bluuebunny/crossref_metadata_2025_split huggingface dataset:
Structural studies on chitosan and other chitin derivatives
Authors: Grant Stuart , Blair Hal S. , McKay Gordon 
Published: April 2003

AbstractChitosan films were prepared by casting from solutions in dilute acetic acid containing methanol, acetone, or dimethyl sulfoxide. Induced changes in the structural orientation of the molecules within the film were studied by wide angle X‐ray diffraction, and it was shown that the presence of a high concentration of organic solvent in solution altered the crystal structure of the resultant films, rendering them insoluble in water. Benzoylated and butyrylated derivatives of chitin and chitosan were prepared and characterised by infrared spectroscopy. Films of these derivatives were prepared by casting from a number of organic solvents and water, and the structures examined in more detail by wide angle X‐ray diffraction. The introduction of the aliphatic and aromatic groups to the polysaccharide backbone was thus shown to disrupt the natural orientation of the polymer chains; the solubility of the acylated derivatives is discussed with respect to these structural changes.
Synthesis and characterization of phthalocyaninatocobalt (II) covalently bound to polyorganosiloxane
Authors: Nemoto Nobukatsu , Asano Makoto , Asakura Tetsuya , Ueno Yukihiko , Ikeda Koji , Takamiya Nobuo 
Published: April 2003

AbstractPolyorganosiloxane containing phthalocyaninatocobalt(II) in the side chain (PCPMSTACo(II)Pc) (4) was synthesized from poly[(3‐carboxypropyl)methylsiloxane] (PCPMS) (1) and 2,9,16,23‐tetraaminophthalocyaninatocobalt(II) (TACo(II)Pc) (3). The wavelength of maximum absorption of TACo(II)Pc in PCPMS‐TACo(II)Pc in solution of N,N‐dimethylformamide (DMF) is shifted depending on the polymer environment. From UV/VIS spectra of PCPMS‐TACo(II)Pc, most of the phthalocyanine moieties in PCPMS‐TACo(II)Pc may be expected to exist monomeric in methanol as well as in DMF. The glass transition temperature (Tg) of PCPMS‐TACo(II)Pc is high compared with that of PCPMS and the maximum Tg is 50°C. Further, the formation of a crosslinked film is reported, and in this film most of the phthalocyanine moieties may be expected to exist dimeric as concluded from the UV/VIS spectrum. This dimer formation and intramolecular bridges between TACo(II)Pc and carboxyl groups are considered to influence Tg, because they reduce the mobility of the main chains.
Photo‐oxydation de résines phénoliques
Authors: Rivaton Agnès , Lemaire Jacques 
Published: April 2003

AbstractAnalytical and kinetic aspects of photo‐oxidation in the solid state of phenolic resins (phenolformaldehyde polycondensates) are described. On the basis of Fourier‐transform infrared analysis it should be noted that resins contain, in addition to methylene‐bridged structures, ether linkages (CH2OCH2) between aromatic structures. Photochemistry of the phenolic resins involves two primary processes. Photolysis of the phenolic groups leads to the formation of quinone methide structures and photo‐oxidation of the dimethylene ether linkages to hydroperoxy groups which are photo‐ and thermo‐unstable. These hydroperoxy groups are converted into ester and formate groups.
Investigations on the decomposition of lateral perester groups in maleic anhydride copolymers
Authors: Steinert Volker , Rätzsch Manfred 
Published: April 2003

AbstractThe reaction of maleic anhydride (MAn) copolymers with tert‐butyl hydroperoxide results in copolymers with lateral perester and carboxyl groups. As these copolymers are of interest as initiators of free‐radical polymerization, their decomposition mechanism and their decomposition constants were investigated. Surprisingly, a dependence of the decomposition constants on the comonomer of MAn was found. The interaction of the carboxyl group with the perester group is discussed as an essential reason of the comonomer influence.
Dehydrochlorination in crystalline structures of commerical poly(vinyl chloride)
Authors: Behnisch Jürgen , Zimmermann Heinz 
Published: April 2003

