bluuebunny/crossref_metadata_2025_split huggingface dataset:
Transfer by weak acids in the slow‐initiation‐no‐termination (SINT) polymerization of butyl cyanoacrylate
Authors: Pepper David Charles 
Published: April 2003

AbstractThe theory of slow‐initiation‐no‐termination polymerization has been extended to take account of transfer by added or adventitious transfer agents (T), giving equations relating the number‐average molecular weight (M̄n) to the ratios of concentrations of transfer agent to monomer ([T]0/[M]0) and of transfer to propagation rate constants (ktr/kp). The equations are shown to give a fair description of the M̄n values found in the polymerization of butyl cyanoacrylate by pyridine and by tetrabutylammonium acetate in presence of known concentrations of cyanoacetic, chloroacetic and acetic acids. Approximate values are yielded for the rate constant ratios, viz. 102(ktr/kp) ≈ 15,5 and 0,3, respectively (in tetrahydrofuran at 20°C). Conversely, the theory is shown to explain variations in M̄n values found in polymerizations of five different samples of this monomer, permitting characterization of the unknown concentrations of transfer‐causing impurity.
On the kinetics and mechanism of thermal degradation of poly(p‐methylstyrene)
Authors: Schröder Ulrich K. O. , Ederer Hanns J. , Ebert Klaus H. 
Published: April 2003

AbstractThe thermal behavior of polydisperse poly(p‐methylstyrene) (PPMS) samples with M̄w's of 99200 and 356000 g/mol was investigated under oxygen‐free conditions at temperatures between 220 and 345°C. The reaction products were analysed by gel permeation chromatography (GPC), gas chromatography (GC) and swelling measurements. In the initial stage of the reaction crosslinking occurs; at higher temperatures the gel decomposes to polymers with a low degree of polymerization and to volatile products with molecular weights in the range up to trimers. A radical chain mechanism is proposed for degradation which explains the experimental results. On this basis a model is evaluated for gel formation, which is discussed in detail. The results of the present investigation are compared with the thermal degradation of polystyrene (PS) which is chemically similar but does not crosslink.
Hydroxytelechelic polybutadiene, 10. Molecular weight and functionality distribution of a radically obtained hydroxytelechelic polybutadiene studied by GPC and 1H NMR
Authors: Deschères Isabelle , Païssé Olivier , Colonna‐Ceccaldi Jean‐Noël , Pham Quang‐Tho 
Published: April 2003

AbstractHydroxytelechelic polybutadiene (HTPB) Arco‐R45M® obtained by free‐radical‐initiated polymerization of butadiene was fractionated by preparative gel permeation chromatography (GPC) using styragel and silicagel as column material. The fractions separated were extensively studied by vapour pressure osmometry (VPO), GPC, and 1H NMR. Commercially available non‐hydroxylated polystyrene and polybutadiene standards cannot be utilized for the proper direct determination of the molecular weight of HTPB by means of GPC. Both high and low hydroxyl functionalities were found for high‐ and low‐molecular‐weight HTPB. The analytical results are discussed in terms of the polymerization mechanism.
Melt rheology of compatible binary blends: Poly(ethylene oxide)‐poly(methyl methacrylate) and poly(ethylene oxide)‐poly(vinyl acetate)
Authors: Martuscelli Ezio , Vicini Loredana , Seves Alberto 
Published: April 2003

AbstractA study of the rheological behaviour of poly(ethylene oxide)‐poly(methyl methacrylate) and poly(ethylene oxide)‐poly(vinyl acetate) compatible blends in the molten state is reported. Zero shear viscosity η0 and the activation energy for the viscous flow ΔE* were obtained as function of both composition and molar mass of the components. Positive and negative deviations from the additivity rule were observed both in the case of log η0 and ΔE*.
Single crystal structure of a polymerization active Nd‐Al bimetallic complex
Authors: Shan Chengji , Lin Yonghua , Ouyang Jun , Fan Yuguo , Yang Guangdi 
Published: April 2003

