bluuebunny/crossref_metadata_2025_split huggingface dataset:
Cis/trans reactivity ratios in the ring‐opening polymerization of bicyclo[2.2.1]hept‐2‐ene; the nature of the propagating species in olefin metathesis
Authors: Greene Ruth M. E. , Hamilton James G. , Ivin Kenneth J. , Rooney John J. 
Published: April 2003

AbstractThe olefinic regions of the 13C NMR spectra of numerous ring‐opened polymers of bicyclo[2.2.1]hept‐2‐ene (norbornene) having cis double bond contents in the range σc = 0,32–0,86, have been analysed in detail. At least six peaks are resolved corresponding to olefinic carbons defined in terms of the double bond sequences tcc, tct + ccc, cct, ttc, ctc + ttt, ctt; for polymers of intermediate cis‐content tct and ccc are also resolved. The relative intensities of the cis‐centred triads may be accounted for in terms of a single parameter, rc, derived from the observed dyad probabilities. The relative intensities of the trans‐centred triads, however, show that at higher cis‐contents, the sequence cttc occurs with greater frequency than expected, requiring interpretation in terms of two trans‐parameters, rtt and rtc. These results show that the generally noted feature of cis/trans blockiness at moderately high cis‐content is sometimes associated with the presence of three kinetically distinct propagating species rather than two. The first is postulated to be the highly cis‐directing olefin‐metal‐carbene complex 4 in which the previously formed cis double bond remains coordinated to the metal centre; this may have both chiral and achiral forms. The second and third are postulated to be isomeric species formed by decoordination of the previously formed trans double bond from the metal centre but in which the initial ligand geometry is governed by the nature of the penultimate double bond: 3tc and 3tt are postulated to have permanent ligands with square pyramidal and octahedral symmetry, respectively. It is shown how the present results and those from related work may be rationalised in terms of this hypothesis.
Studies on the β‐form of isotactic polypropylene, 1. Characterization of the β‐form and study of the β‐α transition during heating by wide angle X‐ray diffraction
Authors: Zhou Gui‐en , He Zhi‐qun , Yu Jian‐min , Han Zhe‐wen , Shi Guan‐yi 
Published: April 2003

AbstractThe conditions for the formation of the β‐form of isotactic polypropylene in the presence of a β‐nucleator and the β‐α transition during heating were studied by wide angle X‐ray diffraction. A conditional crystallinity of the β‐form, X′β, and a structural disorder parameter, S, deduced from WAXD data were defined for the characterization of the β‐form in addition to the K value. The results show that X′β and S obviously depend on the content of β‐nucleator, and that the β‐α transition during heating essentially consists in the melting of the β‐form and the successive recrystallization to the α‐form.
Studies on the β‐form of isotactic polypropylene, 2. The melting behavior of predominantly β‐form samples
Authors: Shi Guan‐yi , Huang Bin , Cao You‐hong , He Zhi‐qun , Han Zhe‐wen 
Published: April 2003

AbstractEffects of crystallization conditions, heating rate, and isothermal annealing on the melting behavior of isotactic polypropylene samples with predominantly β‐form were studied by differential scanning calorimetry. The results show that the β‐form of these samples has a higher thermal stability and a lower recrystallization ability to the α‐form after melting than the β‐form of other samples.
Synthesis of networks in solution, 2. Influence of the primary molecular weight on the kinetics of crosslinking
Authors: Stadler Reimund , Freitas Liane L. De Lucca , Jacobi Marly Maldaner 
Published: April 2003

AbstractThe kinetics of the crosslinking reaction of 4,4′‐[methylenebis(1,4‐phenylene)]‐di‐1,2,4‐triazoline‐3,5‐dione with polybutadienes of narrow molecular weight distribution was studied. At high conversions deviations from the kinetic scheme of a series of first order reactions was observed. The deviations were analyzed by introducing a “retardation” function which includes all informations on the changes in the reaction kinetics. The retardation function was calculated from the experimental data and depends on the polymer concentration and the primary molecular weight. The onset of the deviations in the kinetic behaviour is correlated to the local segment concentration which was calculated assuming unperturbed dimensions of the coils in the semidilute state. Sterical hindrances in the formation of the transition state complex in the gel appear to be of main importance for the observed results.
Decomposition of 18‐crown‐6 solutions in tetrahydrofuran containing dissolved potassium
Authors: Jedliński Zbigniew , Stolarzewicz Andrzej , Grobelny Zbigniew 
Published: April 2003

