bluuebunny/crossref_metadata_2025_split huggingface dataset:
Methylaluminoxane‐free ethylene polymerization with in situ activated zirconocene triisobutylaluminum catalysts and silica‐supported stabilized borate cocatalysts
Authors: Charoenchaidet Sumate , Chavadej Sumaeth , Gulari Erdogan 
Published: August 2002

AbstractHeterogenization of tris(pentafluorophenyl)borane [B(C6F5)3] on a silica support stabilized with chlorotriphenylmethane (CICPh3) and N,N‐dimethylaniline (HNMe2Ph) creates the following supported borane cocatalysts: [HNMe2Ph]+[B(C6F5)3‐SiO2]− and [CPh3]+[B(C6F5)3‐SiO2]−. These supported catalysts were reacted with Cp2ZrCl2 TIBA in situ to generate active metallocene species in the reactor. Triisobutylaluminum (TIBA) was a good coactivator for dichloro‐zirconocene, acting as the prealkylating agent to generate cationic zirconocene (Cp2ZrC4H9+). The catalytic performances were determined from the kinetics of ethylene‐consumption profiles that were independent of the time dedicated to the activation of the catalysts. The scanning electron microscopy‐energy dispersive X‐ray measurements showed that B(C6F5)3 dispersed uniformly on the silica support. Under our reaction conditions, the [CPh3]+[B(C6F5)3‐SiO2]− system had higher productivity and weight‐average molecular weight than the [HNMe2Ph]+[B(C6F5)3‐SiO2]− system. For the [CPh3]+[B(C6F5)3‐SiO2]− system, the productivity increased with the amount catalyst; however, the polydispersity index of polyethylene synthesized did not change. The final shape of polymer particles was a larger‐diameter version of the original support particle. The polymer particles synthesized with supported [CPh3]+[B(C6F5)3‐SiO2]− catalysts had larger diameters. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3240–3248, 2002
Decomposition of model alkoxyamines in simple and polymerizing systems. II. Diastereomeric N‐(2‐methylpropyl)‐N‐(1‐diethyl‐phosphono‐2,2‐dimethyl‐propyl)‐aminoxyl‐based compounds
Authors: Ananchenko Gennady S. , Souaille Marc , Fischer Hanns , Le Mercier Christophe , Tordo Paul 
Published: August 2002

AbstractThermal reactions of the alkoxyamine diastereomers DEPN‐R′ [DEPN: N‐(2‐methylpropyl)‐N‐(1‐diethylphosphophono‐2,2‐dimethyl‐propyl)‐aminoxyl; R′: methoxy‐carbonylethyl and phenylethyl] with (R,R) + (S,S) and (R,S) + (S,R) configurations have been investigated by 1H NMR at 100 °C. During the overall decay the diastereomers interconvert, and an analytical treatment of the combined processes is presented. Rate constants are obtained for the cleavage and reformation of DEPN‐R′ from NMR, electron spin resonance, and chemically induced dynamic nuclear polarization experiments also using 2,2,6,6‐tetramethylpiperidinyl‐1‐oxyl (TEMPO) as a radical scavenger. The rate constants depend on the diastereomer configuration and the residues R′. Simulations of the kinetics observed with styrene and methyl methacrylate containing solutions yielded rate constants for unimeric and polymeric alkoxyamines DEPN‐(M)n‐R′. The results were compatible with the known DEPN mediation of living styrene and acrylate polymerizations. For methyl methacrylate the equilibrium constant of the reversible cleavage of the dormant chains DEPN‐(M)n‐R′ is very large and renders successful living polymerizations unlikely. Mechanistic and kinetic differences of DEPN‐ and TEMPO‐mediated polymerizations are discussed. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3264–3283, 2002
Synthesis and polymerization of phosphorus‐containing acrylates
Authors: Avci Duygu , Mathias Lon J. 
Published: August 2002

