bluuebunny/crossref_metadata_2025_split huggingface dataset:
Polymer strength and chain conformation
Authors: He Tianbai 
Published: April 2003

AbstractIt is found that the expected maximum strength of polymers is not proportional to the number of polymer chains per unit area. Under uniaxial stressing only part of polymer chains, i.e., overstressed chains, contribute to the strength of the polymer. The number of overstressed chains obtained here for some polymers is consistent with the results of electron paramagnetic resonance and stress‐Fourier‐transform IR measurements: (a) Polymers with all‐trans conformation of their chains have more overstressed chains than those with helix conformation; (b) in the case of polymers with helix conformation, those with smaller side groups have more overstressed chains. Under uniaxial stress, the polymer chains change their conformation from gauche to trans which results in a relief of stress. Polymer with helix conformation thus have less overstressed chains and, hence, lower strength than polymers with all‐trans conformation.
Polymer‐bound derivatives of sarcolysin and their antitumour activity against mouse and human leukaemia in vitro
Authors: Ulbrich Karel , Zacharieva Ekaterina I. , Kopeček Jindřich , Hume Isabella C. , Duncan Ruth 
Published: April 2003

AbstractA series of N‐(2‐hydroxypropyl)methacrylamide (HPMA) copolymers containing different oligopeptide side‐chains terminated in an alkylating anticancer agent‐sarcolysin isopropyl ester (SL‐OiP) and occasionally fucosylamine were synthetized. In the first step reactive polymeric precursors were prepared by radical precipitation copolymerization of HPMA with p‐nitrophenyl esters of N‐methacryloylated dipeptides (Gly‐Phe or Gly‐Leu). In the second step the former were aminolyzed with a dipeptide or amino acid derivatives of SL‐OiP, thus forming tripeptide or tetrapeptide side‐chains terminated in SL‐OiP. Two of the polymers synthetized contained also fucosylamine as the terminal moiety, which was introduced as a targeting moiety, able to interact with fucose‐specific membrane receptors of mouse leukaemia L 1210 cells. These polymers were synthetized by consecutive aminolysis of reactive polymeric precursors with fucosylamine and SL‐OiP derivatives. To test the influence of the oligopeptide side‐chain structure on the rate of drug release, the polymers synthetized were incubated with a mixture of lysosomal enzymes isolated from rat liver (tritosomes) and with cathepsin B. The relationship between the structure of polymer bound anticancer drugs and their biological activity was determined in vitro by their effect on the growth of mouse leukaemia L 1210 cells and human lymphoblastoid leukaemia (CCRF) cells. The results demonstrate the potential of these compounds as new types of targetable anticancer agents.
Enthalpy of polymerisation of 7‐oxabicyclo[4.1.0]heptane
Authors: Andruzzi Fulvio , Shaofeng Li , Pilcher Geoffrey , Heatley Frank 
Published: April 2003

AbstractThe enthalpies of combustion in oxygen at 298, 15 K of 7‐oxabicyclo[4.1.0]heptane, ΔH(1) = −3 624,9 ± 0,6 kJ·mol−1, and of poly(oxy‐1,2‐cyclohexylene), ΔH(am) = −3528,2 ± 1,4 kJ · mol−1 were measured by high‐precision bomb calorimetry. The enthalpy of polymerisation was derived, ΔH(1→am) = −96,7 ± 1,5 kJ·mol−1. Polymer samples from three separate preparations were found to be indistinguishable in their enthalpies of combustion and in their 13C NMR spectra.
Spectral simulation and characterization of polymers from ethene and propene by 13C NMR
Authors: Cheng H. N. , Bennett Mark A. 
Published: April 2003

AbstractA general treatment is devised for the 13C NMR spectral analysis of copolymers involving ethene and propene. The basis of the method is the computerized “synthetic approach” proposed earlier (Anal. Chem.) 56, 2320 (1984) and entails the use of first‐order Markovian statistics, Monte Carlo polymer chain generation, spectral prediction, and spectral simulation. By this means, copolymer and homopolymer spectra of increasing complexity are readily simulated. The method is shown to accommodate all structural types (viz. stereosequences, regiosequences, and polymer chain ends) and provides good results for atactic poly(propylene), irregular poly(propylene), isotactic ethene/propene copolymers, ethene/propene rubbers, and ethene/propene oils.
Thermodynamics of random copolymer mixtures
Authors: Panayiotou Constantinos G. 
Published: April 2003

