热重分析法测试玻纤增强PP和改性PA6塑料中低含量炭黑的研究

采用热重分析法(TGA法),分别以通用塑料中的玻纤增强PP和工程塑料中的改性PA6为代表,首先重点研究塑料体系中低含量(小于1%)炭黑测试的通用关键影响因素,随后验证低含量炭黑测试方法的测试准确性和通用性,最后简要分析造成上述两种材料中低含量炭黑结果差异性的原因。结果表明:测试分段程序和处理程序的选择、坩埚的影响和空白样品影响是低含量炭黑测试的三点通用关键影响因素,本文测试程序分为热解段、降温段和煅烧段,处理程序的炭黑处理温度区间根据炭黑母粒煅烧段的DTG曲线确定,坩埚经二次处理,空白样品测试结果作空白刨除;使用本文炭黑测试方法测试上述两种塑料体系中不同浓度的低含量炭黑,结果可控制在(理论添加量±0.05)%以内,准确性高;此外,提出"有机碳+无机碳+其它"模型,有助于快速理解炭黑测试方法并用于日常产品质量监控或材料逆向分析。     

交联低密度聚乙烯交联程度表征方法的研究

硅烷交联法和过氧化物交联法是聚乙烯交联改性的两种重要方法［１］,以往的文献上通常都以凝胶含量来表征这两种方法制备的交联产物的交联程度［２～６］,但是在实践中我们发现,凝胶含量基本相同的硅烷交联聚乙烯和过氧化物交联聚乙烯的性能存在着很大的差异,例如在７０℃的二甲苯中凝胶含量为６２％的过氧化物交联低密度聚乙烯（ＬＤＰＥ）的平衡溶胀比是相同凝胶含量的硅烷交联ＬＤＰＥ的４倍,１５０℃时凝胶含量为７０％的硅烷交联聚乙烯的热延伸率比相同凝胶含量的过氧化物交联聚乙烯小三倍,而且二者的结晶行为和结晶度也有很大的…     

蛇莓果实总花色苷含量测定方法的比较

为了寻求快速、经济地测定蛇莓果实总花色苷含量的方法,采用单-pH法和pH示差法进行测定,比较分析了两种方法测定结果的差异性.结果表明,两种pH法测定的吸光度与浓度均具有良好的线性关系,测定结果没有显著性差异.两种pH法均能用于蛇莓果实总花色苷含量的测定,且需要在相同溶剂中进行,其中单一pH法操作更简便.     

反气相色谱法研究聚丙烯结晶动力学及对熔点和结晶度的测定

<正> 研究聚合物的结晶动力学,过去大多采用膨胀计法和解偏振光法。曾有文献报道采用反气相色谱法测得聚乙烯等温结晶线。通过实验可知,测定聚丙烯结晶度时,试样热历史和测定前陈化温度的选择均影响测定结果。此外在测定聚丙烯试样的熔点时,保留图中出现了两个转折,经反复实验证实:此两转折对应于聚丙烯中不同晶形(α-、β-形)的熔点。     

炭黑填充聚乙烯材料电阻—温度特性研究

研究了炭黑／聚乙烯导电复合材料的ＰＴＣ特性及在不同条件下的电阻变化。发现ＰＴＣ特性与体积膨胀及聚乙烯晶相的熔融有许多一致性。认为材料的体积膨胀及聚乙烯晶相熔融时炭黑颗粒均匀化扩散导致了电阻随温度上升。在较高温度下，炭黑颗粒在分子链段热运动的推动下会发生相对聚集使电阻不断减小，这是材料出现ＮＴＣ现象的原因。材料总的电阻温度特性是体积膨胀、炭黑向聚乙烯熔融区扩散及相互聚集三个因素共同作用的结果。     

微波消解-非萃取分光光度法测定聚乙烯包材中的锑

建立聚乙烯包材中锑含量的测定方法。微波消解法消解处理聚乙烯包材后,利用表面活性剂OP对5-Br-PADAP、碘化钾和锑的三元复合物的增溶作用,采用络合分光光度法测定锑的含量,筛选了分光光度法测定锑含量的显色条件。锑质量浓度(0.100～1.00 mg·L~(-1))与锑吸光度呈良好的线性关系,加标回收率为103.3～104.0%,精密度RSD小于2%,与标准物质和国标方法相比较,该方法的准确性得到了验证。本方法简单、准确性高,精密度好,可用于聚乙烯包材中锑含量的测定。     

离子选择电极分析法测定聚乙烯中氟

提出了一种新的离子选择性电极分析方法,即体积校正-等电位差-标准加入法,并用于聚乙烯中氟含量的测定。对样品干法灰化条件进行了考查。有机化合物标样回收率为98.0％,聚乙烯分析结果的相对标准偏差为1.6％。方法简便、准确。     

