Ⅱ.二元酸与二元醇的聚酯反应动力学

聚酯反应象单元酸与单元醇的酯化反应一样,都是氢离子催化机构。这种机构与现在公认的聚酯反应的氢离子催化机构的区别在于氢离子的来源和氢离子参与反应的详细历程,肯定了氢离子不仅由外酸供给,而且也可由二元酸本身供给。另外,二元酸与二元醇均可作为氢离子的载体。聚酯反应的动力学方程与二元酸与二元醇的起始克分子比有密切关系,应由前篇(3)式表示。当酸与醇以等克分子比起反应,又无外酸存在时,聚酯反应是2(1/2)级反应;若有外酸作催化剂时,当外酸的量加得适当多,由二元酸本身供给的氢离子的贡献可以忽略时,是二级反应,与以往结论相一致:当外酸的量加得少,必须考虑氢离子的同离子效应,它就不再是简单的二级反应,当酸与醇以不等克分子比起反应我们的实验结果亦与理论一致。     

聚酯反应动力学的研究

在最近三年中,我们在聚酯反应动力学方面进行了下列工作:(一)确定了聚酯反应动力学的反应级数,澄清了长久以来关于聚酯反应级数的争论;(二)建议了一种新的酯化反应,聚酯反应和三向聚酯反应的氫离子催化机构;(三)从反应动力学的观点讨论了三向缩聚反应中的凝胶化问题;(四)研究了反应速度常数与二元酸和二元醇的分子结构的关系。下面我们分别作简要说明。     

关于二元酸与二元醇的聚酯反应和酯化与水解反应动力学

关于二元酸与二元醇的聚酯反应动力学,Flory和等人都会做过研究,唐敖庆等在较广泛的实验基础上提出氢离子催化机理及其动力学.酯化机理为:     

聚十二烷二元酸酯及其共聚酯的合成

通过直接熔融缩聚法合成了一系列聚十二烷二元酸酯，用GPC、^1H—NMR、FTIR对产物进行了表征，并讨论了预聚酯合成时催化剂浓度和种类、预聚反应温度、预聚初始醇酸摩尔比对聚合反应的影响。结果表明，在所选的三个催化剂体系中，氮化亚锡二水合物与对甲苯磺酸复合催化剂的催化效果最好；最佳反应条件：n对甲苯横酯／n二元酸=0．0021～0．0032，反应温度为160～180℃，醇酸摩尔比范围为1．05—1.10。     

AA/HPHP与AA/NPG聚酯化反应的动力学研究

考虑缩合水的排除对反应体系的影响,用体积浓度单位推导出一个新的聚酯反应总包动力学方程,并应用到AA/HPHP和AA/NPG两个聚酯化反应的动力学研究中.研究发现,自催化聚酯反应的反应级数并不是固定值,对于AA/HPHP和AA/NPG两个聚酯化反应而言,低温时反应级数为2.5,高温时反应级数为3.0.此外,忽略缩合水的排除对聚酯化反应的动力学参数会产生较大误差.对于AA/HPHP和AA/NPG聚酯化反应,活化能相对误差分别达21.51%和11.33%;指前因子误差达到97.40%和87.96%.     

非均相Schiff碱铬(Ⅲ)配合物的合成及催化苯乙烯环氧化性能的研究

将丙氨酸水杨醛Schiff碱铬(III)配合物嫁接到了介孔分子筛MCM-41上,并利用FTIR、UV-Vis、XRD、N2吸附和元素分析对所制备的非均相配合物结构进行了表征.以30%的H2O2为氧化剂,考察其对苯乙烯环氧化反应的催化性能.结果表明,均相配合物非均相化后,其催化活性明显提高.在较优的反应条件下,苯乙烯转化率可达75.5%,此时苯基环氧乙烷的选择性为68.5%,且该非均相催化剂重复使用四次后仍保持较高的催化活性.     

2-氧代-4-苯基丁酸乙酯不对称加氢反应的动力学和机理探讨

 采用 10,11-二氢辛可尼定修饰的Pt/γ-Al2O3 催化 2-氧代-4-苯基丁酸乙酯不对称加氢合成 (R)-2-羟基-4-苯基丁酸乙酯,考察了修饰剂用量、底物浓度、氢压和反应温度对加氢反应速率和光学选择性的影响. 结果表明,修饰剂用量和底物浓度在适中范围内对反应速率和光学选择性均较为有利;提高氢压和温度均能显著加快反应速率,但氢压对光学选择性影响不大,温度升高则不利于目标产物的生成. 根据反应动力学特征,认为修饰剂喹啉环平行吸附于Pt表面,被质子化后与以si面吸附在催化剂表面的底物作用,经过立体选择生成单一对映体. 用提出的反应机理推导出不对称加氢反应速率方程,可以较好地描述实验结果.     

