bluuebunny/crossref_metadata_2025_split huggingface dataset:
Gel permeation chromatographic analysis of polyurethane prepolymer synthesis kinetics II. The effects of stoichiometry and type of diisocyanate
Authors: Thompson Corley M. , Taylor Sue G. , McGee William W. 
Published: April 2003

AbstractThe kinetics of formation of polyurethane prepolymers is studied by an analytical technique which involves reactive quenching of the isocyanate, separation of the oligomeric species by GPC, and measurement by UV absorbance of the quenched moieties. The precision of the kinetic parameters and the ratios of the oligomers are determined. The effect of changes in reactant stoichiometry on the ratio of oligomers is measured and compared to the value predicted by an equation from Flory. Toluene diisocyanate is shown to give fewer high oligomers than predicted, while methylene diphenylene diisocyanate gives nearly the predicted values. Tetramethylxylene diisocyanate gives more high oligomers than predicted, an unexpected but possibly important result. Catalyst is shown to increase the reaction rate of the last by more than 200 times. © 1994 John Wiley & Sons, Inc.
Silolene‐Bridged zirconocenium polymerization catalysts
Authors: Tsai Woei‐Min , Chien James C. W. 
Published: April 2003

AbstractA new silolene‐bridged compound, racemic (1,4‐butanediyl) silylene‐bis (1‐η5‐in‐denyl) dichlorozirconium (1) was synthesized by reacting ZrCl4 with C4H8Si (IndLi)2 in THF. 1 was reacted with trialkylaluminum and then with triphenylcarbenium tetrakis (penta‐fluorophenyl) borate (2) to produce in situ the zirconocenium ion (1+). This “constraint geometry” catalyst is exceedingly stereoselective for propylene polymerization at low temperature (Tp = −55°C), producing refluxing n‐heptane insoluble isotactic poly(propylene) (i‐PP) with a yield of 99.4%, Tm = 164.3°C, δHf = 20.22 cal/g and M̄w = 350 000. It has catalytic activities of 107−108 g PP/(mol Zr · [C3H6] · h) in propylene polymerization at the Tp ranging from −55°C to 70°C, and 108 polymer/(mol Zr · [monomer] · h) in ethylene polymerization. The stereospecificity of 1+ decreases gradually as Tp approaches 20°C. At higher temperatures the catalytic species rapidly loses stereochemical control. Under all experimental conditions 1+ is more stereospecific than the analogous cation derived from rac‐dimethylsilylenebis (1‐η5‐indenyl)dichlorozirconium (4). The variations of polymerization activities in ethylene and in propylene for Tp from −55°C to +70°C indicates a Michaelis Mention kinetics. The zirconocenium‐propylene π‐complex has a larger insertion rate constant but lower thermal stability than the corresponding ethylene π‐complex. This catalyst copolymerizes ethylene and propylene with reactivity ratios of comparable magnitude rE ˜ 4rp. Furthermore, rE.rp ˜ 0.5 indicating random copolymer formation. Both 1 and 4 activated with methylaluminoxane (MAO) exhibit much slower polymerization rates, and, under certain conditions, a lower stereo‐selectivity than the corresponding 1+ or 4+ system. © 1994 John Wiley & Sons, Inc.
Phosphorus containing polymers. III. Polyimidophosphonates
Authors: Banerjee Susanta , Palit Sunanda K. , Maiti Sukumar 
Published: April 2003

AbstractSynthesis of dihydroxybisimide monomers and their subsequent polycondensation with dichlorophenylphosphine oxide by use of a phase‐transfer catalyst are reported. The monomers were characterized by melting point, elemental analysis, and IR spectroscopy. The polyimidophosphonates were characterized by viscosity measurement, molecular weight determination, elemental analysis, IR, ESCA, 1H‐NMR, 31P‐NMR, and X‐ray diffraction. Thermal stability and glass transition temperature (Tg) of the polymers were evaluated by TGA, DTA, and TMA. These polymers are self‐extinguishing and readily soluble in highly polar solvents like DMF, DMSO, DMAC, NMP, HMPA, etc. © 1994 John Wiley & Sons, Inc.
Synthesis of copolymers of 1,3‐dioxan‐2‐one and oxepan‐2‐one using coordination catalysts
Authors: Albertsson Ann‐Christine , Eklund Maria 
Published: April 2003