AbstractThe polyene formation during degradation of a commercial suspension‐polymerized poly(vinyl chloride) (PVC) in the solid state is discussed with respect to the PVC texture. Above the glass transition temperature (Tg), the polyene length distribution is characterized by a high amount of very short polyenes (conjugation length i < 6) due to the dehydrochlorination in the amorphous phase, and a second population of longer polyenes (i about 14) due to dehydrochlorination in micellar (B‐type) crystals. According to the melting range of these crystals (120–180°C), the formation of longer polyenes reaches a maximum at 120°C. A third population of polyenes could be observed investigating the thermal and photolytical degradation of PVC below Tg. The absorption spectra of the degraded samples show a maximum centred at 550 nm (i = 21) due to the dehydrochlorination in the highly ordered lamellar (A‐type) crystals. This result verifies the existence of highly syndiotactic sequences in commercial PVC formed during the first stage of polymerization, as demonstrated recently. The preferential dehydrochlorination in these crystals during the initial stage of degradation of PVC below Tg should be considered when discussing the long term stability of PVC products.
Synthesis and characterization of 2‐acetoxybenzoic acid‐dextran ester conjugates
Authors: Sánchez‐Chaves Manuel , Arranz Félix , Díaz Carmen 
Published: April 2003

AbstractThis work deals with the modification reaction of dextran with 2‐acetoxybenzoyl chloride (acetylsalicyloyl chloride) using tertiary amines as catalyst/acceptor systems and the DMF/LiCl system as solvent. The structure of the resulting polymers was determined by means of IR, 1H and 13C NMR spectroscopy. Transesterification reactions were observed when 4‐dimethylaminopyridine or pyridine were used as catalysts, with the formation of acetoxy, 2‐hydroxybenzoyloxy (salicyloyloxy) and 2‐acetoxybenzoyloxy (acetylsalicyloxy) groups. When triethylamine was used as catalyst, only acetylsalicyloyloxy groups were found to be grafted onto the polymer chain. A linear dependence of the reaction rate on the concentrations of polymer, acetylsalicyloyl chloride and triethylamine was found. The activation energy was found to be 13,8 kJ/mol.
TiCl4/MgH2‐supported Ziegler‐type catalyst system, 1. Determination of active centres
Authors: Jaber Isam A. , Fink Gerhard 
Published: April 2003

AbstractDetermination of active centres using TiCl4/MgH2‐supported catalyst system in ethylene polymerization is reported. A radio‐tagging technique, whereby 14CO is used to label the polymerization active centres, is employed. Optimization of the 14CO/Ti ratio showed that the polymer radioactivity remained constant after a 14CO/Ti ratio of about 8 was attained. At the optimal 14CO/Ti ratio, it is found that up to 14% of the titanium on the catalyst surface are active in polymerizations at 40°C, 10 min reaction time, and 30 min contact time period of 14CO with the polymerization medium. Moreover, the value of the corresponding propagation rate constant, Kp, was found to be about 230 dm3/(mol·s).
Alignment processes in a smectogenic side‐chain liquid‐crystal copolymer
Authors: Kozak Andrzej , Moura‐Ramos Joaquim J. , Simon George P. , Williams Graham 
Published: April 2003

AbstractThe dielectric properties of the siloxane side‐chain liquid‐crystal (LC) copolymer 1 were investigated using high‐frequency techniques. The copolymer could be aligned homeotropically either by cooling from the melt with the aligning electric field on or by application of the field whilst the sample was in the LC state. Using the latter method the kinetics of the homeotropic alignment process could be determined. Samples of different purity were used and the kinetics and steady‐state properties compared and a strong dependence on polymer purity was found in both cases. Fuoss‐Kirkwood deconvolution of the relaxation peaks allowed examination of the fundamental motion of the mesogenic units.
Effects of ionenes on structure and catalytic activity of cobaltphthalocyanine, 5. The catalytic role of cobaltphthalocyanine aggregates
Authors: van Welzen Joke , van Herk Alex M. , German Anton L. 
Published: April 2003