不对称硼催化反应的理论研究(Ⅰ)——噁唑硼烷催化苯基乙酮还原反应的对映体选择性机理

用AM1方法研究了噁唑硼烷催化苯基乙酮还原反应的对映体选择性机理,结果表明,在此硼催化剂的作用下,苯基乙酮还原的对映体产物主要是R构型,其主要原因是两种对映体的催化过渡态的活化能相差较大所致.用过渡态活化理论计算所得光学产率e.e.=95%,计算结果与实验一致.     

非均相环糊精在水相有机合成反应中的应用

本文详细综述了非均相环糊精在水相有机合成反应中的应用,包括非均相环糊精在水相氧化反应、还原反应、取代反应、加成反应和光催化反应中的应用。同时,全面阐述了在催化或促进水相有机合成反应中环糊精非均相化的策略,包括形成水不溶性交联聚合物和将环糊精固载在水不溶性载体上两种途径。目前非均相环糊精在水相有机合成反应中的应用还基本局限在简单的相转移催化剂领域,相关报道也较少,处于起步阶段;基于非均相环糊精构筑超分子仿酶是今后该领域的发展趋势和必然归属,应在发挥非均相优势的同时,保留环糊精单元在超分子仿酶构筑中的优良功用。     

关于《高分子化学》教材中聚酯化反应速率方程推导的探讨

在不同版本的《高分子化学》教材中,对于不可逆线形缩聚的聚酯化反应历程有两种不同的理解,这导致推导反应速率方程的过程存在一定差异。本文分析和对比了潘祖仁编写的《高分子化学》和乔治·奥迪安(George Odian)编写的《Principles of Polymerization》两版中英文教材,阐述了造成速率方程推导过程存在差异的原因,以期为同行教学与学生学习提供参考。     

The kinetics of polyesterification. II. Succinic acid and ethylene glycol

The polyesterification of succinic acid with ethylene glycol in both equimolar and nonequimolar ratios was investigated at the reaction temperature of 195°C. The experimental results agreed quite well with the kinetic equations proposed in our previous paper for the adipic acid–ethylene glycol system, except in the case of acid-catalyzed equimolar reaction, where a shift of kinetic behavior from reaction control to diffusion control would appear. The apparent rate constants for uncatalyzed and acid-catalyzed reactions were evaluated by using the method of least squares for various values of initial molar ratio between [OH] and [COOH]. The dissociation effect of hydrogen ion from dibasic acid in glycol, as proposed in the adipic acid–ethylene glycol system, could also be applied in the succinic acid–ethylene glycol system to explain the kinetic behavior observed. The kinetic equations previously proposed for polyesterification were again confirmed.     

乙二醇与顺丁烯二酸及邻苯二甲酸酐聚酯化反应动力学的研究

<正> 聚酯化反应是逐步增级的缩聚过程。是由氢离子催化的反应,总的动力学方程为     

Polyesterification reactions of adipic acid-based polyesters

A series of studies of uncatalyzed and catalyzed polyesterification experiments have been investigated using different glycols at different temperatures. The experimental results for uncatalyzed reactions agreed quite well with the kinetic equation as proposed by P. J. Flory. However, Flory proposed a second-order reaction for an externally added strong acid as a catalyst. In contrast to Flory's theory, a mixed mechanism, based on a combination of carboxylic acid groups from the raw material and an external organotin catalyst, was proposed for the catalyzed reaction. In this article, the reaction rate of catalyzed and uncatalyzed polyesterifications using different glycols was compared, and the effect of different temperatures and catalyst levels was also discussed. The reaction rate constant decreases in the following order for both catalyzed and uncatalyzed polyesterification: 1,6-HD > 1,4-BD > NPG > DEG > EG ? PG. © 1993 John Wiley & Sons, Inc.     

