Polymerization behavior of propene with [t-BuNSiMe2Flu]TiMe2: effects of solvents and cocatalysts

The titanum complex [η¹:η³tert-butyldimethylfluorenylsilyl]-amido)dimethyltitanum ([t-BuNSiMe₂Flu]TiMe₂, Cat.A) was synthesized by an alternatively quicker one pot procedure. Polymerization of propene in the presence of [t-BuNSiMe₂Flu]TiMe₂/dried pure methylaluminoxane (d-PMAO) system at 0 °C was investigated in toluene and heptane. A strong enhancement of productivity was observed in toluene compared to heptane. Polymerization of propene was also investigated with Cat.A in heptane, with different cocatalysts, d-PMAO and dried pure modified methylaluminoxane (d-MMAO), which was prepared from the mixture of trimethylaluminum (TMA) and triisobutylaluminum (TIBA). A 10-fold higher number average molecular weight (M_n) and broad molecular weight distribution (MWD) was obtained with d-PMAO in heptane, even though kinetic features and other parameters signified the living nature of the polymerization process. However, the broadening of MWD was attributed to the poor insolubility of d-PMAO in heptane.     

Microwave-assisted McMurry polymerization utilizing low-valent titanium for the synthesis of poly 2,6-[1,5-bis(dodecyloxy)naphthylene vinylene] (PNV)

Poly 2,6-[1,5-bis(dodecyloxy)naphthylene vinylene] is synthesized by microwave-assisted McMurry polymerization utilizing low-valent titanium generated from titanium tetrachloride and zinc. The obtained polymer is fluorescent with an average molecular weight of approximately 65,000 g/mol and a polydispersity of M_w/M_n ≈ 3. Absorption and fluorescence spectroscopy in solution and on spin-cast thin films reveal that the bis-alkoxy substituted PNV has a short effective conjugation length but a quite efficient exciton migration.     

Olefin polymerization by cyclopentadienyltris(dimethylamido)titanium(IV) complexes

Several titanium(IV) complexes of the type Cp′Ti(NMe₂)₃ [Cp′ = cyclopentadienyl ( 1 ), (dimethylaminoethyl)cyclopentadienyl ( 2 ), indenyl ( 3 ), and pentamethylcyclopentadienyl ( 4 )] were prepared, and their catalytic properties in the polymerization of α‐olefins were examined. Complexes 1 and 2 catalyzed the polymerization of ethylene in the presence of methylaluminoxane with a much higher activity than 3 or 4 . Complexes 3 and 4 polymerized ethylene with an activity similar to that of CpTiCl₃ ( 6 ). The preactivation of 2 , 3 , or 4 with trimethylaluminum (TMA) resulted in an increase in ethylene polymerization activities. Also, 1 and 2 were successfully used as ethylene/1‐hexene copolymerization catalysts, producing polymers with various amounts of 1‐hexene incorporation, depending on the amount of 1‐hexene in the feed mixture. Complex 1 likewise effectively polymerized styrene with a higher activity and higher syndiospecificity than the other three catalysts. Complexes 3 and 4 polymerized styrene with low syndiospecificity, whereas 2 produced only atactic polystyrene. The preactivation of 3 or 4 with TMA resulted in an increase in styrene polymerization activities and increased the syndiotacticity percentage of the polymers produced. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 313–319, 2001     

Olefin copolymerization with metallocene catalysts. II. Kinetics,cocatalyst, and additives

The kinetics of ethylene/propylene copolymerization catalyzed by (ethylene bis (indeyl)-ZrCI₂/methylaluminoxane) has been investigated. Radiolabeling found about 80% of the Zr to be catalytically active. The estimates for rate constants at 50°C are k₁₁ = 1104 (M_s)^?1, k₁₂ = 430 (M_s)^?1, k₂₂ = 396 (M_s)^?1,k₂₁ = 1020 (M_s)^?1, and k^A_tr,1 + k^A_tr.2 = 1.9 × 10^?3 s^?1. Substitution of trimethylaluminum for methylaluminoxane resulted in proportionate decrease in polymerization rate. The molecular weight of the copolymer is slightly increased by loweing the [Al]/[Zr] ratio, or addition of Lewis base modifier but at the expense of lowered catalytic activity and increase in ethylene content in the copolymer. Lowering of the polymerization temperature to 0°C resulted in a doubling of molecular weight but suffered 10-fold reduction in polymerization activity and increase of ethylene in copolymer.     