AbstractDipotassium polyoxaalkane‐α,ω‐diolates (1–5) and ethylene were found to be formed in the decomposition reaction of solutions of 18‐crown‐6 in tetrahydrofuran containing dissolved potassium. A mechanism of that decomposition process due to the action of the potassium anion is proposed.
Synthesis of 3′,5′‐bis(morpholinomethyl)‐4′‐hydroxy‐ and 3′,5′‐bis(4‐methyl‐1‐piperazinylmethyl)‐4′‐hydroxymethacrylanilide. Copolymerization and metal ion binding properties of monomers and copolymers
Authors: Ritter Helmut , Rodewald Stephan 
Published: April 2003

Abstract4′‐Hydroxymethacrylanilide was modified by Mannich reaction with morpholine/formaldehyde and 1‐methyl‐piperazine/formaldehyde, respectively. The interaction of the resulting monomers 3 and 4 and their corresponding copolymers with acrylamide (5 and 6) with Cu2 + ions was studied by photometric methods. Incorporation of the aminomethylated phenol derivatives 3 and 4 in an acrylamide‐methylene diacrylamide network system was performed to yield a product which selectively adsorbs Cu2+ in the presence of Ni2+, Co2+, Cd2+ and Ca2+ ions.
Synthesis of homologues of deoxyribouridylic acid in preparative amounts using the triester method
Authors: Schott Herbert , Biedersee Heidereich v. , von Sonntag Clemens , Schulte‐Frohlinde Dietrich 
Published: April 2003

AbstractThe homologous oligodeoxyribouridylic acids dU2, dU4, dU8and dU16were chemically synthesized in amounts of 70 to 800 mg by block condensation using the phosphotriester method. The partially protected hydroxyl and phosphate components were condensed without any protection for the nucleobase uracil, using a mixture of 2,4,6‐triisopropylbenzenesulfonyl chloride and tetrazole in anhydrous pyridine as condensing agent. Demonstrable side reactions of the uracil residue occur under this condensation conditions. However, this undesired derivatisation of uracil residues is totally eliminated by a simple deamination of the deblocked oligodeoxyribouridylic acids. After synthesis, cleavage of the protecting groups and column chromatographical fractionation using QAE‐Sephadex, the oligodeoxyribouridylic acids were deaminated and obtained as pure products, as was positively evidenced by “fingerprints”.
Molecular design of multicomponent polymer systems, 13. Control of the morphology of polyethylene/polystyrene blends by block copolymers
Authors: Fayt Roger , Jerome Robert , Teyssié Philippe 
Published: April 2003

AbstractAs investigated by optical and electron microscopy, the observed morphology of the meltblended polyethylene/polystyrene pair unambiguously supports the interfacial activity of poly(hydrogenated butadiene‐b‐styrene) copolymers. The phase size is significantly reduced, the interfacial adhesion is dramatically increased and the phase dispersion is firmly stabilized against coalescence during subsequent processing. Diblock copolymers with a balanced composition are the most efficient interfacial agents in such an extent that only small amounts (1–2 wt.‐%) are required to obtain homogeneous and stable phase dispersions. The emulsification concept applied to melt‐blended immiscible polymers appears to be a powerful technique to prepare valuable polymer alloys.
Characterization of cellulose ethers by 13C NMR, 1. Studies of high molecular weight polymers in solution and in the solid state
Authors: Hjertberg Thomas , Zadorecki Pawel , Arwidsson Margareta 
Published: April 2003

AbstractCarbon‐13 NMR was used to investigate the structure of a cellulose derivative, ethyl‐O‐(hydroxyethyl)cellulose (EHEC). Analysis of high molecular weight samples in solution showed that the line widths of the main chain carbon resonances are very sensitive to the concentration of the solution. Above a certain concentration, excessive broadening occurs due to gel formation, which makes a quantitative evaluation of the degree of substitution difficult. If the concentration is decreased below the critical value for gel formation, the use of NMR parameters suitable for quantitative measurements (no NOE and long pulse intervals) leads to excessively long accumulation times. Spectra of solid samples obtained by cross‐polarization magic angle spinning (CP‐MAS) NMR exhibit better defined resonances of the main‐chain carbons than do the spectra of solutions with concentrations above the critical value for gel formation. Variable contact time experiments with a specific sample indicated that a suitable contact time should be 400 μs. The quantitative evaluation of the total degree of substitution by CP‐MAS NMR yielded values in agreement with those obtained by GC‐analysis.
The homopolymerization of 2,3‐dimethyl‐1,3‐butadiene and the copolymerization of 1,3‐butadiene/2,3‐dimethyl‐1,3‐butadiene using the catalyst system AlEt2Cl‐Co(acac)2. A structural investigation of the products
Authors: Cabassi Franco , Italia Salvatore , Giarrusso Antonino , Porri Lido 
Published: April 2003

