Synthesis of tailor‐made polyethylene through the control of polymerization conditions using selectively combined metallocene catalysts in a supported system

Tailoring of the molecular weight distribution (MWD) in ethylene polymerization was attempted by selectively combining different types of metallocene catalysts onto a single support. The catalyst produced by supporting Et[Ind]₂ZrCl₂ and Cp₂HfCl₂ onto a single MAO pretreated silica support was able to produce polymers with unimodal or bimodal MWD's. This approach permits the synthesis of polyethylene with different MWD's using the same catalyst as a function of the polymerization conditions. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 331–339, 1999     

Ethylene polymerization reactions with Ziegler–Natta catalysts. II. Ethylene polymerization reactions in the presence of deuterium

Ethylene polymerization reactions with many Ziegler–Natta catalysts exhibit several features which differentiate them from polymerization reactions of α-olefins: a relatively low ethylene reactivity, higher polymerization rates in the presence of α-olefins, a high reaction order with respect to ethylene concentration, and strong reversible rate depression in the presence of hydrogen. A detailed kinetic analysis of ethylene polymerization reactions (see ref. 1 ) provided the basis for a new reaction scheme which explains all these features by postulating the equilibrium formation of a Ti C₂H₅ species with the H atom in the methyl group β-agostically coordinated to the Ti atom in an active center. This mechanism predicts that the β-agostically stabilized Ti C₂H₅ groups can decompose in the β-hydride elimination reaction with expulsion of ethylene and the formation of a Ti H bond even in the absence of hydrogen in the reaction medium. If D₂ is used as a chain transfer agent instead of H₂, the mechanism predicts the formation of deuterated ethylene molecules, which copolymerize with protioethylene. To prove this prediction, several ethylene homopolymerization reactions were carried out with a supported Ziegler–Natta titanium-based catalyst in the presence of large amounts of D₂. Analysis of gaseous reaction products and polymers confirmed the formation of several types of deuterated ethylene molecules and protio/deuterioethylene copolymers, respectively. In contrast, a metallocene catalyst, Cp₂ZrCl₂ MAO, does not exhibit these kinetic features. In the presence of deuterium, it produces only DCH₂ CH₂ (CH₂ CH₂)_x CH₂ CH₂D molecules. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 4273–4280, 1999     

Ethylene polymerization reactions with Ziegler–Natta catalysts. III. Chain-end structures and polymerization mechanism

Ethylene polymerization reactions with many Ziegler–Natta catalysts exhibit a number of features that differentiate them from polymerization reactions of α olefins: (1) a relatively low ethylene reactivity, (2) markedly higher polymerization rates in the presence of α olefins, (3) a high reaction order with respect to ethylene concentration, and (4) a strong reversible rate depression in the presence of hydrogen. A detailed kinetic analysis of ethylene polymerization reactions¹ provided the basis for a new kinetic scheme that postulates the equilibrium formation of Ti C₂H₅ species with the H atom in the methyl group β-agostically coordinated to the Ti atom in an active center. This mechanism predicts several new features of ethylene polymerization reactions, one being that chain initiation via insertion of any α-olefin molecule into the Ti H bond should proceed with an increased probability compared to that via ethylene insertion into the same bond. As a result, a significant fraction of ethylene/α-olefin copolymer chains should contain α-olefin units as the starting units. This article provides experimental data supporting this prediction on the basis of both a detailed structural analysis of co-oligomers formed in ethylene/1-pentene and ethylene/4-methyl-1-pentene copolymerization reactions and a spectroscopic analysis of chain ends in the copolymers. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 4281–4294, 1999     

Ethylene polymerization reactions with Ziegler–Natta catalysts. I. Ethylene polymerization kinetics and kinetic mechanism

Kinetics of ethylene homopolymerization reactions and ethylene/1-hexene copolymerization reactions using a supported Ziegler–Natta catalyst was carried out over a broad range of reaction conditions. The kinetic data were analyzed using a concept of multicenter catalysis with different centers that respond differently to changes in reaction parameters. The catalyst contains five types of active centers that differ in the molecular weights of material they produce and in their copolymerization ability. In ethylene homopolymerization reactions, each active center has a high reaction order with respect to ethylene concentration, close to the second order. In ethylene/α-olefin copolymerization reactions, the centers that have poor copolymerization ability retain this high reaction order, whereas the centers that have good copolymerization ability change the reaction order to the first order. Hydrogen depresses activity of each type of center in the homopolymerization reactions in a reversible manner; however, the centers that copolymerize ethylene and α-olefins well are not depressed if an α-olefin is present in the reaction medium. Introduction of an α-olefin significantly increases activity of those centers, which are effective in copolymerizing it with ethylene but does not affect the centers that copolymerize ethylene and α-olefins poorly. To explain these kinetic features, a new reaction scheme is proposed. It is based on a hypothesis that the Ti—C₂H₅ bond in active centers has low reactivity due to the equilibrium formation of a Ti—C₂H₅ species with the H atom in the methyl group β-agostically coordinated to the Ti atom in an active center. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 4255–4272, 1999     

