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研究了三种不同结构的引发剂,溴代乙酸乙酯(EBrA)、α-溴代丁乙酯(EBrB)、α-溴代异丁酸乙酸(EBriB)引发的苯乙烯的原子转移自由基聚合反应(ATRP)。发现EBrA引发的苯乙烯的ATRP不是“活性”聚合。EBriB引发的苯乙烯的ATRP引发效率不够高,也不是典型的“活性”聚合。EBrB引发的苯乙烯的ATRP是较为典型的“活性”聚合:聚合物的分子量可以通过调节单体/引发剂的投料量及反应时间来控制,所得聚合物的分子量分布很窄,且有随转化率的增加而逐渐变窄的趋势。 相似文献
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本文采用一种新颖的活性自由基聚合-原子转移自由基聚合的方法,以1-溴代苯乙烯作为引发剂,过渡金属卤代物与配位剂络合物为催化体系,环己酮为溶剂,进行了甲基丙烯酸正丁酯和丙烯酸正丁酯的活性聚合。得到具有指定分子量和窄分子量分布的模型聚合物。计算并讨论了两聚合体系的ATRP的动力学数据。 相似文献
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以2-溴异丁酸季戊四醇四酯为引发剂在CuBr/bpy催化下实施苯乙烯和丙烯酸β-羟丙酯原子转移自由基共聚合,结果表明聚合物的分子量与理论分子量接近,聚合反应具有活性聚合的特征。进一步对聚合产物进行GPC,H-NMR,IR和羟值滴定分析,表明合成的星状共聚合物中同时具有苯乙烯和丙烯酸β-羟丙酯结构单元,而且羟基在聚合物中近似均匀分布。 相似文献
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以“Cr~(2+)+BPO”体系,在0~40℃下,引发了一系列烯类单体的聚合。该体系引发的活性自由基聚合反应对单体结构有如下的选择性:α-甲基丙烯酸酯类单体在不高于30℃时能进行活性自由基聚合;其它烯类单体,如丙烯酰胺、丙烯腈、苯乙烯以及α-碳原子上不带甲基的丙烯酸酯类单体,均不能进行;而丙烯酸和α-甲基苯乙烯则不能被引发聚合。当温度高于30℃时,α-甲基丙烯酸酯类单体只能进行一般的自由基聚合。根据聚合结果,讨论了该体系引发活性自由基聚合反应的机理。利用“Cr~(2+)+BPO”体系,使MMA与丙烯腈进行嵌段共聚,共聚产物经分离,得到了较纯的嵌段共聚物,并予以表征。采用ESR和可见光谱,探讨了“Cr~(2+)+BPO”体系陈化反应的机理。 相似文献
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在甲基咪唑/乙酸盐离子液体中,由维生素C(Vc)/Cu^2+/2-溴异丁酸乙酯(EBiB)为引发体系引发的甲基丙烯酸甲酯的聚合反应具有原子转移自由基聚合的特征且反应可控。使用Vc/Cu^2-为催化体系避免了Cu^-易被氧化的缺点。该催化体系有较高的活性,可使聚合反应以较快的速率进行。所用的离子液体具有较高的粘度,它降低了反应中生成的Cu^-在其中的扩散速率,以致聚合反应具有诱导期。增加Vc的浓度能加快聚合反应的速率,Vc过量较多会降低聚合反应的可控度,氧气存在与否对聚合反应无影响。 相似文献
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讨论了以α-溴代丙酸乙酯(EPN-Br)为引发剂、卤化亚铜(CuX)/联二吡啶(bpy)为催化剂,80℃下,甲基丙烯酸甲酯(MMA)地不同溶剂中的原子转移自由基聚合(ATRP)反应。通过对催化剂CuBr或CuCl及几种溶剂的考察,发现在80℃下EPN-Br/CuBr/bpy能有效控制丙烯酸甲酯(MA)的本体ATRP反应,但并不能很好地控制MMA在EAc中的聚合反应为一可控聚合过程,引发效率为0.8 相似文献
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以偶氮二异丁腈(AIBN)为引发剂,首次研究了高转化率下,温度,引发剂用量等对全氘代苯乙烯自由基本体聚合反应的影响。实验发现,较低的反应温度下,氘代单体聚合产物分子量随温度的升高而降低的速率大于非氘代单体;而温度高于90℃时,升高温度对两者分子量的影响均不十分明显。 相似文献
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在培养紫苏植物细胞以生产花色素的过程中,选择或设计了鼓泡式和搅拌式四种不同的生物反应器,考察了各种反应器中的培养条件,结果表明,基于花色素的生产率,鼓泡式和带螺旋桨的搅拌式反应器优于两种涡轮桨反应器,本研究为该细胞培养所用反应器的选择、设计、优化和放大,提供了一定的实验依据。 相似文献
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Data on farm characteristics and the results of the first herd test for brucellosis were collected for 74 reactor and 74 negative herds in Wellington County, Ontario. Each reactor herd was classified as either probably infected or probably not infected using the occurrence of abortions prior to the first herd test or during the testing period, the total number of cattle removed and/or the spread of reactors within the herd as criteria of infection.Statistical techniques were used to select variables which were good "discriminators" between probably infected and noninfected herds. In general, reactor herds were primarily dairy herds and were somewhat larger than negative herds. The presence of only single suspicious reactors on the first test appeared to be a good predictor of lack of infection with Brucella abortus. Among the 37 farms in this category the single reactor was removed from only eight farms and no evidence o fthe spread