AbstractThe homopolymerization of 2,3‐dimethyl‐1,3‐butadiene with the catalyst system AlEt2Cl‐Co(acac)2 affords polymers consisting of about 81% cis‐1,4‐units and 19% 1,2‐units. The copolymerization of 1,3‐butadiene/2,3‐dimethyl‐1,3‐butadiene using the same system is of the ideal type and the composition of the copolymers is practically identical with that of the monomer mixture. The structure of the copolymers depends on their composition. The butadiene units, which are more than 95% cis‐1,4 in the homopolymer, become partially 1,2 in the copolymers; their amount increases with increasing dimethylbutadiene content. Conversely, the fraction of dimethylbutadiene units with 1,2‐structure decreases in the copolymers with increasing butadiene content. In the copolymers containing more than 50% of butadiene, the dimethylbutadiene units are practically all cis‐1,4. The analysis of sequence distribution shows that the 1,2‐butadiene units in the copolymers are not randomly distributed but are mostly adjacent to dimethylbutadiene units. The results obtained with dimethylbutadiene are compared with those reported for the homopolymerization of isoprene and the copolymerization of isoprene/butadiene using the same catalyst system.
Complex formation of polyampholyte with proton‐accepting polymers through hydrogen bonding
Authors: Abe Koji , Hasegawa Mutsuko , Senoh Saburo 
Published: April 2003

AbstractPolyampholytes, copolymers of methacrylic acid and 2‐dimethylaminoethyl methacrylate [C(MA‐AM)x] of various composition, were synthesized. Their isoelectric points (pI) are in the range 5 < pH < 7. Undissociated methacrylic acid residues in the copolymers can interact with ether oxygens of poly(ethylene glycol) (PEG) and ketone groups of poly(N‐vinyl‐2‐pyrrolidone) (PVPo) in the acidic pH region through hydrogen bonding. However, only copolymers having more than about 60 mol‐% of methacrylic acid residues form complexes with PVPo and high molecular weight PEG. The composition of the obtained complexes is 1:1 (mole ratio of methacrylic acid residues of the copolymer to repeating units of PVPo and PEG).
The monomer content of polymers from bis(hydroxyethyl) terephthalate
Authors: Elias Hans‐Georg 
Published: April 2003

AbstractThe monomer content in polymers from bis(hydroxyethyl) terephthalate was previously found by Challa to be up to 63% higher than predicted by the classic equations of Flory. A reexamination shows that the apparent anomaly is caused by the approximative nature of the Flory equations which neglect the molar mass of the leaving molecules. Comparison of the experimental data with the predictions of the rigorous theory lowers the difference between experiment and theory significantly. The remaining differences scatter too much to allow any conclusions about a molar mass dependence of equilibrium or rate constants.
DNA protonation at low ionic strength of solution
Authors: Sorokin Victor A. , Gladchenko Galina O. , Valeev Vladimir A. 
Published: April 2003

AbstractUV differential spectroscopy and thermal denaturation were applied to investigate the protonation of native (6 °C) and denatured (70 °C) DNA at 10−3M of Na+ in the range of pH 7,0 to 3,85. A decrease in the pH was found to deteriorate the thermal stability of DNA and to narrow the range of the helix‐coil transition due to preferential destabilization of G + C pairs. The pH dependence of the degree of helicity for native DNA is non‐monotonic and agrees with the protonation model proposed by Courtois et al. The proton binding to the bases is anticooperative for native DNA and noncooperative for denatured DNA. The ionization of the bases is characterized by pK′ = 4,7 for helical and by pK′ = 5,2 for coil DNA.
Reversible copolymerization at equilibrium
Authors: Szymański Ryszard 
Published: April 2003

AbstractThe relationships for copolymer composition and microstructure in reversible copolymerization at equilibrium are derived. They allow to predict the comonomer equilibrium concentrations and the structure of the copolymer at equilibrium if the initial state and equilibrium constants are known and provided that [I] ≪ [M1]0 + [M2]0 ‐ [M1]e ‐ [M2]e.
Polymerization of propene in the presence of MgCl2‐supported Ziegler‐Natta catalysts, 2. Effects of the co‐catalyst composition
Authors: Busico Vincenzo , Corradini Paolo , De Martino Luigi , Proto Antonio , Albizzati Enrico 
Published: April 2003

