在哪儿可以下载化学类的英文文献啊?免费的!急啊!
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发布时间：2022-04-23 17:06
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时间：2022-05-07 15:18
谷歌学术免费检索，部分可以直接下载。
ABC Chemistry是化学方面的免费全文网上期刊数据库，分为永久期刊和临时期刊两大类。
Science美国的一个科学网站，免费。
FindaRticles是一个强大的能够获取免费出版文献的搜索引擎，它收集到的大部分文献都可免费阅读或打印全文。
HighWire Press是全球最大的提供免费全文的学术文献出版商
下面需要权限的数据库可以去学校图书馆查找，如果学校没有收录的话，可以借助第三方文献机构：
ACS Publications（美国化学会期刊全文数据库）
Royal Society of Chemistry英国皇家化学学会
Wiley Online Library（综合库）
Sciencedirect荷兰Elsevier（综合库）
SpringerLink是全球最大的在线科学、技术和医学(STM)领域学术资源平台。
Reaxys数据库由爱思唯尔（Elsevier）公司出品，是内容丰富的化学数值与事实数据库。
德国Thieme出版社是一家拥有百年历史的医学和科学出版社。其中Synthesis和Synlett是Thieme最为引以为豪的两种化学期刊
热心网友
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时间：2022-05-07 18:10
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时间：2022-05-07 20:02
疏水缔合型聚合物P(AMTA)溶液性质的研究
疏水缔合型水溶性聚合物是指在聚合物亲水性大分子链上带有少量疏水基团的一类水溶性聚合物。在聚合物水溶液中，疏水基团之间由于憎水作用而发生聚集，使大分子链产生分子内和分子间缔合。在临界缔合质量分数以上，形成分子间缔合为主的超分子结构，增大了流体力学体积，故具有较好的增黏性。在盐溶液中，由于小分子电解质的加入增加了溶液极性，使疏水缔合作用增强，表现出明显的抗盐性质。 疏水缔合型水溶性高分子很难合成，且不易表征，把疏水部分连接到水溶性聚合物链上，一般采用胶束共聚合或者使用具有表面活性的大单体进行共聚，胶束聚合需要在体系中加入大量的表面活性剂，这就增加了后处理过程的复杂性。利用表面大单体共聚合，需要事先合成大单体，这方面的技术也有相当大的难度。作者采用丙烯酸十四酯作为疏水单体，直接用沉淀聚合法制备疏水缔合型聚合物P(AM／TA)共聚物，从而使共聚反应及其产物的后处理过程较为简单易行。并用凯达尔定氮法表征共聚物的组成，研究共聚物的溶液性能和对苯丙乳液的增稠性。 1实验
1．1试剂
丙烯酰胺(AM)，质量分数不少于985％，根据文献提供的方法提纯；N,N-甲基甲酰胺(DMF)，分析纯；甲醇、氯化钠，化学纯；丙烯酸十四酯(TA)，实验室自制；苯丙乳液由福建省福州树脂有限公司提供。 1．2P(AM/TA)共聚物的合成
称取一定量的AM和TA单体，用DMF溶解，转入三颈瓶中，通氮除氧。升温至80℃，加入引发剂反应4h，过滤，产物用甲醇洗涤多次，以除去未反应的单体。40℃真空干燥至恒重。
1．3分析测试
凯达尔定氮法测定共聚物的组成。用乌氏黏度计测定共聚物溶液特性黏度[η]，测试温度为(30±O1)℃。聚合物溶液表观黏度用NDJ-I型旋转黏度计测定。
2结果与讨论
2．1共聚物稀溶液性质不同疏水基团摩尔分数的P(AM／TA)共聚物在蒸馏水和w(NaCl)=1.5％的溶液中的特性黏度[η]值列于表1。
聚合物的[η]正比于溶液中大分子线团的流体力学体积，因而能反应大分子线团收敛、卷曲的程度。从表1可知，随共聚物的TA链节摩尔分数的增加，其水溶液的[η]值逐渐减小，在w(NaCl)=1.5％的溶液中也是持续减小。这是因为在稀溶液中，疏水基团缔合以分子内缔合为主，随着TA摩尔分数的增加，分子内缔合增强，导致分子链卷曲。在盐溶液中，由于离子电荷的作用，使疏水链节分子内缔合力增强，分子链收缩，因而[η]值也持续下降。
2．2疏水基团TA摩尔分数对聚合物溶液黏度的影响 图1和图2分别表示P(AM/TA)系列共聚物及PAM在蒸馏水和w(NaCl)=1.5％的溶液中表观黏度与聚合物质量分数的关系曲线。PAM溶液黏度随其质量分数的增加而平缓上升，而疏水共聚物溶液的质量分数为3O％～4O％时其黏度急剧增加，表明疏水基团聚集而导致分子间缔合，形成了物理交联网络。此时共聚物溶液的质量分数即是临界缔合的质量分数。如图1所示，随TA摩尔分数增加，共聚物溶液的黏度显著增加。当疏水基团摩尔分数较高时，其溶液黏度随质量分数增加的速度更快，共聚物的临界缔合质量分数降低。如图2所示，加入Nacl溶液后，溶液表观黏度有较大提高，如质量分数为8.O％的P(AM/TA)-1 5聚合物溶液在20℃，转速为6r／min时，黏度达55.OmPa.s，而在水溶液中的黏度只有374mPa·s。不同TA摩尔分数的聚合物的质量分数均较其在纯水中低。
Hydrophobically associating polymer P (AMTA) the nature of the study solution
Hydrophobically associating water-soluble polymer is the hydrophilic polymer with a small amount of macromolecular chain hydrophobic group of a class of water-soluble polymer. Aqueous solution in the polymer, the hydrophobic groups and between the role as a result of hydrophobic aggregation occurred, so that large molecules have a molecular chain and inter-molecular association. Associating the critical mass fraction of the above, the formation of intermolecular association based supramolecular structure, increases the volume of fluid mechanics, it has good by adhesive. In salt solution, because of the addition of small molecule electrolyte solution increased polarity, so that co-operation with enhanced hydrophobic association, shows that the nature of the salt. Hydrophobically associating water-soluble polymer-based synthesis is difficult and not easily characterized, in part to hydrophobic chains connected to the water-soluble polymer, the general use of micellar copolymerization, or the use of the large surfactant monomer to copolymerization, polymer micelles need in the system by adding a large number of surface-active agent, which, after an increase of the complexity of the process. The use of the surface monomer copolymerization, the need for prior synthesis of large monomer, this technology also has considerable difficulty. Author tetradecyl acrylate used as a hydrophobic monomer, the direct use of precipitation polymerization Preparation of hydrophobically associating polymer P (AM / TA) copolymers, so that the proct of copolymerization and post-processing is more simple and easy process. And characterization of nitrogen determination Kedar copolymer composition, study the solution properties of copolymers of styrene-acrylic emulsion and of the thickening. 1 Experimental