AbstractA new type of copolymer is synthesized in a bulk polymerization from 1,3‐dioxan‐2‐one and oxepan‐2‐one (ϵ‐caprolactone) using either Sn‐oct, ZnAc2, Bu2SnO, or Bu3SnCl as the catalyst. SEC analysis shows that it is possible to achieve high molecular weights and narrow molecular weight distributions. 13C‐NMR analysis confirms the existence of copolymers. Conversion studies have been made and reactivity ratios, r1 and r2, have been determined to distinguish between the reactivities of 1,3‐dioxan‐2‐one and oxepan‐2‐one. The Finemann‐Ross method and the Kelen‐Tüdös method were used to calculate the ratios and the agreement was good between the methods. The composition of the copolymer agrees with the feed composition at high conversions. Thermal analysis of copolymers by DSC shows crystalline melting resulting from a somewhat blocky copolymer. The glass transition temperatures of the copolymers are in agreement with the Fox equation. The corresponding blends of the two homopolymers show a constant melting point and glass transition temperature. A nonionic insertion mechanism and a Lewis acid alcoholysis mechanism are discussed. © 1994 John Wiley & Sons, Inc.
Synthesis and radical polymerization of spiro orthocarbonates bearing exomethylene groups
Authors: Sanda Fumio , Takata Toshikazu , Endo Takeshi 
Published: April 2003

AbstractSynthesis and radical polymerization of spiro orthocarbonates (SOCs) bearing exomethylene groups at the α to the ether oxygen (1a–1e) were studied. SOCs 1a–1e were prepared by the successive reactions of dichlorodiphenoxymethane with two different diols followed by dehydrochlorination. Radical polymerization of the SOCs was carried out in the presence of an appropriate initiator (3 mol % versus monomer) at 130 and 180°C. The obtained polymer insoluble in n‐hexane contained both vinyl polymerization unit 13 and double ring‐opening polymerization unit 14 (ketone‐carbonates). The degree of ring‐opening followed the order: 1a <1b < 1d, 1e. n‐Hexane‐insoluble polymer was not obtained in the polymerization of 1c. Both steric hindrance of methyl group and ring size affected the degree of ring‐opening. The introduction of methyl group into SOC increased the degree of ring‐opening (1a <1b), whereas the degree of ring‐opening of either 1d, consisting of six‐ and seven‐membered rings, and 1e, consisting of two seven‐membered rings, was higher than those of 1a and 1b, consisting of five and seven‐membered rings. From the molecular orbital calculation (PM3, UHF method), it was concluded that if the first single ring‐opening occurs, then the successive second ring‐opening takes place more smoothly. The first ring‐opening requires more energy than the vinyl polymerization does. © 1994 John Wiley & Sons, Inc.
New polymer syntheses. LXXV. 2,5‐biaryloxyterephthalic acids and rigid‐rod polyaramides derived from them
Authors: Kricheldorf Hans R. , Bürger Rolf 
Published: April 2003

AbstractSeveral 2,5‐bisaryloxyterephthalic acids were prepared by a new method, namely arylation of diethyl‐2,5‐bistrimethylsiloxyterephthalate. Rigid‐rod polyaramides were prepared by polycondensation of silylated diamines with a terephthaloylchloride with two diphenylsulfone side chains. Another polyamide was prepared from 2,5‐bis(4′‐cyanophenoxy) terephthalic acid and 1,4‐diaminobenzene. None of these polyaramides is meltable and their solubilities differ largely. A copolymer of 1,4‐diaminobenzene and 3,3′‐dimethoxybenzidine is soluble in various organic solvents including polar vinyl monomers. © 1994 John Wiley & Sons, Inc.
Quantification of end groups in polystyrenes by pyrolysis–gas chromatography
Authors: Ito Yoshiro , Ohtani Hajime , Ueda Shouji , Nakashima Yasuki , Tsuge Shin 
Published: April 2003