AbstractThe interaction of several ionenes with tetrasodium phthalocyaninatocobalttetrasulfonate (1) was investigated spectrophotometrically, both in the unreduced and reduced state. The 2,10‐ and 2,12‐ionenes 2d, e appeared to induce monomerization of the phthalocyanine moiety, especially of the reduced form which is ascribed to hydrophobic effects. All other ionenes studied strongly induced aggregation of the cobalt complex. Kinetic thiol oxidation experiments revealed large differences between the macromolecular effects of the hydrophobic 2,10‐ionene 2d and the hydrophilic ionenes. These phenomena are explained by the different catalytic activity of phthalocyanine in its monomeric and aggregated form.
On the probability of the existence of periodical substructures in cellulose
Authors: Stoll Manfred , Fengel Dietrich 
Published: April 2003

AbstractLinters cellulose was degraded in an inert and water‐free atmosphere using thermic and ultrasonic energy. The fragments were nitrated and fractionated by precipitation. A mathematical analysis of the degree of polymerization (DP) values of the differential and individual fractions resulted in a common denominator of 40 for all DPs of degraded celluloses. Also, the value of 120 occurs very frequently. Similar results were found for a series of 33 industrial pulps and some other celluloses. The smallest units in higher molecular‐weight celluloses are multiples of 40 or 120 in the range of 360 to 720. The results and the calculations of this study suggest that preformed substructures obviously exist in the cellulose of higher plants which are independent of the origin of the cellulose. The sizes of the resistant substructures seem to be independent of the kind of degradation applied.
Poly(vinylsaccharide)s, 5. Synthesis and characterization of poly(vinylsaccharide)s of the amide type with disaccharides in the side chain
Authors: Klein Joachim , Begli Alireza Haji 
Published: April 2003

AbstractThe synthesis of well‐defined monovinylsaccharide monomers containing disaccharide units is described. Four different monomers, N‐disaccharide‐substituted acryl‐ and methacrylamides, were prepared and polymerized to the corresponding polymers by free‐radical polymerization in aqueous solution using different initiator systems. The influence of the structural differences of the disaccharide units on the solution properties was studied by viscosity and light scattering measurements. A comparison with known poly(vinylsaccharide)s with monosaccharides in the side chain is made.
Crystallization and thermal behaviour of blends of isotactic polypropylene and hydrogenated oligo(cyclopentadiene)
Authors: Martuscelli Ezio , Silvestre Clara , Canetti Maurizio , de Lalla Claudia , Bonfatti Anna , Seves Alberto 
Published: April 2003

AbstractThe crystallization and the thermal behaviour of thin films of isotactic polypropylene/hydrogenated oligo(cyclopentadiene) of low molecular weight (iPP/HOCP) are studied using optical microscopy and differential scanning calorimetry (DSC). The spherulite growth rate, the overall crystallization rate and the equilibrium melting temperature of iPP are decreased by the addition of HOCP to iPP. This leads to the hypothesis that iPP and HOCP form a miscible blend in the amorphous phase. This hypothesis is also supported by the detection of a single blend‐composition‐dependent glass transition temperature of each blend as determined by DSC.
Vinyl polymers containing amido and carboxyl groups as side substituents, 2. Thermodynamic and fourier‐transform infrared spectroscopic studies for the protonation of poly(N‐acryloylglycine) and poly(N‐acryloyl‐6‐aminocaproic acid)
Authors: Barbucci Rolando , Casolaro Mario , Magnani Agnese 
Published: April 2003