Effect of a cocatalyst modifier in the synthesis of ultrahigh molecular weight polyethylene having reduced number of entanglements

The use of a hindered phenol to trap free trimethylaluminum (TMA) in methylaluminoxane (MAO) solutions has been reported to improve the performance of single‐site, homogeneous catalysts for olefin polymerization. In the present study, with the help of rheological analyses, we have investigated and compared the molecular weight, molecular weight distribution and entanglement density of ultrahigh molecular weight polyethylene synthesized with a single‐site catalyst activated by MAO and phenol‐modified MAO. While the number average molecular weight (M_n) of the obtained polymers remains the same for both activations, a higher yield and a higher entanglement density are found in the initial stages of polymerization on using phenol‐modified MAO as the cocatalyst. These results suggest that on using the phenol‐modified MAO as activator, a higher number of active sites are obtained. Surprisingly in the presence of untreated MAO, a tail in the higher molecular mass region is produced. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013     

Synthesis of high‐molecular‐weight elastomeric poly(propylene) with half‐titanocene/MAO catalyst

A novel catalyst precursor, (η⁵‐pentamethylcyclopentadienyl)titanium triallyloxide (Cp*Ti(OCH₂—CH=CH₂)₃), was prepared and employed in a study of propylene polymerization in the presence of methylaluminoxane (MAO). This work has revealed that the half‐titanocene catalyst is desirable for the production of elastomeric poly(propylene) with high molecular weight (M_w = 8–69×10⁴) as well as in good yields under typical polymerization conditions.     

Control of molecular weight in polymerization of vinyl chloride with Cp*Ti(OPh)3/MAO catalyst

Polymerization of vinyl chloride (VC) with titanium complexes containing Ti‐OPh bond in combination with methylaluminoxane (MAO) catalysts was investigated. Among the titanium complexes examined, Cp*Ti(OPh)₃/MAO catalyst (Cp*; pentamethylcyclopentadienyl, Ph; C₆H₅) gave the highest activity for the polymerization of VC, but the polymerization rate was slow. From the kinetic study on the polymerization of VC with Cp*Ti(OPh)₃/MAO catalyst, the relationship between the M_n of the polymer and the polymer yields gave a straight line, and the line passed through the origin. The M_w/M_n values of the polymer gradually decrease as a function of polymer yields, but the M_w/M_n values were somewhat broad. This may be explained by a slow initiation in the polymerization of VC with Cp*Ti(OPh)₃/MAO catalyst. The results obtained in this study demonstrate that the molecular weight control of the polymers is possible in the polymerization of VC with the Cp*Ti(OPh)₃/MAO catalyst. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3872–3876, 2007     

Ethylene polymerization promoted by dinuclear titanium p-tert-butylthiacalix[4]arene complexes

The dinuclear titanium p-tert-butylthiacalix[4]arene complexes 1 and 2 after activation with methylaluminoxane have been tested as homogeneous catalysts for the polymerization of ethylene. The results show that the catalytic activity of 1, although still poor, is higher than those of the related mononuclear titanium complexes bearing calix[4]arene as ligand. The molecular weight of the polyethylene produced are high (M_W up to 1.4 × 10⁶ Dalton) with broad molecular weight distribution. The polyethylenes have high melting point (133-142 °C) indicating a linear polymer microstructure which was confirmed by ¹³C NMR analysis.     

