Saturated End Groups Research Articles

Synthesis of low-molecular-weight poly-α-olefins using silicon-bridged zirconocene catalyst for lubricant basestock

The oily oligomers with low-molecular-weight, medium kinematic viscosity and high viscosity index are yielded through oligomerizations of higher α-olefins (1-hexene, 1-octene, 1-decene, 1-dodecene and 1-tetradecene) and co-oligomerization of 1-decene with 1-butene in the presence of the silicon-bridged Ph2Si(Cp)(9-Flu)ZrCl2 catalyst and the methylaluminoxane co-catalyst. The oligomerization activity is affected by the bulkiness and lateral size of monomer, and the viscosity of oligomer obtained. Through adding of 1-butene to 1-decene, the oligomerization activity is decreased, but viscosity index of oligomer obviously is increased. The highest co-oligomerization activity of 1-decene with 1-butene is presented at the temperature of 60 °C and Al/Zr molar ratio of 300. 1H and 13C NMR spectroscopy reveal that four types of vinylidene are existed in oligomers and the major olefinic bonds are internal disubstituted vinylidene, which are produced through 2,1-misinsertion and β-hydride elimination, or 2,1-misinsertion and rearrangement followed by β-hydride elimination. The chain termination of oligomerization of α-olefins favors chain transfer to the co-catalyst to produce saturated end group. The oligomerization pathways are summarized.

Poly(10-undecene-1-ol) characterized by MALDI-TOF MS and NMR spectroscopy

Poly(10-undecene-1-ol)s were synthesized by metallocene-catalyzed polymerization. MALDI-TOF MS allows obtaining detailed information on the monomer units in the polymer chains and the nature of the head and end groups of these polymers in dependence on the Al alkyl triisobutyl aluminum (TIBA) as well as methylalumoxan (MAO), both used as protecting agent for the hydroxyl groups of the monomer. The peak-to-peak distances of the main peaks could be distinctly assigned to the monomer unit 10-undecene-1-ol. Evaluating the MALDI-TOF peak distributions, polymers with -H, -C4H9, -CH3 head groups in combination with vinylidene and saturated (–CH3) end groups could be detected. By 1H NMR spectroscopy, it was verified that with the used catalysts polymers with vinylidene end groups were obtained predominantly. The presence of saturated end groups could be proved qualitatively by combination of 1H and 13C NMR spectroscopy for polymers produced by TIBA protection, which strikingly confirm the results from MALDI-TOF MS. For the polymers prepared with only MAO protection, saturated groups are also proved but discrimination between head and end groups was not possible. A polymerization mechanism corresponding to the detected different head and end groups is proposed.

Suppression of 4-coumarate-CoA ligase in the coniferous gymnosperm Pinus radiata.

Severe suppression of 4-coumarate-coenzyme A ligase (4CL) in the coniferous gymnosperm Pinus radiata substantially affected plant phenotype and resulted in dwarfed plants with a "bonsai tree-like" appearance. Microscopic analyses of stem sections from 2-year-old plants revealed substantial morphological changes in both wood and bark tissues. This included the formation of weakly lignified tracheids that displayed signs of collapse and the development of circumferential bands of axial parenchyma. Acetyl bromide-soluble lignin assays and proton nuclear magnetic resonance studies revealed lignin reductions of 36% to 50% in the most severely affected transgenic plants. Two-dimensional nuclear magnetic resonance and pyrolysis-gas chromatography-mass spectrometry studies indicated that lignin reductions were mainly due to depletion of guaiacyl but not p-hydroxyphenyl lignin. 4CL silencing also caused modifications in the lignin interunit linkage distribution, including elevated beta-aryl ether (beta-O-4 unit) and spirodienone (beta-1) levels, accompanied by lower phenylcoumaran (beta-5), resinol (beta-beta), and dibenzodioxocin (5-5/beta-O-4) levels. A sharp depletion in the level of saturated (dihydroconiferyl alcohol) end groups was also observed. Severe suppression of 4CL also affected carbohydrate metabolism. Most obvious was an up to approximately 2-fold increase in galactose content in wood from transgenic plants due to increased compression wood formation. The molecular, anatomical, and analytical data verified that the isolated 4CL clone is associated with lignin biosynthesis and illustrated that 4CL silencing leads to complex, often surprising, physiological and morphological changes in P. radiata.