固体酸对醇酸树脂聚酯反应的催化作用

本文研究了固体酸对醇酸树脂缩聚酯反应的催化作用,讨论了催化剂的表面酸度、制备条件及反应物分子构型等对催化聚酯反应的影响。在接近生产条件下研究了醇酸树脂聚酯反应动力学,发现多相酸催化聚酯反应与均相酸催化聚酯反应具有相似的动力学规律。     

Models for Polyesterification Kinetics. III. Preliminary Studies on the Catalysis by Titanium(IV) Tetraalkoxides

The catalytic behavior of tetrabutoxytitanium in polyesterification between diacids and diols is studied with the help of two model reactions. One is the esterification between two mono-functional oligomers. The second is the reaction of 1-octa-decanol with octadecanoic acid either in octadecanyl octadecano-ate or in an excess of octadecanol. The behavior of this catalyst is complex since it depends on the reaction medium. A decrease of the vacuum and an increase of the acid concentration lead to poor catalytic efficiency which is also observed when the reaction is carried out in a hydrophilic medium such as polyoxy-ethylene. When the alcohol is in excess, the catalyst is much more efficient and experimental results fit with a zero overall order, although deviations are observed at the highest conversions. The existence of a complex between carboxyl groups and titanium is postulated.     

三组分共聚酯数均聚合度和数均分子量的计算方程

为便于生产控制以制得预定分子量的产物，根据直接酯化法合成聚对苯二甲酯乙二酯（ＰＥＴ）共聚酯的特点，综合考虑各种主、副反应，从统计观点出发，对三组分ＰＥＴ共聚酯体系的齐聚物和缩聚物，分别建立了其数均聚合度Ｘｎ和数均分子量Ｍｎ的简化和非简化计算方程．将简化Ｘｎ方程与Ｃａｒｏｔｈｅｒｓ方程进行计算比较，其结果完全相同；将简化Ｘｎ方程应用于二组分聚酯体系，其形式与传统的二组分线型缩聚物Ｘｎ方程形式相同，各Ｘｎ和Ｍｎ方程可推广应用于二组分聚酯体系和三组分以上的多组分共聚酯体系．     

焦炭催化CO还原NO的反应机理研究

利用密度泛函理论,研究了焦炭催化作用下CO还原NO的化学反应机理,优化得到了均相反应路径以及在Zigzag和Armchair型焦炭表面上的异相反应路径中所有驻点的几何构型与能量,并对三条反应路径进行了动力学分析。结果表明,均相NO还原反应的活化能为254.06 kJ/mol,而Zigzag型与Armchair型焦炭表面NO异相还原反应的活化能分别为86.94与52.16 kJ/mol,说明焦炭在NO还原反应中能够起到催化作用。在焦炭表面进行的CO还原NO的反应路径经历N_2形成、N_2释放及两步CO_2释放四个阶段,最终生成一个N_2分子与两个CO_2分子。此外,通过对比不同路径下异相反应的能量变化与动力学参数可知,焦炭表面结构对NO还原反应特性存在较大影响;与Zigzag型焦炭表面相比,基于Armchair型焦炭表面的NO还原反应决速步能垒值更低且反应速率更快,表明在Armchair型焦炭表面上的NO还原反应更易进行。     

Studies on polyesterification reactions: Calculation of the rates of reverse reactions

Reactions between dicarboxylic acids and diols in the melt and leading to an equilibrium yield quantitative results which may be applied to the kinetics of some partial reactions of polyesterification. The relationship of the rate constants of the forward and the reverse reaction as well as of the equilibrium constant furnish valid results both in the absence of catalyst and in the presence of acid or basic catalysts. The values obtained for the energy of activation of the forward and the reverse reaction and of the overall reaction (13 ± 1 kcal/mole) also are in good agreement.     

硅氮负离子引发六甲基环三硅氧烷开环聚合的动力学研究

以二甲基亚砜(DMSO)或四氢呋喃(THF)作为促进剂,六苯基环三硅氮烷三锂盐(P3NLi)可以引发六甲基环三硅氧烷(D3)进行开环聚合,通过29Si-NMR谱的硅峰面积比例确定了不同反应时间D3的转化率,经过计算得到聚合反应对THF、DMSO、D3、P3NLi的反应级数,并给出了对应的动力学方程.     

Esterification of Carboxylic Acids and Diacids by Trialkyl Borate under Solvent- and Catalyst-Free Conditions

Esterification or transesterification reactions are usually carried out in the presence of homogeneous or heterogeneous catalysts. However, recently a new method was reported for the esterification of carboxylic acids by tributyl borate under solvent- and catalyst-free conditions. In order to show the synthetic ability of trialkyl borate esters in the esterification reactions, here, the esterification of other carboxylic acids and diacids by tributyl-, triisoamyl-, and tribenzyl borate under the same conditions were reported. Some of the prepared ester and diester products have found wide applications as plasticizers and synthetic ester base lubricants. The esterification reactions have been cleanly carried out in the absence of any solvent under catalyst-free conditions. The maximum rate belongs to isoamyl trichloroacetate （VIb） which reached about 76% within about 6.5 h. On the basis of obtained findings, it seems that electron withdrawing groups on carboxylic acid facilitate the esterification reaction.