Synthesis of aluminum methyl and isopropoxide complexes bearing ketiminate ligands and catalysis in the ring-opening polymerization of cyclic esters
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- Tez No: 403353
- Danışmanlar: Prof. Dr. HAIYAN MA
- Tez Türü: Doktora
- Konular: Kimya, Kimya Mühendisliği, Chemistry, Chemical Engineering
- Anahtar Kelimeler: Aluminum complexes, Ketiminate, Polymerization, rac-LA, ε-CL
- Yıl: 2012
- Dil: İngilizce
- Üniversite: East China University of Science and Technology
- Enstitü: Yurtdışı Enstitü
- Ana Bilim Dalı: Belirtilmemiş.
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: 150
Özet
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Özet (Çeviri)
A series of aluminum methyl (C1a, C2a, C4a, C5a, C6a, C2b) and isopropoxide (C2c, C7c) complexes bearing ketiminate ligands were synthesized from the reaction of corresponding ketiminate ligands with AlMe3 and Al(OiPr)3, respectively. Except for C7c, all the other complexes were characterized by 1H and 13C NMR spectroscopy. Besides, either HRMS or EA analysis data were obtained for these complexes. Single crystals in suitable size and shape could be isolated for complexes C2a and C4a from toluene solution and were further identified by single crystal X-ray diffraction analysis. It is confirmed that complex C2a exists as a tetrahedron structure in monoclinic crystal system with the aluminum atom surrounded by the oxygen and nitrogen donors of the chelating ketiminate ligands, and two methyl groups. Complex C4a possesses similar coordination geometry but belongs to orthorhombic crystal system. From the reaction of AlMe3 with the ketiminate ligand L4 bearing isopropyl substituent on the para-position in 1:2 ratio, aluminum complex“(L4)3Al”bearing three ketiminate ligands was isolated, instead of the target aluminum monomethyl complex“(L4)2AlMe”. Other ligands of L1, L3, L5-L6 resulted a mixture of L2AlMe and LAlMe2 complexes under same reaction conditions. All aluminum methyl complexes proved to be active catalysts in the ring-opening polymerization (ROP) of rac-LA and ε-CL. ROP of rac-LA was investigated in the presence of iPrOH and without iPrOH at 70 °C. The ring-opening polymerization reactions of rac-LA initiated with these complexes resulted isotactic-enriched polylactide (Pm = 0.57~0.78). It was clearly observed that the use of alcohol increased the catalytic activities as well as decreasing the molecular weights of produced polymers. A decreasing tendency of catalytic activities for complexes C4a, C5a, C6a was found in the order: C6a (p-Cl) > C4a (p-iPr) > C5a (p-OMe), indicating that the electron-donating substituent at the para-position was a disadvantage for catalytic activity. All the complexes catalyzed ε-CL polymerization with monomer conversions up to 95% within 12 h at 70 °C. Bis(ketiminate) monoalkyl aluminum complex C2b was found to be more active than the corresponding monoketiminate complex C2a with the same ligand for both monomers. Meanwhile, complex C2b also supplied polymer of higher molecular weight with lower polydispersity. Bis(ketiminate) aluminum isopropoxide complexes (C2c, C7c) were found to be active catalysts in the ROP of rac-LA at 70 °C. Nearly complete conversion of 100 equiv. of rac-LA could be reached within 12 h. Complex C7c with CF3 on the para-position of the phenyl ring was found to be more active than C2c, and yielded polymer with significantly higher molecular weight. Catalysts C2c and C7c were also active for the polymerization of ε-CL at room temperature. C7c proved to be more active than C2c, indicating 96% monomer conversion within half reaction time of that of C2c. Furthermore, complex C7c was used to initiate ε-CL/rac-LA copolymerization via different polymerization methods. Diblock copolymer of poly(rac-LA)-block-poly(ε-CL) was obtained from the sequential addition of two monomers. Tapered copolymer could be obtained when the copolymerization started with equal amount of ε-CL and rac-LA monomer.
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