AbstractNovel phosphorus‐containing acrylate monomers were synthesized by two different routes. The first involved the reaction of ethyl α‐chloromethyl acrylate and t‐butyl α‐bromomethyl acrylate with diethylphosphonoacetic acid. The monomers were bulk‐ and solution‐polymerized at 56–64 °C with 2,2′‐azobisisobutyronitrile. The ethyl ester monomer showed a high crosslinking tendency under these conditions. The selective hydrolysis of the ethyl ester phosphonic ester compound was carried out with trimethylsilyl bromide, producing a phosphonic acid monomer. In the second route, ethyl α‐hydroxymethyl acrylate and t‐butyl α‐hydroxymethyl acrylate were reacted with diethylchlorophosphate. The bulk homopolymerization and copolymerization of these monomers with methyl methacrylate and 2,2′‐azobisisobutyronitrile gave soluble polymers. The attempted hydrolysis of the monomers was unsuccessful because of the loss of the diethylphosphate group. The relative reactivities of the monomers in the photopolymerizations were also compared. The ethyl α‐hydroxymethyl acrylate/diethylphosphonic acid monomer showed higher reactivity than the other monomers, which may explain the crosslinking during the polymerization of this monomer. The reactivities of other derivatives were similar, but the rates of polymerization were slow in comparison with those of methyl methacrylate. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3221–3231, 2002
Diels–Alder modification of poly(ethylene terephthalate‐co‐anthracene‐2,6‐carboxylate) with N‐substituted maleimides
Authors: Vargas Marian , Kriegel Robert M. , Collard David M. , Schiraldi David A. 
Published: August 2002

AbstractDimethyl 2,6‐anthracene dicarboxylate is used as a comonomer in the synthesis of functional copolymers that are subject to modification with Diels–Alder reactions. The formation of poly(ethylene terephthalate‐co‐2,6‐anthracenate), containing less than 20 mol % of the anthracene‐2,6‐dicarboxylate structural units, provides materials that are tractable and soluble. The anthracene units of the copolymers undergo Diels–Alder reactions with N‐substituted maleimides. The grafting of N‐alkylmaleimides affords soluble, hydrophobic polymers, whereas grafting with maleimide‐terminated poly(ethylene glycol) affords hydrophilic polymers. Because this reaction proceeds below the melting point of the copolymers, the procedure can be applied to thin films, whereby the surface properties are modified. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3256–3263, 2002
Isobutene polymerization initiated by [CP*TiMe2]+ in the presence of a series of novel, weakly coordinating counteranions
Authors: Kumar K. Rajesh , Hall Chernoff , Penciu Anca , Drewitt Mark J. , McInenly Paula J. , Baird Michael C. 
Published: August 2002

AbstractThe highly electrophilic borane B(C6F5)3 reacts with n‐octadecanol (n‐C18H37OH) and n‐octadecanethiol (n‐C18H37SH) to form the 1:1 adducts (n‐C18H37EH)B(C6F5)3 (E = O or S). The latter are acidic and react with Cp*TiMe3 in methylene chloride and toluene to give methane and the complexes [Cp*TiMe2][(n‐C18H37E)B(C6F5)3], which are very good initiators for the carbocationic polymerization of isobutene (IB) from −40 to −20 °C. High conversions to high molecular weight polyisobutene (PIB) in methylene chloride and moderate conversions to high molecular weight PIB in toluene are observed and are consistent with the anions [(n‐C18H37E)B(C6F5)3]− being very weakly coordinating. Although polymerization in methylene chloride is too rapid for the temperature to be controlled, polymerization in toluene is slower, and the temperatures can be controlled so that Arrhenius‐type plots of the logarithm of the number‐average molecular weight versus T−1 = 1/T may be obtained. Activation energies for the degree of polymerization in these polymerization reactions and similar polymerizations carried out with n‐C18H37EH:borane ratios of 1:2 and with the activators [Ph3C][B(C6F5)4] and Al(C6F5)3 range from −11 to −27 kJ mol−1, values comparable to those for most conventional IB polymerization initiators. However, the values of the weight‐average and number‐average molecular weights are unusually high for the temperatures used, and this is consistent with current theories of the role of weakly coordinating anions. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3302–3311, 2002
Synthesis and characterization of functional aliphatic copolyesters
Authors: Mani Ramaswamy , Bhattacharya Mrinal , Leriche Christian , Nie Li , Bassi Sukh 
Published: August 2002