Atactic polymerization of propylene catalyzed by mono(η5-cyclopentadienyl)titanium tribenzyloxide combined with methylaluminoxane

Propylene has been polymerized with mono(η⁵-cyclopentadienyl)titanium tribenzyloxide activated with methylaluminoxane (MAO). It was found that the content of residual trimethylaluminium (TMA) in MAO has a determinative effect on the polymerization. An excess of TMA in the catalyst system reduces the Ti species to inactive lower valent states. The catalyst system gives medium molecular-weight atactic polypropylene (M_v = 2–7 × 10⁴) with narrow molecular weight distribution (M_w/M_n = 1.4–1.8). The polymer has a stereoirregular structure described by Bernoullian statistics. Statistical analysis of the regiotriad distribution of the polypropylene chains indicates a regioblock microstructure. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 2051–2057, 1998     

Olefin Polymerization and Copolymerization with Alkylaluminum-lnitiator Systems. VII. Initiation by Electrophilic Halogens

Abstract

The discovery of initiation of cat ionic polymerization of isobutylene and styrene by electrophilic chlorine generated by the reaction of chlorine and trimethylaluminum in the temperature range -40 to -100° is reported. Bromine and trimethylaluminum is a very poor initiating system, and iodine and trimethylaluminum does not initiate the polymerization of either isobutylene or styrene. Polymerization of isobutylene initiated by chlorine and trimethylaluminum shows a linear plot of log M_v vs 1/T with an overall E_DPof ～1.9 kcal, mole. The molecular weights (M_w) of polystyrene obtained with the Cl₂/Me₃Al system appear to be the highest ever reported for cationic polymerization of this monomer under comparable conditions. The mechanism of initiation has been investigated by model experiments: The reaction between Cl₂/ Me₃Al and 2,2,4-trimethyl-l-pentene gave three chlorinated products (2-chloromechyl-4,4-dimethyl-l-pentene, 1-chloro-2,4,4-trimethyl-1-pentene, and 2-chioromethyl-2,4,4-trimethyl-pentane). The position of chlorine in these compounds indicate initiation by electrophilic chlorine, Cl. Some preliminary results obtained using diethylaluminum chloride-halogens as coinitiator-initiator systems are also described.     

Effect of Free Trimethylaluminum Content in Methylaluminoxane on Performances of Bis(salicylaldiminate)nickel(II)‐Based Catalysts for Ethylene Polymerization

Summary: The performances of ethylene polymerization catalysts based on III and commercial methylaluminoxane were investigated by reducing the content of free trimethylaluminum in methylaluminoxane by its reaction with 2,6‐di‐tert‐butylphenol. This allowed optimization of the formulation of the catalyst, affording a high‐molecular‐weight linear polyethylene (PE) with a productivity [(1 900 kg of PE/(mol of Ni × h)], ten‐fold higher than that previously achieved for the same system adopting commercial methylaluminoxane not pre‐treated with the above phenol derivative.

     

Novel titanium(iv) complexes with 2,4-di-tert-butyl-6-(1,1,1,3,3,3-hexafluoro-2-hydroxypropan-2-yl)phenol in ethene polymerization

Dinuclear (2) and mononuclear dichloride complexes (3) of titanium(iv) isopropoxide with a bidentate phenol alcohol ligand, viz., 2,4-di-tert-butyl-6-(1,1,1,3,3,3-hexafluoro-2-hydroxy-propan-2-yl)phenol, were obtained. The structures of the complexes were confirmed by X-ray diffraction. The dimeric structure of complex 2 is typical of alkoxy compounds and contains the bridging fragment Ti(??-OPrⁱ)₂Ti; the coordination polyhedron of the Ti atom is a distorted tetragonal pyramid. In complex 3, the Ti atom has a distorted octahedral environment made up of the O atoms of the ligand, the Cl atoms, and the O atoms of two coordinated propan-2-ol molecules. The catalytic properties of complexes 2 and 3 in ethene polymerization were studied with such promoters as polymethylaluminoxane (MAO), trimethylaluminum, triisobutylaluminum, diethylaluminum chloride, and Et₂AlCl-MgBu₂. Both the complexes were catalytically active (635 and 540 kg of polyethylene (PE)/(mol of Ti) h atm, respectively) only in the presence of the binary promoter Et₂AlCl-MgBu₂. The dichloride complexes obtained from a lithium or magnesium salt of the same ligand and TiCl₄ without separation from lithium and magnesium chlorides formed as by-products were catalytically active in the presence of MAO, Buⁱ ₃Al, and Me₃Al. For the catalytic system containing the dichloride complex and MgCl₂, the best promoter is Me₃Al (1082 kg of PE/(mol of Ti) h atm). The polymer obtained on all the catalytic systems is linear polyethylene characterized by high molecular weight (M_w = = 593900?C2000000 g mol^?1) and high polydispersity indices (M_w/M_n = 2.8?C15). Various conjectures were made about why lithium and magnesium chlorides have the promoting effects.     