矿区植物重金属元素测定的两种前处理方法比较

分别采用酸消解法和干灰化法处理16种矿区植物,并用原子吸收分光光度法测定其中的Mn、Cd、Cr和Zn的含量。结果表明:除Cd外,两种处理方法对Mn、Cr、Zn的测定结果有明显影响。测定植物组织Cd时,两种处理方法都可采用;测定Mn、Cr元素,采用酸消解法较为合适;测定Zn则宜采用干灰化法,并可适当延长木质部分(根、茎)的灰化时间。     

熏蒸提取法对比测定不同土种中的微生物碳含量

土种是土壤发生分类中的最基础分类单元,基于土种的微生物量调查是土壤生物调查中的重要工作,其中微生物量以微生物碳含量表征。采用氯仿熏蒸提取法-碳光谱分析法和重铬酸钾氧化法对比测定土壤中的微生物碳含量,对于提取液中的有机碳含量,碳光谱分析法的检出限为0.11 mg/L,重铬酸钾氧化法的检出限为1.55 mg/L。在精密度试验中,对于熏蒸后的土样,碳光谱分析法的RSD为8.8%~9.9%,重铬酸钾氧化法的RSD为7.0%~17.6%。对于未熏蒸处理的土样,两种方法的RSD分别为5.3%~9.3%和9.3%~12.0%。微生物碳测试结果与土壤的水分含量相关性显著（p<0.05）。对比两种方法的测定结果,发现熏蒸土样的相对偏差范围为0.1%~49.4%,未熏蒸土样的相对偏差范围为0.0%~60.9%,低浓度样品的偏差较大。对于不同土种中微生物碳含量的测定,碳光谱分析法测得结果范围为146 μg/g dry soil~414 μg/g dry soil,重铬酸钾氧化法的范围为131 μg/g dry soil~407 μg/g dry soil,两种方法测定结果间无显著差异。结果表明,低浓度样品测定时采用重铬酸钾氧化法造成的误差较大,宜采用碳光谱分析法,两种方法均能有效测定不同土种中的微生物碳含量。     

GFAAS和ICP-MS对比测定大米中三种重金属含量

分别采用石墨炉原子吸收光谱法(GFAAS)与电感耦合等离子体质谱法(ICP-MS)同时测定大米中铅、镉和铬三种重金属含量,从分析方法的准确度、精密度等方面比较两种方法的优缺点。研究结果表明,两种方法测定结果均能满足分析要求,但ICP-MS法的测定结果更接近样品真实值,操作更加简便。     

A carbanion induced synthesis of highly congested pyrazole and imidazole containing heterocycles

An efficient approach to the synthesis of highly congested di, penta and hexacyclic pyrazoles as well as imidazole fragment containing novel heterocyclic molecule has been developed through a carbanion induced transformation of suitably functionalized 2H-pyran-2-ones, benzo[h]chromene and thiochromeno[4,3-b]pyrans. Due to the presence of fluorescence, we report their prime application metal sensor as off/on switching in ferric ions.     

α-Amino acid derived enaminones and their application in the synthesis of N-protected methyl 5-substituted-4-hydroxypyrrole-3-carboxylates and other heterocycles

A new and simple synthesis of novel N-protected methyl 5-substituted-4-hydroxypyrrole-3-carboxylates, which exist in equilibrium with their 4-oxo tautomers, has been developed in two steps starting from N-protected α-amino acids. The key intermediates are enaminones, which can also be isolated, characterized, and used for the construction of other functionalized heterocycles, before they spontaneously decompose to pyrrole products. 4-Hydroxypyrroles are prone to partial aerial oxidation but can be efficiently alkylated or reduced to stable polysubstituted pyrrolidine derivatives.     

Specific intramolecular aromatic CH insertion of diazosulfonamides

The chemoselectivity in the intramolecular CH insertion of various diazosulfonamides has been experimentally studied. The results reveal that the aliphatic 1,4-, 1,5-, or 1,6-C(sp³)?H insertions of diazosulfonamides are not accessible, while the aromatic 1,5-C(sp²)?H insertion can be realized specifically by adjusting the diazo-adjacent group. In addition, the general chemoselectivities in the intramolecular CH insertions of diazosulfonyl compounds are summarized. Generally, diazosulfones undergo both aromatic 1,5-C(sp²)?H and aliphatic 1,5- and 1,6-C(sp³)?H insertions, while diazosulfonates undergo aliphatic 1,5- and 1,6-C(sp³)?H insertions. However, diazosulfonamides only undergo aromatic 1,5-C(sp²)?H insertion.     