Thermal degradation behavior of PMMA synthesized by emulsifier‐free emulsion polymerization with a Cu2+/HSO3− redox system

AbstractIn this study, poly(methyl methacrylate) (PMMA) latex was synthesized in an emulsifier‐free emulsion polymerization at 60°C using a Cu2+/HSO redox initiator system with different concentrations of Cu2+. The experimental results showed that the monomer conversion reached above 90% for all systems. Zeta potential was all negative due to the bonded bisulfite ion and the magnitude was greater than 30 mV, providing the stability of PMMA emulsion. The morphology of the latex observed by scanning electron microscope revealed a uniform particle size, and the average particle size increased from 181.9 to 234.2 nm as the Cu2+ ion concentration increased from 2.0 to 6.0 mM in 1M of MMA solution. Thermal degradation behavior of synthesized PMMA was studied by thermogravimetric analysis, in which a two‐stage degradation behavior was observed. These two stages were found to be caused by the degradation of unsaturated end group (PMMACRCH2) and saturated end group (PMMAH), respectively. In addition, the higher the concentration of Cu2+ ion, the greater the proportion of PMMACRCH2 in the final product, and in turn rendering more weight loss in the first‐stage degradation. The copper ion not only played a role in the redox initiation, but also acted as a chain transfer agent to terminate growing polymer chains, thus producing PMMACRCH2. The apparent activation energies of the first stage (Ea1) and second stage (Ea2) were calculated by Ozawa's and Boswell's method. The results showed that Ea1, representing the degradation of PMMA‐CRCH2, was lower than Ea2 for the degradation of PMMA‐H. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Octahedral Alkylbis(phenoxy‐imine)tin(IV) Complexes: Effect of Substituents on the Geometry of the Complexes and Their Reactivity Toward Ionizing Species and Ethylene

AbstractThe synthesis and characterization of the organo‐tin compounds L2SnR2 [L = N‐(3,5‐dichlorosalicylidene)aniline; R = CH3 (1), R = CH2Ph (2)] and L′2SnR2 [3: L′ = N‐(3‐tert‐butylsalicylidene)aniline, R = CH2Ph] are described herein. NMR studies showed a highly symmetric structure for complex 1, with the alkyl groups in a trans configuration, and thepresence of at least two isomers in fluxional equilibrium for compounds 2 and 3. Single‐crystal X‐ray characterization for compound 2 showed an octahedral geometry with the alkyl groups in trans relationship. The reactivity of the synthesized compounds toward ionizing agents was studied by NMR spectroscopy. For compounds 1 and 2 formation of cationic species through alkyl abstraction by B(C6F5)3 was observed. For compound 3, a cationic species was obtained by reaction with 1 equiv. of [C(C6H5)3]+[B(C6F5)4]–; in this species a ηn coordination of the benzyl group with the metal centre was recognized by NMR solution study. All the obtained cationic species promoted ethylene oligomerization under mild conditions, producing oligomers with saturated end groups and methyl branches. Oligoethylene end‐group NMR analysis and deuteriolysis experiments excluded the migratory‐insertion mechanism. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

Preparation of telechelic oligomers by thermal degradation of propylene copolymers

The reactive end groups of nonvolatile oligomers obtained by controlled thermal degradation of poly(propylene- ran-ethylene) and poly(propylene- ran-1-butene) were determined by 1H and 13C NMR spectroscopy. The molar ratio of unsaturated to saturated end groups was found to be about 9:1. The average number of unsaturated end groups per molecule was between 1.6 and 1.8, indicating that 60–80 mol% of the oligomer molecules were telechelic, having two terminal unsaturated end groups. These oligomers had a lower polydispersity than the raw material, despite their lower molecular weight and melting temperature. Although the end groups resulting from each monomer unit could be detected by 13C NMR, the end group composition differed from that of the main chains of the raw materials. The end group composition was satisfactorily explained by the differences in bond dissociation energy and activation energy of elementary reactions that occurred during thermal degradation, based on the monomer composition of the raw materials.