Anionic bulk oligomerization of ethylene and propylene carbonate initiated by bisphenol‐A/base systems

When the bulk oligomerization of 1,3‐dioxolan‐2‐one (ethylene carbonate, EC) and 4‐methyl‐1,3‐dioxolan‐2‐one (propylene carbonate, PC) with the 2,2‐bis(4‐hydroxyphenyl)propane (bisphenol‐A, BPA)/base system (bases such as KHCO₃, K₂CO₃, KOH, Li₂CO₃, and t‐BuOK) was investigated at elevated temperature, significant differences were observed. Oligomerization of EC initiated by BPA/base readily takes place, but the oligomerization of PC is inhibited. The very first propylene carbonate/propylene oxide unit readily forms a phenolic ether bond with the functional groups of BPA phenolate, but the addition of the second monomer unit is rather slow. The oligomerization of EC yields symmetrical oligo(ethylene oxide) side chains. According to IR studies the oligomeric chains formed from PC with BPA contain not only ether but also carbonate bonds. The in situ step oligomerization of the BPA dipropoxylate was also identified by SEC, and a possible reaction mechanism is proposed. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 545–550, 1999     

Effect of the alkylaluminum cocatalyst on ethylene polymerization by a nickel–diimine complex

Different chlorine-free alkylaluminum compounds were active cocatalysts for ethylene polymerization in the presence of 1,4-bis(2,6-diisopropylphenyl)-acenaphthenediimine-dichloronickel (II) (1). The combination of 1 with trimethylaluminum or triisobutylaluminum produced catalytically active species that polymerized ethylene with productivities up to 469 kg_polymer/(mol_Ni · h). The activity of the catalytic system and the properties of the polymeric materials were influenced strongly by the reaction temperature. The polymers had a high molecular weight (up to 642 × 10³ g · mol⁻¹), and the molecular weight increased with the reaction time. The polyethylenes were branched, and the branching could be modulated by the proper choice of reaction parameters. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 4656–4663, 1999     

Ethylene/1-hexene copolymerizations by syndioselective metallocenes: Direct comparison of Me2C(Cp)(Flu)ZrMe2 with Et(Cp)(Flu)ZrMe2

Copolymerizations of ethylene with 1-hexene have been carried out by using two metallocenes: highly syndiospecific isopropylidene(1-η⁵-cyclopentadienyl)(1-η⁵-fluorenyl)-dimethylzirconium (Me₂C(Flu)(Cp)ZrMe₂, 1) and less syndiospecific (1-fluorenyl-2-cyclopentadienylethane)-dimethylzirconium (Et(Flu)(Cp)ZrMe₂, 2), in the presence of [Ph₃C][B(C₆F₅)₄] as a cocatalyst. The effect of different types of bridges on the catalytic activity and comonomer reactivity was reported. The ethano bridged 2 compound of a smaller dihedral angle showed much higher activity than the 1 compound in the ethylene homo- and copolymerizations. The catalytic activities of the two compounds were enhanced about twice when a suitable amount of 1-hexene comonomer is present in the feed. The copolymerization of ethylene with 1-hexene revealed a noticeable influence of the type of bridge on the relative reactivity of the 1-hexene. ¹³C-NMR analysis of copolymers showed that compound 1 is characterized by lower r_E, taken as an index of ethylene reactivity, and higher reactivity of 1-hexene. The bridge also affects the distribution of the 1-hexene along the copolymer chain, investigated through their product of reactivity ratios, r_Er_H. The thermal properties and the density of copolymers were not affected by the type of bridge of the metallocenes, but mainly depended on 1-hexene content in the copolymer. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2763–2772, 1999     

Continuous solution copolymerization of ethylene and octene-1 with constrained geometry metallocene catalyst