1.1 Reagents
Acrylamide (AM), the mass fraction of not less than 985 percent, according to documents provided by purification methods; N, N-dimethylformamide (DMF),分析纯; methanol, sodium chloride, chemical pure; acrylic 10 four acetate (TA), laboratory-made; styrene-acrylic emulsion resin from Fuzhou in Fujian Province Limited. 1.2P (AM / TA) Copolymer
Check that a certain amount of monomer AM and TA, using DMF dissolved into three-neck bottle, pass oxygen nitrogen. Warming to 80 ℃, reaction by adding initiator 4h, filtering, washing the proct several times with methanol to remove unreacted monomer. 40 ℃ vacuum drying to constant weight.
1.3 Analysis and Testing
Determination of nitrogen Kedar will be the composition of copolymer. Determination of intrinsic viscosity with copolymer solution viscosity [η], the test temperature (30 ± O1) ℃. Apparent viscosity of polymer solution with NDJ-I-type rotary viscometer determination.
2 Results and Discussion
2.1 Dilute Solution Properties of Copolymers of different mole fraction of hydrophobic groups of the P (AM / TA) copolymers in distilled water, and w (NaCl) = 1.5% of the solution intrinsic viscosity [η] values listed in Table 1.
Polymer [η] is proportional to the solution of the fluid dynamics of macromolecular coil volume, which can respond to the convergence coil macromolecules, the degree of curl. We can see from Table 1, with the copolymer chain of the TA increase in mole fraction, the aqueous solution of [η] value decreases in w (NaCl) = 1.5% of the solution is continued to decrease. This is because in dilute solution, the hydrophobic group to intramolecular association based association, with the mole fraction of the increase in TA, to enhance intramolecular association, resulting in the molecular chain curly. In salt solution, because of the role of ionic charge, so that intramolecular hydrophobic chain to enter into force enhancement, molecular chain contraction, so [η] value continued to drop.
TA hydrophobic group 2.2 mole fraction of polymer solution viscosity on the impact of figures 1 and 2, respectively, P (AM / TA) series of copolymers and PAM in distilled water, and w (NaCl) = 1.5% in the apparent viscosity of the solution and the relationship between the mass fraction of polymer curve. PAM solution viscosity with the increase of mass fraction of gentle rise, and the hydrophobic copolymer solution for the mass fraction of 3O% ~ 4O%, when a sharp increase in viscosity, indicating that aggregation of hydrophobic groups and lead to intermolecular association, forming a physical crosslinking网络. At this point the mass fraction of copolymer solution that is the critical mass fraction of the association. As shown in Figure 1, with the mole fraction of TA increased, the viscosity of copolymer solution increased significantly. When the mole fraction of hydrophobic groups is high, the solution viscosity increases with the mass fraction of the faster, the critical aggregation copolymer mass fraction lower. As shown in Figure 2, by adding Nacl solution, the solution has greatly enhanced apparent viscosity, such as the mass fraction of 8.O% for the P (AM / TA) -1 5 polymer solution at 20 ℃, rotation speed 6r/min , the viscosity of 55.OmPa.s, and viscosity in aqueous solution only 374mPa s. TA different mole fraction of the mass fraction of polymer in water were low.