AbstractSynthetic poly(N‐acryloylglycine) (poly[1‐(carboxymethylcarbamoyl)ethylene], 1a) and poly‐(N‐acryloyl‐6‐aminocaproic acid) (poly{1‐[5‐(carboxypentyl)carbamoyl]ethylene}, 1b) were studied in aqueous solution by thermodynamic (potentiometry, calorimetry) and Fouriertransform infrared (FT‐IR) spectroscopic methods. The values of the basicity constant (log K), calculated with the Henderson‐Hasselbalch equation, relative to the protonation of the carboxylate group, decreases with increasing degree of protonation (a), while the enthalpy changes are “real” for both polymers. The increased length of the lateral aliphatic chain causes a decrease in the polyelectrolyte effect and a greater entropy change ΔS° of protonation due to liberation of water molecules. At low pH the FT‐IR spectra reveal a strong band at 1 628 cm−1 for polymer 1b which does not occur in the spectra of polymer 1a. At this pH the more compact macromolecular structure of 1b may favour interactions among the amido groups of several monomeric units.
Spontaneous copolymerization of 1‐(2‐hydroxyethyl)aziridine with β‐butyrolactone, 14
Authors: Rivas Bernabé L. , Canessa Guido S. , Pooley Sonia A. 
Published: April 2003

AbstractThe copolymerization of 1‐(2‐hydroxyethyl)aziridine (1) as nucleophilic monomer with β‐butyrolactone (2) as electrophilic monomer without initiator in solution at 45°C was investigated. Copolymers were characterized by IR and 1H NMR spectroscopy. By elemental analyses it could be shown that their compositions depend on the monomer ratio in the feed. From the copolymer composition and 1H NMR spectra it was possible to suggest four probable copolymer structures.
Analysis of fluorinated polymers: Several approaches by wide‐line nuclear magnetic resonance
Authors: Lutringer Gilbert , Meurer Bernard , Weill Gilbert 
Published: April 2003

AbstractTwo different ways of analyzing the composition of insoluble, partly hydrogenated, partly fluorinated copolymers by NMR are described. The first relies on a quantitative comparison of 1H and 19F free induction decays, as observed in the solid state, with those of reference samples. The second relies on medium resolution spectra which can be achieved, thanks to the large scale of 19F chemical shifts, on softening of the samples at high temperature. A special probe working up to 400°C was built for this purpose. The two methods are in good agreement in the case of vinylidene fluoride (VF2)/tetrafluoroethylene (VF4) copolymers, leading to a determination of the rectivity ratios; the special usefulness of the second method is illustrated by the identification of a third comonomer in VF2/VF4 terpolymers.
UV‐induced polymerization of maleimides in solution
Authors: Aida Hiroshi , Takase Iwao , Nozi Takashi 
Published: April 2003

AbstractMaleimide and N‐ethylmaleimide were irradiated in various solvents with a high pressure mercury lamp at 30°C. The polymerization of maleimides is promoted in the presence of hydrogen donating solvents such as tetrahydrofuran, 1,4‐dioxane, ethanol and basic solvents such as dimethylformamide, dimethyl acetamide, pyridine. ESR spectra suggest that a radical mechanism is responsible for the polymerization in the former solvents and an anionic mechanism in the latter solvents.
Graph theory of configurational and viscoelastic properties of polymers, 6. The square radii distribution functions of copolymer chains
Authors: Yang Yuliang 
Published: April 2003

AbstractThe general expression of square radii distribution functions for copolymer chains is derived in this paper. Particularly, the distribution function of the sum of two random orthogonal components, S, for cyclic AB alternate block copolymer chains is derived, and it can be reduced to the case of cyclic homopolymer chain when δ = mA/mB = 1.
Solution studies of chitosan 6‐O‐sulfate
Authors: Terbojevich Maria , Carraro Claudio , Cosani Alessandro , Focher Bonaventura , Naggi Anna Maria , Torri Giangiacomo 
Published: April 2003