The solution copolymerization of ethylene (1) with octene-1 (2) in Isopar E using constrained geometry catalyst system, [C₅Me₄(SiMe₂N^tBu)]TiMe₂ (CGC-Ti)/tris(pentafluorophenyl)boron (TPFPB)/modified methylaluminoxane (MMAO), has been carried out in a high-temperature, high-pressure continuous stirred-tank reactor (CSTR) at 140°C, 500 psig and with a mean residence time of 4 min. A series of copolymer samples with octene-1 content up to 0.337 mole fraction were synthesized and characterized. The estimated reactivity ratios were r₁ = 7.90 and r₂ = 0.099. The CGC-Ti showed a higher ability to incorporate high α-olefins than other metallocene catalysts investigated in the literature due to its open structure. The presence of octene-1 lowered the catalyst activity, particularly at octene-1 levels higher than 0.45 mole fraction. Octene-1 was also found to reduce the molecular weight of polymer and broaden the molecular weight distributions. The triad distributions were measured by ¹³C-NMR. A minor penultimate effect was observed. The penultimate octene-1 unit appeared to slow down monomer insertion rates. A comparison of the propagation rate of octene-1 with the incorporation rate of macromonomer in the homopolymerization of ethylene suggests that the addition of macromonomer is effectively instantaneous after it is generated with diffusion to or from the active center reaction volume playing a minor role. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2949–2957, 1999     

Isomeric effect of the Et(H4Ind)2Zr(CH3)2 catalyst on the copolymerization of ethylene and styrene: A computational study

A density functional theory (B3LYP) computational study of the ethylene–styrene copolymerization process using meso‐Et(H₄Ind)₂Zr(CH₃)₂ as the catalyst is presented. The monomer insertion barriers in meso species are evaluated and compared with previously obtained barriers in rac diastereoisomers. Differences related to ethylene homopolymerization and ethylene–styrene copolymerization activities as well as styrene incorporation into the copolymer are found between the meso and rac diastereoisomers. Nevertheless, a migratory insertion mechanism seems to hold for both diastereoisomeric species. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4752–4761, 2006     

Kinetics and mechanism of the cationic polymerization of trioxane. I. Crystallization during polymerization

Cationic polymerizations of trioxane in 1,2‐ethylene dichloride and benzene were heterogeneous and reversible. Phase separation accompanying with crystallization occurred during the polymerization. Three morphological changes were found in the course of the polymerization as were investigated by dilatometry and precipitation method. Based on the findings of morphological changes and three reversible processes for the polymerization, a rate equation was proposed to describe the polymerization. The proposed rate equation was fairly good in describing the experimental data, and kinetics constants including K_p, K_d, K_p′, K_d′, M, M, and K_dis/K_cr for the polymerization at 30, 40, and 50°C in 1,2‐ethylene dichloride and benzene were obtained. Factors that affected the kinetics constants were discussed. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 483–492, 1999     

Intramolecular excited state complexes in trichromophoric model compounds for polyesters derived from 2,6‐naphthalenedicarboxylic acid and aliphatic glycols: experiment,rotational isomeric state model,and molecular dynamics

Steady‐state fluorescence was used to measure the ratio of emission intensities, denoted I_D/I_M, for excited state complexes and excited monomers of five trichromophoric compounds, 2‐naphthyl‐COO‐(CH₂)_m‐OOC‐2,6‐dinaphthyl‐COO‐(CH₂)_m‐OOC‐2‐naphthyl, m = 2–6. The linear aliphatic alcohols H(CH₂)_nOH, n = 1–7, as well as mixtures of ethylene glycol and methanol, were used to change the viscosity of the medium, η. The values of I_D/I_M depend on η and m. A Rotational Isomeric State model and Molecular Dynamics simulations were used for interpretation of the experimental results. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 253–266, 1999     

Polymerization with TMA-protected polar vinyl comonomers. I. Catalyzed by group 4 metal complexes with η5-type ligands