AbstractThe determination of end groups in polystyrenes (PSts) polymerized anionically with n‐butyllithium as the initiator was carried out by pyrolysis‐gas chromatography (Py‐GC). The relative proportions of the end groups decrease with increasing molecular weight (MW). Consequently, the peaks which reflect the structure of the end groups can be distinguished by comparing pyrograms of samples with different MW. By comparing the intensities of these peaks relative to total intensities of all the peaks in the pyrogram, the numberaverage molecular weight (Mn) of the polymer can be estimated. The observed Mn values of PSts estimated by this method are compared with those determined by size exclusion chromatography (SEC). By this method it was possible to make direct determination of Mn values of PSts with MWs between 1000 and ca. 1 million. Furthermore, the calibration curve produced by the relative intensity of one of the most characteristic peaks (2‐phenyl‐1‐heptene; C4H9CH2C (Ph) = CH2) for the end group to total intensity of all the peaks in the pyrogram, gave rapid and highly reproducible Mn values. © 1994 John Wiley & Sons, Inc.
New poly(amide‐imide)s syntheses. VIII. Preparation and properties of poly (amide‐imide)s derived from 2,3‐bis(4‐aminophenoxy)naphthalene, trimellitic anhydride, and various aromatic diamines
Authors: Yang Chin‐Ping , Chen Wen‐Tung 
Published: April 2003

AbstractThe new polymer‐forming diimide‐diacid, 2,3‐bis(4‐trimellitimidophenoxy) naphthalene (I), was readily obtained by the condensation reaction of 2,3‐bis (4‐aminophenoxy) naphthalene with trimellitic anhydride. A series of novel aromatic poly (amide‐imide)s were prepared by the direct polycondensation of diimide‐diacid I with various aromatic diamines using triphenyl phosphite in N‐methyl‐2‐pyrrolidone (NMP)/pyridine solution containing dissolved calcium chloride. The resultant polymers have inherent viscosities in the range of 0.65–1.02 dL/g at 30°C in N, N‐dimethylacetamide. These polymers were readily soluble in various organic solvents and could be cast into transparent, tough, and flexible films. Their casting films showed tensile strength at break up to 86 MPa, elongation to break of 5–9%, and initial moduli up to 2.35 GPa. The wide‐angle X‐ray diffraction revealed that those polymers containing p‐phenylene or p‐oxyphenylene group are partially crystalline, and the other polymers are evidenced as amorphous patterns. These polymers show a glass transition in the range of 213–290°C in their differential scanning calorimetry (DSC) traces. The thermal stability of the polymers was evaluated by thermogravimetry analysis, which showed the 10% weight‐loss temperatures in the range of 508–565°C in nitrogen and 480–529°C in air atmosphere. © 1994 John Wiley & Sons, Inc.
Photo‐ and thermoinitiated oxidation of high‐impact polystyrene. I. Characterization by FT‐IR spectroscopy
Authors: Israeli Y. , Lacoste J. , Lemaire J. , Singh R. P. , Sivaram S. 
Published: April 2003

AbstractThe photo‐ and thermooxidative degradation of different grades of high‐impact polystyrene (HIPS) has been studied by FT‐IR spectroscopy. The oxidized films were treated with NH3 and SF4 for the rapid identification and resolution of the various carbonyl species, alcohols, and hydroperoxides. All the sample gave similar oxidation products, but in varying quantities. The heterogenity in the film was also determined by micro‐FT‐IR spectroscopy. The thermal degradation processes at different temperature were compared. © 1994 John Wiley & Sons, Inc.
Two reaction routes for the preparation of aromatic polyoxadiazoles and polytriazoles: Syntheses and properties
Authors: Hensema E. R. , Boom J. P. , Mulder M. H. V. , Smolders C. A. 
Published: April 2003

