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低浓度HPAM/AlCit交联体系的27Al NMR研究 总被引:2,自引:0,他引:2
用27Al NMR谱研究了高分子量低浓度的部分水解聚丙烯酰胺(HPAM)与柠檬酸铝(AlCit)体系交联反应过程中Al的化学位移和Al的自旋-晶格弛豫时间的变化. 结果表明, HPAM与AlCit反应后, 与HPAM分子链上的羧基发生配位交联的Al的化学位移向低场移动, 而不参与交联反应的AlCit分子结构中Al的化学位移基本不变. HPAM/AlCit交联体系中存在三种形态的Al, 分别对应三种不同的自旋-晶格弛豫时间. 当HPAM的质量浓度≤200 mg/L时, HPAM与AlCit反应过程中交联态Al的自旋-晶格弛豫时间τ13随反应进行变小, HPAM与AlCit主要发生分子内交联反应. 当HPAM的质量浓度≥250 mg/L时, HPAM与AlCit反应过程中交联态Al的自旋-晶格弛豫时间τ13随反应进行变大, HPAM与AlCit主要发生分子间交联反应. 相似文献
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低浓度HPAM/AlCit交联聚合物溶液性质研究 总被引:3,自引:0,他引:3
采用粘度法、扫描电镜(SEM)、核孔膜过滤、动态光散射(DLS)和27Al NMR法,研究了高分子量低浓度的部分水解聚丙烯酰胺(HPAM)与柠檬酸铝(AlCit)体系交联反应过程溶液性质变化.结果表明,HPAM与AlCit反应在低剪切速率时体系粘度随反应进行而降低,在剪切速率较高时具有剪切稠化现象,HPAM与AlCit反应过程中交联态Al的自旋 晶格弛豫时间随反应进行变短.低浓度的HPAM与AlCit发生分子内交联反应形成交联聚合物线团(LPC)在水中的分散体系,即交联聚合物溶液(LPS).交联聚合物溶液中LPC的平均流体力学半径约为238 nm,其形态接近球形,具有多分散性. LPS对1.2 μm核孔膜的封堵程度与其反应时间有关. 相似文献
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溶胶凝胶分配理论是在分子水平上表征交联网络结构的有效工具。由Flory等建立和发展起来的这一理论,由于引用了溶胶相无分子内环化反应的假定,特别是在理论推导中将分子内交联反应与分子间的链增长反应对两相分配的贡献未能加以区别,致使理论与实验不符。本文充分考虑了经典理论的这些缺欠,建立了更为符合客观实际的理论模型。同时,用十分简便的方法推导了反应溶胶分数,溶胶反应程度,分子内和分子间总反应程度等量宏观联系的参数方程组。以聚酯为模型化合物的实验研究与本文所得理论结果基本相符。 相似文献
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可溶解的聚氨酯脲微凝胶的合成及其分子尺寸的测定 总被引:2,自引:0,他引:2
以聚氧化四亚甲基二醇、4,4′ 二苯甲烷二异氰酸酯和己二胺为原料 ,利用高分子在溶液中基本形态是无规线团的特征 ,设计了一个含有分子内和分子间反应的交联聚合体系 ,由于分子内反应与分子间反应是一对竞争反应 ,使得交联过程得以控制 ,在溶液聚合体系中合成了可溶解的微凝胶 .在分子尺寸测定过程中 ,发现了这种高分子在溶液中非常容易形成分子簇 ,且分子簇的形成与解离处于不平衡之中 ,这可能是交联高分子的一种特殊的溶液行为 相似文献
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甲基迁移反应在合成化学和生命科学领域具有重要意义.迄今为止,所报道的甲基迁移反应大多数发生在不同种类分子之间.因此,寻找新型甲基迁移反应具有一定的研究价值.本研究以环境中常见的杀虫剂倍硫磷为研究对象,采用电喷雾质谱技术为分析工具对反应体系进行高灵敏分析,探究在CF3COOH及纳米二氧化钛(TiO2)条件下,倍硫磷分子中发生甲基迁移反应的可能性.结果表明,在CF3COOH和TiO2共同作用下,倍硫磷分子中的甲基可以从同一分子的氧原子上迁移到不饱和硫原子上,发生分子内1,3-甲基迁移反应,形成异构体硫甲基化产物;同时,异构体产物中的甲基还可以从硫原子上再继续迁移到另一分子倍硫磷的不饱和硫原子上,发生分子间甲基迁移反应.同时结合密度泛函理论计算对倍硫磷分子内和分子间甲基迁移反应的过程进行动态模拟,并对其迁移机理进行解释.本研究发现了倍硫磷能发生分子内和分子间甲基迁移反应,提供了一种研究甲基迁移反应的质谱方法,为倍硫磷的降解研究提供了新思路. 相似文献
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反应性聚合物微凝胶的合成及应用 总被引:9,自引:0,他引:9
反应性聚合物微凝胶是一种具有反应活性,分子内交联的高分子。它具有优良的加工性能,涂膜的力学性能及耐久性也十分优异,主要应用于制备高档涂料或对涂料进行改性,本文着重介绍了反应性聚合物微凝胶的合成方法及其在涂料改性方面的应用。 相似文献
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线型聚(苯乙烯-乙烯)(PSE)嵌段共聚物在氯甲基化过程中,容易发生交联反应。为了表征交联反应的程度,先采用间接氯甲基化方法,在均相反应体系中实现了PSE的氯甲基化,然后通过傅里叶红外光谱(FT-IR)、氢核磁共振(1H-NMR)、差示扫描量热仪(DSC)和热失重分析仪(TGA),对氯甲基化产物进行了分析表征。结果表明:氯甲基化产物用溶剂抽提称重与氢核磁谱图计算相结合的方法,可以准确地测定其交联程度;氯甲基化产物在220℃左右发生降解;交联反应会使产物的玻璃化温度升高,但会导致氯甲基基团更容易发生热分解。 相似文献
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以1,3─二苯丙烷(DPP)作为煤相关模型化合物,考察了在400℃下分子氢和催化剂对DPP分解反应的作用。DPP的分解反应主要经C_烷─C_烷键的断裂进行,由DPP的分解产生的苄基自由基(PhCH_2)等活性自由基显著促进DPP中C_烷─C_烷键的断裂。分子氢与PhCH_反应,产生可夺取DPP中a-亚甲基上的氢或附加在DPP中苯环的ipso位上游离氢原子;分子氢还可以还原作为DPP分解产物的苯乙烯,从而防止其与PhCH_2反应。由于这些作用,分子氢促进DPP的分解反应。在加压氢气存在下添加二硫化铁进一步加速DPP分解反应的进行,而添加超细铁粉抑制DPP的分解反应。 相似文献
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Stephen A. Canary Malcolm P. Stevens 《Journal of polymer science. Part A, Polymer chemistry》1992,30(8):1755-1760