AbstractAs a part of a study on the polymerization of propene in the presence of MgCl2‐supported catalysts, new results were obtained when polymerizing at variable ethyl benzoate (EB)/alkylaluminium and alkylaluminium/Ti mole ratios. The pre‐treatment of MgCl2 with the Lewis base is essential to achieve high stereoregularities without an unacceptable decrease of polymerization rate, apparently because it prevents the formation of nonstereospecific active sites of low Lewis acidity, which require high EB/alkylaluminium mole ratios in the co‐catalyst in order to be poisoned. The data may be explained in the framework of a model of catalytic sites preliminarily presented in Part 1 of this series.
Liquid crystalline polyesters with 1,4‐cyclohexylene units
Authors: Braun Dietrich , Schülke Ulrike 
Published: April 2003

AbstractA new series of liquid crystalline polyesters (5a – f) containing 1,4‐cyclohexylene dibenzoate moieties as mesogenic units in the main chain was prepared and characterized. The rigid segments in the polymers are connected by α,ω‐alkanedioyl units containing 4–8 or 10 methylene groups.
Properties of polyelectrolyte complexes containing poly(N‐tert‐butylaziridine)
Authors: Kabanov Victor A. , Zezin Alexander B. , Rogacheva Valentina B. , Grishina Nadajda V. , Goethals Eric J. , Van de Velde Marleen 
Published: April 2003

AbstractInterpolymer reactions between poly(acrylic acid) (PAA) or poly(methacrylic acid) (PMAA) and poly(N‐tert‐butylaziridine) (PTBA) were studied and compared with the corresponding reactions of these polyacids with linear polyethyleneimine (LPEI). In aqueous alkaline and salt media the presence of the bulky non‐polar N‐substituent in the main chain of PTBA results in a decrease of stability of polyacid‐PTBA polyelectrolyte complexes. LPEI, which forms stronger salt bonds with PAA, substitutes PTBA in the PAA‐PTBA polyelectrolyte complexes. Addition of simple salts to aqueous solutions of non‐stoichiometric polyelectrolyte complexes (N‐PEC) PAA‐PTBA and PMAA‐PTBA at room temperature causes a phase separation due to macromolecular exchange and disproportionation reactions. At elevated temperatures (T = 40 ‐ 60 °C), however, the macromolecular exchange between different N‐PEC particles does not occur and phase separation in aqueous salt solution of the N‐PEC's PAA‐PTBA, PMAA‐PTBA is not observed. This is attributed to hydrophobic interactions in polyacid‐PTBA complexes due to the presence of the tert‐butyl groups in the latter.
Influence of various apolar groups in polycationic polyorganosiloxanes upon polyion complexation with poly(methacrylic acid)
Authors: Nozuyama Kiyoshi , Ueno Yukihiko , Kato Takashi , Sekine Yoshiro 
Published: April 2003

AbstractPolyion complexes are formed from poly(methacrylic acid) and polycationic polyorganosiloxanes modified with various apolar groups in the main chain or in the side chains. Potentiometric titration measurements with solutions of the complexes indicate that the chemical structure of the composed polycation influences complexation in aqueous solution. From a binding study with methyl orange, it is seen that the electrostatic interaction of the polyion complexes is enhanced by an increase of the hydrophobicity in the composed polycations. In water/ethanol solutions, however, such a tendency is not observed.
Polymerization of α‐olefins in the presence of δ‐TiCl3/Al(CH3)3: Chain propagation rate constants for ethylene and propene
Authors: Ammendola Paolo , Zambelli Adolfo , Oliva Leone , Tancredi Teodorico 
Published: April 2003

AbstractThe chain propagation rate constants for the polymerization of ethylene and propene in the presence of δ‐TiCl3/Al(CH3)3 at 22 °C are determined by means of a 13C NMR analysis of suitable block copolymers. The numerical values of the rate constants are compared with those previously reported.
Electroinitiated polymerization of maleic anhydride
Authors: Pattanayak Nirmal K. , Nayak Bimbadhar 
Published: April 2003

AbstractThe electroinitiated polymerization of maleic anhydride was studied in N,N‐dimethylformamide medium using sodium acetate (saturated solution) as the electrolyte. A dark brown polymer is formed only after the passage of an electrical current. Its yield increases in the presence of the electrolyte and depends on several factors such as the magnitude of the current flow, the duration of the electrolysis, the temperature of the cell solution and the monomer concentration. Split‐cell experiments showed that the polymer is formed in the anode compartment from a red coloured precursor, which is generated in the cathode compartment, but subsequently migrates to the anode compartment. The IR spectrum suggests that the polymer is mainly a cis‐poly(vinyleneketoanhydride), containing also other moieties in the chain such as cyclopentanone and maleic anhydride.
Synthetic polymers containing sugar residues, 8. Novel polyureas from 2,6‐diamino‐2,6‐dideoxy‐d‐gulose and diisocyanates
Authors: Kurita Keisuke , Murakami Kaori , Kobayashi Koichiro , Takahashi Mitsunori , Koyama Yoshiyuki 
Published: April 2003

