bluuebunny/crossref_metadata_2025_split huggingface dataset:
Polymerization of propene to syndiotactic polymer: Effect of incomplete regiospecificity on propagation rate
Authors: Sacchi Maria Carmela , Rigamonti Ennio , Locatelli Paolo 
Published: April 2003

AbstractThe analysis of ethylene/propene copolymers prepared in the presence of a vanadium based syndiospecific catalyst, gives direct evidence that the syndiospecific propagation rate of secondary inserted propene is lower than the non‐stereospecific propagation rate of primary inserted propene.The analysis of propene/1‐butene copolymers obtained with the same catalyst, confirms that regiospecificity and stereospecificity are nearly unaffected by 1‐butene units in the syndiotactic polymerization of propene.
Trifluoracetylierung von aminosäureestern und dipeptidestern mit N‐trifluoracetyl‐polyamid 66.
Authors: Tesch Helmut W. , Schulz Rolf C. 
Published: April 2003

AbstractN‐Trifluoroacetyl‐Polyamid 66 (1) is used for the trifluoroacetylation of amino acid‐ and dipeptide esters. Advantages and limitations of the polymeric reagent compared with low molecular trifluoroacetylating reagents are discussed. A mixture of amino acid methyl esters can be converted by 1 to the N‐trifluoroacetyl derivatives, which are separated and identified by gas chromatography.
Über polymere koronanden auf der basis von 18‐krone‐6 enthaltenden vinylmonomeren
Authors: Manecke Georg , Krämer Andreas 
Published: April 2003

AbstractVinyl group containing derivatives of 18‐crown‐6 were synthesized and copolymerized with styrene and p‐divinylbenzene of p‐divinylbiphenyl. The selectivity of the alkali metal cation complexation of one of the polymers was investigated. The prepared polymers were applied as catalysts in several nucleophilic substitution reactions. The influence of the crosslinking agent as well as the degree of crosslinking on the catalytic activity of the polymers was studied.
13C NMR sequence analysis, 20. Stereospecificity of the polymerization of D,L‐Leu‐NCA and D,L‐Val‐NCA
Authors: Kricheldorf Hans R. , Mang Thomas 
Published: April 2003

AbstractThe copolymerization of D‐ and L‐Leu‐NCA as well as that of D‐ and L‐Val‐NCA was studied under various conditions. Even nonpolar solvents, such as diethyl ether or ligroin, used for the precipitation of the poly(D,L‐amino acid)s, were found to have an influence on yield and tacticity of the isolated polypeptides indicating that atactic polypeptides of low molecular weight may be soluble in these solvents. 13C NMR spectra of the isolated poly(D,L‐amino acid)s were measured in trifluoroacetic acid and the carbonyl signals were used for the evaluation of the teacticity. Under all reaction conditions only a moderate degree of stereospecificity was found. D,L‐Leu‐NCA initiation with protic nucleophiles, such as benzylamine or diethylamine, favors the formation of isotactic blocks. In the case of D,L‐Val‐NCA again isotactic blocks are slightly favored if benzylamine is used as initiator, while diethylamine, like other strong bases, causes preferred formation of syndiotactic sequences. With strong aprotic bases and electrophilic cocatalysts, i.e. under conditions favoring the “activated monomer mechanism”, the highest degrees of stereospecificity were observed. However, in the case of D,L‐Leu‐NCA isotactic blocks are predominantly formed, while in the case of D,L‐Val‐NCA syndiotactic blocks are favoured. Changing the solvent may result in a reversal sense of the stereospecificity. The absence of long isotactic blocks in all samples of this work was also demonstrated by the good solubility of all samples in various organic solvents.
Polymerisationsauslösung mit substituierten ethanen, 4. Kinetik der polymerisation von methylmethacrylat mit 1,1,2,2‐tetraphenyl‐1,2‐diphenoxyethan
Authors: Błedzki Andrzej , Balard Henri , Braun Dietrich 
Published: April 2003

AbstractThe polymerisation of methyl methacrylate (MMA) by 1,1,2,2‐tetraphenyl‐1,2‐diphenoxyethane is characterised by three steps: during the initial period oligomers from MMA and initiator radicals are formed by primary radical termination. These oligomers produce free macroradicals and initiator radicals by cleavage at the bonds between the last monomer unit and the end group from the initiator. After consumption of the initiator radicals with increasing conversion the normal propagation and termination processes occur. The kinetics derived from this reaction scheme is in good agreement with the experimental results.
Differentialthermoanalytische untersuchungen bei verschiedenen drücken an einer molekulargewichtsreihe von polyethylenoxiden
Authors: Altmeyer Andreas , Karl Veit‐Holger , Ueberreiter Kurt 
Published: April 2003