Pressure and trimethylaluminum effects on ethene/1‐hexene copolymerization with methylaluminoxane‐activated (1,2,4‐Me3Cp)2ZrCl2: Trimethylaluminum suppression of standard termination reactions after 1‐hexene insertion

AbstractEthene homopolymerizations and copolymerizations with 1‐hexene were catalyzed by methylaluminoxane‐activated (1,2,4‐Me3Cp)2ZrCl2. Investigations of the effects of various pressures on the homopolymerizations and copolymerizations and of the effects of different concentrations of trimethylaluminum (TMA) on the copolymerizations were performed. The characteristics of the ethene/1‐hexene copolymers agreed with expectations for changes in the ethene concentration: the incorporation of 1‐hexene decreased, whereas the melting point and crystallinity increased, with increasing pressure. The main termination mechanism of the homopolymerizations was β‐hydrogen transfer to the monomer. Termination mechanisms resulting in vinylidene unsaturations dominated in the copolymerizations. Standard termination mechanisms producing vinyl and trans‐vinylene unsaturations occurred in parallel and were not influenced by the ethene or TMA concentration. In addition, some chain transfer to TMA, producing saturated end groups after hydrolysis, occurred. Copolymerizations with different additions of TMA, with the other polymerization conditions kept constant, showed that the catalytic productivity [tons of polyethylene/(mol of Zr h)], the 1‐hexene incorporation, and the molecular weight (from gel permeation chromatography) were independent of the TMA concentration. Surprisingly, the vinylidene content decreased almost linearly with increasing TMA concentration. TMA might have coordinated to the catalytic site after 1‐hexene insertion and rotation to the β‐agostic state and, therefore, suppressed the standard termination reactions after 1‐hexene insertion. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2584–2597, 2005

Octahedral Bis(phenoxy-imine)tin(IV) Alkyl Complexes: Synthesis, Characterization, and Reactivity toward Ionizing Species and Ethylene

The synthesis of new organotin compounds of the general formula L2SnR2 (L = N-(3-tert-butylsalicylidene)-2,3,4,5,6-pentafluoroaniline; R = CH3 (1), n-C4H9 (3)) and L‘2SnR2 (L‘ = N-(3-tert-butylsalicylidene)aniline; R = CH3 (2), n-C4H9 (4)) is described herein. The compounds were characterized by 1H, 13C, and 119Sn NMR in solution; in some cases a fluxional behavior was observed by variable-temperature experiments. Characterization by single-crystal X-ray diffraction analysis has been obtained for compounds 1, 2, and 4. The reactivity of the synthesized compounds toward ionizing agents was studied by an NMR-tube reaction. Compounds 2 and 4 underwent an alkyl abstraction reaction with the carbenium salt [C(C6H5)3]+[B(C6F5)4]-. The obtained cationic species exhibited some activity in the oligomerization of ethylene under mild conditions, producing short-chain oligomers, with saturated end groups and methyl branches.

On the effects of He + ions bombardment of polyphenylacetylene

Polyphenylacetylene (PPA) thin films deposited on silicon substrates have been bombarded with a beam of 30 keV of He + ions. The radiation damage of the film has been monitored by FT-IR spectroscopy at fluences between 0.8×10 19 and 1.1×10 20 ions/m 2. The spectral changes undergone by the PPA film have been interpreted in terms of chain scission with formation of acetylenic and saturated end groups, and in terms of crosslinking reaction and extensive radiolytic degradation. The expected PPA cyclization reaction, a reaction which transforms a linear polymer into a ladder polymer has not been observed, although polystyrene (PS) is able to give this kind of reaction under somewhat similar conditions to those adopted in the present work. The results have been discussed in an astrochemical context in relation to the infrared emission spectra of certain astrophysical object and molecules present in the interstellar medium.

