bluuebunny/crossref_metadata_2025_split huggingface dataset:
Reactivity ratios for grafting of vinyl acetate and methyl acrylate mixtures onto cellulose at high conversions
Authors: Casinos Ismael 
Published: April 2003

AbstractThe heterogeneous graft copolymerization of a mixture of vinyl acetate (VAc) and methyl acrylate (MA) onto cellulose was carried out in an aqueous medium through a radical mechanism. Copolymerization led, as usual, to the simultaneous formation of grafted and non‐grafted poly(vinyl acetate‐co‐methyl acrylate). The reactivity ratios of VAc and MA were determined from high‐conversion data by using an integrated form of the copolymerization equation. Values of the reactivity ratios for VAc (r1 = 0,020) and MA (r2 = 6,750) were calculated. The capacity of the methods for determining reactivity ratios based on the differential copolymerization equation is discussed for the present copolymerization system. Some significant characteristics of the copolymer and the copolymerization reaction are deduced from the copolymerization parameters. It is concluded that the polymerization sites of the grafting and homopolymerization reactions are identical. Also, the present aqueous dispersion technique yields similar results as bulk polymerizations.
A new selective agent for poly(tetrahydrofuran) degradation as a tool for the determination of the crystallite core size
Authors: Ishikawa Satoshi , Ishizu Koji , Fukutomi Takashi 
Published: April 2003

AbstractThe method formerly used to determine the crystallite core size of polyethylene was applied to poly(tetrahydrofuran) (PTHF). This method is based on the different diffusivity of a chaincleaving agent in crystalline and amorphous parts of the polymer. Butyllithium was used as a cleaving agent of PTHF. The degree of polymerization of the undecomposed part of the polymer (PTHF crystallites) was determined by gel permeation chromatography. This value agrees well with the value to be expected from the size of the crystallites determined small‐angle X‐ray scattering.
Thermotropic polyesters, 7.. Liquid‐crystalline polymers with meta‐phenylene units in the mesogenic moiety
Authors: Tenkovtsev Andrey V. , Piraner Olga N. , Bilibin Alexander Yu. 
Published: April 2003

AbstractPolyesters containing 3,3′‐substituted azobenzene and benzanilide moieties as a part of conformationally mobile aromatic blocks were synthesized. Polymers based on 3,3′‐substituted azobenzene residues exhibit liquid‐crystalline properties and unusual thermal properties such as opposite odd‐even effect and unexpected cis‐trans isomeric ratio of azo group. Similar polymers with an amide group between the 1,3‐substituted benzene rings cannot form liquid crystals.
Polymères photoréticulables à unités cinnamiques, 2. Synthèse par modification chimique et par polycondensation
Authors: Brosse Jean‐Claude , Remmas Miloud , Soutif Jean‐Claude 
Published: April 2003

AbstractPolymers containing cinnamic acid units were obtained by chemical modification of poly(vinyl alcohol) by cinnamic acid derivatives with a carbon‐carbon double bond in para position. The reactivity of the acid chloride is lowered by the inductive effect of the double bond. Polycondensation of these derivatives, when difunctional, leads to low‐molecular‐weight polyamides and polyesters with good yields. The introduction of acrylic or methacrylic groups on photosensitizers has also been studied, leading to monomers which can be polymerized by a radical process, or copolymerized with the previous monomers, the polymer bearing then the photosensitizer and the cinnamic double bond on the same chain.
The influence of the H‐bonded association of COOH groups on the copolymerization of unsaturated carboxylic acids
Authors: Hrabák František , Bezděk Milan 
Published: April 2003

AbstractThe monomer reactivity ratios of styrene with unsaturated acids—4‐(acryloyloxy)phenylacetic acid, α‐(methacryloyloxy)phenylacetic acid and 4‐(methacryloyloxy)phenylacetic acid—and their alkyl esters were determined in acetone and acetic acid solutions. Due to the isolation of the COOH and COOR groups from the benzene ring owing of the CH2 group the electron densities on the polymerizable CC double bonds of these acids, their H‐dimers, the H‐associates with the solvent and their alkyl esters are identical. In spite of this, however, in the copolymerization of styrene with unsaturated acids the rate of addition to the polymeric radical was fastest for the H‐dimers of the acids, less fast for a mixture of H‐dimers and H‐associates “unsaturated acid‐acetic acid”, and slowest for the acid esters. The preferential enrichment of the copolymer with the acid is explained through a bimolecular addition of the first CC of the H‐dimer to the polymeric radical and a faster “monomolecular” addition of the CC of the second dimer acid unit associated with the polymeric radical. If however, there is some steric hindrance to an immediate radical propagation between the CC of two acid units joined by H‐bonds between the carboxyl groups, several elementary acts of bimolecular addition of the other comonomer molecules may take place between the addition of the first and the second dimer acid unit.
SEM study on fracture behavior of ethylene/propylene block copolymers and their blends
Authors: Sun Zhenhua , Yu Fusheng 
Published: April 2003