AbstractTwo reaction routes for the preparation of aromatic poly‐1,3,4‐oxadiazoles and poly‐1,2,4‐triazoles are studied and their influence on the physical properties, i.e., inherent viscosity, glass transition, degradation temperature, and film integrity of the final products are discussed. Aromatic poly‐1,3,4‐oxadiazoles are prepared by means of a polycondensation reaction of terephthaloyl chloride and isophthalic dihydrazide yielding a precursor polymer, poly(p, m‐phenylene) hydrazide, which is converted into the corresponding poly‐1,3,4‐oxadiazole by means of a cyclodehydration reaction. Poly‐1,3,4‐oxadiazoles are also prepared by means of a polycondensation reaction between terephthalic and isophthalic acid and hydrazine yielding poly‐1,3,4‐oxadiazoles with higher inherent viscosities. Flexible poly‐1,3,4‐oxadiazole films are obtained only if the inherent viscosities of the polymers used are higher than 2.7 dL/g. The thermal stability is found to increase with increasing content of p‐phenylene groups in the polymer backbone. Aromatic poly‐1,2,4‐triazoles are prepared using polyhydrazides with alternating para‐ and meta‐phenylene groups and poly‐1,3,4‐oxadiazoles with a random incorporation of para‐ and meta‐phenylene groups in the main chain as precursor polymers. The glass transition temperatures are found to increase with increasing content of p‐phenylene groups in the main chain of these polymers. Cold crystallization is observed only for the alternating polymer. © 1994 John Wiley & Sons, Inc.
Free radical exit in emulsion polymerization. I. Theoretical model
Authors: Casey Brendan S. , Morrison Bradley R. , Maxwell Ian A. , Gilbert Robert G. , Napper Donald H. 
Published: April 2003

AbstractThe exit or desorption of free radicals from latex particles is an important kinetic process in an emulsion polymerization. This article unites a successful theory of radical absorption (i.e., initiator efficiency), based on propagation in the aqueous phase being the rate determining step for entry of charged free radicals, with a detailed model of radical desorption. The result is a kinetic scheme applicable to true “zero‐one” systems (i.e., where entry of a radical into a latex particle already containing a radical results in instantaneous termination), which is still, with a number of generally applicable assumptions, relatively simple. Indeed, in many physically reasonable limits, the kinetic representation reduces to a single rate equation. Specific experimental techniques of particular significance and methods of analysis of kinetic data are detailed and discussed. A methodology for both assessing the applicability of the model and its more probable limits, via use of known rate coefficients and theoretical predictions, is outlined and then applied to the representative monomers, styrene and methyl methacrylate. A detailed application of the theory and illustration of the methodology of model discrimination via experiment is contained in the second article of this series. © 1994 John Wiley & Sons, Inc.
Free radical exit in emulsion polymerization. II. Model discrimination via experiment
Authors: Morrison Bradley R. , Casey Brendan S. , Lacik Igor , Leslie Gregory L. , Sangster David F. , Gilbert Robert G. , Napper Donald H. 
Published: April 2003

AbstractIn emulsion polymerizations, desorption (exit) from latex particles of monomeric radical species that arise from transfer can be an important determinant of the overall kinetics. An examination of various methodologies for the testing of postulated free radical exit mechanisms is made. These utilize the model descriptions for the exit process presented in the accompanying article of Casey et al., employing data consisting of conversion as a function of time for the approach to steady state polymerization conditions. Experimental data are presented on the exit rate coefficients as a function of such experimental parameters as: particle size, monomer concentration, and aqueous‐phase free‐radical concentration for a series of styrene polymerizations at 50°C, where the average number of free radicals per particle (n̄) never exceeds 0.5. It is demonstrated for these systems that while the conversion/time dependence from a single run, under conditions sensitive to exit, is insensitive to mechanistic assumptions as to the fate of desorbed free radicals, the variation of the exit rate coefficient with particle size so obtained suggests a second order dependence on n̄, implying complete re‐entry of desorbed free radicals under all conditions studied. Once the monomeric radicals have re‐entered, they are more likely to remain inside the particle where they will either propagate or undergo termination rather than re‐escape. The article also presents an estimate for the rate coefficient at 50°C of the first propagation step of the monomeric radical subsequent to transfer. The conclusions drawn here for seeded systems should prove useful for study of particle nucleation mechanisms, when exit is particularly likely in small, newly formed, particles. © 1994 John Wiley & Sons, Inc.
Syndioselective propylene polymerization catalyzed by rac‐2,2‐dimethylpropylidene (1‐η5‐cyclopentadienyl) (1‐η5‐fluorenyl) dichlorozirconium
Authors: Fierro Ricardo , Yu Zhengtian , Rausch Marvin D. , Dong Sizhong , Alvares Dellyo , Chien James C. W. 
Published: April 2003

