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排序方式: 共有245条查询结果,搜索用时 15 毫秒
1.
S. Shen E. D. Sudol M. S. El-Aasser 《Journal of polymer science. Part A, Polymer chemistry》1994,32(6):1087-1100
The mechanism for the formation of micron-size polymer particles in the dispersion polymerization of methyl methacrylate was investigated by applying dynamic light scattering to monitor the evolution of the average particle size in the early stages of the polymerization. In addition, the contributions of physically adsorbed stabilizer and graft copolymer were evaluated by measuring the bound, unbound (adsorbed), and free stabilizer, and by determining the amount of added stabilizer required in seeded dispersion polymerizations. Twenty nanometer particles (termed nuclei) were the smallest particles detected and are considered to be formed by aggregation of growing polymer chains precipitating from solution as they exceed their critical chain length. Aggregation of these nuclei with themselves and their aggregates continues until mature and stable particles are formed. This occurs when sufficient stabilizer occupies the particle surface which includes both the polymeric stabilizer [poly(vinylpyrrolidone)] and its graft copolymer which is created in situ. The effects of process variables are discussed based on this mechanistic picture of the dispersion polymerization process. © 1994 John Wiley & Sons, Inc. 相似文献
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3.
表面修饰纳米CdS制备中两个重要影响因素及结构表征 总被引:12,自引:0,他引:12
利用溶胶-凝胶法制备了PVP表面修饰的CdS纳米晶粒。考察了影响纳米CdS制备的两个重要因素Cd2+/S2-和PVP,及其作用机理。确证表面过剩S2-和PVP在反应体系中的作用是在较高浓度下制备纳米CdS的两个重要因素,进一步确定了PVP的最佳用量。通过TEM、ED、XRD、FT-IR等手段对合成的纳米粒子进行了结构表征,最小粒径为7~10nm,闪锌矿构型,粒子大小及形貌可通过改变Cd2+/S2-及反应物浓度来控制。最后给出了CdS/PVP纳米晶粒的结构模型。 相似文献
4.
Shan Shan Tang Chang Lu Shao Shou Zhu Li 《中国化学快报》2007,18(4):465-468
Nanofibers of poly(vinyl pyrrolidone) (PVP)/Eu^3+ with diameters of 300-900 nm were prepared by using sol-gel processing and electrospinning technique. The products were characterized by scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FT-IR), and photoluminescence (PL). The results indicated that, Eu^3+ was successfully embedded in the onedimensional hybrid nanofibers, and the PVP/Eu^3+ hybrid nanofibers had favorable photoluminescence properties. 相似文献
5.
Ying Xia WANG Feng HE Ren Xi ZHUO 《中国化学快报》2006,17(2):239-242
Amphiphilic copolymer of 5-benzyloxytrimethylene carbonate (BTMC) with poly (vinyl pyrrolidone) (PVP) was successfully synthesized using immobilized porcine pancreas lipase (IPPL) or SnOct2 as catalyst. Hydroxyl terminated PVP, synthesized with 2-mercaptoethanol as a chain transfer reagent, was employed as a rnacroinitiator. The resulting copolymers were characterized by GPC, ^1H NMR and IR. Increasing the BTMC/PVP-OH feed ratio ([B]/[P]) resulted in the increase of Mn of corresponding copolymers and the decrease of Mw/Mn. Immobilized enzyme has comparable catalytic activity to SnOct2 for the copolymerization. 相似文献
6.
PVA/PVP共混物的聚集态结构 总被引:2,自引:0,他引:2
热处理前后不同组份比二元共混物聚乙烯醇(PVA)和聚乙烯吡咯烷酮(PVP)的聚集态结构研究表明,热处理可明显提高共混物的结晶性。热处理前样品仅观察到(101)晶面衍射,热处理后可观察到4个以上衍射晶面。结晶度和微晶大小随共混物中PVP含量增加而降低。第二类晶格畸变则随PVP含量增加而增大。 相似文献
7.
Carl F. Brunius Ulrica Edlund Ann‐Christine Albertsson 《Journal of polymer science. Part A, Polymer chemistry》2002,40(21):3652-3661
This work is devoted to the design of a novel family of hydrosoluble biomaterials: poly(N‐vinyl‐2‐pyrrolidone) (PVP)‐based graft copolymers. A synthesis route has been elaborated in which ω‐functionalized PVP is prepared via chain‐transfer radical polymerization, end‐group modified, and subsequently grafted onto a polyhydroxylated backbone, typically dextran or poly(vinyl alcohol). The resulting graft copolymer biomaterials are designed for use in various biomedical applications, particularly as materials with a stronger potential for plasma expansion than already existing products have. The graft copolymers are potentially degradable because the PVP grafts are connected to the polyol backbone via a hydrolytically labile carbonate or ester linkage. The degradation of the graft copolymers was performed in vitro over a period of 6 weeks. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3652–3661, 2002 相似文献
8.
