新型稀土催化剂催化开环聚合及Monte Carlo模拟研究

【作者】 凌君；

【导师】 沈之荃；

【作者基本信息】 浙江大学 ， 高分子化学与物理， 2002， 博士

【摘要】 脂肪族聚酯、聚碳酸酯等可降解型高分子材料因为当前环境问题的日益严峻而倍受关注。开环聚合具有聚合条件温和、能有效地控制聚合产物的分子量、分子量分布以及聚合物结构等优点，是合成可降解型生物医用高分子材料的重要手段。迄今为止，可用以催化环碳酸酯、内酯开环聚合、制备生物医用高分子材料的催化剂仅有Sn（Oct）₂等少数几种，且一般聚合温度较高（大于100℃）、时间较长（几十小时），聚合机理研究尚存较多争议。本论文为环碳酸酯、内酯的开环聚合开发了两类新型低毒性稀土催化剂：三（2，6-二叔丁基-4-甲基苯氧基）稀土配合物和对叔丁基杯芳烃稀土配合物，都可以在温和的反应条件下单组分引发2,2-二甲基三亚甲基环碳酸酯（DTC）、三亚甲基环碳酸酯（TMC）和ε-己内酯（CL）聚合，合成各种分子量的均聚和共聚材料，考察了催化剂结构、聚合条件等对聚合的影响，深入研究了聚合机理。 Monte Carlo方法是计算化学的重要研究方法之一，在高分子化学方面的应用能深入微观分子水平模拟聚合反应。本文首次将Monte Carlo模拟方法用于稀土催化配位聚合体系，克服了解析法解决复杂实际问题的诸多困难，首次提出了多分散性共聚合Monte Carlo模拟算法，成功地用于开环共聚合研究，考察了DTC和CL无规共聚反应机理，图形输出方法形象地显示了共聚合单体的序列分布。首次将Monte Carlo模拟用于稀土催化剂催化1，3-丁二烯气相聚合体系和苯乙烯本体聚合高粘体系，验证聚合反应机理和动力学模型，深入讨论了反应条件和各基元反应对聚合的影响。 三（2,6-二叔丁基-4-甲基苯氧基）稀土配合物引发DTC、TMC和CL聚合。本文首次发现芳氧基稀土——三（2，6-二叔丁基-4-甲基苯酚氧基）稀土配合物（Ln（OAr）₃，Ln=La,Nd,Y,Dy,Er）用于环碳酸酯、内酯的开环聚合，能单组分高效引发DTC、TMC和CL的均聚和共聚，酚氧-稀土键对开环聚合具有很高的活性，引发DTC均聚时催化效率可达492kgPDTC·mol^-1La·hr^-1。聚合反应条件温和，室温下DTC、TMC、CL均聚及共聚合在30min内都可以达到90％以上的转化率。聚合产物分子量高，PDTC和PCL均聚物的分子量分别可达25.4×10⁴和21.5×10⁴。环碳酸酯聚合时不发生脱除CO₂等副反应，聚合产物不含聚醚链段，为纯净的聚碳酸酯和聚酯链节，能完全降解。 研究了单组分La（OAr）₃引发DTC和TMC无规共聚合，产物P（DTC-ran-TMC）的二次差热扫描曲线中只发现了一个玻璃化转变，T_g=-8.3℃，显著高于PTMC的T_g=-27.1℃，没有观测到110～130℃范围内PDTC的结晶熔融现象。 浙江大学博士学位论文 芳氧基稀土配合物单组分引发DTC和 CL共聚合过程具有活性聚合特征，可合成嵌段共聚物和无规共聚物。各种不同比例无规共聚物的分子量和组成可以通过两种方法控制：固定两种单体投料比时控制聚合反应时间和总转化率；或者两种单体按预定组成加人聚合，在高转化率时聚合物组成非常接近投料比。考察了影响共聚反应的因素，用常规的实验计算方法测得DTC和 CL的竞聚率分别为13．现和0．ZO。合成的无规共聚物表现出不同于均聚物的热性能，二次差热扫描分析发现DTC含量大于50％的P（DTC－rn－CL）出现了两个均聚物或者其他比例共聚物未曾发现的处于p3．8℃到河．5℃的玻璃化转变，且Tg随DTC含量增加而升高，表明得到了没有结晶性，只有玻璃化转变的弹性体。 本文首次研究了 Ln＊Af)。引发DTC、TMC和 CL聚合的机理，证实都符合“配位插入阴离子机理”：单体首先以环外联基和引发剂中稀土原子配位，并发生联基加成，随之通过酚氧键断裂开环而插入到LnO键中实现链引发，然后各单体重复上述稀土原子参与的配位、加成、开环、插入聚合步骤，活性链在Ln—O端增长。活性链中引发剂的芳氧基碳酸酯片断在聚合终止时被终止剂（沉淀剂）醇的烷氧基替换而从聚合物中脱离，稀土原子则与盐酸反应生成LnC13除去，引发剂的残留量极小，NMR方法检测不出。 2，6－H叔丁基一甲基苯酚和稀土都具有来源丰富、价格低廉、毒性低等优点，LnpAf)。引发剂合成简便、结构明确／性质稳定、催化活性高，可作为开环聚合催化剂广泛应用于环碳酸酯、内酯等生物医用高分子材料的合成。 多分散性共聚合Monte Cario方法模拟DTC和CL无规共聚合。本文首次提出了一个改进的适用于多链多分散性共聚体系研究的 Monte Carlo模拟算法和程序框图，在通常的共聚合 Mollte Carlo模拟中增加了控制不同链长聚合物的动力因子，充分考虑了同一体系中不同长度高分子增长链相互间的单体竞争。上述Monte Carlo模拟程序研究 LnpAr)一发DTC和 CL无规共聚合结果符合实验分析数据，验证了DTC和CL无规共聚过程符合一级Markov模型，活性链末端链节对新插入单体有较大影响。应用多分散性共聚合Monie Caro方法可全程模拟中高转化率的共聚合反应，与各不同单体投料比时低转化率共聚合结果完全吻合，从而简化了共聚机理和产物结构分析，能提供聚合实验和宏观表征手段难于或不能获得的更多信息。Mollte Carlo模拟计算得到共聚物微更多还原