N-Heterocyclic carbene-palladacyclic complexes: synthesis,characterization and their applications in the C-N coupling and α-arylation of ketones using aryl chlorides

N-Heterocyclic carbene-palladacyclic complexes 3 were successfully achieved in a one-pot procedure under mild conditions. The structure of 3a was unambiguously confirmed by X-ray single crystal diffraction and it was an active catalyst in the Buchwald-Hartwig amination and α-arylation of ketones even at very low catalyst loadings (0.01?mol%).     

Selective synthesis of 4,5-dihydroimidazo- and imidazo[1,5-a]quinoxalines via modified Pictet–Spengler reaction

An efficient tandem approach for the selective synthesis of 4,5-dihydroimidazo[1,5-a]quinoxalines 6a–g and imidazo[1,5-a]quinoxalines 7a–h by the reaction of 2-imidazolyl anilines 4a–c with aryl aldehydes 5a–k under mild reaction conditions is described. Introduction of electron releasing alkyl groups in substrates 4a–b was found to be instrumental for the success of the reaction.     

Understanding the Diels-Alder reactivity of 1,2-azaborine analogues

The Diels-Alder reactivity of 1,2-heteroborines (H₄C₄B(H)X, X?=?NH, PH, AsH; O, S, Se) has been computationally explored by means of Density Functional Theory (DFT) calculations. The influence of the HB?=?X fragment on the reactivity of the system has been quantitatively analyzed in detail by means of the so-called Activation Strain Model (ASM) of reactivity. It is found that the interaction between these species and the dienophile is significantly stronger than that computed for their all-carbon isoelectronic counterpart, benzene. In addition, the strain energy plays a key role in the observed reactivity trends. The role of the aromaticity strength of these heteroarenes on the reactivity is also assessed.     

Synthesis of N-substituted carbazolones from α-iodo enaminones via Pd(0)-catalyzed intramolecular coupling under microwave irradiation

A variety of N-aryl and N-alkyl carbazolones were conveniently achieved in good to high yields via Pd₂(dba)₃-mediated intramolecular coupling of N-substituted α-iodo enaminones under microwave irradiation. The Pd(0)-catalyzed cyclization was found to proceed favorably with the more electron-deficient phenyl ring during the reactions involving unsymmetrical N,N-diaryl α-iodo enaminones. This unique property enables the construction of carbazolone skeleton containing nitro substituted benzenoid ring.     

Iodine-mediated oxidative Pictet-Spengler reaction using terminal alkyne as the 2-oxoaldehyde surrogate for the synthesis of 1-aroyl-β-carbolines and fused-nitrogen heterocycles

An efficient iodine-mediated oxidative Pictet-Spengler reaction in dimethyl sulphoxide (DMSO) using terminal alkynes as the 2-oxoaldehyde surrogate for the synthesis of aryl (9H-pyrido[3,4-b]indol-1-yl)methanones is described. The scope of the protocol includes the total synthesis of Fascaplysin, Eudistomins Y₁ and Y₂. The methodology is extended for preparing pyrrolo[1,2-a]-quinoxaline and indolo[1,5-a]quinoxaline derivatives. The utility of 1-aroyl-β-carbolines was demonstrated by performing palladium-catalyzed β-carboline directed ortho-C(sp2)-H functionalization of the phenyl ring with thiomethyl (SMe) group using DMSO as source and for accessing 4-aryl-canthin-6-ones.     

Facile synthesis of bicyclic 1-arylpyrazol-5-ones

In this Letter, we described a facile method for constructing fused bicyclic 1-arylpyrazol-5-one ring system. We employed various methylene-containing carboxylic acids as the substrates and proved that the pyrazolone ring closure requires activated methylene group in intermediate II. Accordingly, a series of structurally diversified, fused bicyclic 1-arylpyrazol-5-ones was prepared in moderate to high yields using the requisite substrates.     

Synthesis of substituted 2,4,5,6-tetrahydrocyclopenta[c]pyrazoles and 2,4,5,6-tetrahydropyrrolo[3,4-c]pyrazoles by intramolecular nitrilimine cycloaddition

Both substituted 2,4,5,6-tetrahydrocyclopenta[c]pyrazoles and 2,4,5,6-tetrahydropyrrolo[3,4-c]pyrazoles have been synthesized by the 3+2 intramolecular dipolar cycloaddition of nitrilimines to alkynes. This cyclization has been extended to more versatile 3-bromo derivatives by the use of alkynylbromides as dipolarophiles.