This paper describes the use of several kinds of group IV Cp based catalyst systems, in the synthesis of co- and terpolymers of ethylene, propylene and α-olefins endowed with OH and COOH functional groups. The hydroxy monomers used were 5-hexen-1-ol (4) and 10-undecen-1-ol (5) and the carboxy monomer was 10-undecen-1-oic acid (6). The three catalyst systems used were the C₂ symmetric ansa-zirconocene (1) the “in-site” titanium complex (2) and the non-rigid zirconocene (3), all activated by methylaluminoxane. Trimethylaluminium was used to protect the functional group of polar monomers. The first two catalyst systems suffer similar activity loss in the presence of polar monomer whereas the third one exhibited better tolerance toward the hydroxyolefins. NMR and FTIR spectroscopies were used to characterize the polymerization products. All three catalyst systems afforded functionalized co- and terpolymers by direct polymerization of ethylene/propylene/hydroxy-α-olefins but only the catalyst system (1)/MAO displays appreciable activities for direct polymerization of ethylene, propylene and carboxy-α-olefins. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2457–2469, 1999     

Catalytic systems Me2SiCp*NtBuMX2/(CPh3)(B(C6F5)4) (MTi,XCH3, MZr,XiBu) in copolymerization of ethylene with styrene

Catalytic activity of Me₂SiCp*N^tBuMX₂/(CPh₃)(B(C₆F₅)₄) [MTi, XCH₃ (1); MZr, X=ⁱBu (2)] systems in the ethylene/styrene (E/S) feed was examined. Experimental data revealed high activity for the catalytic system (1) for copolymerization ethylene with styrene, whereas the system with enhanced catalytic activity for ethylene homopolymerization (2) was temporarily blocked in the styrene presence yielding, even at high styrene content, homopolyethylene as the final product. Properties of thus obtained polymers were analyzed. Catalytic system (1) occurred very sensitive to S/E ratio in the comonomers feed. The 10‐fold acceleration for ethylene consumption was shown in two experimental sets conducted at S/E = 1.3 ratio, 1 bar, and 7.5 bar ethylene pressure, respectively. The consequent enhancement in S/E ratio resulted in slowing down both ethylene consumption and catalyst deactivation rates. Atactic polystyrene was formed at high styrene content with the catalyst (1). Catalytic system (1) allowed design of products with the highest styrene content (20 mol %) at low ethylene pressure, moderate temperature, and high S/E ratio. The apparent activation energy estimated from the initial rates of ethylene consumption was 54.6 kJ/mol. Analysis of apparent reactivity factors (r_E = 9 and r_S = 0.04; r_E × r_S = 0.4) and ¹³C‐NMR copolymer spectra revealed an alternating tendency of the comonomers for active center incorporation. DSC measurements showed considerable decrease of melting points and crystallinity even for copolymers with low styrene content. The catalyst produced relatively high–molecular weight copolymers (140–150 kg/mol) even at 80°C. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1083–1093, 1999     

UV-curable poly(ethylene glycol)–based polyurethane acrylate hydrogel

Poly(ethylene glycol) (PEG) with molecular weight (M_n) of 1000, 2000, 3000, and 4000 g/mol, four types of diisocyanate [hexamethylene diisocyanate (HDI), 4,4′-dicyclohexylmethane diisocyanate (H₁₂MDI), isophorone diisocyanate (IPDI), and toluene diisocyanate (TDI)], two types of comonomers [acrylamide (AAm) and acrylic acid (AAc)] that comprised up to 60% of the total solid were used to prepare UV-curable PEG–based polyurethane (PU) acrylate hydrogel. The gels were evaluated in terms of mechanical properties, water content as a function of immersion time and pH, and X-ray diffraction profiles of dry and swollen films. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2703–2709, 1999     

Cationic copolymerization of tetrahydrofuran with ethylene oxide in the presence of diols: Composition,microstructure, and properties of copolymers

Cationic copolymerization of tetrahydrofuran (THF) with ethylene oxide (EO) in the presence of diols leads to dihydroxy terminated telechelic copolymers. In the present article the influence of copolymerization conditions on the copolymer structure was studied in view of conclusions derived from studies of copolymerization kinetics and mechanism. It was shown that according to established copolymerization mechanism, the number average molecular weights increase linearly with conversion up to M_n ≅ 2500, hydroxyl end groups are bound exclusively to EO units and copolymers are composed of [EO]–[THF]_y segments. Microstructure of copolymers may be to some extent regulated by changing reaction conditions. Some physical properties of copolymers also were studied. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3455–3463, 1999     

Peroxide initiated maleic anhydride grafting: Structural studies on an ester‐containing copolymer and related substrates