AbstractThe toughening effect of the separate phases of ethylene/propylene block copolymers and their blends was studied by scanning electron microscopy (SEM). The results obtained show that the interfacial adhesion between separate phases and the isotactic polypropene (iPP) matrix in ethylene/propylene block copolymers is strong at room temperature, but poor at low temperature; specimens exhibit tearing of separate phases during fracture at room temperature, but interfacial fracture between separate phases and the iPP matrix at low temperature. From the characteristics of fractographs of ethylene/propylene block copolymers and their blends, it could be concluded that the separate phases improve the toughness of specimens in several ways: they promote the plastic deformation of the iPP, and they can be deformed and fractured themselves during the fracture process. However, it was shown that the plastic deformation processes, such as multiple‐crazing, shear yielding, etc. of the matrix are the dominant mechanisms of energy absorption in highly toughened ethylene/propylene block copolymers and their blends. The deformation and fracture of separate phases are only of secondary importance.
Polymeric chiral crown ethers, 7. Synthesis of polymers incorporating methyl glycosides of α‐D‐altrose, α‐D‐galactose, α‐D‐glucose and α‐D‐mannose residues via copolymerization of divinyl ethers
Authors: Kakuchi Toyoji , Haba Osamu , Yokota Kazuaki 
Published: April 2003

AbstractPolymers with chiral asymmetric crown ether units (5, 6, 7 and 8) were synthesized via cationic cyclopolymerization of methyl 2,3‐bis{O‐[2‐(2‐vinyloxyethoxy)ethyl]}‐4,6‐O‐benzylidene α‐D‐altro‐, α‐D‐galacto‐, α‐D‐gluco‐ and α‐D‐manhopyranosides (1, 2, 3 and 4), respectively. The enantioselective transport of the methyl ester of phenylglycine (PhGlyOCH3) and phenylalanine (PhAlaOCH3) was examined through a bulk chloroform solution of chiral polymers from one aqueous solution to another. The transport rate of PhAlaOCH3 was larger than that of PhGlyOCH3 for every host polymer. For polymer 7, the optical purity of PhAlaOCH3 transported from one to the other phase was 12,6%, and the ratio of rate constants for the faster moving enantiomer A and the slower moving enantiomer B (kA*/kB*) was 1,48. The faster moving enantiomer was the L‐isomer except for the systems polymer 7 − PhAlaOCH3 and polymer 8 − PhAlaOCH3. This enantioselectivity is caused by the diastereotopic faces of the crown ether units in the host polymers.
Novel degradable methacrylate‐ and p‐vinylphenoxy‐based oligomers, 2. Photopolymerization and acid‐catalysed degradation
Authors: Ericsson Jan , Hult Anders 
Published: April 2003

AbstractFive novel photocrosslinkable oligomers were evaluated with regard to polymerization and acid‐catalysed degradation. The oligomers include either a methacrylate or p‐vinylphenoxy unit as the polymerizable moiety. A carbonate functionality susceptible to acid‐catalysed degradation is also incorporated. This work shows that it is possible to formulate an oligomer‐based photo‐curable coating which can be polymerized to an insoluble matrix. In the case of the styrene‐type dicarbonates, no pure coatings can be studied at room temperature, and at elevated temperatures cationic polymerization competes with degradation. They can, however, be degraded to soluble products at reasonable temperatures if the system is exposed to a strong acid catalyst.
Characterisation of macroporous polystyrene and its relationship to the adsorption of Cephalosporin C
Authors: Huxham Ian Maximillian , Rowatt Brian 
Published: April 2003