AbstractMelt‐ and crystallization‐temperatures were measured of poly(ethylene oxide)s with increasing molecular weight and at various pressures up to 5 000 bar by differential thermal analysis (DTA). Both these temperatures increase with pressure and display a different molecular weight dependence below and above M ≈ 3 000. A similar behaviour is shown by the melt enthalpies, constants a and c of the Simon‐equation and by the undercooling ΔT.The transition from a zig‐zag‐ to a helix‐structure found by various authors changes to higher molecular weights with pressure, whereas chain folding does not depend upon pressure. The pressure coefficient of the melting temperature and the undercooling as well as the chemical potential are investigated as functions of the molecular weight for poly(ethylene oxide).
Thermomechanical analysis of linear aromatic polyesters
Authors: Ng Tie Hwee , Leverne Williams H. 
Published: April 2003

AbstractThe thermomechanical properties of linear aromatic polyesters, studied using thermomechanical analysis techniques, have been related to the chemical structure and methylene chain length. An increase in the number of methylene groups, the use of an asymmetric diacid, or random copolymerization of the repeating units of these polyesters, resulted in a lower linear thermal expansion coefficient α, a lower Vicat softening temperature Ts, a lower heat deflection temperature Td, and a lower glass transition temperature Tg. With longer methylene sequence lengths, the influence of the methylene groups on the thermomechanical properties is predominant, the data are closer together. The values are generally highest for the terephthalate series and lowest for the copolymer series. Glass transition temperatures calculated from group contributions and measured experimentally agreed. The deflection temperatures approximated the glass transition temperatures and the Vicat softening points the melting temperatures.
Glass transition of styrene/n‐alkyl methacrylate copolymers
Authors: Podešva Jiří , Biroš Jan 
Published: April 2003

AbstractDependences of the glass transition temperatures (Tg) of copolymers of styrene (ST) with the n‐alkyl methacrylates [methyl, ethyl, butyl and octyl methacrylate (MMA, EMA, BMA, and OMA)] on their overall chemical composition were measured. All the dependences investigated in this study satisfy the dyad approximation suggested earlier for the description of the sequential distribution effect on Tg of the copolymer either (1) using reciprocal Tg's and weight fractions of the dyads (according to Johnston), or (2) by means of Tg's and mole fractions of rotatable bonds corresponding to the respective dyads (according to Barton). It was shown that for copolymers the monomeric units of which did not differ too much in their number of rotatable bonds in the molecule (e.g., ST/MMA), both these approaches are satisfactory; if the comonomeric units differ markedly in the number of rotatable bonds (e.g., ST/OMA), approach (1) yields more realistic results than (2). Extrapolation to zero content of the styrene component in the copolymer ST/OMA gave Tg of poly(OMA) (245 K), which is experimentally inaccessible by the method employed (differential scanning calorimetry).
Copolymerization of oxetanes, 2. Co‐oligomers in the copolymerization of oxetane with 3,3‐dimethyloxetane
Authors: Bucquoye Marc R. , Goethals Eric J. 
Published: April 2003

AbstractThe cyclic oligomers which are formed during the cationic copolymerization of oxetane (1) with 3,3‐dimethyloxetane (2) were analyzed qualitatively and quantitatively by means of gas chromatography and mass spectroscopy. Cyclic oligomers from trimer up to octamer were detected but, as with the homopolymerizations, the cyclic tetramers were the most abundant. The relative abundances of the different tetramer co‐oligomers were compared with the theoretical abundances, calculated from the reactivity parameters of the copolymerization and the monomer feed ratio, using the method of Ito and Yamashita. There was no agreement between the calculated and experimental values. This was attributed to a lower tendency to cyclize for polymer chains having a 2‐oxonium chain end compared with polymer chains having a 1‐oxonium chain end.
Photoinitiation, 8. Polymerization of methyl methacrylate and copolymerization of methyl methacrylate with maleic anhydride in the presence of zinc dichloride
Authors: Bartoň Jaroslav , Capek Ignác 
Published: April 2003