【Abstract】 There has been a growing interest on the polymers having the properties of biodegradability, biocompatibility and low toxicity to cope with the serious environmental problems and medical demands. Aliphatic polyesters and polycarbonates belong to these materials with expecting uses as drug delivery medium, surgical sutures, body implant materials, cell culture substrate, agricultural membranes and so forth. However, only a few catalysts (such like Sn(Oct)2) have been studied to synthesize medical-use materials with debating mechanisms. In this dissertation, two series of rare earth initiators: rare earth tri(2,6-di-tert-butyl-4-methylphenolate) and rare earth calixarene complex have been developed to ring-opening polymerize 2,2-dimethyltrimethylene carbonate (DTC), trimethylene carbonate (TMC) and s-caprolactone (CL) at mild conditions. Both the polymerization features and mechanisms are discussed in details.Monte Carlo method is a powerful tool in computational chemistry to investigate polymerization mechanisms and kinetic behaviors at the molecular level. Theoretically speaking, it can handle all kinds of polymerization systems with presumed mechanisms, intimating every occurrence of microcosmic species and the structure of every polymer chain. A Monte Carlo algorithm for multi-dispersive copolymerization system has been established and successfully used in the copolymerization of DTC with CL. Monte Carlo method has been firstly applied to simulate the polymerization systems catalyzed by rare earth compounds, including the gas phase polymerization of 1,3-butadiene and the high viscous bulk polymerization system of styrene, by which the polymerization mechanisms and kinetic processes are fully discussed.Rare earth tris(2,6-di-tert-butyl-4-methylphenolate) initiated polymerizations of DTC, TMC and CL. Rare earth tris(2,6-di-tert-butyl-4-methylphenolate) (Ln(OAr)3, Ln=La,Nd,Y,Dy,Er) was firstly studied in the polymerizations of cyclic carbonates and lactones. Ln(OAr)3 was found active in initiating polymerizations of DTC, TMC and CL. The efficiency of DTC polymerization initiated by La(OAr)3 was 492kgPDTC-mol-1La-hr-1. Homo- and copolymerizations of DTC, TMC and CL were carried out in mild conditions, achieving high conversions (>90%) in 30min at room temperature. The molecular weights of obtained PDTC and PCL were 25.4 104 and21.5 l04, respectively. No ether unit, no rare earth metal and no 2,6-di-tert-butyl-4-methylphenol were found in (co)polymers.Random copolymerization of DTC with TMC was performed by the initiator of La(OAr)3. Only a Tg of -8.3 was observed for P(DTC-ran-TMC) in the second DSC heating scan, higher than PTMC’s Tg of -27.TC, and no Tm at the range of 110~130 for PDTC was found.Copolymerization of DTC with CL initiated by Ln(OAr)3 exhibited living features, producing block and random copolymers. The molecular weight and composition of P(DTC-ran-CL) could be controlled by two different ways: controlling polymerization time and total conversion with fixed feeding concentrations of monomers; or controlling co-monomers feeding ratio and processing high conversion polymerization. The reactivity ratios of DTC and CL were measured as 13.43 and 0.20, respectively. New thermal behaviors of P(DTC-ran-CL) differed from those of the two homopolymers. In the second heating scan of DSC, Tms of the random copolymers (DTC%>50%) was disappeared, and a Tg from -33.8 to -7.5癈 were detected instead, which indicates the elastic polymer.The polymerization mechanisms of DTC, TMC and CL initiated by Ln(OAr)3 were fully studied for the first time, and proved to be a "coordination insertion anionic mechanism". Monomer coordinated to rare earth metal on the carbonyl group, and opened ring via acyl-oxygen bond cleavage, forming a growing chain. The following monomer repeated these steps to insert into the Ln-0 bond in propagation process. The aryl carbonate end group of growing chain was replaced by alcohol in termination (or precipitation) resulting alkyl carbonate end更多还原