AbstractLow‐temperature specimen preparation techniques, energy‐filtering electron microscopy, quantitative image analysis and elemental mapping are applied to an analysis of two macroporous, hydrated, polystyrene sorbents (XAD4® and PS50X2T) in order to determine whether or not minor differences in the apparent binding behaviour of Cephalosporin C to each hydrated sorbent can be related to specific determinants of polymer porosity. Mercury intrusion volume calculations suggest that each polymer has almost identical characteristics in the dry state. In contrast, electron microscopically‐derived pore profile measurements from the hydrated polymer suggest that XAD4® has a greater proportion of pore area associated with small (5–50 nm) diameter pores and a correspondingly smaller proportion of its pore area associated with the larger (80–150 nm) pore diameters as compared to PS50X2T, and that these differences are associated with changes in the local distribution of adsorbed Cephalosporin C within the polymer's porous domains.
Polymerization reaction with diphenylphosphoryl azide. Preparation of polyamides, polyureas and polyurethanes
Authors: Nishi Norio , Tsunemi Masahiko , Nakamura Kunio , Tokura Seiichi 
Published: April 2003

AbstractThe preparation of various polyamides, polyureas and polyurethanes by polymerization reactions with diphenylphosphoryl azide (DPPA) was investigated. Various polyamides were obtained very conveniently by polymerization of aminocarboxylic acids or copolymerization of dicarboxylic acids and diamines. Polyureas were mainly obtained by conversion of dicarboxylic acids to acyl azides with DPPA and then to isocyanates, followed by copolymerization of these diisocyanates with diamines. Further, the polymerization of some aminocarboxylic acids that have an amino group of low nucleophilicity (such as p‐aminobenzoic acid) was found to give polyureas instead of polyamides by direct polymerization. Polyurethanes were also obtained from dicarboxylic acids and diols through the Curtius rearrangement of acyl azides, similarly as in the polyurea preparations. The products were identified with the help of IR spectra and elemental analyses, and their molecular weights were evaluated viscometrically.
Polymères photoréticulables à unités cinnamiques, 3. Photoréticulation
Authors: Remmas Miloud , Soutif Jean‐Claude , Brosse Jean‐Claude 
Published: April 2003

AbstractPhotocrosslinking of polymers, prepared from cinnamic acid derivatives, by chemical modification of poly(vinyl alcohol) or polycondensation of difunctional cinnamic acid derivatives has been studied. With Michler's ketone (sytem. name: 4,4′‐bis(dimethylamino)benzophenone), crosslinking of copolymers is improved. 2‐Nitrofluorene or 9‐xanthenone have little effect on the crosslinking rate. Photocrosslinking of poly(α‐cyano‐4‐vinylcinnamic acid), poly(ethyl α‐cyano‐4‐vinylcinnamate) and their copolymers is enhanced in the presence of 2‐hydroxy‐2‐methylpropiophenone, but the effect is lowered in the case of its acrylic esters or their (co)polymers.
Emulsion polymerization of butadiene, 4. Effect of thiols
Authors: Weerts Pierre A. , van der Loos Jos L. M. , German Anton L. 
Published: April 2003

AbstractThe role of thiols of low water solubility, commonly used in the emulsion polymerization of butadiene, has been considered. The following effects have become apparent: (1) dodecanethiols act as efficient chain transfer agents in limiting the formation of heavily cross‐linked polymer networks; (2) the monomer concentration within the particles is not influenced by such thiols; (3) C12‐thiol radicals do not desorb because of their extremely low water solubility. The ‘promoting effect’ of thiols in emulsion polymerizations of diene‐hydrocarbons is still poorly understood, but it appears to be related to impurities present in the emulsifier, as it was found completely absent in emulsifier‐free polymerizations.
4‐(α,α‐dimethylbenzyl)phenyl methacrylate, 2. Polymerization in N,N‐dimethylformamide
Authors: van Ekenstein Gert O. R. Alberda , Tan Y. Yong 
Published: April 2003

AbstractThe polymerization rate of 4‐(α,α‐dimethylbenzyl)phenyl methacrylate in DMF at 70°C is of the order 1,6 in [monomer] and first order in [AIBN], which deviates from classical kinetics. This could be reconciled by a reaction scheme in which dimeric monomer associates and a spontaneous termination are postulated. The scheme is supported by the dependence of the kinetic chain length, v, on the 1,6‐th power in [monomer] and zeroth power in [AIBN]. The degree of polymerization is smaller than v, which indicates some chain transfer. A remarkable feature is the constancy of the dispersion degree, M̄w/M̄n, of the polymers of about 1,4 up to high degrees of conversion. The overall activation energy of the polymerization, Ea, is 60,1 kJ · mol−1, and the preexponential factor ln A ≈ 15,5 (A in (mol · dm−3)−1,5 · s−1). The polymer chains seem to have a rod‐like character in THF as deduced from the Mark‐Houwink exponent of 1,46. In toluene the polymer tends to form associates.
Regular folding in solution‐grown polyethylene crystal, 2. Supportive evidences
Authors: Chang Hwei‐Liang , Hu Andrew Teh 
Published: April 2003

