【作者】 任伟民；

【导师】 吕小兵；

【作者基本信息】 大连理工大学 ， 应用化学， 2010， 博士

【摘要】 二氧化碳(CO2)与环氧烷烃共聚生成聚碳酸酯的反应是最有潜力的绿色聚合过程之一。在该共聚反应中,存在着聚合物与小分子环状碳酸酯选择性、聚合产物中碳酸酯单元与聚醚单元选择性问题,以及人们往往忽视的区域和立体选择性共聚问题等。因此,选择性催化合成高碳酸酯单元含量和高分子量聚合物一直是本领域的研究重点之一,而实现对聚合产物的立体化学及其性能的精确调控则是更具挑战性的研究目标。本论文旨在阐明基于SalenCo(Ⅲ)X配合物的催化体系在CO2与环氧烷烃交替共聚高效合成聚碳酸酯的反应机理,重点设计耐热稳定性好的高活性催化剂,从聚合产物区域和立体化学以及性能控制着手在以下几个方面开展了研究工作：针对基于SalenCo(Ⅲ)X配合物的双组分或双功能体系在催化CO2与环氧烷烃共聚反应中有关机理尚不清楚,设计合成了在Salen配体中一个苯环3位上引入大位阻有机碱1,5,7-三氮杂双环[4.4.0]癸-5-烯(TBD)的三价钴配合物。该配合物可以在高温(100℃),低压甚至常压下高活性、高选择性地催化CO2与环氧丙烷(PO)的交替共聚反应,生成相应的聚碳酸丙稀酯(PPC)。通过电喷雾质谱、原位红外吸收光谱以及一系列验证实验研究了该配合物催化CO2和PO共聚反应的机理,证明了催化剂配体上连接的功能基团TBD在反应过程中形成了碳酸酯中间体,该中间体在聚合过程中与中心金属离子可逆的键合和解离起到了稳定Co(Ⅲ)的作用,避免形成无催化活性的Co(Ⅱ)物种。该反应机理也很好地解释了本课题组先前研究的SalenCo(Ⅲ)X配合物／季铵盐或大位阻有机碱双组分体系所涉及的机理,即轴向配体和亲核性助催化剂引发的碳酸酯链依次在SalenCo(Ⅲ)X配合物两面发生交替的链增长与解离,也起到稳定Co(Ⅲ)的作用,使得聚合反应可以在较高温度或低压下顺利进行。根据分子内协同催化理念,通过在配体中一个苯环的3位引入季铵盐,合成了一类双功能SalenCo(Ⅲ)X配合物。其中通过1,3-亚丙基在配体中引入季铵盐的配合物能(?)效地催化CO2和环氧烷烃的共聚反应。当反应温度为120℃时,该配合物催化CO2和环氧环己烷(CHO)共聚反应的TOF值可以达到目前最高的6105 h-1,生成的聚碳酸环己烯酯(PCHC)中碳酸酯单元含量超过99%。该配合物也能在常温或高温下,高活性、高选择性地催化CO2／端位环氧烷烃／CHO的三元共聚反应。生成的共聚物只有一个玻璃化转变温度和一个热分解温度,并可以通过改变碳酸环己烯酯(CHC)单元的含量对玻璃化转变温度进行调控。利用分子内含有大位阻有机碱TBD的SalenCo(Ⅲ)X配合物,第一次成功地制备了PPC-b-PCHC-b-PPC嵌段聚合物。该聚合物具有一个宽的玻璃化转变温度和两个热分解温度。将衍生化的联-2-萘酚和大位阻有机碱TBD同时引入Salen配体,设计合成了一类新型多手性位点的SalenCo(Ⅲ)X配合物,成功实现了CO2与外消旋环氧烷烃的不对称、区域和立体选择性交替共聚反应。其中,空间位阻较大的配合物作为催化剂时,以近乎完美的区域选择性和良好的立体选择性实现了CO2与外消旋PO的共聚反应。聚合产物中碳酸酯单元的头尾连接含量超过99%；催化动力学拆分常数(Krel)为24.4,均为迄今报道的最高值。更多还原