AbstractFunctional aliphatic copolyesters of succinic acid (SA) and citric acid (CA) were synthesized via direct copolycondensation in the presence of 1,4‐butanediol, with titanium(IV) butoxide as a catalyst. The effects of the comonomer and comonomer ratio on the polycondensation and the melting and glass‐transition temperatures were investigated. The melting temperature was very sensitive to the molar ratio of the SA–CA comonomer units. The chain extension of this poly(butylene succinate citrate) was carried out with hexamethylene diisocyanate. The intrinsic viscosity, crystallinity percentage, and rheological properties of these copolyesters were also studied. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3232–3239, 2002
Photoinitiated polymerization of styrene from self‐assembled monolayers on gold. II. Grafting rates and extraction
Authors: Paul Rituparna , Schmidt Rolf , Feng Jianxin , Dyer Daniel J. 
Published: August 2002

AbstractUltrathin films of polystyrene (PS) were grown from self‐assembled monolayers by the “grafting‐from” technique. The initiating system consisted of a dithiol azobisisobutyronitrile‐type free‐radical initiator that was activated by irradiation at 300 nm. The thickness of the PS films ranged from 7 to 190 nm and could be controlled by varying the reaction time or the monomer concentration. The films were characterized by ellipsometry and Fourier transform‐reflection absorption infrared spectroscopy after Soxhlet extraction of residual physisorbed polymer. These films were unstable above 60 °C, and a water‐jacketed Soxhlet extractor was designed to maintain solvent temperatures below 45 °C during extraction. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3284–3291, 2002
Chemiluminescence of polyethylene: The comparative antioxidant effectiveness of phenolic stabilizers in low‐density polyethylene
Authors: Catalina Fernando , Peinado Carmen , Allen Norman S. , Corrales Teresa 
Published: August 2002

AbstractThe thermal stabilizing efficiency of a range of phenolic antioxidants (Lowinox CA22, Lowinox WSP, Lowinox TBP6, Irganox 3114, Irganox 1330, and Cyanox 1790) was determined in polyethylene films with chemiluminescence and hydroperoxide analysis and compared with standard systems based on Irganox 1010 and 1076. Under both nitrogen and oxygen conditions, good correlations were obtained between the two methods, confirming the importance and role of the hydroperoxide functionality and its stability in the oxidative process. Chemiluminescence decay rates correlated well with the initial corresponding hydroperoxide contents, which were measures of the antioxidant efficiencies in the polymer. The antioxidant structure and volatility (melting points) were important parameters to consider in any such correlations and related very much to the methodology and conditions of analysis (i.e., the temperature and atmosphere). Some of the antioxidants themselves under nitrogen exhibited strong chemiluminescence, which appeared to be a legacy associated with their manufacturing history and the partial oxidation of their structures, which gave peroxide functionalities. This was more notable for the complex antioxidant structures. Under oxygen, higher levels of chemiluminescence were observed, and this was indicative of some level of oxidation associated with the antioxidant structures. With temperature‐ramping experiments, the chemiluminescence emission was significant and only observed at temperatures close to the melting points of the additives and/or polymer. Mobility was clearly an essential feature of this reaction emission because chemiluminescence was well observed when the molten state was reached. Under normal practical conditions, such levels of chemiluminescence, because of employed stabilizers, do not contribute significantly to the chemiluminescence emissions of stabilized polymer materials. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3312–3326, 2002
Dramatic decrease of the cis content and molecular weight of cis‐transoidal polyphenylacetylene at 23 °C in solutions prepared in air
Authors: Percec Virgil , Rudick Jonathan G. , Nombel Paul , Buchowicz Wlodzimierz 
Published: August 2002

AbstractThe thermal cis–trans isomerization of cis‐transoidal polyphenylacetylene (PPA) synthesized with Noyori's catalyst [Rh(CCPh)(norbornadiene)(PPh3)2] has been investigated under both ambient and inert atmospheres in solution and in bulk. In all cases, an intramolecular cyclization results in cis–trans isomerization, and subsequent chain cleavage produces 1,3,5‐triphenylbenzene. This reaction is accelerated by the presence of air, particularly when the reaction takes place in solution. Decreases in the cis content and molecular weight show that the intramolecular cyclization process takes place at 23 °C in solution. The mechanism of this reaction is identical to that reported previously for cis‐cisoidal and cis‐transoidal PPA synthesized with Ziegler–Natta catalysts. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3212–3220, 2002
Copolymerization of ethene and propene in the presence of Cs symmetric group 4 metallocenes and methylaluminoxane
Authors: Longo Pasquale , Siani Ermelinda , Pragliola Stefania , Monaco Guglielmo 
Published: August 2002

