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Preparation of Organometallic Complexes for CO2/epoxide and Olefin/styrene Copolymerizations
- Author(s)
- Jeon jong yeob
- Advisor
- 이분열
- Department
- 일반대학원 분자과학기술학과
- Publisher
- The Graduate School, Ajou University
- Publication Year
- 2016-08
- Language
- eng
- Keyword
- Organometallic chemistry; Homogeneous catalyst; Olefin block copolymer; Ethylene trimerization; Carbon dioxide
- Alternative Abstract
- Organometallic catalyst for polymerization is one of the interesting subjects in the chemistry world. My work at Ph.D. primarily involves the synthesis of various organometallic complexes for CO2/epoxide and ethylene oligomerization, and the development of polymerization method for olefin/styrene copolymerization. Chapter 1 reviews the organometallic catalysts for CO2/epoxide copolymerization, and olefin oligomerization and polymerization in terms of historical background and mechanistic study. Chapter 2 presents investigations on CO2/propylene oxide copolymerization with various cobalt(III) complexes. The related cobalt(III) complexes were prepared through variations of the ligand framework of highly active catalyst, (salen)Co(III) complex tethering four quaternary ammonium salts, by replacing the trans-1,2-diaminocyclohexane unit with 2,2-dimethyl-1,3-propanediamine, trans-1,2-diaminocyclopentane, or 1,1'-binaphthyl-2,2'-diamine or by replacing the aldimine bond with ketimine. These ligand frameworks are thought to favor the formation of the cis- configuration in complexation, and the formation of the cis- configuration in the catalysts was confirmed through NMR studies or X-ray crystallographic studies of model complexes not bearing the quaternary ammonium salts. Complexes which adopt the cis- configuration even in DMSO did not show any activity for CO2/Propylene oxide (PO) copolymerization. Complex which was constructed with trans-1,2-diaminocyclopentane and fluctuate in DMSO between the coordination and de-coordination of the acetate ligand as observed for highly active catalyst, showed fairly high activity (TOF, 12400 h-1). This fluctuating behavior may play a role in polymerization. A facile back-side attack onto the coordinated epoxide from the carbonate anion is possible after de-coordination. The highly active catalyst, (salen)Co(III) complex, also showed high activity (TOF, 25900 h-1; TON, 518000; 2.72 Kg-polymer/g-cat) and selectivity (>98%) for CO2/ethylene oxide (EO) copolymerization that results in high-molecular-weight polymers (Mn, 200000 - 300000). Propylene oxide/phthalic anhydride (PO/PA) copolymerizations and PO/CO2/PA terpolymerizations were carried out using the highly active catalyst. In PO/PA copolymerizations, full conversion of PA was achieved within 5 h and strictly alternating copolymers of poly(1,2-propylene phthalate)s were afforded without formation of any ether linkages. In PO/CO2/PA terpolymerizations, full conversion of PA was also achieved within 4 h. The terpolymers bearing substantial amount of PA units (fPA, 0.22) showed higher Tg (48 °C) than that of CO2/PO alternating copolymer (40 °C). Chapter 3 discloses the real structure of some commercial sources of CrCl3(THF)3. Results of X-ray crystallographic studies showed that the correct structure was CrCl3(H2O)(THF)2, where a water molecule included in the coordination sphere. Use of this chromium precursor may have resulted in experimental failures, especially when strongly basic reagents that can deprotonate the coordinated water were reacted. CrCl3(THF)3 prepared through Soxhlet extraction of anhydrous CrCl3 using THF is the correct form of CrCl3(THF)3. The reaction of this correct form with the strongly basic (CH3)3SiCH2MgBr afforded Cr(CH2Si(CH3)3)4 in good yield (70%), while the reaction with the commercial source of incorrect CrCl3(THF)3 resulted in poor yield (7%). A new chromium precursor (EH)2CrOH (EH = 2-ethylhexanoate) for the Phillips ethylene trimerization catalyst was introduced which improves the catalytic activity. The conventional Phillips ethylene trimerization catalyst was prepared by reacting Cr(EH)3, 2,5-dimethylpyrrole (Me2C4H2NH), Et3Al, and Et2AlCl in an aromatic hydrocarbon solvent. Reaction of CrCl3 with 3 equivalent Na(EH) in water did not generate Cr(EH)3, but unexpectedly produced (EH)2CrOH. In comparison with the erratic catalytic performance of the original Phillips system due to ill-defined nature of the Cr(EH)3 source (16 or 6.8 106 g/mol-Cr·h depending on the source), the improved system exhibited consistently high activity (54 106 g/mol-Cr·h). Reaction of (EH)2CrOH with (Me2C4H2N)AlMe2·OEt2 afforded the dimeric Cr(II)-complex (6) coordinated by (5-Me2C4H2N)AlMe2(NC4H2Me2) and 2-1:2-Me2C4H2N ligands. 6 provided highly active species when activated with Et3Al·ClAlEt2. Chapter 4 describes a new method of block copolymerization of polyolefin and polystyrene by sequential performance of the coordination and the anionic polymerizations in one pot. Ethylene/1-octene copolymerization was performed using a typical ansa-metallocene catalyst rac-[Me2Si(2-methylindenyl)]2ZrCl2 activated modified methylaluminoxane (MMAO) in the presence of di(benzyl)zinc to grow polyolefin-chains attaching to zinc site. The anionic polymerization was subsequently performed by feeding nBuLi·(tmeda) (tmeda, N,N,N',N'-tetramethylethylenediamine) initiator and styrene monomer to grow polystyrene-chains at the zinc site consequently attaching to polyolefin-chains. Addition of tmeda played a key role in the growth of the polystyrnene-chains at the zinc site. The composition and the molecular weight in the polyolefin-blocks were controllable depending on the feed amounts of 1-octene and di(benzyl)zinc (1-octene fraction, ~20, ~40 wt%; PO-Mw, 77000–174000) and the polystyrene-block size was also controlled (PS-Mn, ~21000) with the complete conversion of styrene monomer. Formation of block copolymers was evident in the GPC curves, in the TEM images, and in the strain-stress curves especially contrasting with those of the corresponding polyolefin/polystyrene blend.
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- Graduate School of Ajou University > Department of Molecular Science and Technology > 4. Theses(Ph.D)
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