AbstractThe lattice‐fluid theory of polymer solutions, previously applied to homopolymer‐solvent and homopolymer‐homopolymer mixtures, is now extended to random copolymer mixtures. A generalized, though simple, formalism is presented which is valid for binary copolymer mixtures, each copolymer having any number of different monomeric units (groups). Mixtures of a homopolymer with a random copolymer are treated as a special subcase. Particular emphasis is given to the phase stability of copolymer mixtures. Equations for the spinodal and the critical point are presented. The model is applied satisfactorily to various cases which attracted special attention in recent studies on the miscibility of copolymer mixtures.
Solid state and solution characterization of caprolactam cyclic dimer, a by‐product in the synthesis of nylon 6
Authors: Di Silvestro Giuseppe , Sozzani Piero , Brückner Sergio , Malpezzi Luciana , Guaita Cesare 
Published: April 2003

AbstractThe dimer of ϵ‐caprolactam (1,8‐diazacyclotetradecan‐2,9‐dione), an impurity always present in industrial nylon 6, was characterized by mass spectrometry and solution 13C NMR analysis. DSC and X‐ray diffraction lead to the complete description of the behavior of two crystalline phases: the one stable at room temperature and showing a transition to the other form at 244°C; the second one, more symmetrical, melting at 347°C and slowly converting to the first one at temperatures below 200°C. Both structures are stabilized by intermolecular hydrogen bonds, and the transition is due to conformational changes (from G+TTG− to G+G+TG+ on the aliphatic sequence and from eclipsed to ≈90° on the NCH2 bonds) which can be taken into account in the discussion about the tight chain folding of nylon 6.
Thermal crosslinking of styrene/p‐methylstyrene copolymers
Authors: Schröder Ulrich K. O. 
Published: April 2003

AbstractThermal crosslinking of polydisperse styrene/p‐methylstyrene copolymers with compositions of between 0 and 100 mol‐% of styrene and weight‐average molecular weights of about 300000 was investigated under oxygen‐free conditions at 260°C and 275°C. At these temperatures the formation of oligomers was negligible. The reaction products were analysed by gel permeation chromatography and by swelling experiments. Two competing reactions — degradation and crosslinking — were found which occur to an extent proportional to copolymer composition. By comparing the properties of the treated copolymer samples—molecular weights, amount and characteristics of the gel—with the properties of pure poly(p‐methylstyrene) samples degraded at 275°C it can be concluded that samples with 83 mol‐% and 79 mol‐% of styrene treated at 275°C and 260°C, respectively, should remain unchanged with respect to molecular weight and composition, because degradation and crosslinking compensate each other. In the samples containing less styrene crosslinking predominates. The ratio of the reaction rates determined experimentally agrees well with the value calculated from the reaction rates of the homopolymers given in the literature. A simple radical‐chain mechanism is proposed that explains the experimental results.
Stereoelective polymerization of propylene oxide with a chiral aluminium alkoxide initiator
Authors: Haubenstock Howard , Panchalingam Vaithilingam , Odian George 
Published: April 2003

AbstractThe polymerization of propylene oxide (PO) was studied with an initiator prepared by the reaction of (R)‐(−)‐3,3‐dimethyl‐1,2‐butanediol (1) with aluminium hydride. When mixed with zinc chloride in a 1:1 mole ratio, the initiator was found to be highly reactive and also stereoelective in the polymerization of PO, preferentially incorporating (R)‐(+)‐PO into the polymer chain. Analysis of the polymer structure by 13C NMR spectroscopy showed that chlorine, hydroxyl and alkoxy end groups, derived from the initiator, were present. Fractionation of poly(propylene oxide) (PPO) in acetone at −30°Cgave about 10% insoluble PPO, shown to be isotactic by 13C NMR. The soluble, largely atactic fraction contained irregular head‐to‐head (h,h) and tail‐to‐tail (t,t) structures. In the absence of coinitiator zinc chloride the PPO product was completely soluble in acetone at −30°Cand contained a greater proportion of irregular h,h and t,t structure.
Polyesters prepared by polycondensation in the presence of carbodiimides, 1. Preparation of polyesters from aliphatic dicarboxylic acids and diols under mild conditions
Authors: Panayotov Ivan M. , Belcheva Nadya , Tsvetanov Christo 
Published: April 2003

