Seok Kyun Noh

Polyethylene/MMT nanocomposites prepared by in situ polymerization using supported catalyst systems

Abstract A polyethylene/montmorillonite(MMT) nanocomposite was prepared by in situ polymerization method using MMT-supported methylaluminoxane(MAO) cocatalyst and/or Cp2ZrCl2 catalyst. The catalyst components had been supported on the unmodified MMT-Na and modified commercial product, Cloisite 25A. With XRD it was found that the layered silicate gallery of Cloisite 25A was exfoliated by incorporating MAO cocatalyst and zirconocene catalyst while the d-spacing of MMT-Na was less changed. The in situ polymerization of ethylene was carried out to prepare the nanocomposite by using the supported MMT, and the fully exfoliated product was obtained with Cloisite 25A. The decomposition temperature of the obtained nanocomposite increased up to 25 °C, but the melting temperature was not improved much.

SYNTHESES OF POLYMETHYLENE BRIDGED DINUCLEAR ZIRCONOCENES AND INVESTIGATION OF THEIR POLYMERISATION ACTIVITIES

Abstract The polymethylene bridged dinuclear zirconocenes [(CH2)n (C5H4)2][(C9H7)ZrCl2]2 (n=3 (10), 5 (11), 7 (12), 9 (13)) have been synthesised by treating not only the respective disodium salts of the ligands with two equivalents of (C9H7)ZrCl3 in THF, but also the distannylated derivatives of the ligands with two equivalents of (C9H7)ZrCl3 in toluene. All complexes are characterised by 1H- and 13C-NMR and mass spectrometry and elemental analysis. It turned out that the values of Δδ=[δd−δp], the chemical shift difference between the distal (δd) and proximal (δp) protons, for the produced dinuclear compounds (0.1 for 10 and 11, and 0.11 for 12 and 13) were smaller than the Δδ values of the known polysiloxane bridged dinuclear compounds. The chemical shifts of the bridgehead carbons in these complexes are about 135 ppm shifted downfield with respect to the other two resonances at cyclopentadienyl ring (113.7 and 113.7 ppm, respectively). In order to investigate the catalytic properties of the dinuclear complexes and mononuclear metallocenes, ethylene polymerisation has been conducted in the presence of MMAO. The most important feature is that the polymethylene bridged dinuclear metallocenes represent enormously improved activities compared with the activities from the corresponding mononuclear metallocene as well as the polysiloxane bridged dinuclear zirconocenes. In addition, the influence of both the nature and length of the bridging ligand upon the reactivities of the dinuclear metallocenes has also been observed.

Investigation of the polymerization behavior of polysiloxane‐bridged dinuclear zirconocenes as model compounds for a heterogenized metallocene at the silica surface

The polymerization of ethylene was studied by using a series of polysiloxane-bridged dinuclear zirconocenes [(SiMe 2 O) n SiMe 2 (C 5 H 4 ) 2 ][(C 9 H 7 )ZrCl 2 ]2 (7, n = 1; 8, n = 2; 9, n = 3), the corresponding mononuclear zirconocene (C 5 H 5 )(C 9 H 7 )ZrCl 2 , 10, and the pentamethylene-bridged dinuclear zirconocene [(CH 2 ) 5 (C 5 H 4 )2][C 9 H 7 )-ZrCl 2 ] 2 , 13. From the polymerization studies using these catalysts it was found that (i) activities of the polysiloxane dinuclear zirconocenes 7-9 were lower than that of the corresponding mononuclear zirconocene 10, (ii ) molecular weights of polyethylenes produced by the dinuclear metallocenes are greater than that of polyethylene produced by the mononuclear metallocene, (iii) the complex 9 holding the longest bridging ligand exhibited the highest activity but produced a polymer having the smallest molecular weight among the polysiloxane-bridged dinuclear zirconocenes, and (iv)the pentamethylene-bridged dinuclear metailocene 13 showed higher activity than the complexes 7-9 and the mononuclear zirconocene 10. The formation of the lowest molecular weight of polyethylene by 9 was attributed to the influence of electron withdrawal caused by the Lewis acid-base interaction between the acidic aluminum of the cocatalyst and the basic oxygen at the polysiloxane linkage as well as the lack of a steric problem. An increase in steric congestion around the metal center led to not only a decrease in catalytic activity due to preventing facile monomer access to the active site but also an increase in the molecular weight of polyethylenes due to supressing β-H elimination.