Synthesis, characterization, and ethylene polymerization behavior of [(RR′-admpzp)2Ti(OPr)2] complexes (RR′-admpzp = 1-dialkylamino-3-(3,5-dimethyl-pyrazol-1-yl)-propan-2-olate)

[(RR′-admpzp)₂Ti(OPrⁱ)₂] complexes (2a-c), synthesized from reaction of Ti(OPrⁱ)₃Cl (0.5 equiv) with 1-dialkylamino-3-(3,5-dimethyl-pyrazol-1-yl)-propan-2-ol compounds in the presence of triethylamine (0.5 equiv), are pseudo-octahedral with each RR′-admpzp ligand κ²-O,N(pyrazolyl) coordinated to the titanium center. In solution, 2a-c adopt isomeric structures that are in dynamic equilibrium. At 23 °C, 2a-c/1000 MAO catalyst systems furnished high molecular weight polymers with narrow molecular weight distributions (M_w/M_n = 2.7-2.8). At 100 °C, 2a-c/MAO catalyst systems exhibited increased polymerization activity and 2c/1000 MAO system furnished high molecular weight polyethylene with a molecular weight distribution (M_w/M_n = 2.1) that is close to that found for single-site catalysts.     

Synthesis and properties of hydrophilic segmented poly(urethanes) based on poly(ethylene glycols) and glycerol monostearate

Poly(urethanes) having the structure of comb-shaped copolymers were synthesized from glycerol monostearate, poly(ethylene glycols) with M _n = 300–6000, and 1,6-hexamethylene diisocyanate. Effects of the molecular mass of segments and of the contents of soft segments and side chains on both the glass transition temperature of the soft segment and on the melting point and the enthalpy of melting of crystalline phases involving soft segments and side chains were studied by DSC and IR spectroscopy. The resulting comb-shaped copolymers were shown to exhibit thermoplastic and hydrophilic behavior. It was demonstrated that the ultimate tensile strength, yield stress, and Young’s modulus of copolymer films increase with an increase in the molecular masses of soft and hard segments with their ratio maintained constant.     

Highly active ethylene polymerization and copolymerization with norbornene using bis(imino‐indolide) titanium dichloride–MAO system

A catalytic system of new titanium complexes with methylaluminoxane (MAO) was found to effectively polymerize ethylene for high molecular weight polyethylene as well as highly active copolymerization of ethylene and norbornene. The bis (imino‐indolide)titanium dichlorides (L₂TiCl₂, 1 – 5 ), were prepared by the reaction of N‐((3‐chloro‐1H‐indol‐2‐yl)methylene)benzenamines with TiCl₄, and characterized by elemental analysis, ¹H and ¹³C NMR spectroscopy. The solid‐state structures of 1 and 4 were determined by X‐ray diffraction analysis to reveal the six‐coordinated distorted octahedral geometry around the titanium atom with a pair of chlorides and ligands in cis‐forms. Upon activation by MAO, the complexes showed high activity for homopolymerization of ethylene and copolymerization of ethylene and norbornene. A positive “comonomer effect” was observed for copolymerization of ethylene and norbornene. Both experimental observations and paired interaction orbital (PIO) calculations indicated that the titanium complexes with electron‐withdrawing groups in ligands performed higher catalytic activities than those possessing electron‐donating groups. Relying on different complexes and reaction conditions, the resultant polyethylenes had the molecular weights M_w in the range of 200–2800 kg/mol. The influences on both catalytic activity and polyethylene molecular weights have been carefully checked with the nature of complexes and reaction conditions. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3415–3430, 2007     