Analysis of technical lignins by two- and three-dimensional NMR spectroscopy.

Modern multidimensional NMR spectroscopic methods were applied to investigate the effects of kraft pulping and oxygen delignification on lignin side-chain structures. In addition to the two-dimensional HSQC measurements, the three-dimensional HSQC-TOCSY technique was utilized to elucidate the (1)H-(1)H and (1)H-(13)C correlations of individual spin systems and thus indicate a certain lignin side-chain structure. Unlike earlier, nonlabeled samples were used for 3D measurements. According to 2D and 3D NMR spectra, most of the structures identified in milled wood lignin (MWL) are still present in technical lignins after kraft pulping and oxygen delignification. Although the main reaction during kraft pulping is the cleavage of beta-O-4 linkages, these structures are still left in spent liquor lignin as well as in residual lignin. The amount of coniferyl alcohol and dihydroconiferyl alcohol end groups, as well as some unidentified saturated end groups, is higher in technical lignins than in MWL. Contrary to our earlier observations, no diphenylmethane structures were observed in any technical lignins. Vinyl aryl ether structures could not be detected in technical lignins either.

Alternating Copolymerization of Ethylene and Propylene: Evidence for Selective Chain Transfer to Ethylene

C1-symmetric ansa-metallocenes Me2E(Ind)(Flu)ZrCl2 (E = Si (1) and C (2)), upon activation with methylaluminoxane (MAO), produce atactic alternating ethylene−propylene copolymers (up to 92% EP dyads) with low molecular weight (less than 20K). Quantitative 13C NMR analysis of copolymer chain ends produced with 2/MAO indicates that the chain initiation/termination process is highly selective to generate a vinylidene as the unsaturated end group (terminating end) and an ethyl group as the saturated end group (initiating end). The high selectivity for sec-butyl end groups reveals a highly selective chain-initiation process where ethylene insertion is followed by propylene insertion at the initiating end. Chain transfer from a propylene-terminated polymer chain to a coordinated ethylene monomer is proposed to explain this selectivity. The facile cross-monomer chain-transfer process explains the much lower molecular weights obtained for the EP copolymers relative to the ethylene or propylene homopolymers.

Chain transfer reactions in metallocene catalyzed polymerization of allylbenzene

Allylbenzene was polymerized in the presence of two types of homogeneous zirconocene catalysts (co-catalyst methylaluiminoxane). Selective chain termination through β-hydride elimination or chain transfer to aluminum was observed depending upon the catalysts employed. The rac-Et(Ind)2ZrCl2, and rac-Me2Si(Ind)2ZrCl2, catalysts gave the polyallylbenzenes with saturated end groups due to chain transfer to aluminum, while the Cp2ZrCl2 catalyst gave the polyallylbenzenes with vinylidene end groups due to β-hydride elimination.

Identification, Composition, and Asymmetric Formation Mechanism of Glycidyl Methacrylate/Butyl Methacrylate Copolymers up to 7000 Da from Electrospray Ionization Ultrahigh-Resolution Fourier Transform Ion Cyclotron Resonance Mass Spectrometry

Glycidyl methacrylate (GMA) and butyl methacrylate (BMA) have the same nominal mass (142 Da) but differ in exact mass by 0.036 Da (CH(4) vs O). Therefore, copolymers formed from the two isobaric monomers exhibit a characteristic isobaric distribution due to different monomer compositions. Here, we show that electrospray ionization FT-ICR mass spectrometry at 9.4 T resolves the isobaric components of copolymers as large as 7000 Da with a resolving power (m/Δm(50%)) of ∼500 000 in a gel permeation chromatography fractionated polymer sample. That resolution provides for complete and unequivocal component analysis of such copolymers of the size used for high solid content automobile coatings. All five possible copolymer products predicted by the polymerization mechanism are resolved and identified in the mass spectrum. Two of those polymer series (each with saturated end group) were previously unresolved by mass spectrometry because they differ in mass from the two other unsaturated products by only 0.0089 Da. Finally, analysis of the asymmetrical isobaric distribution for the copolymer n-mers, (GMA)(m)(BMA)(n)(-)(m), 0≤ m ≤ n, in which species with adjacent values of m differ from each other in mass by 36 mDa (i.e., the mass difference, CH(4) vs O, between GMA and BMA) proves that GMA is less reactive than BMA in the polymerization process.