AbstractSyndioselective propylene polymerization has been promoted by rac‐2,2‐dimethylpropylidene (1‐η5‐cyclopentadienyl) (1‐η5‐fluorenyl) dichlorozirconium (1). The active catalytic species were generated using either triphenylcarbenium tetrakis (pentafluorophenyl) borate (2) (Zr+ method) or methylaluminoxane (MAO method). The former exhibited much higher activity than the latter, especially at low polymerization temperatures (Tp). Syndiotactic poly (propylene) (s‐PP) obtained at Tp = −20°C has Tm approaching 160°C, [rrrr] pentad fraction of 0.92 to 0.95, and 45% crystallinity (Xc). It crystallized in two antichiral unit cells B and C. The C structure is favored by low temperature of polymerization, slow crystallization from melt, and annealing. The s‐PP has M̄w/M̄n ranging from 3.6 to 4.4, which can be separated into stereoregular fractions soluble in heptane and hexane and stereoirregular fractions soluble in pentane, ether, and acetone. Therefore, this system cannot be considered to be a single‐site catalyst. A parallel study was made on the isopropylidene (1‐η5‐cyclopentadienyl) (1‐η5‐fluorenyl) dichlorozirconium (3)/MAO catalyst. Molecular mechanics calculations were performed for all combinations of the configuration of asymmetric centers. The steric energy favors syndiotactic enchainment for both catalysts 1 and 3, with 1 forming the more syndioselective catalyst. © 1994 John Wiley & Sons, Inc.
Synthesis of tert‐butyl‐substituted poly (ether ketone) by nickel‐catalyzed coupling polymerization of aromatic dichloride
Authors: Ueda Mitsuru , Seino Yoshikatu , Haneda Yuko , Yoneda Masanobu , Sugiyama Jun‐Ichi 
Published: April 2003

Abstracttert‐Butyl substituted poly (aryl ether ketone)s with relatively high molecular weights were prepared by the Ni‐catalyzed polymerization of tert‐butyl substituted aromatic dichlorides containing ether ketone unit. These polymers were amorphous and soluble in common organic solvents, such as THF, dichloromethane, and chloroform. De‐tert‐butylation of the polymer by the treatment of trifluoromethanesulfonic acid in the presence of toluene proceeded smoothly and produced crystalline poly (aryl ether ketone). © 1994 John Wiley & Sons, Inc.
Chemical derivatization as a mean to improve contact angle goniometry of chemically heterogenous surfaces
Authors: Holländer A. , Behnisch J. , Zimmermann H. 
Published: April 2003