Maleic anhydride (MAn) was grafted onto the low molecular weight esters methyl decanoate (MD) and methyl 2‐ethylhexanoate (MEH) using the free‐radical initiators Lupersol‐101 and ‐130; the esters were used as model compounds for the copolymer poly(ethylene‐co‐methyl acrylate). The grafted products in both cases were isolated from the unreacted ester and were subjected to extensive analysis using spectroscopic and chromatographic techniques. Analysis of the grafted material indicated the presence of one or more succinic anhydride (SAn) residues grafted to the ester. In the case of the multiply grafted material it has been established conclusively by ¹³C‐NMR using 2,3‐¹³C₂ labeled MAn that the multiple grafts exist as single units. A limited number of grafting experiments was performed on the copolymer in the melt and the graft‐modified copolymer was characterized spectroscopically. Single graft units were observed. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1609–1618, 1999     

Non‐equilibrium phase behavior of diblock copolymer melts and binary blends in the intermediate segregation regime

The phase behavior of intermediately segregated (χN = 45) poly(ethylene)‐poly(ethylethylene) (PE–PEE) diblock copolymers and PE–PEE binary blends are characterized using transmission electron microscopy and small‐angle X‐ray scattering. Surprisingly, the preparation‐dependent, nonequilibrium phase behavior can be overwhelming even at this degree of segregation. A pure diblock with a poly(ethylene) volume fraction of f_PE = 0.46 exhibited coexisting lamellae and perforated layers when prepared using a precipitation technique, but contained only the lamellar morphology when solvent cast. This preparation dependence was more dramatic in binary diblock copolymer blends with average compositions of 〈f_PE〉 = 0.44, 0.46, and 0.48. Precipitated blends exhibited a microphase separated structure that was disordered and bicontinuous; however, solvent cast samples exhibited either a cylindrical, coexisting cylindrical and lamellar, or lamellar morphology. This nonequilibrium behavior is attributed to the high degree of segregation and the proximity to the cylinder/lamellae phase boundary. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2229–2238, 1999     

Lithium chloride as catalyst for the ring-opening polymerization of lactide in the presence of hydroxyl-containing compounds

Lithium chloride was found to be an effective and biocompatible catalyst for the ring-opening polymerization of lactide in the presence of hydroxyl-containing compounds. Ethylene glycol (EG) and methyl α-D -glucopyranoside (MGlc) were used as multifunctional initiators. The polymerization was carried out at 128°C in bulk with 1% (w/w) of LiCl. Polylactide (PLA) of different molecular weights was obtained with varied molar ratios of monomer/initiator ([M]₀/[I]₀). The LiCl-catalyzed ring-opening polymerization was applied to the synthesis of a number of amphiphilic PLA copolymers when poly(ethylene glycol) (PEG), hydroxyethyl cellulose (HEC), and hydroxypropyl cellulose (HPC) were used as macroinitiators. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3486–3491, 1999     

In situ drawing of high molecular weight poly(ethylene terephthalate) in subcritical and supercritical CO2

The effects of draw conditions were studied for initially amorphous melt‐spun poly(ethylene terephthalate) fibers in the presence of subcritical and supercritical (SC) CO₂. Both in situ and posttreatment mechanical behavior along with morphological characteristics were investigated. Fibers soaked in subcritical CO₂ could be drawn to 30% higher draw ratios (DRs) compared with fibers that were cold‐drawn. In situ force response measured with a custom apparatus showed that fibers in subcritical CO₂ had no measurable resistance to deformation until strain hardening occurred. In contrast, fibers drawn in SC CO₂ displayed a yield response, a significant decrease in ductility, and a significant difference in postyield behavior. Fibers drawn in subcritical CO₂ showed slightly lower tensile properties compared with cold‐drawn samples whereas fibers treated in SC CO₂ had much lower tensile properties because of the limited DR achieved. X‐ray diffraction studies indicated that CO₂ enhances the development of the crystalline phase compared with cold‐drawn samples. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1881–1891, 1999     

Synthesis,characterization, and nucleotidic chain cleavage ability of uncharged water soluble poly(ethylene glycol)‐fullerene derivatives with an amphiphilic character

Water‐soluble fullerenes containing two poly(ethylene glycol) branches [Full‐(PEG)₂] were prepared starting from commercial poly(ethylene glycol)‐monomethyl ethers and C₆₀ [Full‐(PEG)₂]s chemical characterization was made by FT‐IR, NMR, and MALDI‐TOF mass spectrometric analyses. Their thermal stability was determined by TGA experiments. The capability of C₆₀‐derivatives to induce oligonucleotide cleavage under visible light irradiation was also ascertained. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2154–2153, 2008