AbstractEthene–propene copolymerizations were performed in the presence of Cs symmetric group 4 metallocenes. The reactivity ratios were strongly influenced by both the transition metal and the ancillary ligands. Substantially alternate, almost random, and blocky copolymers were obtained with titanocene, zirconocene, and hafnocene, respectively, with the bis(dimethylsilyl)‐1,1′‐2,2′‐diyl‐(3′,5′‐diisopropyl)(4‐isopropyl)‐(cyclopentadienyl) ligand, and a blocky copolymer was obtained with (diphenyl methylidene)(cyclopentadienyl)(9‐fluorenyl)TiCl2. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3249–3255, 2002
Structural analysis of polyethene prepared with rac‐dimethylsilylbis(indenyl)zirconium dichloride/methylaluminoxane in a high‐temperature, continuously stirred tank reactor
Authors: Kokko Esa , Wang Wen‐Jun , Seppälä Jukka V. , Zhu Shiping 
Published: August 2002

AbstractA study of ethene solution polymerization with the rac‐dimethylsilylbis(indenyl)‐zirconium dichloride/methylaluminoxane catalyst system in a high‐temperature (140 °C), continuously stirred tank reactor system was carried out. 13C NMR, gel permeation chromatography, Fourier transform infrared, and rheological measurements were used for polymer analyses. Polyethylenes with low molecular weights (weight‐average molecular weight ≈ 35–55 kg/mol) and small amounts of methyl, ethyl, and long‐chain branching were produced. 13C NMR measurements showed that the long‐chain and methyl branches increased and that the ethyl branch contents decreased with decreasing monomer concentrations. At high monomer concentrations, the chain transfer to the coordinated monomer was concluded to be the predominant chain termination mechanism, whereas the chain transfer to aluminum was dominant at low monomer concentrations, which was evidenced by the fact that the selectivity of end groups was reduced to about 50%. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3292–3301, 2002
Phytophthora infestans: populations, pathogenicity and phenylamides
Authors: Shattock Richard C 
Published: August 2002

AbstractIsolates of Phytophthora infestans (Mont) de Bary (the potato and tomato late blight pathogen) resistant to phenylamides appeared in Europe and North America in the late 1970s and early 1990s respectively. Concurrent, but coincidentally, with both these events there were radical structural shifts in the pathogen populations as immigrant genotypes from Mexico displaced the indigenous populations. Both A1 and A2 mating type isolates are now present in blighted crops, permitting alternative inoculum via germinating sexually produced oospores to influence dynamics of late blight populations. Studies of inheritance of ploidy, host‐specific pathogenicity, mating type and resistance to antibiotics and phenylamide fungicides have provided insight into mechanisms of variation in this potent pathogen.© 2002 Society of Chemical Industry
EU regulatory aspects of resistance risk assessment
Authors: Heimbach Udo , Kral Gregor , Niemann Peter 
Published: August 2002

AbstractThe EPPO Standard PP 1/213(1) on resistance risk analysis is the basis for risk assessment within the authorisation process in Germany. Data for resistance risk analysis have to be provided by the applicant and risk‐mitigation strategies prepared if necessary. The extent of data requirements and the intensity of the evaluation process depend mainly on the type of target organism, crop, mode of action of the active substance and the resistance history of the organism in combination with products of similar mode of action as the one being applied for. Because resistance risk is a very complicated issue during the authorisation of plant‐protection products, intensive co‐operation between applicants and regulators is essential prior to submission of the dossier, with due consideration of the amount of data necessary and, where required, the proposed resistance‐management strategy.© 2002 Society of Chemical Industry
A non‐Mendelian inheritance of resistance to strobilurin fungicides in Ustilago maydis
Authors: Ziogas Basil N , Markoglou Anastasios N , Tzima Aliki 
Published: August 2002