Mixtures of maleimidomethylated polystyrene with difurfuryl adipate or with furfuryl alcohol-esterified poly[styrene-co-(maleic anhydride)] underwent thermally reversible Diels–Alder crosslinking. Reversal of crosslinking occurred rapidly at 150°C. The instability of the furfuryl group, however, limits the practicability of the reaction. © 1992 John Wiley & Sons, Inc. 相似文献
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医用高分子水凝胶的设计与合成 总被引:5,自引:0,他引:5
作为一类重要的医用功能材料,高分子水凝胶可望在药物控释、软骨支架构建、活性细胞封装等方面获得广泛应用。综述了基于化学交联和物理交联的有关水凝胶的设计与合成方法,重点介绍了通过自由基共聚反应、结构互补基团间化学反应形成的化学交联水凝胶以及通过荷电相反离子问相互作用、两亲性嵌段或接枝共聚物疏水缔合、结晶与氢键相互作用形成的物理交联水凝胶。 相似文献
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AbstractStretchable and tough hydrogels have attracted a lot of attention due to their great potential in applications such as wound healing, drug delivery, tissue culture, etc. They can also be paired with electronic components to create artificial skin, wearable electronics, and patches. To promote the development of more hydrogels, we will summarize methods and materials that have been used to develop these gels, and then we will compare the performance of these gels in an aim to guide the future development of gels for superior performance, especially for specific applications. 相似文献
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The present work reports on the synthesis and evaluation of a crosslinkable thiolated gelatin derivative. The effect of varying two parameters including the pH of the reaction buffer and the thiolating agent applied (i.e. N-acetylhomocysteine thiolactone versus Traut’s reagent) on the obtained modification degree was studied in a first part. The gelatin derivatives synthesized starting from N-acetylhomocysteine thiolactone and Traut’s reagent were characterized in depth using size exclusion chromatography and UV–VIS spectrophotometry. In a subsequent part of the present work, hydrogel films were prepared starting from the thiolated gelatin derivative developed using N-acetylhomocysteine thiolactone. The contributions of both the chemical and the physical crosslinking of the hydrogels developed were studied in depth using rheology, swelling experiments and texturometry. The results indicate that the physical structuring, inherent to gelatin, contributes to a large extent to the mechanical properties. However, the chemical crosslinking mostly determines the final hydrogel properties and can be controlled to a large extent. The gelatin-based gels are flexible, strong and transparent. A major advantage of disulfide-crosslinked hydrogels is the fact that the crosslinking is reversible. The latter could be interesting in view of future applications as cell carriers for tissue engineering. 相似文献
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Oil-containing gelatin-gum Arabic microparticles were prepared by complex coacervation followed by crosslinking with glutaraldehyde or transglutaminase. A fluorescent mixture, khusimyl dansylate (KD) as the fluorescent compound mixed to the vetiver essential oil, was used as oil model. The effect of the type of crosslinking of the coacervated gelatin-gum Arabic membrane, the physical state of microparticles, wet or freeze-dried and the type of release media, aqueous with surfactants, Sodium Dodecyl Sulphate (sds) or Tween 80 (tw) and