Zinc(II) complexes of Triaza and Amidinate ligands: Efficient initiators for the ring‐opening polymerization of ε‐Caprolactone and rac‐Lactide

Zinc complexes supported by tertiary 1,3,5‐triazapenta‐1,3‐dienate ligand (L¹) and N ‐benzoyl‐N′ ‐arylbenzamidinate [aryl =2,6‐diisopropylphenyl (L²), phenyl (L³)] ligands have been synthesized and characterized. The reaction of L¹H with ZnEt₂ affords a mononuclear zinc complex [L¹ZnEt] ( 1 ) in good yield. Tetra nuclear zinc complex [(L¹)₂Zn₄O(OAc)₄] ( 2 ) is prepared by treating L¹H with one equivalent of Zn(OAc)₂ in toluene. Further, dinuclear zinc complexes [L²ZnEt]₂ ( 3 ) and [L³ZnEt]₂ ( 4 ) are obtained in good yields from L²H and L³H with ZnEt₂ in toluene respectively_. The complexes 1–4 have been characterized by ¹H/¹³C NMR spectroscopy and single crystal X‐ray diffraction studies. All of the complexes have been explored for their catalytic activity toward the ring‐opening polymerization (ROP) of ε ‐caprolactone. It has been found that complex 1 is an active catalyst for the polymerization of ε ‐caprolactone in presence of a cocatalyst benzyl alcohol (BnOH). While complex 2 is as active as 1 there is no need for a cocatalyst for the polymerization to proceed. Dinuclear zinc complexes 3 and 4 show very high activity for the ROP of ε ‐caprolactone (CL) and rac ‐lactide (LA) without requiring a cocatalyst. The resultant polymers are found to have very high molecular weight (M _n = 296 X 10³ g mol⁻¹) and relatively narrow polydispersity index compared to 1 and 2 .     

合成丙交酯的催化剂研究进展

丙交酯作为合成聚乳酸的重要中间体,它的制备效率是影响两步法聚合高分子量PLA的关键因素。寻找高效催化剂是其中一个重要的解决方案,本文就与日俱增交酯合成过程中不同催化剂体系的选择进行了综述,未来的工作应放在催化剂和制备效率上。     

rac-Lactide polymerization using aluminum complexes bearing tetradentate phenoxy-amine ligands

A family of aluminum-methyl complexes supported by tetradentate phenoxy-amine ligands has been prepared and employed in the ring-opening polymerization of rac-lactide; the ligands include N,N-bis(3,5-dimethyl-2-hydroxybenyl)-N′,N′-dimethyl-1,2-diaminoethane (L¹), N,N-bis(3,5-diisopropyl-2-hydroxybenyl)-N′,N′-dimethyl-1,2-diaminoethane (L²) and N,N-bis(3,5-dichloro-2-hydroxybenyl)-N′,N′-dimethyl-1,2-diaminoethane (L³). Polymerizations of rac-lactide were carried out by treatment of the aluminum-methyl complexes with PhCH₂OH and rac-lactide at 70 °C, affording well-controlled formation of polylactide (PLA) and a moderate isotactic bias for initiators bearing L¹ and L²; the chloro-substituted ligand L³ afforded largely atactic PLA.     

The micellar behavior of linear triblock terpolymers of styrene (S), isoprene (I), and methyl methacrylate (MMA) in selective solvents for PS and PMMA

A series of linear triblock terpolymers consisting of polystyrene (PS), polyisoprene (PI) and poly(methyl methacrylate) (PMMA) were examined in tetrahydrofuran (THF), a good solvent for all the blocks and in dimethylacetamide (DMA) and dimethylformamide (DMF), selective solvents for PS and PMMA. In DMA and DMF, which are both non-solvents for PI, multimolecular micelles were formed. The micelles were characterized by low-angle laser light scattering (LALLS), dynamic light scattering (DLS) and viscometry. The aggregation number of the triblock terpolymers was greater in DMF than in DMA, reflecting the higher non-solvent strength of DMF for PI. The aggregation number was also found to increase with increasing PI content of the terpolymers in both DMA and DMF. The hydrodynamic radii depended on the aggregation number of the micelle and the length of the corona forming PS and PMMA blocks. The complexity involved in studying a system consisting of three different polymer blocks is discussed in the context of the results obtained.     