AbstractMutants of Ustilago maydis (DC) Corda with high resistance to azoxystrobin (RF 164 to 4714, based on EC50 values), an inhibitor of mitochondrial electron transport at the cytochrome bc1 complex, were isolated in a mutation frequency of 2.3 × 10−7 after nitrosoguanidine mutagenesis and selection on media containing 1 µg ml−1 azoxystrobin in addition to 0.5 mM salicylhydroxamate (SHAM), a specific inhibitor of cyanide‐resistant (alternative) respiration. Oxygen uptake in whole cells was strongly inhibited in the wild‐type strains by azoxystrobin (1.5 µg ml−1) in addition to SHAM (1 mM), but not in the mutant isolates. Genetic analysis with nine such mutant isolates resulted in progeny phenotypes which did not follow Mendelian segregation, but satisfied the criteria of non‐Mendelian (cytoplasmic) heredity. In crosses between three mutant isolates with the compatible wild‐type strains, the sensitivity was inherited by progeny maternally from the wild‐type parent strain (criterion of uniparental inheritance). In crosses between wild‐type strains and remaining mutant isolates, a continuous distribution of sensitivity in the progeny was found (criterion of vegetative segregation). The third criterion of cytoplasmic resistance (criterion of intracellular selection) was fulfilled by experiments on the stability of resistance phenotypes. With two exceptions, a reduction of resistance was observed in the mutant strains when they were grown on inhibitor‐free medium. Recovery of the high resistance level was observed after they were returned to the selection medium. Cross‐resistance studies with other fungicides, which also inhibit electron transport through complex III of respiratory chain, showed that mutations for resistance to azoxystrobin were also responsible for reduced sensitivity to kresoxim‐methyl (RF 18 to 1199) and to antimycin‐A (RF 20 to 305), which act at the Qo and Qi sites of the cytochrome bc1 complex, respectively. Studies of the fitness of azoxystrobin‐resistant isolates showed that these mutations appeared to be pleiotropic, having significant adverse effects on growth in liquid culture and pathogenicity on young corn plants.© 2002 Society of Chemical Industry
Amplified esterase genes and their relationship with other insecticide resistance mechanisms in English field populations of the aphid, Myzus persicae (Sulzer)
Authors: Field Linda M , Foster Stephen P 
Published: August 2002

AbstractMyzus persicae samples were collected from populations present on a range of field crops between 1997 and 2000. A combination of biochemical, DNA‐based diagnostics and bioassays was used to assess the presence of three insecticide resistance mechanisms: elevated carboxylesterase (E4 or FE4), insensitive acetylcholinesterase and insensitive sodium channels (knockdown resistance, kdr). For the carboxylesterases, both the levels of enzyme and the type of gene present (E4 or FE4) were determined. The results showed that during the time period studied there was a dramatic reduction in the proportion of aphids with very high levels of E4 and an increase in those with lower levels of FE4. There was also a slightly different E4 gene present in a limited number of samples. The change in esterase genes was accompanied by a virtual loss of the insensitive AChE variant and a maintenance of aphids with kdr. The selection pressures and other factors leading to these changes in field populations of M persicae are discussed.© 2002 Society of Chemical Industry
Temporal and spatial dynamics of insecticide resistance in Myzus persicae (Hemiptera: Aphididae)
Authors: Foster Stephen P , Harrington Richard , Dewar Alan M , Denholm Ian , Devonshire Alan L 
Published: August 2002

AbstractAdvances in understanding insecticide resistance in the peach‐potato aphid, Myzus persicae (Sulzer), at the genotypic, biochemical and molecular levels have led to rapid and precise methods for the detection of several resistance mechanisms (elevated carboxylesterase, modified acetylcholinesterase or MACE, and knockdown resistance or kdr) in individual insects, and for monitoring their frequencies over space and time. This paper summarises the results of two long‐term surveys of resistance dynamics in M persicae in England, based on samples collected directly from field and glasshouse crops or from four 12.2‐m suction traps. The study showed marked fluctuations in resistance frequencies that probably reflect the counteracting forces of selection imposed by insecticides for aphids possessing more copies of esterase resistance genes, and selection against these forms when insecticide use is relaxed. There is growing evidence that several different resistance mechanisms in M persicae have associated fitness costs. In the case of esterase and MACE, these costs are apparently strong enough to effect a decline in resistance frequency over winter, and a more prolonged decline over successive cropping seasons when aphid numbers are insufficient to trigger intensive chemical applications. Changes in the overall frequency of resistance genotypes may also be influenced by the predominance of year‐round parthenogenesis in M persicae in the UK, leading to non‐random associations between mechanisms and selection operating on clonal lineages rather than individual genotypes.© 2002 Society of Chemical Industry