Novel Complex Catalyst of η3‐(Pentamethylcyclopentadienyl)dimethylaluminum/Titanium(IV) Butoxide (Cp*AlMe2/Ti(OBu)4) for Syndiotactic Polystyrene

A novel metallocene catalyst was prepared from the reaction of (η³‐pentamethylcyclopentadienyl)dimethylaluminum (Cp*AlMe₂) and titanium(IV) n‐butoxide Ti(OBu)₄. The resulting titanocene Cp*Ti(OBu)₃ was combined with methylaluminoxane (MAO)/tri‐iso‐butylaluminum (TIBA) to carry out the syndiotactic polymerization of styrene. The resulting syndiotactic polystyrene (sPS) possesses high syndiotacticity according to ¹³C NMR. Catalytic activity and the molecular weight of the resulting sPSs were discussed in terms of reaction temperature, concentration of MAO, amounts of scavenger TIBA added, and the hydrogen pressure applied during polymerization.     

X-ray structural study of poly(ethylene terephthalate) after solid-state postpolycondensation

The structure of PET samples exposed to multistep annealing below the melting temperature T _m in high vacuum (the so-called solid-state postpolycondensation) has been studied by wide-angle X-ray diffraction. The sizes of crystallites have been calculated through the analysis of half-widths of corresponding reflections via the Rietveld, Scherrer, and Hosemann methods. As the molecular mass (M _η) of PET is increased from 4.5 × 10⁴ to 3 × 10⁵, the sizes of crystallites increase in three crystallographic directions (100, 010, and 001). An increase in the thickness of the crystal core of a lamella (the fold length in direction $\bar 1$ 05) $D_{\bar 105} $ from 40 to 58 Å (the Rietveld method) in the molecular mass range under study is accompanied by a rise in T _m by 19°C. The role of the $D_{\bar 105} $ size and intercrystallite tie links formed in the course of postpolycondensation in the rise in T _m with molecular mass is discussed. The free surface energy σ _e of the crystal end face (the surface of folds) has been calculated through the Tomson-Gibbs equation. The values of σ _e for PET samples with M × 10^?3 = 45, 100, and 300 have been estimated as 24.3, 23.5, and 15 mJ/m², respectively. These values turn out to be comparable with the lateral surface energy of crystallites available from the literature (13–19 mJ/m²). It has been inferred that the proportion of tie bridges in the intercrystallite space is appreciably higher than the proportion of folds on the face end surface of PET with not only M = 300 × 10³, but also with M = 45 × 10³ and 100 × 10³.     

Novel titanium complexes bearing two chelating phenoxy‐imine ligands and their catalytic performance for ethylene polymerization