AbstractA polynuclear Nd‐Al bimetallic complex in single crystalline form, which is active for diene polymerization, was isolated and its detailed structure was determined by X‐ray diffraction technique. The results indicate that the crystal is triclinic, space group P1; the lattice parameters are: a = 15,195(6), b = 15,263 (5), c = 13,749 (4) Å; α = 90,01 (2), β = 95,12 (3), γ = 82,65 (3)°; V = 3149,5 Å3; Z = 1. The coordination number of the Nd atom is seven and the configuration is monocap‐prism. Nd atoms can be divided into three groups according to their coordination environment.
Stress‐induced orientation in lightly crosslinked liquid‐crystalline side‐group polymers
Authors: Zentel Rudolf , Benalia Mokhtar 
Published: April 2003

AbstractX‐ray measurements of stretched crosslinked liquid‐crystalline side group polymers show that two types of orientation of the mesogenic groups relative to the polymer chains (parallel or perpendicular) are possible, depending on the structure of the polymer chain. For two liquid‐crystalline polymethacrylates with long spacer groups (6 methylene units) the mesogenic groups orient preferably perpendicularly to the polymer chains (axis of strain). For three liquid‐crystalline polyacrylates with long or short spacer groups (6 or 2 methylene units), the mesogenic groups orient preferably parallel to the polymer chains (axis of strain). The reason for this difference is not yet clear. These results are compared with earlier results of melt‐drawn fibres of uncrosslinked polymers.
Emulsion polymerization of butyl methacrylate initiated by 2,2′‐azoisobutyronitrile, 3. On the applicability of the modified Smith‐Ewart model
Authors: Capek Ignác , Bartoň Jaroslav , Kárpátyová Angela 
Published: April 2003

AbstractThe applicability of the modified Smith‐Ewart model to the butyl methacrylate emulsion polymerization in interval II, initiated by both 2,2′‐azoisobutyronitrile (AIBN) and ammonium persulfate at 60°C, was tested. The equilibrium monomer concentration in the latex particles in interval II was found to be constant and independent of the emulsifier concentration and the initiator type used. The rate of initiation increases with increasing emulsifier concentration for the polymerizations initiated with a water‐soluble initiator. In the systems with the oil‐soluble initiator, the rate of initiation is independent of the emulsifier concentration. The rate of polymerization increase with increasing emulsifier concentration for both initiator systems. In the system with the oil‐soluble initiator lower values of the polymerization rate and higher values of the viscosity‐average molecular masses of the polymer were observed. The number of particles, the radical concentration within polymer particles and the calculated rate of polymerization increase, while the mean particle radius decreases with increasing concentration of the emulsifier for both systems. The average‐number of radicals per particle and the ratio of the rate constants for propagation and termination was found to be independent of the emulsifier concentration and the initiator type. A good agreement was observed between the estimated and observed particle radii for both initiator systems. The Smith‐Ewart model was found to be applicable for the emulsion polymerization of butyl methacrylate initiated by both ammonium persulfate and AIBN.
Synthesis of monoazacrown ether containing styrene derivatives and monoazacrown ether end‐capped 3‐(or 4‐)vinyl substituted styrene oligomers and polymers
Authors: Akashi Ryojiro , Nagasaki Yukio , Tsuruta Teiji 
Published: April 2003

AbstractMonoazacrown ether containing styrene derivatives and monoazacrown ether end‐capped 3‐(or 4‐)vinyl substituted styrene oligomers and polymers were synthesized using 1,4,7,10,13‐pentaoxa‐16‐azacyclooctadecane (1a). N‐Lithio‐1,4,7,10,13‐pentaoxa‐16‐azacyclooctadecane (1b) reacts with styrene to form a 1:1 adduct, N‐phenethyl‐1,4,7,10,13‐pentaoxa‐16‐azacyclooctadecane (4). The reactivity of 1b toward styrene, however, is lower than that of other lithium dialkylamides such a lithium diethylamide. 1b reacts also with divinylbenzene to form a 1:1 adduct, N‐(4‐vinylphenethyl)‐1,4,7,10,13‐pentaoxa‐16‐azacyclooctadecane (7), in non‐polar media. The reactivity of 1b toward divinylbenzene is much higher than toward styrene. The yield of the 1:1 adduct 7 was found to attain more than 70% in cyclohexane. In polar media, however, 1b induced a prompt polymerization of divinylbenzene to form a soluble polymer, each molecule of which was found to have one crown ether unit at the end of the polymer chain and a pendant vinyl group on each monomeric unit.
Zerlegung von hemicellulosereichem biologischem material mit wasser in einem strömungsreaktor
Authors: Köll Peter , Lenhardt Herbert 
Published: April 2003