AbstractThe possibility of the preparation of aliphatic polyesters from dicarboxylic acids and diols by polycondensation in the presence of carbodimides under mild conditions was investigated. The following three possible routes were checked: the polycondensation of dicarboxylic acids with diols in the presence of 4‐dimethylaminopyridine, the polycondensation of dicarboxylic acids with diisourea derivatives and the polycondensation in the presence of pyridine and p‐toluenesulfonic acid. The last method was found to give polyesters with high molecular weights in good yields. This carbodiimide method can be utilized in the synthesis of biodegradable and surface active aliphatic polyesters.
Water‐insoluble dextrans by grafting, 3. Reaction of dextran with butyl isocyanate. Chemical hydrolysis
Authors: Arranz Félix , Sánchez‐Chaves Manuel , Martínez Rafael 
Published: April 2003

AbstractThe modification reaction of dextran with butyl isocyanate using 1,4‐diaza[2.2.2]bicyclooctane as catalyst was studied. The structure of the resulting polymers was determined by means of IR, 1H and 13C NMR spectroscopy as well as by chemical analysis. A linear dependence of the reaction rate on the concentrations of polymer, butyl isocyanate and catalyst was found. The activation energy was found to be 38,5 kJ/mol (9,2 kcal/mol). The homogeneous hydrolysis in alkaline medium was found to be first order with respect to both the base and the butyl urethane concentrations. The activation energy, obtained for the base catalyzed homogeneous hydrolysis, was 83,7 kJ/mol (20,0 kcal/mol). The heterogeneous hydrolysis of a water insoluble modified dextran (degree of substitution = 0,72) showed that no hydrolysis takes place under the applied conditions.
Design of vinyl functional copolymers with main chain chirality through chemical modifications
Authors: Wulff Günter , Dhal Pradeep K. 
Published: April 2003

AbstractOptically active poly(styrene‐co‐methyl methacrylate) and poly(styrene‐co‐methacrylonitrile) were obtained by means of asymmetric copolymerization of 3,4‐cyclohexylidene‐D‐mannitol‐1,2; 5,6‐bis{O‐[(4‐vinylphenyl)boronate]} (1) with methyl methacrylate and methacrylonitrile, respectively, removal of the D‐mannitol template and splitting off boric acid from the resulting copolymers. By polymer analogous reactions, various functional groups were introduced to obtain optically active functional vinyl copolymers. The polymers were characterized by spectral and other analytical methods.
Deuteron NMR study of molecular motion and phase behaviour in a polymer model membrane
Authors: Ebelhäuser Rainer , Spiess Hans Wolfgang 
Published: April 2003

AbstractPulsed 2H NMR was used to study the molecular mobility of a polymer model membrane. The polymerizable lipid analogue consists of a quaternary ammonium ion with two C18 alkyl chains and a methacryloyl moiety attached to the hydrophilic head group via an alkyl spacer. The bilayer spacing as obtained from small angle X‐ray scattering was found to be 3 nm in the lamellar Lβ gel phase of the monomer and 3,5 nm in the polymer indicating an interdigitated structure. The molecular mobility in both the monomer and the polymer below and above the phase transition Lβ → Lα was investigated by the NMR lineshapes and the transverse relaxation time T2 at five positions of the monomeric unit: a methylene group of the spacer, the head group and three methylene groups of the alkyl chains (1‐, 2‐, and 7‐position). In contrast to the monomer a pronounced motional gradient was observed in the polymer, where the spacer is almost completely immobilized, whereas the mobility in the middle of the hydrophobic chains is largely retained. A quantitative analysis of the NMR lineshapes shows a gradual increase of molecular mobility in the polymer above the phase transition due to an increase in both the jump rate and the number of conformational transitions.
Molecular motions in a liquid‐crystalline lipid bilayer. Molecular dynamics simulation
Authors: Khalatur Pavel G. , Pavlov Alexander S. , Balabaev Nikolai K. 
Published: April 2003