AbstractThe rate of photoinitiated (at wavelength λ = 365 nm) polymerization of methyl methacrylate (MMA) in acetone in the presence and/or absence of N,N‐dimethylaniline is retarded by zinc dichloride and by maleic anhydride (MAn). The rate of photoinitiated copolymerization of MMA with MAn in acetone is greatly enhanced in the presence of ZnCl2. The maximum copolymerization rate for a given ZnCl2 concentration is obtained for 1:1 mole ratio of MMA and MAn in the feed. It was established that ZnCl2 has no effect on the chemical composition of the MMA/MAn copolymer.
Modifizierte ionenaustauscherharze — synthese und eigenschaften, 1. Sulfomethylierte styrol‐divinylbenzol‐harze
Authors: Döscher Frank , Klein Joachim , Pohl Fritz , Widdecke Hartmut 
Published: April 2003

AbstractSulfomethylated resins are prepared by polymer analogous reactions, starting from macroporous poly(styrene‐co‐divinylbenzene) matrices. Different reaction paths are discussed and used in the synthesis. Sulfomethylation can be achieved by reaction of a chloromethylated resin with dimethyl sulfide and sodium sulfonate or alternatively by oxidation of polymer‐bound thiol groups. Both methods give high conversions as shown by IR spectra and titration of the sulfonic acid groups. Poly[1‐(4‐hydroxysulfomethylphenyl)ethylene] (3) is obtained by reaction of poly[1‐(4‐hydroxyphenyl)ethylene] (2) resin with formaldehyde/sodium sulfonate. The thermal stability, catalytic activity, and ion exchange equilibria of the sulfomethylated resin are investigated.
Stereoregularity of polystyrene derivatives, 2. Poly(methoxystyrene)s Obtained by Anionic Catalysts.
Authors: Kawamura Tokiji , Uryu Toshiyuki , Matsuzaki Kei 
Published: April 2003

AbstractThe stereoregularity of poly(methoxystyrene)s was determined from the absorption of the aromatic C1 carbon assuming a first‐order Markov statistics holds for the polymerization as well as polystyrenes. The stereoregularity of poly(p‐methoxystyrene)s prepared by sodium, potassium, or rubidium cations as catalysts in THF hardly varied and syndiotactic‐rich polymers were obtained, whereas a random polymer was formed with cesium‐naphthalene. In the polymerization of p‐methoxystyrene in toluene, syndiotactic‐rich polymers were obtained with butyllithium and random polymers were prepared by sodium or potassium cations as catalysts. The stereoregularity of poly(o‐methoxystyrene)s prepared by sodium or potassium cations in tetrahydrofuran changed with the polymerization temperatures, and highly syndiotactic polymers were formed at−78°C. The structure of poly(o‐methoxystyrene)s obtained in toluene, markedly depended on the initiators; that is, with increasing the size of the ionic radius of the counterions, the isotacticity of the polymers decreased. The mechanism of the polymerization and the substituent effect of the stereoregularity are discussed.
Polymerizations of 1‐(4‐pyridyl)‐1,3‐butadiene
Authors: Kohjiya Shinzo , Fujiwara Shigehiro , Fujii Kentaro , Yamashita Shinzo 
Published: April 2003

AbstractPolymerization of 1‐(4‐pyridyl)‐1,3‐butadiene (PyBu) initiated by 2,2′‐azoisobutyronitrile (AIBN) or butyllithium (BuLi) was studied. Radical polymerization gave poly(PyBu) of low molecular weight, soluble in chloroform, tetrahydrofuran, or methanol. PyBu was polymerized by BuLi more rapidly than by AIBN, but the produced polyanion was not living. IR and 1H NMR spectra of poly(PyBu) indicate the presence of trans‐1,4‐and trans‐3,4‐units. The content of trans‐1,4‐units was found to be 75 mole‐% (for radical polymerization) or 90 mole‐% (for anionic polymerization). From radical copolymerization with styrene the following reactivity ratios resulted: r1 (PyBu) = 7,21, r2 (styrene) = 0,12; Q = 6, 1 and e = −0,42 (for PyBu). Reaction of PyBu with ethyl bromide in benzene at 30°C produced a polyelectrolyte, as observed in the case of 4‐vinylpyridine.
Study on models of double bond saturation during the synthesis of unsaturated polyesters
Authors: Fradet Alain , Marechal Ernest 
Published: April 2003

AbstractThe addition of hydroxyl groups on double bonds during the synthesis of unsaturated polyesters is studied with the help of model molecules. These are diesters of unsaturated diacids (maleic and fumaric acids) or monoesters of unsaturated monoacids (crotonic, cinnamic and p‐cyanocinnamic acids) with 1,2‐propanediol. The addition reaction take place to appreciable extents only with bis(hydroxypropyl) maleate and fumarate. The reaction is catalyzed by strong acids such as p‐toluenesulfonic acid; it is reversible and favoured by high temperatures. A mechanism is discussed.
Interpolymer complex between poly(ethylene oxide) and poly(acrylic acid): Viscometric studies in THF‐water mixtures
Authors: Chatterjee Saroj Kumar , Chatterjee Nandita , Riess Gérard 
Published: April 2003