AbstractIt is shown here that the coordinated pair chain folding (CPCF) model can explain the evidences reported about polymer chain conformation in solution‐grown polyethylene (PE) single crystals from neutron scattering and infrared (IR) studies. Thus the CPCF model can revive the consideration that a polymer chain should fold regularly rather than randomly in solution‐grown PE single crystals. The start‐to‐crystallization position of a polymer chain, dominantly from the inner part (other than chain ends) of the polymer chain itself, explains the “superfolding” effect. The scattering function calculated from those stems allocated in the form of a CPCF model with superfolding coincides with the reported data from small angle and intermediate angle neutron scattering experiments. Interchain interference destroys the neutron peak at Q = 0,7 Å−1, thus settling the “no peak” argument for equivalent Bragg spacing 8,9 Å. The CPCF model satisfies the reported statement from IR studies: “The correlation splitting of the CD2 bending vibration is not generally observed.” The splitting observed in other experiments coincides with the stem arrangement of the CPCF model with partial intrachain coalescence, which is caused by a faster crystallization rate, the energy state being a little higher than that without local coalescence.
Soluble polystyrene‐block‐poly(p‐phenylene) block copolymers prepared from polystyrene‐block‐poly(1,3‐cyclohexadiene) precursors. Study of the aromatization process
Authors: Zhong Xing Fu , François Bernard 
Published: April 2003

AbstractPolystyrene‐block‐poly(p‐phenylene) block copolymers were prepared from polystyrene‐block‐poly(1,3‐cyclohexadiene) (PS‐PCHD) precursors. The PS‐PCHD copolymers were initiated by sec‐butyllithium in benzene. The aromatization of poly(1,3‐cyclohexadiene) sequences was carried out by dehydrogenation with substituted quinones. Secondary reactions occur during this reaction leading to defects in the poly(p‐phenylene) (PPP) sequences which limit the mean length of conjugated blocks at about 11–12 phenylene units. The defects result from the addition of hydroquinone ether groups to the chain. The influence of experimental conditions (nature of quinone, additives, temperature) on the aromatization yield and defect content is studied. The reaction with p‐chloranilSystem. name: tetrachloro‐p‐benzoquinone.
at 130°C gives the best results. The formation of aggregates during this reaction is observed and explains the final slow kinetics. The purified copolymers are partly aggregated into micelles with a PPP core. For a given polystyrene sequence the fraction of aggregated chains and the size of PPP core increases with the length of PPP sequences. Improvements of PPP blocks are expected by a better control of the aggregation process.
Concentration of aqueous alcoholic solutions through a modified silicone rubber membrane by pervaporation and evapomeation
Authors: Uragami Tadashi , Shinomiya Hidenori 
Published: April 2003

AbstractPermeation and separation characteristics for aqueous alcoholic solutions through a modified silicone rubber membrane containing poly(propylene glycol) in the polymer chain were studied by both pervaporation and evapomeation. Both the permeation rates in pervaporation and evapomeation increase, and the selectivity for ethanol in pervaporation does not change but that in evapomeation increases with an increase in the permeation temperature. When the temperature in the membrane surroundings was kept constant and the temperature of the aqueous ethanol solution was varied, or vice versa, it was found that the permeation rate and the permselectivity for ethanol are significantly influenced by the temperature in each permeation condition. The selectivity for alcohols through the modified silicone rubber membrane in the evapomeation method with control of the temperature difference decreases in the order methanol > ethanol > 1‐propanol.
Dimensions of poly(methyl methacrylate) molecules in poor solvents
Authors: Guaita Marino , Chiantore Oscar , Burchard Walther 
Published: April 2003

AbstractDilute solutions of narrow distribution poly(methyl methacrylate) (PMMA) samples in the poor solvents, 2‐ethoxyethanol and acetonitrile, are studied by dynamic and static light scattering and viscometry. Theta temperatures at 37,8°C and 32,3°C, respectively, are found, where the constants KΘ of the Mark‐Houwink‐Sakurada relation are 5,6 · 10−2 cm3/g and 4,0 · 10−2 cm3/g. This implies that the unperturbed dimensions of PMMA molecules in 2‐ethoxyethanol are greater by 12% than in acetonitrile. The hydrodynamic radii in the two solvents and the radii of gyration in acetonitrile are found to decrease smoothly with decreasing temperature passing the theta temperatures. Data treatment according to the thermal blob model shows that the macromolecular coils, still close to Gaussian statistics, move toward the excluded volume regime above the theta temperature Θ and toward the collapse regime below Θ.
Conformational volume in statistics of chain molecules
Authors: Bleha Tomás̆ 
Published: April 2003