Mechanism of olefin polymerization by a soluble zirconium catalyst

A mechanistic study has been carried out on the homogeneous olefin polymerization/oligomerization catalyst formed from Cp 2ZrMe 2 and methylaluminoxane, (MeAlO) x , in toluene. Formal transfer of CH 3 from Zr to Al yields low concentrations of Cp 2ZrMe + solvated by [(Me 2AlO) y (MeAlO) x− y ] y . The cationic Zr species initiates ethylene oligomerization by olefin coordination followed by insertion into the Zr–CH 3 bond. Chain transfer occurs by one of two competing pathways. The predominant one involves exchange of Cp 2Zr–P + (P=growing ethylene oligomer) with Al–CH 3 to produce another Cp 2ZrMe + initiator plus an Al-bound oligomer. Terminal Al–C bonds in the latter are ultimately cleaved on hydrolytic workup to produce materials with saturated end groups. Concomitant chain transfer occurs by sigma bond metathesis of Cp 2Zr–P + with ethylene. Metathesis results in cleavage of the Zr–C bond of the growing oligomer to produce materials also having saturated end groups; and a new initiating species, Cp 2Zr-CHCH 2 +. The two chain transfer pathways afford structurally different oligomers distinguishable by carbon number and end group structure. Oligomers derived from the Cp 2ZrMe + channel are C n ( n=odd) alkanes; those derived from Cp 2Zr–CHCH 2 + are terminally mono-unsaturated C n ( n=even) alkenes. Chain transfer by beta hydride elimination is detectable but relatively insignificant under the conditions employed. Propylene and 1-hexene react similarly but beta hydride elimination is the predominant chain transfer step. The initial Zr-alkyl species produces a Cp 2ZrH + complex that is the principle chain initiator. Chain transfer is fast relative to propagation and the products are low molecular weight oligomers.

Microstructure of Ethylene−1-Butene Copolymers Produced by Zirconocene/Methylaluminoxane Catalysis

Low molecular weight (ca. 2000) ethylene−1-butene copolymers were synthesized at 90 °C using rac-(dimethylsilyl)bis(4,5,6,7-tetrahydro-1-indenyl)zirconium dichloride (I) catalyst and methylaluminoxane (MAO) cocatalyst. Comonomer composition, triad sequence distribution, and end groups were analyzed by 1H and 13C NMR. The average polymer molecule contains about one double bond and one saturated end group. The unsaturated end groups were formed almost exclusively by transfer from propagating chains containing 1-butene as the terminal unit. At least 98% of the unsaturated end groups are vinylidene and trisubstituted double bonds, which are present in the approximate ratio 3:1. Saturated end groups result from the initiation process. Both ethylene and 1-butene are involved in initiation, but ethylene more than 1-butene. The product is a random copolymer with very short blocks (no longer than 2−3 monomer units) of both ethylene and 1-butene. The comonomer sequence distributions determined by 13C NMR were fitted to first-order Markovian statistics, which allowed calculation of the monomer reactivity ratios. The results are discussed in terms of a reaction mechanism consisting of initiation, propagation, and chain transfer reactions.