AbstractSystematic studies were performed on interpolymer complex formation between Poly(acrylic acid) (PAA) and poly(ethylene oxide) (PEO) in THF‐water mixtures of different compositions. Viscosity behaviour during complex formation in mixed solvents was found to be entirely different from that observed by other workers in aqueous and in pure organic solvents. The result are interpreted in terms of, (a) preferential solvation of the polymer, (b) Probable change in conformation of the polyelectrolyte moleculer. (c) association of complex molecules in a medium of low dielectric constant, and (d) expected disordering of bound water molecules around PEO by THF. Irrespective of solvent composition, interpolymer complex of PAA and PEO was always found to have 1:1 unit mole ratio.
Über die bestimmung der zahl polymerisationsaktiver zentren von ziegler‐natta‐katalysatoren. Eine modifizierte methode mit 14C‐markierten kohlenstoffoxiden
Authors: Warzelhan Volker , Burger Tycho F. , Stein Dieter J. 
Published: April 2003

AbstractA modified method for the determination of the number of isotactic sites C* and the overall propagation rate constant k̄p of propene polymerization catalysts with 14C‐labelled carbon oxides is proposed: an excess of 14CO2 or 14CO is added in the abscence of propene and alkylaluminium to a non‐deactivated polymer sample drawn from the polymerization slurry.The specific radioactivity of the polymer as a function of the time of contact with the radio‐actively labelled inhibitor sharply increases within short times of contact (14CO2 ≤ 20 min, 14CO ≤ 5 min). This is followed by a slower further increase reaching a finite value after 5 to 7h. The initial and end values differ by a factor of 2 to 3. The results are explained in terms of sites with different reactivity assuming that the total number of isotactic sites is determined only after long times of contact with the inhibitor.So far c* was determined with 14CO2 or 14CO by adding the inhibitor during the polymerization in the presence of propene and alkylaluminium; c* was calculated after short times of contact with the inhibitor, whereas the further steady increase in specific radioactivity was exclusively attributed to side reactions caused by reaction with propene and alkylaluminium.By this modified method we obtained for TiCl3·(1/3)AlCl3 at 60°C k̄p = 13 dm3/(mol·s) and c* = 0,012 mol Ti*/mol Titotal. Addition of a free Lewis base to the polymerization mixture increases c* leaving k̄p unchanged. In contrast to this, if TiCl3·(1/3) AlCl3 is milled with a Lewis base k̄p can be increased by a factor of ≈ 2,5 with lower or equal c* ‐values. The higher activity of extracted TiCl3‐catalyst is due to higher k̄p and c* ‐values as compared to those using TiCl3·(1/3) AlCl3.
Kinetics of free radical oligomerization: Styrene in carbon tetrachloride
Authors: Chen Show‐An , Chang Min‐Ju 
Published: April 2003

AbstractFor the free radical oligomerization of styrene monomer in the presence of carbon tetrachloride, a simplified reaction mechanism is proposed from which a simple scheme for predicting monomer conversion and molecular weight distribution is obtained. The kinetic constants other than those of the initiator decomposition step are determined by use of conversion data. In the scheme development, the kinetic constants for chain transfer and propagation steps are considered to be chain length independent, except that for the propagation step, an extra rate constant is considered for the reaction of monomer with radical produced in the transfer reaction with solvent. The mechanism proposed is found to be in reasonable agreement with out experimental data.
Determination of the parameters of equation of state for melts of linear polymers according to the model of thermal expansion of polymers
Authors: Roszkowski Zbigniew 
Published: April 2003

AbstractThe previously deduced four‐parameter equation of state for melts of linear polymers was reduced to a three‐parameter form, consistent with the theorem of corresponding states. The methods of determining the characteristic parameters of the new and the previous equation are given. The characteristic parameters for polystyrene, poly(o‐methylstyrene), poly(vinyl acetate), linear polyethylene, isotactic polypropylene and poly(butyl methacrylate) are calculated, using the experimental pVT data from literature. The dependence of the characteristic pressure on the temperature, observed in the case of poly(butyl methacrylate) is explained in terms of bending of the valency angle at the —CH2‐group in the backbone, due to strong steric hindrances in vinylidene chains.
Polymer‐solvent interactions in mixed solvents, 3. Poly(methacrylic acid) and poly(sodium methacrylate) in water‐dioxane mixtures
Authors: Vorreux Gérard , Morcellet Michel , Loucheux Claude 
Published: April 2003

