共沸缩聚-解聚法高效合成乙交酯

乙交酯是聚羟基乙酸的单体,乙交酯的合成直接影响聚羟基乙酸的合成。一般用羟基乙酸(酯)制备乙交酯,但是,制备乙交酯的缩聚过程需要真空高温的条件,消耗大量的能量。共沸缩聚-解聚法制备乙交酯的缩聚过程,具有条件温和、无催化剂、溶剂可回收的优点。羟基乙酸通过共沸缩聚-解聚法得到乙交酯。用X-射线粉末衍射、红外分析、差热分析等方法对聚羟基乙酸低聚物进行了表征。结果表明：羟基乙酸制备的聚羟基乙酸低聚物是一种半结晶聚合物,聚羟基乙酸低聚物解聚得到产率为81.26%和纯度为89.29%的乙交酯,并且解聚反应残渣可以重复利用来制备乙交酯。     

丙交酯开环均聚合

生物可降解脂肪族聚酯--聚丙交酯由可再生资源获得.聚丙交酯独特的物理性质使得它在包装、涂层、纤维、薄膜等方面有着广泛的应用.聚丙交酯低成本、大规模的生产及应用将极大地减轻对石油产品的依赖.高分子量的聚丙交酯主要由丙交酯开环聚合制备.本文总结了催化丙交酯开环聚合的3大类催化剂及其反应机理;综述了近年来国内外在丙交酯均聚合催化剂开发上的研究进展,并重点论述了稀土催化剂在丙交酯开环聚合中的优势及由其催化合成的聚丙交酯在生物学应用中的优点.     

酯交换法合成丙烯酸氯乙醇酯

丙烯酸卤代烷酯是重要的精细化工原料和中间体,一般的合成方法是直接酯化法。已有文献报道采用酯交换工艺以丙烯酸甲酯为原料制备丙烯酸高碳烷酯和丙烯酸二甲氨基烷酯[1-4]。Nolan等人曾报道了氮杂环卡宾作为催化剂通过酯交换反应合成甲基丙烯酸卤代烷酯[5,6],但是其催化剂制备     

丙交酯立体选择性聚合研究进展

聚乳酸是一类以可再生资源为原料的具有生物可降解性和生物相容性的热塑性材料,已被广泛应用于生物医学、制药和环境等领域.聚乳酸通常是由单体丙交酯开环聚合得到.丙交酯单体有三种旋光异构体,分别为左旋,右旋和内消旋.由于聚合物链段的立体构型对材料的热力学和力学性能起着决定性的作用,因此制备对丙交酯不同立体选择性的催化剂是一个重要的研究课题.目前在丙交酯开环聚合反应中具有良好立体选择性的单活性点金属配合物的设计和合成方面已经取得了显著的进展.本文基于本课题组的研究工作,讨论了金属配合物的金属中心种类、配体结构等对丙交酯立体选择性聚合的影响.     

低毒锌类催化剂制备聚乳酸的研究

采用低毒锌类催化剂制备了一系列具有高分子量、不同光学纯度及热力学性质的聚乳酸材料. 以金属锌作催化剂制备丙交酯, 研究了不同裂解温度对产物光学纯度的影响. 随后在低毒催化剂乳酸锌的作用下使丙交酯开环聚合, 进一步研究了单体的光学纯度对聚乳酸立体规整性的影响, 以及聚合过程中的结晶对聚合物分子量和热力学行为的影响. 并用旋光仪、核磁共振氢谱(1H NMR)、凝胶渗透色谱(GPC)、差示扫描量热分析(DSC)等方法对产物进行表征. 结果表明, 合适的裂解温度有利于合成高光学纯度的丙交酯; 在低毒乳酸锌的催化作用下, 高光学纯度的单体以及聚合过程中的结晶都有利于制备高分子量聚乳酸.     