【Abstract】 The selective transformation of carbon dioxide (CO2) into biodegradable polycarbonates by the alternating copolymerization with epoxides has attracted much attention during the last decades due to economic and environmental benefits arising from the utilization of renewable source and the growing concern on the greenhouse effect. For CO2/aliphatic epoxides copolymerization, there exists much interesting information, such as polymer/cyclic product selectivity, ether and carbonate linkages, regiochemistry of epoxide ring-opening, and stereochemistry of carbonate unit sequence in a polymer, which bears a memory of the reaction pathway leading to its formation. Therefore, the catalytic synthesis of polycarbonates with high carbonate linkages and high molecular weight is one of the important issues, while approaching to the accurate control of polymer stereochemistry and its properties remains challenge. The present dissertation focuses on exploring the mechanistic aspects of the CO2/epoxides copolymerization with SalenCo(Ⅲ)X catalyst systems, as well as further designing highly active catalyst with excellent thermal stability with an emphasis of polycarbonate property or its regio- and stereochemistry.Considering that the mechanism of the binary or bifunctional catalyst systems based on cobalt-Salen complexes is not clear, a Co(Ⅲ)-salen complex with 1,5,7-triabicyclo[4.4.0] dec-5-ene (designated as TBD, a sterically hindered organic base) anchored on the ligand framework has been developed for the alternating copolymerization of CO2 and propylene oxide (PO). This catalyst exhibits highly active and selective poly(propylene carbonate) (PPC) formation even at high temperatures (up to 100℃), high [epoxide]/[catalyst] ratios, and/or low CO2 pressures. Electrospray ionization mass spectrometry (ESI-MS) and Fourier transform infrared spectroscopy (FTIR) studies, in combination with some verified experiments, confirmed the formation of the carboxylate intermediate with regard to the anchored TBD on the catalyst ligand framework. This analysis demonstrated that the formed carboxylate intermediate helped to stabilize the active Co(Ⅲ) species against decomposition to inactive Co(Ⅱ) by reversibly intramolecular Co-O bond formation and dissociation. These studies provide a new mechanistic understanding of our previously studied binary catalyst systems based on Co(Ⅲ)-Salen complexes in which alternating chain-growth and dissociation of propagating carboxylate species derived from the nucleophilic axial ligand and the nucleophilic cocatalyst take turns at both sides of the Co(Ⅲ)-Salen center. This arrangement significantly increases the reaction rate and also helps to stabilize the active Co(III) species against decomposition to inactive Co(Ⅱ) even at low CO2 pressures and/or relatively high temperatures.According to the intramolecular cooperative catalysis mechanism, a series of new bifunctional Co(Ⅲ)-salen complexes have been synthesized. The complex anchored a quaternary ammonium salt on the three position of one aromatic ring by three methylene units exhibited excellent activity and polymer selectivity even at a high temperature for the copolymerization of CO2 with PO or with cyclohexene oxide (CHO). The catalytic activity is highly sensitive to the reaction temperature. The highest TOF up to 6105 h-1 was obtained at 120℃for the copolymerization of CO2 and CHO, without sacrificing polymer selectivity. This functionalized Co(Ⅲ)-salen complex could operate very efficiently for the terpolymerization of CHO and aliphatic epoxides with CO2 to provide selectively polycarbonates with a narrow polydispersity at various temperatures. The resulting terpolymers have only one thermolysis peak and one adjustable glass-transition temperature (Tg) dependable on cyclohexene carbonate unit content. Also, with the use of a TBD-appended SalenCo(Ⅲ) catalyst, a novel triblock polymer (PO-alt-CO2)x-b-(CHO-alt-CO2)y-b-(PO-alt-CO2)z was synthesized for the first time. The resulting triblock polymer has only a broad Tg, but two thermolysis peaks. Furthermore, several novel chiral cobalt-based complexes containing a derived chiral-BINOL and TBD were developed for asymmetric, regio- and stereoselective alternating copolymerization of CO2 and racemic PO. The (S,S,S)-Co(Ⅲ) complex with sterically hindered substituent group resulted in a near perfectly regioregular PPC, with>99% head-to-tail connect and a Krel of 24.4 for the enchainment of (R)-PO over (S)-PO, which all are the highest record.更多还原