AbstractCommercial chitosan, and highly deacetylated congeners thereof, can be selectively and extensively sulfated at the O‐6 level. Either a 2:1 mixture of sulfuric and chlorosulfonic acid (Method I) or a pyridine‐SO3 complex, following protection of the 2‐NH2 and 3‐OH groups with copper ions (Method II), can be used. The properties of sulfated chitosan with different degrees of acetylation are studied at pH conditions which promote a polyampholyte structure. Light scattering and intrinsic viscosity ([η]) measurements of chitosan 6‐O‐sulfate with a degree of acetylation of 20%, prepared by Method II, indicate the presence of molecular and structural heterogeneity, probably due to ordered structures in highly acetylated regions of the parent chitosan. This hypothesis is confirmed by the NMR analysis of the fragments obtained by depolymerization with nitrous acid. The heterogeneity is not observable in compounds obtained by Method I and in highly deacetylated chitosan 6‐O‐sulfate. The [η] increase of the polyampholyte on decreasing ionic strength can be explained in terms of a more rigid conformation stabilized by electrostatic interactions between the sulfate groups and the protonated amino groups on neighbouring residues.
Structural chemistry of polymerizable monomers, 4. Crystal and molecular structure of N‐methyldimethacrylamide and its effects on the initial stage of solid‐state cyclopolymerization
Authors: Higuchi Taiichi , Kodaira Toshiyuki 
Published: April 2003

AbstractThe structure of N‐methyldimethacrylamide was solved by direct methods and refined to a discrepancy index (reliability factor) R = 0,055 and weighted discrepancy index Rw = 0,068. C9H13NO2, relative molecular mass Mr = 167,21, monoclinic, C 2/c, a = 11,882 (1), b = 8,130 (1), c = 10,079 (1) Å, β = 94,21 (1)°, V = 971,0 (1) Å3, Dcal (Z = 4) = 1,143, D obs = 1,16 Mg · m−3, μ(MOKa) = 0,087 mm−1, mp 364 K, colourless needle crystal by sublimation. The molecule has a crystallographic C2 symmetry. The shortest spacing between vinyl carbon atoms in the molecule is 2,908 (2) Å (C(3)…C(3′)). Planes of two intramolecular vinyl groups assume a dihedral angle of 40,6 (4)°. It seems that the location of the vinyl carbon atoms allows an intramolecular closure in the initiation process, that is, tail‐to‐tail cyclization as observed. The subsequent solid‐state reaction probably proceeds through dimerization predominantly along a plane near the (101) plane in the lattice.
Protection and polymerization of functional monomers, 14. Anionic living polymerization of 4‐[N,N‐bis(trimethylsilyl)‐aminomethyl]styrene and 4‐{2‐[N,N‐bis(trimethylsilyl)amino]ethyl}styrene
Authors: Suzuki Ken , Hirao Akira , Nakahama Seiichi 
Published: April 2003

AbstractAnionic polymerization of 4‐[N,N‐bis(trimethylsilyl)aminomethyl]styrene (1) and 4‐{2‐[N,N‐bis(trimethylsilyl)amino]ethyl}styrene (2) were carried out at −78°C in tetrahydrofuran (THF)/pentane mixtures with butyllithium, oligo(α‐methylstyryl)lithium, oligo(α‐methylstyryl)potassium, and cumylpotassium. Polymerizations of 1 and 2 proceed without chain transfer and termination reactions to give stable “living polymers” when butyllithium or oligo(α‐methylstyryl)lithium are used as initiator. The resulting polymers have predictable molecular weights and narrow molecular weight distributions (ratio of weight‐ to number‐average molecular weights, M̄w/M̄n = 1,04–1,14). Under mild acidic conditions (pH 3–5 in THF/water), cleavage of the NSi bonds in the polymers is completely achieved to give well‐defined poly(4‐aminomethyl)styrene and poly[4‐(2‐aminoethyl)styrene]. The triblock copolymers of polystyrene‐block‐poly(1)‐block‐polystyrene and polystyrene‐block‐poly(2)‐block‐polystyrene are readily prepared in quantitative yields by sequential polymerization of styrene with living poly(1) or living poly(2).
The macrocycle ⇌ copolymer equilibrium in equilibrium copolymerization
Authors: Szymański Ryszard 
Published: April 2003