AbstractThe results of a molecular dynamics study of a lipid bilayer are discussed. As a model we consider an ensemble of 2 × 10 flexible chains consisting of 16 groups in a box with lateral (x, y) periodicity conditions. The chains interact with each other and with the aqueous medium. Terminal groups are bound near to the bilayer surfaces by a harmonic potential. All numerical results are compared with those obtained for an isotropic polymer liquid with the same density as for the bilayer. From a study of the order parameters we conclude that the bilayer is in the liquid‐crystalline state with the chains expanding in the z‐direction normal to the surfaces. Segmental order parameters are in reasonable agreement with experimental NMR data. Dynamic properties discussed include the frequency spectrum of the velocity autocorrelation function of particles, the incoherent dynamic structure factor, dielectric absorption, and luminescence polarization. It is found that compared with the bulk polymer liquid, the molecular motions in the bilayer are quite different. Such features arise mainly from existing strong correlations in the bilayer and from a different molecular organization of the chains in the bilayer and in the bulk liquid.
Polymerization of lactams, 80. Anionic polymerization of lactams accelerated with N‐iminolactams, 1 2‐pyrrolidone
Authors: Brožek Jiří , Řehák Petr , Marek Miroslav , Roda Jan , Králíček Jaroslav 
Published: April 2003

AbstractThe anionic polymerization of 2‐pyrrolidone (PD) was initiated with the potassium salt of PD at 30–50°C and accelerated with the following N‐iminolactams (NIL): 1‐(1‐pyrrolin‐2‐yl)‐2‐pyrrolidone (1), 1‐(1‐azacyclohept‐1‐en‐2‐yl)‐2‐pyrrolidone (2), 1‐(1‐azacyclonon‐1‐en‐2‐yl)‐2‐pyrrolidone (4), 1‐(1‐azacyclohept‐1‐en‐2‐yl)‐1‐ azacycloheptan‐2‐one (3) and 1‐(phenyliminomethyl)‐2‐pyrrolidone (5). The polymerizations exhibit formal kinetics of zero order with respect to the monomer with substantially differing apparent rate constants depending on the type of NIL used. The same limit conversions are attained in all cases. The possible role of NIL in the polymerization system is discussed.
Terpolymerization of maleic anhydride, styrene and electron‐acceptor monomers
Authors: Florjańczyk Zbigniew , Krawiec Włodzimierz 
Published: April 2003

AbstractThe free‐radical terpolymerization of maleic anhydride, styrene, and acrylic monomers such as acrylonitrile, methyl acrylate and methyl methacrylate was studied. The alternating copolymerization of maleic anhydride with styrene was found to be favored in those systems. Contrary to theoretical predictions, maleic anhydride is more reactive than styrene in ternary systems. The relative reactivity of the acrylic monomers studied was found to decrease in the order: methyl methacrylate ≥ methyl acrylate > acrylonitrile. In the presence of a Lewis acid, such as ZnCl2 or C2H5AlCl2, the relative reactivity of acrylic monomers increases and at the respective complexing agent concentration the copropagation of the acrylic monomer with styrene can dominate. On the basis of the results obtained, some aspects of the mechanism of alternating propagation in systems comprising an electron‐donor monomer and two electron‐acceptor monomers are discussed.
Polymérisation de monomères carbonates de vinyle
Authors: Freire Maria Telma Gomes , Danicher Louis , Lambla Morand 
Published: April 2003

AbstractFree‐radical polymerizations of several aliphatic and aromatic N‐substituted vinyl carbonates are described. The bulk polymerization was initiated at 35°C with di‐tert‐butylcylohexyl peroxydicarbonate yielding high‐molecular‐weight poly(vinyl carbonate)s. The structure of these polymers was examined by FTIR spectroscopy and the molecular weight by GPC. The effects of the substituents on the physical properties of the resulting polymers were studied. A comparison of the properties with those of similar compounds described in the literature was made.
In‐situ photopolymerization of an oriented liquid‐crystalline acrylate
Authors: Broer Dirk J. , Finkelmann Heino , Kondo Katsumi 
Published: April 2003

AbstractThe photoinitiated polymerization of 4‐biphenylyl 4‐(6‐acryloyloxyhexyloxy)benzoate (1) in its oriented liquid‐crystalline state was studied. Monomer1has a thermotropic nematic phase between 88°C and 98°C, a monotropic nematic phase between 76°C and 88°C, and a monotropic smectic phase below 76°C. The orientation of1was established in a glass cell provided with a rubber polyimide coating and characterized by birefringence measurements. During polymerization both the birefringence and the liquid‐crystalline transition temperatures increase, indicating that the orientation was maintained. The oriented poly(1) is polycrystalline at room temperature, becomes smectic at 90°C, nematic at 172°C, and isotropic at 190°C. The order parameter of the nematic poly(1) is lower than that of the nematic monomer1at equal reduced temperatures.
Interference effects from liquid‐crystalline block copolymers: Matrix method and analytical approach
Authors: Bonart Richard , Dietrich Johann , Zott Hans 
Published: April 2003