13Carbon nuclear magnetic resonance of ethylene–propylene–1‐decene terpolymers

Many studies have been reported on the ¹³C NMR characterization of ethylene–α‐olefin copolymers, but only a few have been reported on terpolymers. The incorporation of an α‐olefin into the polyethylene chain changes the structure and, consequently, the properties of the polymer obtained. Looking for new products, we obtained a series of ethylene–propylene–1‐decene terpolymers with the metallocenic system rac‐ethylene bisindenyl zirconium dichloride/methylaluminoxane. We performed a complete ¹³C NMR characterization of these terpolymers qualitatively and quantitatively. Here we present a detailed study of the ¹³C NMR chemical shifts, triad sequence distributions, monomer average sequence lengths, and reactivity ratios for these terpolymers. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2531–2541, 2003     

Living Nitroxide‐Mediated Radical Terpolymerization: General Concept and Synthetic Possibilities

The general concept for nitroxide‐mediated radical terpolymerization is advanced. This concept is based on activation‐deactivation equilibria for terminal polymer‐nitroxide adducts. Depending on monomer activity and the stability of terminal nitroxide adducts, terpolymerization can be equilibrium living, quasi‐equilibrium (gradient) living, decaying living, decaying gradient, or non‐living. Expressions for the effective activation‐deactivation equilibrium constant, K_ef, and the rate of terpolymerization are derived from theoretical speculations on equilibrium living and decaying living terpolymerization. For quasi‐equilibrium living terpolymerization, various types of gradient terpolymers are predicted. When activity of the active monomer M₁ is, at least, one order of magnitude different from that of the two other monomers, the effective constant K_ef is shown to approach K₁ of the most active monomer. Experimental kinetic and equilibrium constants agree with the advanced concept for the equilibrium living terpolymerization of styrene with methyl methacrylate, and acrylonitrile in the presence of nitroxide SG1, as well as for decaying living terpolymerization in the same system in the presence of nitroxide TEMPO.

     

A refinement of the terpolymer equation and its simple extension to two- and four-component systems

Terpolymer composition estimation with an established equation has been found to give results that vary with the feed monomer ratio substitution pattern used. A new copolymer equation has been derived that overcomes this difficulty to give the same composition results regardless of the order of monomer substitution. The new equation also gives comparable or better agreement with experimentally determined copolymer compositions than obtained by use of the established Alfrey-Goldfinger terpolymer equation. In addition, this new terpolymer equation demonstrates a versatility not shown by the present terpolymer equations in that it can be readily adapted by inspection to enable estimation of copolymer compositions for two- or for four-component polymer systems. It is also readily adaptable for copolymers with more than four components, and may also be valid for composition estimation of these because of the derivation method used, although it has not as yet been possible to test this possibility. © 1996 John Wiley & Sons, Inc.     

稀土复合氧化物催化合成丙交酯的研究

以新型稀土La—Ti复合氧化物作为催化剂，催化乳酸合成丙交酯，考察了催化剂对反应体系粘度、丙交酯产率、反应时间、反应温度的影响，获得了较佳的反应工艺条件：减压下，70～90℃脱自由水1．5h；随后加入催化剂，用量为乳酸重量的0．8％，缓慢升温到120～140℃进行缩聚反应3～4h；再在170～260℃，保持升温速率为4℃／10min进行裂解，产物纯度和结构分别由Thiele管和红外光谱进行测定，丙交酯粗产率达88．5％，纯产率为40．2％，表明该催化剂具有良好的催化性能。     

苯乙烯-丙烯酸酯-丙烯腈三元共聚物的合成及表征

在可控核聚变领域,惯性约束聚变(ICF)用空心靶球的研究[1-3]十分活跃。以聚苯乙烯为基材制备ICF有机物空心靶球已有广泛的研究,微球的制备技术、工艺等都已相当成熟,但聚苯乙烯阻气性差,难以阻挡氢同位素的扩散,不能满足ICF靶球的需要。目前应用比较好的ICF靶球制备条件极为苛刻,工艺复杂[4]。丙烯腈、丙烯酸酯、偏二氯乙烯、醋酸乙烯酯等一类单体的均聚物都有较好的阻气性[5],本文探讨苯乙烯与丙烯腈、丙烯酸酯类单体的共聚方法,研究了共聚物的一些基本性能。1　实验部分1 1　试剂及仪器苯乙烯、丙烯腈、丙烯酸甲酯、丙烯酸丁酯均…