Three substituted salicylaldimine ligands ( 1a, 2a, 3a ) and their titanium complexes bis[N‐(5‐nitrosalicylidene)‐2,6‐diisopropylanilinato]titanium(IV)dichloride ( 1 ), bis[N‐(5‐chlorosalicylidene)‐2,6‐diisopropylanilinato]titanium(IV)dichloride ( 2 ) and bis[N‐(5‐bromosalicylidene)‐2,6‐diisopropylanilinato]titanium(IV)dichloride ( 3 ) were synthesized and characterized by mass spectra, ¹H NMR and elemental analyses, as well as complex 1 by X‐ray structure analysis. In the presence of methylaluminoxane (MAO), 1, 2 and 3 are efficient catalysts for ethylene polymerization in toluene. Under the conditions of T = 60 °C, p = 0.2 MPa, and n(MAO)/n(cat) = 1500, the activities of 1–3 reached 4.55–8.80 × 10⁶ g of PE (mol of Ti h bar)^?1, which is much higher than that of the unsubstituted complex bis[N‐(salicylidene)‐2,6‐diisopropylanilinato]titanium(IV)dichloride ( 4 ). The viscosity‐average molecular weight of polyethylene ranged from 24.8 × 10⁴ to 44.9 × 10⁴ g/mol for 1–3 and the molecular weight distribution M_w/M_n from 1.85 to 2.34. The effects of reaction conditions on the polymerization were examined in detail. The increase in ethylene pressure and rise in polymerization temperature are favorable for 1–3 /MAO to rise the catalytic activity and the molecular weight of polyethylene. Copyright © 2007 John Wiley & Sons, Ltd.     

Synthesis of hyperbranched-linear star block copolymers by atom transfer radical polymerization of styrene using hyperbranched poly(siloxysilane) (HBPS) macroinitiator

Hyperbranched-linear star block copolymers, hyperbranched poly(siloxysilane)-block-polystyrene (HBPS-b-PSt), were prepared by atom transfer radical polymerization (ATRP) of styrene in xylene, using bromoester-terminated HBPS (HBPS-Br (P3), M_n = 7500, M_w/M_n = 1.76) as a macroinitiator. The number-average molecular weights of the obtained polymers (M_n) were in the range of 21,800-60,000 and molecular weight distributions were unimodal throughout the reaction (M_w/M_n = 1.28-1.40). These polymers showed 5 wt.% decomposition temperature (T_d5) over 300 °C. The DSC thermograms of the resulting polymers indicated two glass transition temperatures (T_g). The T_g of HBPS segment shifted to higher value while the T_g of PSt segment shifted to lower value compared with those of the homopolymers. Preliminary physical characterization related to the solution viscosity of the resulting block copolymers is also reported.     

The influence of soft segment length on the properties of poly(butylene terephthalate-co-succinate)-b-poly(ethylene glycol) segmented random copolymers

Three series of poly(butylene terephthalate-co-succinate)-b-poly(ethylene glycol) segmented random copolymers with starting PEG number-average molecular weight (M_n(PEG)) at 600, 1000 and 2000, respectively, as well as hard segment poly(butylene succinate) (PBS) molar fraction (M_PBS) increasing from 10% to 30% were synthesized through a transesterification/polycondensation process and characterized by means of GPC, NMR, DSC, WAXD and mechanical testing etc. The investigations were mainly focused on the influence of M_n(PEG) on the properties of resulting copolymers bearing two sorts of hard segments. It is revealed that all the samples show a relatively symmetrical GPC curves with the number-average molecular weight more than 4 × 10⁴, while the polydispersity decreases from 1.9 to 1.4 as the increasing M_n(PEG) because of the prolonged time for polycondensation and the faster exclusion of small molecules by-product with the decreased molten viscosity. The sequence distribution analysis shows that the average sequence length of hard segment PBT decreases while that of PBS increases with the increasing M_PBS and are independent of the soft segment length. The approximate unit degree of randomness as well as the soft segment length turns out that the segments take a statistically random distribution along the backbone. Micro-phase separation structure is verified for the appearance of two glass transition temperatures and two melting points, respectively, in DSC thermograms of most samples. The depression of melting points and the reduction of crystallinity of hard segments with increasing M_PBS are related to the crystal lattice transition from α-PBT to PBS and discussed in the viewpoint of cohensive energy. Mechanical testing results demonstrate that the increase of amorphous domains the increase of M_PBS as well as M_n(PEG) will provide high elongation and good flexibility of copolymer chain. The in vitro degradation experiments show that the partial substitution of aromatic segment PBT with aliphatic PBS will substantially accelerate the degradation rate with enhanced safety of degradation by-products and while changing M_n(PEG) broaden the spectrum to tailor the properties.