AbstractIn order to calculate the interference effects from liquid‐crystalline block copolymers, Biswas and Blackwell have presented an elegant matrix method. For the cases where an analogous, analytical approach can be made, we show that the matrix method leads to the same result as the analytical method. In addition to the conventional reciprocal lattice with reciprocal lattice points at h2π/〈c〉, where 〈c〉 is the average periodicity, one has to consider three further reciprocal lattices with reciprocal lattice points h′2π/cA, h″2π/cB, and h″′2π/(cB + cB). cB and cB are the lengths of the comonomer units. This method will be illustrated by model calculations for p‐benzoate/biphenyl‐4,4′‐diylisophthalate copolyestersPoly[(isophthalic acid‐alt‐biphenyl‐4,4′‐diol)‐co‐4‐hydroxybenzoic acid].
. Further, interesting possibilities of the matrix method will not be treated here.
Infrared spectroscopic studies on polyethylene, 7. The use of the methyl deformation band for branch characterisation
Authors: Maddams William F. , Parker Stewart F. 
Published: April 2003

AbstractThe factors relating to measuring the position of the methyl deformation mode at about 1378 cm−1 with sufficient precision to permit its use for the identification of the different branches present in the various types of “linear” low density polyethylene(as manufactured by the copolymerization of ethylene and a 1‐alkene) have been examined systematically. With a data density of eight points per wavenumber, and the well established subtraction procedure with polymethylene or with a near‐linear polyethylene to remove the overlapping methylene deformation band, it is possible to achieve a precision of ±0,15 cm−1. This is ample to distinguish between methyl, ethyl, and butyl or hexyl branches, but not to characterise uniquely these last two. The use of Fourier self‐deconvolution to separate the methyl band has also proved very effective. The precision obtainable when these methods are applied to spectra measured with one data point per wavenumber is somewhat lower, but is still adequate for characterisational purposes. The results for a series of polymers containing ethyl branches at various concentrations suggest a small difference for the peak position for branches present in crystalline and amorphous regions.
Terpolymérisation acrylonitrile‐styrène‐acrylate de méthyle, 4. Copolymérisation en emulsion styrène‐acrylate de méthyle en réacteur fermé (batch) en présence de persulfate de potassium
Authors: Ramirez‐Marquez Walter , Guillot Jean 
Published: April 2003

AbstractTo improve the knowledge of emulsion copolymerization of monomers both swelling their copolymers, but which are of quite different polarity (water solubility), a series of styrene (S)/methyl acrylate (MeA) copolymerizations was carried out in batch at 50°C with potassium persulfate as initiator. The overall rates of copolymerization increase with the amount of MeA in the monomer feed. Copolymer composition follows the usual copolymerization equation if bulk/solution reactivity ratios (rij) and monomer partition between aqueous and organic phase are taken into account (simulation). However, accurate kinetic data at low conversion (gas chromatography) put in evidence an enhanced polymerization of the more hydrophilic monomer (MeA), which can be attributed to polymerization in the water phase. Particle sizes increase with conversion and tend to a limiting value, the higher the MeA content is. Particle number (Np), which is practically constant with conversion of S homopolymerization, tends to increase with MeA content as polymerization proceeds. This trend is enhanced if the emulsifier (sodium dodecanesulfonate, SDS) concentration is increased. Overall propagation rate constants were estimated as function of the experimental conditions and monomer concentration within the particles. From kinetic data (rate of polymerization) and Np, it was found that the average number of radicals per particle, ñ, remains close to 0,5. It was then possible considering S(kp = 125 1 · mol−1 · s−1) as a standard monomer, to estimate the polymerization rate constant for MeA (335 1 · mol−1 · s−1). Since adsorption of emulsifier was shown to be closely related to particle surface composition, the specific area As of SDS was measured on latices at various conversions and initial monomer feeds. As conversions increases, the particle surface appears to be richer and richer in MeA, which corresponds to a particle structuration. Strong and weak acid group titration is also in quite good agreement with the colloidal behaviour.