AbstractThe preferential solvation of poly(methacrylic acid) and poly(sodium methacrylate) in waterdioxane mixtures was investigated by means of specific refractive index increment measurements on dialysed and undialysed solutions. The correlation with the solvent‐induced conformational transition of poly(methacrylic acid) was also studied. Potentiometric titrations indicate that this transition occurs at around 25–30 vol.‐% of dioxane. Comparison with previous results on poly(acrylic acid) and poly(sodium acrylate) in the same solvent system and on poly(methacrylic acid) in water‐2‐chloroethanol mixtures, shows differences in the mode of solvation of the compact conformation. It is suggested that this may be dependent on the existence of water‐organic solvent specific interactions such as the formation of a water‐dioxane hydrogen‐bonded complex.
The flexibility of biphenyl and related species utilizable as molecular swivels in rodlike polymers. A CNDO/2 analysis
Authors: Welsh W. J. , Jaffé H. H. , Kondo N. , Mark J. E. 
Published: April 2003

AbstractAromatic heterocyclic polymers are exceedingly attractive high performance materials because of their unusually high mechanical strength, chemical resistance and thermal stability, but are very difficult to process unless “swivel” atoms or groups are inserted along the chains to increase conformational flexibility. The present theoretical investigation employs the CNDO/2 method with direct geometry optimization to calculate such flexibility for the wholly aromatic swivels biphenyl, 2,2′‐bipyridyl, 2‐phenylpyridine, 2,2′‐bipyrimidyl, and 2‐phenylpyrimidine. The most important result is the prediction that both flexibility and accessibility of coplanar conformations should increase significantly with the number of ortho‐CH groups replaced by N‐atoms. The calculations also provide information on other conformation‐dependent properties such as optimized geometries, charge distributions, and dipole moments, and these results are found to be in satisfactory agreement with the results of previous theoretical and experimental studies. Finally, since these chains are soluble only in strongly acidic media, the species mono‐ and diprotonated 2,2′‐bipyridyl, 2,2′‐bipyridyl · H3O+, and 2,2′‐bipyrimidyl · 2H2O were also investigated with regard to some of these conformational characteristics.
Effect of the catalyst‐monomer ratio on the molar mass and glass transition temperature of poly(oxy‐2,6‐dimethoxy‐1,4‐phenylene)
Authors: Jauhiainen Tuure‐Pekka 
Published: April 2003

Abstract2,6‐Dimethoxyphenol was polymerized using Ag2O‐triethylamine complex as catalyst and a study made of the effect of the catalyst‐monomer ratio on the yield, molar mass and polydispersity of poly(oxy‐2,6‐dimethoxy‐1,4‐phenylene). The glass transition temperatures Tg were measured with a computerized differential scanning calorimeter. The effect of the molar mass on Tg of poly(oxy‐2,6‐dimethoxy‐1,4‐phenylene) is discussed. The equation, Tg = Tg, ∞ − K/M, describes well the dependence of Tg on the viscosity‐average molar mass Mv from 1900 to 176000 g/mol. Some poly(oxy‐2,6‐dimethyl‐1,4‐phenylene) samples were studied as reference material.
Polymerization of ethylene oxide. A novel binary catalyst system consisting of triphenylantimony dibromide and triphenylphosphine
Authors: Nomura Ryoki , Hisada Hitoshi , Ninagawa Akira , Matsuda Haruo 
Published: April 2003

AbstractPolymerization of ethylene oxide (EO)‐catalyzed by a binary system consisting of triphenyl‐antimony dibromide (TPAB) and triphenylphosphine (TPP) was carried out. TPAB itself could induce the polymerization, but the addition of TPP to TPAB greatly enhances the catalytic activity. A characteristic inflection point, which appeared clearly in the time‐polymerization curves, divided the polymerization into two successive steps. The preceding process is a cationic step in which an intermediate antimony dialkoxide is produced and the following a coordinated polymerization. The mean consumption of EO per catalyst at the inflection point was calculated to be 45 and was independent of the mole ratio of [TPP]/[TPAB]. It is assumed that TPP coordinates to the central antimony atom to produce an active complex salt in the second step. The effect of p‐substitution of TPAB in the polymerization was also investigated; the Hammett parameters p for the first and the second polymerization step were found to be +1,7 and +1,0, respectively.