.
Several low‐powered gas plasmas were employed to treat a biomedical poly(ester)urethane using the treatment gases of CO2, O2, NH3, and SO2 with different treatment time (2, 5, 10, and 15 min). The changes of the physical and chemical characteristics of the biopolymer surface were studied. Surface morphology was evaluated by scanning probe microscopy, which showed increased roughness of the surface after plasma treatment. The wettability of the surface was examined by static water contact angle (SCA) measurements, which presented that there was a decrease of SCA in all plasma treatments compared with the untreated surface and that each gas plasma had an optimum treatment time accompanied by a minimum contact angle. X‐ray photoelectron spectroscopy indicated the changes of the surface functional groups. The data demonstrated that CO2 and O2 plasmas resulted in the incorporation of oxygen‐containing groups, while NH3 plasma resulted in the combination of nitrogen‐containing groups, and SO2 plasma resulted in the formation of sulfur‐containing groups. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1273–1282, 2006 相似文献
996.
997.
S. A. Katovich P. D. Swedenborg M. Giblin E. W. Underhill 《Journal of chemical ecology》1989,15(2):581-590
The sex pheromone ofCydia toreuta (Grote), the eastern pine seedworm, was investigated using electroantennogram (AG) measurements, gas chromatography (combined GC-FID-EAD) measurements, and field tests. (E,Z)-8,10-dodecadienyl acetate (E,Z8,10-12:Ac) and (E,E)-8,10-dodecadienyl actetate (E,E8,10-12: Ac) produced both the highest EAG and EAD responses. Only a single antennal stimulatory peak was observed when female abdominal tip extracts were analyzed by GC-FID-EAD, which corresponded exactly with that of authenticE,Z8,10-12: Ac. Field tests confirmedE,Z8,10-12: Ac as the major pheromone component. TheE,Z isomer by itself caught equivalent numbers of male moths as did caged females. The addition of theE,E isomer to theE,Z form increased trap catch, although not significantly (P = 0.05). The addition of (Z,Z)-8,10-dodecadienyl acetate to theE,Z isomer significantly (P=0.05) reduced trap catch, while the addition of (Z,E)-8,10-dodecadienyl acetate to theE,Z form also decreased trap catch, but not significantly (P=0.05). 相似文献
998.
Miscibility has been investigated in blends of poly(butylene succinate) (PBSU) and poly(vinyl phenol) (PVPh) by differential scanning calorimetry in this work. PBSU is miscible with PVPh as shown by the existence of single composition dependent glass transition temperature over the entire composition range. In addition, the polymer–polymer interaction parameter, obtained from the melting depression of PBSU using the Nishi–Wang equation, is composition dependent, and its value is always negative. This indicates that PBSU/PVPh blends are thermodynamically miscible in the melt. Preliminary morphology study of PBSU/PVPh blends was also studied by optical microscopy (OM). OM experiments show the spherulites of PBSU become larger with the PVPh content, indicative of a decrease in the nucleation density, and the coarseness of PBSU spherulites increases too with increasing the PVPh content in the blends. 相似文献
999.
The thermal conductivity of a filler and the thermal conductivity of a composite made from that filler influence the heat‐transfer process during melt processing. The heat‐transfer process from the melt to the mold wall becomes an important factor in developing the skin–core morphology. These aspects were examined in this study. The thermal conductivity of polypropylene–filler composites was estimated with a standard model for various fillers such as calcium carbonate, talc, silica, wollastonite, mica, and carbon fibers. The rate of cooling under given conditions, including the melting temperature, mold wall temperature, mass of the composite, and filler content, was estimated with standard heat‐transfer equations. The time to attain the crystallization temperature for polypropylene was evaluated with a regression method with differential temperature steps. The crystallization curves were experimentally determined for the different fillers, and from them, the induction period for the onset of crystallization was estimated. These observations were correlated with the expected trends from the aforementioned formalism. The excellent fit of the curves showed that in all these cases, the thermal conductivity of the filler and composite played a dominant role in controlling the onset of the crystallization process. However, the nucleation effects became important in the later stages after the crystallization temperature was attained. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2994–2999, 2003 相似文献
1000.
Effect of sodium monofluorophosphate treatment on microstructure and frost salt scaling durability of slag cement paste 总被引:1,自引:0,他引:1
Sodium-monofluorophosphate (Na-MFP) is currently in use as a surface applied corrosion inhibitor in the concrete industry. Its basic mechanism is to protect the passive layer of the reinforcement steel against disruption due to carbonation. Carbonation is known as the most detrimental environmental effect on blast furnace slag cement (BFSC) concrete with respect to frost salt scaling. In this paper the effect of Na-MFP on the microstructure and frost salt scaling resistance of carbonated BFSC paste is presented. The results of electron microscopy, mercury intrusion porosimetry (MIP) and X-ray diffraction (XRD) are discussed. It is found that the treatment modifies the microstructure and improves the resistance of carbonated BFSC paste against frost salt attack. 相似文献