AbstractA diamino monosaccharide, 2,6‐diamino‐2,6‐dideoxy‐D‐gulose (7), was prepared as a new difunctional sugar monomer with high reaction selectivity, to synthesize a new type of linear polyureas containing sugar residues in the main chain. As a result of a study of the polymerization conditions, the polymerization of the diaminogulose 7 with diisocyanates 8a‐d was successfully carried out in N,N‐dimethylacetamide or hexamethylphosphoric triamide without blocking the hydroxyl groups. The resulting polyureas 9a‐d show inherent viscosities in the range 0,16–0,62 dl · g−1 in dichloroacetic acid. Some properties were studied, including solubility and crystallinity.
Practical approach to termination kinetics in radical copolymerization
Authors: Chee Kam K. 
Published: April 2003

AbstractA novel expression has been developed for the instantaneous rate of radical copolymerization, Rp, based on a combined form of the diffusion‐controlled and terminal models of copolymerization. This treatment introduces a characteristic parameter, θ, which can be correlated to the monomer feed composition, β, empirically. In this connection, two equations have been proposed for θ, to cope with the drastic change in the Rp versus β relationships when the θ values drop below unity. The validity of these two‐parameter formulations are positively tested by the rate data of a number of representative copolymerizations, including the ideal and alternating systems. It is found that the present approach to Rp is more practical, adaptable, and reliable than the other contemporary kinetic schemes of binary copolymerization reactions.
Dégradation contrôlée des polyisoprènes‐1,4 par le couple phénylhydrazine/oxygène, 3. Molécules modèles de structures phénylhydrazone conjuguées
Authors: Filho Eurico de Barros Lobo , Reyx Danièle , Campistron Irène , Casals Pierre‐François 
Published: April 2003

AbstractIn order to identify phenylhydrazone structures in the reaction products of oxidized polyisoprene or its models with phenylhydrazine, the UV, 1H NMR, 13C NMR and MS spectra as well as the steric exclusion chromatography parameters were determined for phenylhydrazones derived from aldehydes and ketones, selected as models of conjugated carbonyl structures, which could result from the oxidation of polyisoprene units. By comparison with possible coexistent structures, inclusively phenylhydrazones of non‐conjugated carbonyl derivatives, oxidized polyisoprene structures can be identified.
A novel synthesis of polystyrene macromonomers
Authors: Nagasaki Yukio , Tsuruta Teiji 
Published: April 2003

AbstractLithium diisopropylamide (2) was found to undergo a metalation reaction with 4‐methylstyrene (1) to form 4‐vinylbenzyllithium (3), but to induce neither addition reaction nor vinyl polymerization. The equilibrium constant between 2 and 3 in THF was calculated to be 0,54 at 20°C. The 4‐vinylbenzyllithium formed initiates the polymerization of styrene derivatives to form oligomers. The resulting oligomers have a polymerizable vinyl group at the chain end quantitatively and can be regarded as a “macromonomer”. Synthesis of polystyrene, having a primary amino group at the chain end, was carried out through the reaction of polystyrene macromonomer with N‐methylethylenediamine. More than 97% of polystyrene were aminated within 6 h reaction.
The copolymerization of maleic anhydride with propene and isobutene
Authors: Arnold Manfred , Rätzsch Manfred 
Published: April 2003

AbstractAlternating copolymers were obtained by radical copolymerization of propene (Pr) and isobutene (IB) with maleic anhydride. Both polymers (Pr and IB) do not homopolymerize under the applied reaction conditions. The copolymerization rates were determined.
Kinetics of the copolymerization of styrene with maleic anhydride in ethyl methyl ketone
Authors: Chen Show‐An , Chang Gwo‐Yang 
Published: April 2003

AbstractThe copolymerization of styrene and maleic anhydride in ethyl methyl ketone as solvent and with benzoyl peroxide as initiator at 60–80°C in the entire feed composition range was studied. The resulting copolymers appear to have negative and positive deviations from alternation as determined by use of elemental analysis. The experimental data were found to fit a three‐reactivity‐ratio copolymer composition equation from the penultimate model. The inclusion of the reactivity ratio, kSM (=kSMM/kSMS), in addition to rSS (=kSSS/kSSM) and rMS (=kMSS/kMSM), allows prediction of a positive deviation from the alternation, i.e. the mole fraction of maleic anhydride in the copolymer being higher than 0,5.