外消旋丙交酯立体选择聚合研究进展

脂肪酸聚酯聚乳酸具有生物降解性和生物相容性,可用于生物医学、药物和环境材料等领域。本文综述了丙交酯聚合研究的最新进展,突出强调了催化活性高、能够控制聚合物立构规整性的丙交酯开环聚合催化剂。由于选用的催化剂和丙交酯单体的不同,聚乳酸有等规、无规、杂同、间规以及立体嵌段等不同的微观结构,不同微观结构的聚乳酸的力学、物理和降解性能不同。本文重点列举了单活性中心的铝、稀土金属和环境友好型铁、锌、镁以及不含金属的有机催化剂在外消旋丙交酯的立体选择开环聚合方面的最新进展,强调低毒性、生物相容性好的催化剂是目前研究的重点。最后指出,随着环境友好聚乳酸材料的合成和应用的增加,开发单活性中心以及无金属催化剂研究丙交酯立体选择开环聚合是今后研究的一个重要的课题。     

稀土配位催化合成聚乳酸

本文开发了合成聚乳的一类新型催化剂, 它是由稀土化合物-三烷基铝-水组的配位催化剂。试验表明稀土配位催化剂可以使丙交酯在甲苯溶液中以高转化率聚合, 得到分子量可控的聚乳酸。并研究了稀土元素种类、不同配位基团及聚合条件变化对丙交酯开环聚合的影响。     

固体超强酸SO2-4/TiO2-SnO2的制备、表征及催化合成D, L-丙交酯

采用沉淀法在不同工艺条件下制备了稀土改性的新型固体超强酸SO2-4/TiO2-SnO2催化剂, 考察了其对D, L-乳酸合成D, L-丙交酯的催化活性, 并通过Hammett指示剂法测定了催化剂的酸强度, 用FT-IR和FT-Raman技术考察了焙烧温度、硫酸浸渍液浓度和浸渍时间以及La2O3的负载量对该固体超强酸结构和性能的影响. 研究结果表明: SnO2的存在促进了金红石相TiO2的形成, 在600 ℃焙烧3 h、 3.0 mol/L H2SO4溶液浸渍12 h、 n(Ti4+): n(Sn4+): n(La3+)=1:1:0.05条件下制备的SO2-4/TiO2-SnO2的酸强度最大, 达-13.75以上, 催化合成丙交酯的产率最高(78.4%). 并且考察了催化剂用量对D, L-丙交酯粗产率的影响和催化剂重复使用的性能.     

合成丙交酯中微量水分分析

合成丙交酯中微量水分分析徐溢，柳胜春（重庆大学化工学院分析教研室６３００４４）关键词丙交酯，微量水，定量分析丙交酯是人工合成骨材料聚乳酸的合成中间体，其性能决定着合成产品的品质，要获得高质量的合成材料，对中间体的分析和监测十分重要。一般要求丙交酯中间...     

固体超强酸SO4^2-／TiO2-SnO2的制备、表征及催化合成D，L-丙交酯

采用沉淀法在不同工艺条件下制备了稀土改性的新型固体超强酸SO4^2-／TiO,-SnO2催化剂,考察了其对D,L-乳酸合成D,L-丙交酯的催化活性,并通过Hammett指示剂法测定了催化剂的酸强度,用Fr—IR和FT-Raman技术考察了焙烧温度、硫酸浸渍液浓度和浸渍时间以及La2O3的负载量对该固体超强酸结构和性能的影响．研究结果表明：SnO2的存在促进了金红石相TiO2的形成,在600℃焙烧3h、3．0mol／LH2SO4溶液浸渍12h、n（Ti^4＋）：n（Sn^4＋）：n（La^3＋）=1：1：0．05条件下制备的SO4^2-／TiO2-一SnO2的酸强度最大,达-13．75以上,催化合成丙交酯的产率最高（78．4％）．并且考察了催化剂用量对D,L-丙交酯粗产率的影响和催化剂重复使用的性能．     

丙交酯开环聚合反应的新型有机催化剂

作为生物高分子降解材料,聚乳酸具有良好的生物相容性和生物降解性,已经广泛应用于包装材料、农用薄膜等环境领域和药物控制释放体系、医用缝合线、组织工程支架等医学领域。丙交酯开环聚合是制备聚乳酸的理想之选,其催化体系目前以金属催化剂为主,但金属离子在聚合物中的痕量残留和细胞毒性限制了聚乳酸在生物医学及微电子领域的应用,而有机催化剂能够克服这些缺点,是目前聚乳酸合成领域的研究热点。本文从不同的活化机理角度,阐述了近年来有机催化剂在合成聚乳酸中的研究进展,总结了各种催化体系在活性、结构可控性及选择性方面的特点,同时展望有机催化剂在开环聚合反应中所面临的机遇与挑战。     