AbstractPlasma‐oxidized polyethylene (O‐PE) was derivatized with various chemicals and the advancing and receding contact angles with water, formamide, and tricresylphosphate were measured. The contact angles were used to evaluate the surface free energy (SFE) components in terms of the Lifshitz‐van der Waals‐acid base (LW‐AB) model. The derivatization was directed to couple alkyl chains to carbonyl, hydroxyl, and carboxyl groups generated on the surface of O‐PE. Carbonyl groups were treated with hydrazine and then reacted with dodecanoyl chloride. Hydroxyl groups were first reacted with reactive dicarboxylic acid dichlorides or cyanuric chloride, respectively, and then with alkylamines because the direct bonding of long‐chain alkyl carboxylic acid chlorides proceeds slowly and is, therefore, completed by surface restructuring. Carboxyl groups were chlorinated and in a second step reacted with alkylamines. The bonding of C12‐alkyl chains can be sensitively detected by the LW part of the SFE. Concerning the receding contact angles, it is pointed out that the carbonyl groups are present on the surface in a higher concentration than hydroxyl and carboxyl groups. The combination of contact angle goniometry (CAG) and chemical derivatization reactions supplies semiquantitative information about functional groups in the uppermost surface layer. In this way, a major shortcoming of CAG can be overcome. © 1994 John Wiley & Sons, Inc.
Synthesis and characterization of polyarylates derived from 4,4′‐dihydroxy‐meta‐terphenyl and aromatic diacid chlorides
Authors: Nye S. A. , Swint S. A. 
Published: April 2003

AbstractPolyarylates derived from 4,4″‐dihydroxy‐meta‐terphenyl (DHmTP) were prepared by the phase‐transfer catalyzed, two‐phase polycondensation with aromatic diacid chlorides. The resulting polymers were crystalline, solvent resistant, and produced brittle films. Copolymers with bisphenol‐A were also synthesized using isophthaloyl diacid chloride. At low to moderate levels of DHmTP in the copolymers (25–75%), the materials had high glass transition temperatures (186–201°C), good solvent resistance, and gave tough, clear films. Terpolymers of DHmTP and BPA with 50:50 isophthaloyl and terphthaloyl diacid chloride were prepared with not much improvement over Ardel D‐100®. All the DHmTP‐polyarylates had good thermal stability (5% weight loss in air > 415–460°C) and had a high % char (20–48%). © 1994 John Wiley & Sons, Inc.
Thermotropic copolyamides from triethyleneglycol bis (4‐carboxyphenyl) ether, aromatic diamines, and p‐aminobenzoic acid
Authors: Higashi Fukuji , Nakajima Khoji , Zhang Wen Xion 
Published: April 2003

AbstractIt is proposed that depression of the transition temperatures, especially the melting point (Tm), can be achieved by the introduction of a different amide bond structure into the copolyamides of dicarboxylic acids and diamines by copolymerization of aminocarboxylic acids, such as p‐aminobenzoic acid. The effect was examined by the amount and distribution of the structure in the copolylamindes. Copolycondensations of PEG3, p‐aminobenzoic acid, and diamines with different chain lengths showed that the structural change of the amide bond in the copolymers, especially its distribution, was more important than its total amount in them. Several types of aminocarboxylic acids were briefly examined to study the effect. © 1994 John Wiley & Sons, Inc.
Pyrazoles—A novel class of blocking agents for isocyanates
Authors: Mühlebach Andreas 
Published: April 2003

AbstractPyrazoles were found as a novel class of blocking groups for isocyanates. Adhesive mixtures of pyrazole blocked isocyanates and amine terminated prepolymers like Jeffamines® (Texaco Chem. Co.) combine excellent reactivities (gelation times within minutes at 100–120°C), good latencies (more than 170 days at 40°C), and good adhesion properties on many substrates. The reactivity of pyrazole blocked isocyanates toward nucleophiles increases with the number of electron donor substituents on the pyrazole nucleus and, thus, can be fine tuned by the appropriate substitution pattern. This behavior contrasts sharply with that of phenolic blocked isocyanates, where reactivities with the same nucleophiles decrease with more and stronger electron donor substituents on the phenol nucleus. Therefore, different deblocking reaction mechanisms were proposed for pyrazole vs. phenol blocked isocyanates. The excellent latency of pyrazole blocked isocyanate/Jeffamine® mixtures is due to the insolubility of the two components at ambient temperature and the slow endothermic dissolution process at higher temperature. The good adhesion of formulations with pyrazole blocked isocyanates as reactive components on most plastic and metal substrates is ascribed to the primer action of the released blocking group. © 1994 John Wiley & Sons, Inc.