Syntheses of dinuclear titanium constrained geometry complexes with polymethylene bridges and their copolymerization properties

Abstract The polymethylene bridged dinuclear half-sandwich constrained geometry catalyst (CGC) [Ti(η 5 :η 1 -C 9 H 5 SiMe 2 NCMe 3 )] 2 [(CH 2 ) n ] ( n =6 ( 10 ), n =9 ( 11 ), n =12 ( 12 )) have been prepared by treating two equivalents of TiCl 3 (THF) 3 with the corresponding tetralithium salts of the ligands followed by oxidation by AgCl. Proton and Carbon-13 NMR spectra of the synthesized complexes provide firm evidence for the anticipated dinuclear structure. The important feature associated with the chemical shift of Carbon-13 NMR is the downfield chemical shift of 63.0 ppm due to the ipso -carbon of t -butyl group bonded at the coordinated nitrogen. In addition the chemical shift of the bridge head carbon at the indenyl ring is shifted toward highfield from 119 to 97 ppm. In order to investigate the catalytic behaviors of the prepared dinuclear catalysts copolymerization of ethylene and styrene was conducted in the presence of modified methylaluminoxane. The prime observance is that their activities increase in the order of 10 11 12 which indicates the presence of longer bridge between two active sites contributes to facilitate the polymerization activity of the dinuclear CGC. The melting points of the generated copolymers decrease as the styrene portion in feed increases. An interesting point is that styrene content in copolymers formed by the dinuclear catalysts is actually bigger than that in copolymer formed by the mononuclear CGC, which demonstrates the superior comonomer response of the dinuclear CGC comparing to the normal CGC.

Synthesis, characterization, and reactivities of the polysiloxane-bridged binuclear metallocenes tetramethyldisiloxanediylbis(cyclopentadienyltitanium trichloride) and hexamethyltrisiloxanediylbis(cyclopentadienyltitanium trichloride)

Abstract The reaction of dithallium salts of tetramethyldisiloxanediylbis(cyclopentadienyl), 3, and hexamethyltrisiloxanediylbis(cyclopentadienyl), 4, with two equivalents of TiCl4 gives the title compounds tetramethyldisiloxanediylbis(cyclopentadienyltitanium trichloride), 5 and hexamethyltrisiloxanediylbis(cyclopentadienyltitanium trichloride), 6 respectively. The stoichiometric reaction of 5 and 6 with water results in the formation of new oxygen-bridged metallocenes [(TiCl2)2(μ2-O)-(η5-C5H4)2-μ2-(SiMe2)2O], 7, and [(TiCl2)2(μ2-O)-(η5-C5H4)2-μ2-(SiMe2)3O2}], 8. In addition, further reaction of 7 and 8 with another one equivalent of water or the treatment of 5 and 6 with an excess amount of water gives rise to the formation of the metallocene compounds having Ti4O4 rings [(TiCl)2(μ2-O)-(η5-C5H4)2-μ2-(SiMe2)2O]2(μ2-O)2, 9, and [(TiCl)2(μ2-O)-(η5-C5H4)2-μ2-(SiMe2)3O2]2 (μ2-O)2, 10. All the new kinds of metalocenes prepared have been characterized by IR, NMR, mass spectrometry, or elemental analysis. Especially an investigation of the Δδ values in 1H NMR and a comparison between the theoretical and observed isotopic ratio in a mass spectra among the synthesized bridged compounds have been very conveniently utilized to study their structures. Polymerization experiments with the dinuclear complexes in the presence of methylaluminoxane as a cocatalyst indicate that the compounds 5 and 6 do exhibit catalytic activity for syndiotactic polymerization of styrene.