Thiourea-based bifunctional organocatalysis: supramolecular recognition for living polymerization

A versatile, metal-free, organocatalytic approach to the living ring-opening polymerization of lactide using a bifunctional thiourea-tertiary amine catalyst is described. Mild and highly selective polymerization conditions produced poly(lactides) with predictable molecular weights and extremely narrow polydispersities ( approximately 1.05), characteristic of a living polymerization. The extraordinary selectivity of this catalyst system for polymerization relative to transesterification is remarkably unusual. The low polydispersities and exceptional control observed are a consequence of selective transesterification of lactide relative to the open chain esters. Presumably, the ring strain of lactide provides both a driving force for the polymerization and a kinetic preference for polymerization relative to transesterification with catalyst. We postulate that the initiating/propagating alcohol is activated by acid-base interaction with the tertiary amine moiety and the carbonyl of the lactide monomer is simultaneously activated by hydrogen bonding to the thiourea moiety of the catalyst.     

Chemical Recycling of End-of-Life Poly(lactide) via Zinc-Catalyzed Depolymerization and Polymerization

The chemical recycling of poly(lactide) was investigated based on depolymerization and polymerization processes. Using methanol as depolymerization reagent and zinc salts as catalyst, poly(lactide) was depolymerized to methyl lactate applying microwave heating. An excellent performance was observed for zinc(II) acetate with turnover frequencies of up to 45000 h⁻¹. In a second step the monomer methyl lactate was converted to (pre)poly(lactide) in the presence of catalytic amounts of zinc salts. Here zinc(II) triflate revealed excellent performance for the polymerization process (yield: 91 %, M_n ∼8970 g/mol). Moreover, the (pre)poly(lactide) was depolymerized to lactide, the industrial relevant molecule for accessing high molecular weight poly(lactide), using zinc(II) acetate as catalyst.     

A highly active zinc catalyst for the controlled polymerization of lactide

We report the preparation, structural characterization, and detailed lactide polymerization behavior of a new Zn(II) alkoxide complex, (L(1)ZnOEt)(2) (L(1) = 2,4-di-tert-butyl-6-{[(2'-dimethylaminoethyl)methylamino]methyl}phenolate). While an X-ray crystal structure revealed the complex to be dimeric in the solid state, nuclear magnetic resonance and mass spectrometric analyses showed that the monomeric form L(1)ZnOEt predominates in solution. The polymerization of lactide using this complex proceeded with good molecular weight control and gave relatively narrow molecular weight distribution polylactide, even at catalyst loadings of <0.1% that yielded M(n) as high as 130 kg mol(-)(1). The effect of impurities on the molecular weight of the product polymers was accounted for using a simple model. Detailed kinetic studies of the polymerization reaction enabled integral and nonintegral orders in L(1)ZnOEt to be distinguished and the empirical rate law to be elucidated, -d[LA]/dt = k(p)[L(1)ZnOEt][LA]. These studies also showed that L(1)ZnOEt polymerizes lactide at a rate faster than any other Zn-containing system reported previously. This work provides important mechanistic information pertaining to the polymerization of lactide and other cyclic esters by discrete metal alkoxide complexes.     

乙酰丙酮铁催化丙交酯开环聚合的研究

以乙酰丙酮铁 [Fe(acac) 3]为催化剂进行D ,L 丙交酯的开环聚合及在聚乙二醇 (PEG)存在下的开环共聚 ,研究了催化剂用量、反应温度和反应时间对聚合反应的影响以及PEG用量对共聚反应的影响 ,并探讨了丙交酯开环聚合机理 .结果表明 ,Fe(acac) 3是按配位 插入机理催化丙交酯开环聚合的 ;在本文的聚合条件下 ,大部分聚合的单体转化率都达 90 %以上 ,聚合产物的粘均分子量最高可达 6 6 0 0 0 ,均显示出较好的催化性能 .在PEG存在下 ,PEG作为引发剂参入了丙交酯的开环聚合 ,D ,L 丙交酯是沿着PEG分子两端开环聚合的 ,分子链的链端结构是以羟基为端基的乳酰基结构单元 ,Fe(acac) 3有促进PEG参与聚合成酯的作用 .     