Perfluorooctanoyl modified poly(vinyl alcohol)s (FPVA) were prepared by means of substituting a small amountof hydroxyl groups on the backbone of poly(vinyl alcohol), for which the initial degree of polymerization is equal to 1750.The substitution extent, defined by the number of substituting units in a chain, for the four FPVA samples was in the range of0.5-5 perfluorooctanoyl groups per chain. The FPVA samples with the highest substitution extent still had good solubility inwater. It was shown by experimental measurement at 30.0±0.1℃ that the surface tension of the aqueous solution of thehighest substituted FPVA decreased to 16.6 mN/In at a higher concentration, e.g about 0.1 g/mL. Obviously,macromolecules of FPVA exhibit a very strong tendency to adsorb at the air-water interface, because the hydrophobicperfluorooctanoyl groups in FPVA have a very high surface activity as they are in small molecular fluorinated surfactants.The chain conformation of such a model polymer adsorbed on the air-water interface was also discussed. 相似文献
9.
添加剂PVP和MTS对合成Beta分子筛结构与性能的影响 《燃料化学学报》2017,45(4):468-474
分别以铝酸钠和硅溶胶为铝源和硅源,四乙基氢氧化铵为模板剂,在水热条件下,考察了添加剂(聚乙烯吡咯烷酮(PVP)和甲基三乙氧基硅烷(MTS))对合成Beta分子筛结构与性能的影响,并通过XRD、TEM、BET、ICP、~(29)Si-NMR和NH_3-TPD等方法对合成样品进行了结构表征和作用机理讨论,同时以催化裂化异丙苯为模型反应评价其催化性能。结果表明,与传统Beta分子筛相比,加入PVP后所得样品具有更高结晶度和较高的硅铝物质的量比(25.68)以及较大的比表面积(772 m~2/g);而加入MTS后尽管具有较大比表面积(657 m~2/g)和较高硅铝物质的量比(25.76),但是结晶度却相对降低,且粒径减小(160-320 nm)。两种添加剂作用下所得样品均具有更多酸量,在催化裂化异丙苯的反应中表现出较高的催化活性。 相似文献
10.
《应用有机金属化学》2017,31(11)
The phosphorus ylide [Ph3PCHC(O)C6H4‐NO2–4] reacted with Pd(OAc)2 to give the C,C‐orthometallated complex [Pd{κ2(C,C)‐C6H4PPh2C(H)CO(C6H4‐NO2–4)}(μ‐OAc)]2, which underwent bridge exchange reaction with NaN3, NaCl, KBr and KI, respectively, to afford the binuclear C,C‐orthopalladated complexes [Pd{κ2(C,C)‐C6H4PPh2C(H)CO(C6H4‐NO2–4)}(μ‐X)]2 (X = N3 ( 1 ), Cl ( 2 ), Br ( 3 ) and I ( 4 )). The complexes were identified using spectroscopy (infrared and NMR), CHNS technique and single‐crystal X‐ray structure analysis. Thereafter, palladium nanoparticles with narrow size distribution were easily prepared using the refluxing reaction of iodo‐bridged orthopalladated complex 4 with poly(N ‐vinyl‐2‐pyrrolidone) (PVP) as the protecting group. The PVP‐stabilized palladium nanoparticles were characterized using a variety of techniques including X‐ray diffraction, transmission and scanning electron microscopies, energy‐dispersive X‐ray spectroscopy, inductively coupled plasma analysis and Fourier transform infrared spectroscopy. The catalytic activity of the PVP‐stabilized palladium nanoparticles was evaluated in the Suzuki reaction of phenylboronic acid and the Heck reaction of styrene with aryl halides of varying electron densities. This catalyst exhibited excellent catalytic activity for Suzuki cross‐coupling reactions in ethanol–water. Notably, aryl chlorides which are cheaper and more accessible than their bromide and iodide counterparts also reacted satisfactorily using this catalyst. After completion of reactions, the catalyst could be separated using a simple method and used many times in repeat cycles without considerable loss in its activity. 相似文献