Synthesis and characterization of Group 4 metallocene complexes with two disiloxanediyl bridges

Group 4 metallocene complexes with two disiloxanediyl bridges [μ,μ-(Me 2 SiOSiMe 2 ) 2 (C 5 H 3 ) 2 ]ZrCl 2 ( 3 ) and [μ,μ-(Me 2 SiOSiMe 2 ) 2 (C 5 H 3 ) 2 ]HfCl 2 ( 4 ) have been prepared by the reaction of MCl 4 (M=Zr, Hf) with distannylated bis(cyclopentadienes), while the zirconium complex, 3 , was subjected to a single-crystal X-ray diffraction study. The reaction of TiCl 4 with two equivalents of doubly disiloxane bridged distannylated bis(cyclopentadienes) gives rise to the formation of the doubly bridged dinuclear titanocene [μ,μ-(Me 2 SiOSiMe 2 ) 2 (C 5 H 3 ) 2 ][TiCl 3 ] 2 ( 5 ) . Methylation and benzylation of the complex 3 results in [μ,μ-(Me 2 SiOSiMe 2 ) 2 (C 5 H 3 ) 2 ]ZrMe 2 ( 6 ) and [μ,μ-(Me 2 SiOSiMe 2 ) 2 (C 5 H 3 ) 2 ]-Zr(CH 2 C 6 H 5 ) 2 ( 7 ), respectively, without complications. Furthermore, the dibridged zirconium compound 3 polymerizes ethylene very efficiently in the presence of methylaluminoxane with an activity of 5 ton of PE/[Zr] mol h atm.

Iron catalyzed atom transfer radical polymerization of methyl methacrylate using diphenyl-2-pyridylphosphine as a ligand

The living radical polymerization of methyl methacrylate (MMA) by atom transfer radical polymerization, (ATRP) employing a Fe(II)X2/diphenyl-2-pyridyl phosphine (PyP) catalytic system (X = Cl, Br ), was investigated using several initiators and solvents at various temperatures. Most of the polymerizations with the PyP ligand were well controlled, with a linear increase in the number average molecular weights (Mn) vs. conversion, with relatively low molecular weight distributions (Mw/Mn = 1.2–1.4) throughout the reactions. The measured weights matched those of the predicted values. The ethyl-2-bromoisobutyrate (EBriB) initiated ATRP of MMA, with the Fe(II)X2/diphenyl-2-pyridyl phosphine catalytic system (X = Cl, Br), was better controlled in p-xylene at 80°C than the other solvents used in this study.

Development of new atom transfer radical polymerization system by iron (III)-metal salts without using any external initiator and reducing agent.

Atom transfer radical polymerization (ATRP) catalyzed by high oxidation state metal salts of FeX3 is developed for the first time in the absence of both external initiator and reducing agent. Methyl methacrylate (MMA) and styrene are polymerized successfully using FeX3 /Phosphorous ligands with well-controlled molecular weight distributions (=1.5). The molecular weight of the polymers increases with monomer consumption with the progress of time and the polymerization behaviors show a decent ATRP trend. Activators and initiators are suggested to generate in situ by the addition reaction of MMA and one equivalent of FeX3 . The PMMA synthesized from without-initiator system is characterized by (1) H, (13) C and DEPT (distortionless enhancement by polarization transfer nuclear magnetic resonance) nuclear magnetic resonance spectroscopy. Chain extension and copolymerization experiments prove the livingness of the obtained polymer.

PPM amount of Fe(III)-mediated ATRP of MMA with phosphorus-containing ligands in the absence of any additives

MMA was polymerized via new oxidation-free ATRP by using ppm amounts of a Fe(III)-mediated ATRP system with four phosphorus containing ligands without any external reducing agent or free radical initiator. Well-controlled polymerizations were able to be achieved to produce PMMA with a high molecular weight (>300 000) and low polydispersity (PDI < 1.3) with a 10 ppm amount of FeBr3.

Density functional study of the insertion mechanism for ethylene-styrene copolymerization with constrained geometry catalysts

The ethylene-styrene copolymerization with two constrained geometry catalysts (CGCs), CGC1 and CGC2 was investigated by the density functional theory. Structures and energetics of reactants, π complexes, transition states, and products during insertion of ethylene and/or styrene monomers into the catalytic reactive site of the CGCs are analyzed using the software DMOL3. The general gradient approximation correction was applied to the total energy calculation after being calculated at the local density approximation level. The relativistic effective core potential is used for titanium while all other electrons are treated explicitly. Structures at stationary points on the energy profile were generated by minimizing the energy with respect to all the degrees of freedom except for the reaction coordinate which is defined as the distance between the Cα carbon and the nearest carbon of inserting monomer. The CGC2 with an electron-rich ligand shows a weaker coordination with monomers, resulting in longer Ti–Cp,...