AbstractThe relationships describing the concentrations of macrocycles of any size and composition in copolymerization at equilibrium are derived. They allow, together with presented earlier equations, prediction of all features of copolymerization system at equilibrium, provided the corresponding equilibrium constants and initial conditions are known. In the Appendix the equation for the equilibrium constant of polymerization of a composed monomer is given.
Facilitation of quantitative estimation of the composition of starch‐iodine blue by specific precipitation
Authors: Pal Medini Kanta , Pal Prasun Kumar 
Published: April 2003

AbstractThe fact that potassium fluoride specifically and quantitatively precipitates the blue starch‐iodine complex from an excess of starch was used for the direct estimation of the composition of starch‐iodine blue for the first time. The result shows starch‐iodine blue to be extremely stable in nature and with a definite stoichiometry regarding starch, iodine and iodide, which is in good agreement with the result computed from X‐ray data obtained with cyclodextrin in place of starch. The mole ratio of starch monomeric units/iodine atoms was found to be 2,90 and the iodine/iodide ratio 4,28. The spectra of precipitated starch‐iodine blue dissolved in water are identical with those of the original starch‐iodine blue in the UV and visible regions. 1 M KF also quantitatively precipitates the adduct of starch‐iodine blue with the dye 1,9‐dimethyl‐methylene blue (DMMB), thus facilitating the estimation of starch‐iodine and the dye adduct.
Dielectric spectroscopy on liquid‐crystalline main chain polymers with crossing mesogens
Authors: Kresse Horst , Rötz Uwe , Lindau Jürgen , Kuschel Frank 
Published: April 2003

AbstractA newly synthesized series of liquid‐crystalline main chain polymers with crossing mesogens is investigated using dielectric spectroscopy. The crossing mesogenic units are endowed with hexyl as well as with CN‐wing groups. We examined the change of mobility of these crossing segments with increasing spacer length in the main chain, the relaxation behaviour at the phase transition nematic‐isotropic and the temperature dependence of the absorption intensity. The main results are: there is an alternation of the dielectric relaxation times with respect to the length of the spacer in such a way that the molecular mobility is raised in case of an odd number of methylene groups in the spacer. The steps in the relaxation frequencies at the clearing temperatures are obviously due to a change in the short‐range order caused by the formation of the nematic structure. Owing to a strong dipol‐dipol interaction between neighbouring segments, a decrease of the absorption intensity with decreasing temperature was observed. Furthermore, apart from the low‐frequency absorption a high‐frequency relaxation process could be monitored.
Zum copolymerisationsverhalten des 1,3,5‐triacryloylhexahydro‐1,3,5‐triazins
Authors: Kerber Robert , Pöllmann Klaus , Samarian Heidi , Sluka Peter 
Published: April 2003

AbstractRadical homo‐ and copolymerizations of 1,3,5‐triacryloylhexahydro‐1,3,5‐triazine (1) with methyl methacrylate (MMA), styrene (S) and a‐methylstyrene (MS) were investigated at 60°C in DMF, varying the total concentrations of the monomers as well as the contents of 1. The monomer reactivity ratios were evaluated using the copolymer composition obtained by elemental analysis, according to the Kelen‐Tüdős method applying the equation of Gibbs. The resulting values for the system 1/MMA, based on the concentration of the CC double bonds, are: r1 = 0,50, rMMA = 1,76 and for the system 1/S: r1 = 0,17, rS = 1,03. Furthermore, the double bond content of the copolymers was determined by thiophenol addition showing a significant variation with the overall monomer concentration in the reaction mixtures concerned. This fact has to be considered when calculating the real monomer reactivity ratios yielding in the case of the system 1/S the values r1 = 0,43 and rS = 0,41.