of infection was observed. The presence of one or more positive reactors on the first herd test appeared to be a good predictor of the presence of infection. Of the 24 farms in this category, evidence of the spread of infection was present in ten farms and seven of these ten farms were eventually depopulated.The brucella milk ring test appeared to be the most effective means of identifying infected herds under the conditions present in Wellington County. 相似文献
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Cultures of leukocytes from patients with sarcoidosis were stimulated with Kveim antigen or PPD-S and the macrophage reactions were compared with those obtained under similar conditions with leukocyte cultures from healthy tuberculin reactors. The non-stimulated control cultures of Kveim-positive sarcoid patients showed signs of macrophage activation, namely an increase in cytoplasmic pyroninophilia in small and enlarged macrophages, together with a higher than normal rate of lymphoblast transformation. In the presence of Kveim antigen this activation was more marked, even in cases where the blast response to the antigen was of low magnitude. Stimulation with tuberculoproteins produced a slight activation of macrophages only in cultures from Kveim reactors who had also shown positive tuberculin reactions.
These observations suggest that the study of lymphocyte transformation together with that of macrophage activation will improve the immunocytological assessment of sarcoidosis.
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根管长度电测法准确性的研究 总被引:5,自引:1,他引:4
目的探讨根尖炎症及根管干、湿状态对电测法测量根管工作长度准确性的影响.方法临床上随机选择拟做根管治疗的120颗牙共140个根管进行研究,其中无根尖炎和有根尖炎者分别为56、84个根管.常规根管清理后,采用ROOT ZX根管长度电测仪在干、湿两种根管状态下进行根尖位置的探测,根管充填后,根据X线片影像确定根管长度电测法的准确性. 结果根管充填后X线片显示恰填者104个(74.29%)根管,欠填者6个(4.28%)根管,超填者30个(21.43%)根管.干燥的根管较湿润的根管更易测得准确的根管工作长度(P<0.01);有、无根尖炎其测量结果准确性无显著性差异(P>0.05).结论根管长度电测法是一种准确度高、操作简便且实用的确定根管工作长度的方法.根尖炎症对其测量根管工作长度的准确性无明显影响,干燥的根管较湿润的根管更易测得准确的根管工作长度. 相似文献
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在对文题仿真研究的基础上,对基本模型进行了简化,并应用自伴随算子性质,导出了温度波的显式表达式。结果表明,简化模型和仿真结果有较好的一致性。 相似文献
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F C Thomas A Girard P Boulanger G Ruckerbauer 《Canadian journal of comparative medicine》1976,40(3):291-297
The plaque neutralization, complement fixation, and agar gel precipitin tests were compared by measuring bluetongue virus antibody in 137 serums from experimental animals (cattle and sheep) and suspected field reactors (cattle and deer). In general, the tests agreed well with each other. Plaque neutralization titers began earlier than the other two and went much higher than the complement fixation titers. Plaque neutralization titers usually peaked between two and three weeks after exposure and complement fixation titers from four to six weeks. The greater sensitivity of the plaque neutralization test allowed the detection of all complement fixation and agar gel precipitin reactors whereas occasionally the latter two tests failed to detect plaque neutralization reactors. 相似文献