AbstractThe conformational volume Vc represents a contribution to the partial molar volume V̄ of solutes which arises due to the non‐identical volume of conformers in chain molecules. The paper presents expressions for calculations of the term Vc based on the matrix method of conformational statistics. Starting from literature data on the volume differences in conformational diads, the conformational volume of poly(methylene) was calculated as a function of temperature and pressure. The combination of the results calculated with experimental data for nonane shows that the conformational term amounts to about 2% of the value of V̄ and several percent in the temperature coefficient of V̄. The theory of the conformational volume is presented as a generalization of existing empirical additive schemes for the calculation of the partial molar volume of linear‐chain solutes.
Sequence analysis and comonomer interactions in poly[(4‐chlorophenyl methacrylate)‐co‐(methyl methacrylate)]s
Authors: Hiller Wolf‐Gerald , Pasch Harald , Lampe Irene V. 
Published: April 2003

AbstractCopolymers of 4‐chlorophenyl methacrylate and methyl methacrylate were prepared and investigated by 1H and 13C NMR spectroscopy. The copolymer composition, determined by chlorine analysis, 1H and 13C NMR, was found to be close to the initial composition of the monomer mixture. The sequence analysis was carried out by analyzing the methoxy signals of the 1H NMR spectra. Six out of ten tactic and compositional triads could be resolved. It was found that the copolymers are predominantly syndiotactic and the compositional and tactic triad populations are given. The aromatic carbon atoms are sensitive towards compositional and tactic sequence effects, which results in a switch of the order of the tactic signals at different aromatic carbon atoms.
Application of projection matrices to the calculation of unperturbed dimensions of chain polymers
Authors: Hoshino Yoshiaki , Miyake Akira 
Published: April 2003

AbstractThe projection operator method of matrix algebra is applied to calculate the unperturbed dimensions of an independently hindered rotating bond model for linear chain molecules. It does not require eigenvectors of a given transformation matrix in order to evaluate products of that matrix. This is an advantage to usual matrix diagonalization methods. As a result, we obtained four different types of conformations depending upon the values of parameters adopted. One of them shows a typical dependence on the number of bonds N, which has also been given by the usual matrix diagonalization method. Two further conformations are rather extended compared with the first one. In addition, as the fourth one we obtained also a helix‐like conformation. These conformation types correspond to those previously obtained by continuous models for stiff‐chain polymers.
Blend phase diagrams recorded with cast films
Authors: Yu Dan , Andradi Laksiri N. , Hellmann Goetz P. 
Published: April 2003

AbstractPhase diagrams of amorphous polymer blends are discussed that are recorded using cast films. Films of all blend compositions were cast at temperatures ranging over a wide interval, using different solvents, both above and below the glass transition temperatures of the blends. Phase diagrams thereby obtained can, if there is a proper choice of solvents and conditions, show the miscibility of polymers not only in the liquid but also in the glassy state. The theory of blend film casting is analyzed using the classical Flory‐Huggins model for compatibility and the Fox‐equation for the glass transition. It turns out that miscibility is reliably determined when slightly selective solvents are used. Errors made with non‐selective and too selective solvents are estimated. The film‐casting method was tested with blends of poly(methyl methacrylate) and random copolymers of styrene and methyl methacrylate.
4‐(α,α‐dimethylbenzyl)phenyl methacrylate, 3. Synthesis, tacticity and glass transition temperatures of its polymers
Authors: van Ekenstein Gert O. R. Alberda , Tan Y. Yong 
Published: April 2003

AbstractDepending on the kind of initiator, anionic polymerization of 4‐(α,α‐dimethylbenzyl)phenyl methacrylate in toluene at −78°C led either to highly isotactic or predominantly syndiotactic polymers as determined by 13C NMR spectroscopy. The glass transition temperature difference between the syndiotactic and isotactic polymer appeared to be smaller than in case of poly(alkyl methacrylates), probably because of a larger stiffening effect by the bulky aromatic ester group on the isotactic backbone than on the syndiotactic one.