Preparation of .alpha.,.omega.-Diisopropenyloligopropylene by Thermal Degradation of Isotactic Polypropylene

It was found that α,ω-diisopropenyloligoprcpylene (M n = 3300-4800) is prepared as the nonvolatile oligomers isolated from the polymer residues resulting from the thermal degradation of isotactic polypropylene at 370 °C. Their structures were determined by 1 H and 13 C NMR spectroscopies in regard to the reactive end groups. Both the terminal vinylidene double bonds composed of an isopropenyl end group [CH 2 -C(CH 3 )-] and the saturated end group [CH 3 CH 2 CH 2 CH(CH 3 )-] were mainly detected with a molar ratio of about 9 :1. The average number of isopropenyl end groups per molecule f t ) is about 1.8, and therefrom it is indicated that about 80 mol % of the oligomer molecules is symmetric α,ω-diene-oligomer having two terminal isopropenyl groups. This oligopropylene retains highly the stereoregularity (microtacticity) of the original polymer and has a sharper dispersity of molecular weight (M w /M n : ca. 1.5) than the original polymer, in spite of lower molecular weights and T m (ca. 150 °C). This compound is useful as a new telechelic oligomer. These oligomers are considered to be formed by the intramolecular hydrogen abstraction (back-biting) of secondary terminal macroradicals followed by β scission at the end of the main chain (eq 3) and the intermolecular hydrogen abstraction of secondary terminal volatile radicals (eq 4), which are formed by the back-biting and other elementary reactions, followed by β scission.

End Groups in 1-Butene Polymerization via Methylaluminoxane and Zirconocene Catalyst

Poly(1-butene) was obtained by polymerization of 1-butene at 100 o C using rac-(dimethylsilyl)bis(4,5,6,7-tetrahydro-1-indenyl)zirconium dichloride (1) as catalyst and methylaluminoxane (MAO) as cocatalyst. The product was characterized by NMR ( 1 H and 13 C), SEC, and vapor pressure osmometry (VPO). The molecular weight M n of the polymer was determined as 1910, 2025, and 2055 by SEC, VPO, and NMR, respectively. The poly(1-butene) is 84% isotactic and has high regioselectivity (ca. 95% 1,2-addition). Both saturated and unsaturated end groups were characterized by NMR. Vinylidene and trisubstituted double bonds comprise approximately 67% and 29%, respectively, of the unsaturated end groups with the remainder consisting of vinylene, vinyl, and tetrasubstituted double bonds. n-Butyl and sec-butyl groups constitute the saturated end groups in the approximate ratio 10:1. There is a slight excess of saturated end groups relative to unsaturated end groups. These results are discussed in terms of a reaction mechanism of initiation and propagation with various chain-transfer reactions (β-hydride transfers with and without rearrangement, transfer to aluminum, transfer to vinylidene end groups, and β-alkyl transfer)

NMR spectroscopy of poly(vinyl chloride) defects. 2. 1H and 13C NMR analysis of the terminal vinyl end group, 1,3‐dichlorobutyl end group and chloromethyl branch

AbstractWe have been able to obtain the 1H NMR subspectra of most of the major saturated end groups in PVC. In order to assign the terminal vinyl (TV) group, CH2CH‐CHCl‐, we synthesized and analyzed the symmetrical model compound 3,5‐dichloro‐1,6‐heptadiene (4) containing a racemic (r) and a meso (m) isomer. They exhibit distinct NMR signals for the vinyl protons, which allowed us to subsequently assign the r diad and the previously unreported m diad terminal vinyl resonances present in very small amounts in commercial PVC. The study of the solvent induced chemical shifts of the vinyl protons in an experimental PVC sample containing an unusually high level of this end group allowed us to further assign it in terms of the terminal rr, rm, mm and mr triads.

Carbon-13 Nuclear Magnetic Resonance Analysis of Model Compounds of Saturated End Groups in Polypropylene

Carbon-13 Nuclear Magnetic Resonance Analysis of Model Compounds of Saturated End Groups in Polypropylene

Carbon-13 Nuclear Magnetic Resonance Analysis of Tail-to-Tail Monomeric Units and of Saturated End Groups in Polypropylene

Carbon-13 Nuclear Magnetic Resonance Analysis of Tail-to-Tail Monomeric Units and of Saturated End Groups in Polypropylene