anhydrous ethanol as organic media on the release rate of the KD from the microparticles, was experimentally investigated.It was shown that the oil was dispersed uniformly throughout the microparticles and the chemical crosslinked microparticles were more resistant to swelling, presenting smaller sizes after hydration. Also the crosslinking effect, transglutaminase or glutaraldehyde, could be confirmed by the integrity of the crosslinked gelatin-gum Arabic microparticles after incubation in the aqueous sds media, compared to complete dissolution of the uncrosslinked microparticles in this media.The cumulative fluorescent KD release from the gelatin-gum Arabic microparticles decreased in the following order of dissolution media: anhydrous ethanol > tw > sds and the wet microparticles have shown a faster KD release than freeze-dried ones. A mathematical model was used to estimate the diffusion coefficient (D). The chemically crosslinked gelatin-gum Arabic microparticles ensured a pronounced retard effect in the KD diffusion, presenting a D varying from 0.02 to 0.6 × 10−11 cm2/s, mainly in an aqueous media, against D varying from 1.05 to 13.9 × 10−11 cm2/s from the enzymatic crosslinked microparticles. 相似文献
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Jianxin Chen Andrew R. Vaino Rosemary L. Smith Scott C. Collins 《Journal of polymer science. Part A, Polymer chemistry》2008,46(11):3482-3487
Polydimethylsiloxane (PDMS) polymers incorporating pendant cinnamate groups have been synthesized and evaluated for their ability to form patterned thin films via photo‐crosslinking. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3482–3487, 2008 相似文献
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An inexpensive and simple method was adopted for the preparation of chitosan microspheres, crosslinked with glutaraldehyde (GA), for the controlled release of an insoluble drug‐ibuprofen, which is a commonly used NSAID (non‐steroidal anti‐inflammatory drug). The chitosan microspheres were prepared by different methods and varying the process conditions such as rate of stirring, concentration of crosslinking agent, and drug:polymer ratio in order to optimize these process variables on microsphere size, size distribution, degree of swelling, drug entrapment efficiency, and release rates. The absence of any chemical interaction between drug, polymer, and the crosslinking agent was confirmed by Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC), and thermogravimetric analyses (TGA) techniques. The microspheres were characterized by optical microscopy, which indicated that the particles were in the size range of 30–200 µm and scanning electron microscopy (SEM) studies revealed a smooth surface and spherical shape of microspheres. The microsphere size/size distributions were increased with the decreased stirring rates as well as GA concentration in the suspension medium. Decreasing the concentration of crosslinker increased the swelling ratio whereas extended crosslinking exhibited lowered entrapment efficiency. The in vitro drug release was controlled and extended up to 10 hr. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献