About formation of cycles in Sn(II) octanoate‐catalyzed polymerizations of lactides

At first, formation of cycles in commercial poly(l ‐lactide)s is discussed and compared with benzyl alcohol‐initiated polymerizations performed in this work. This comparison was extended to polymerizations initiated with 4‐cyanophenol and pentafluorothiophenol which yielded cyclic polylactides via end‐biting. The initiator/catalyst ratio and the acidity of the initiator were found to be decisive for the extent of cyclization. Further polymerizations of l ‐lactide were performed with various diphenols as initiators/co‐catalysts. With most diphenols, cyclic polylactides were the main reaction products. Yet, only catechols yielded even‐numbered cycles as main reaction products, a result which proves that their combination with SnOct₂ catalyzed a ring‐expansion polymerization (REP). The influence of temperature, time, co‐catalyst, and catalyst concentrations was studied. Four different transesterification reactions yielding cycles were identified. For the cyclic poly(l ‐lactide)s weight average molecular weights (M_w's) up to 120,000 were obtained, but ¹H NMR end group analyses indicated that the extent of cyclization was slightly below 100%. The influence of various parameters like structure of initiator and catalyst and temperature on the formation of cyclic poly(l ‐lactide)s has been investigated. Depending on the chosen conditions, the course of the polymerization can be varied from a process yielding exclusively linear polylactides to mainly cyclic polylactides. Three different reaction pathways for cyclization reactions have been identified. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 1915–1925     

Mechanistic Insight into the Stereochemical Control of Lactide Polymerization by Salan–Aluminum Catalysts

Alkyl aluminum complexes of chiral salan ligands assembled around the 2,2′‐bipyrrolidine core form as single diastereomers that have identical configurations of the N donors. Active catalysts for the polymerization of lactide were formed upon the addition of benzyl alcohol. Polymeryl exchange between enantiomorphous aluminum species had a dramatic effect on the tacticity of the poly(lactic acid) (PLA) in the polymerization of racemic lactide (rac‐LA): The enantiomerically pure catalyst of the nonsubstituted salan ligand led to isotactic PLA, and the racemic catalyst exhibited lower stereocontrol. The enantiomerically pure catalyst of the chloro‐substituted salan ligand led to PLA with a slight tendency toward heterotacticity, whereas the racemic catalyst led to PLA of almost perfect heterotacticity following an insertion/auto‐inhibition/exchange mechanism.     

Single-component catalyst/initiators for the organocatalytic ring-opening polymerization of lactide

The synthesis and characterization of a series of primary and secondary alcohol adducts of 1,3-dimesitylimidazolin-2-ylidene is described. These adducts are stable as solids at room temperature, but readily release alcohol and the free carbene in solution. These alcohol adducts function as excellent single-component catalyst/initiators for the ring-opening polymerization of lactide under mild conditions, providing polymers with controlled molecular weights and narrow polydispersities. Multifunctional adducts were used to prepare poly(lactide)s of more complex architectures.     

Block Copolymerization of Lactide and an Epoxide Facilitated by a Redox Switchable Iron‐Based Catalyst

A cationic iron(III) complex was active for the polymerization of various epoxides, whereas the analogous neutral iron(II) complex was inactive. Cyclohexene oxide polymerization could be “switched off” upon in situ reduction of the iron(III) catalyst and “switched on” upon in situ oxidation, which is orthogonal to what was observed previously for lactide polymerization. Conducting copolymerization reactions in the presence of both monomers resulted in block copolymers whose identity can be controlled by the oxidation state of the catalyst: selective lactide polymerization was observed in the iron(II) oxidation state and selective epoxide polymerization was observed in the iron(III) oxidation state. Evidence for the formation of block copolymers was obtained from solubility differences, GPC, and DOSY‐NMR studies.