AbstractBiological materials, rich in hemicelluloses (birch and pine wood, wheat straw and rice hulls) were disintegrated batchwise in a flow reactor with pure water at elevated temperatures and pressures. The resulting extractives and residual fibre compounds were characterized. Because of rapid removal of carbohydrate based extractives from the hot reaction zone, the degradation of pentosans and hexosans to furfural and hydroxymethylfurfural could be limited to only a small amount. Contrary to normal prehydrolysis conditions employing a sealed batch reactor, temperatures of 190 to 210°C and residence times of goods of 60 min are the optimum. Thus, hemicelluloses are dissolved and isolated with up to more than 90% yield. At temperatures above 225°C severe destruction of hemicelluloses and solvolysis of cellulose starts. Depending on disintegration temperatures, pentosan average molecular weights (M̄w) vary in case of birch wood between 3800 at 150°C and 900 at 225°C. The content of monomers rises with temperature and reaches a maximum of 45% at 225°C. DPw of residual cellulose is also temperature dependent and varies in case of birch wood and wheat straw between 1500 and 450. Lignin, which is mostly not dissolved, can be removed almost quantitatively by further treatment of the residue with ethanol/water at 250°C, thus allowing the isolation of relatively pure cellulose.
Preparation of poly(N‐methylmethacrylamide) microspheres containing peroxy ester groups and their use in graft copolymerization
Authors: Sato Tsuneyuki , Matsumoto Yoshitada , Tanaka Hitoshi , Ota Tadatoshi 
Published: April 2003

AbstractPoly(N‐methylmethacrylamide) [poly(1)] microspheres, carrying peroxy ester groups, were prepared by radical copolymerization of 1 with a small amount of di‐tert‐butyl perfumarate (2) in benzene. Thermal and photo‐induced polymerizations of vinyl monomers with the microspheres were carried out, to produce graft copolymers. Ethanol as additive was found to accelerate the polymerization of benzyl methacrylate (3) at 80°C although the accelerating effect levels off at higher concentrations of ethanol. The grafting efficiency was not high (up to 16,5%) and exhibited a maximum on varying the ethanol concentration. On the other hand, in the photo‐induced polymerization the conversion of 3 increased with increasing ethanol concentration. The grafting efficiency similarly showed a maximum on varying the ethanol concentration. The effects of reaction variables on the thermal and photo‐induced graft copolymerizations of 3 onto the microspheres in the presence of a definite amount of ethanol were examined in the light of the conversion of 3, the grafting efficiency and the percentage of grafting. Long‐lived propagating poly(1) radicals (6) were observed by ESR during heating at 70°C or UV‐irradiation at 30°C of the microspheres in a toluene/ethanol mixture. Thermolysis or photolysis of the microspheres in the presence of 3 yielded a stable propagating poly(3) radical (7). Similarly, this microsphere method was applied to the preparation of long‐lived propagating polymer radicals of some other vinyl monomers.
New thermo‐crosslinking reactions of copolymers of phenyl methacrylates by use of polyfunctional epoxy compounds
Authors: Nishikubo Tadatomi , Saita Seiji 
Published: April 2003

AbstractSuccessful new thermo‐crosslinking reactions of copolymers of various phenyl methacrylates by use of polyfunctional epoxy compounds were carried out in the film state at 100–150°C in presence of quaternary ammonium salts, quaternary phosphonium salts, tert‐amines, or the crown ether dicyclohexyl‐18‐crown‐6/potassium salt systems as a catalyst. Addition reactions of 4‐nitrophenyl, 4‐chlorophenyl or phenyl ester groups in the copolymers with ethylene glycol diglycidyl ether (EGGE) result in gel compounds without other side reactions. The rate of gel production of the copolymer having electron‐attracting groups such as the 4‐nitro group on phenoxide is faster than that of the other copolymers. It was also found that the rate of gel production of the copolymer is affected by the amount of phenyl methacrylate component in the copolymer, the glass transition temperature (Tg) of the copolymer, the structure of polyfunctional epoxy compounds as a crosslinking reagent, the length of alkyl chain in the catalyst, and the kind of counter anion of the catalysts, respectively.
Molecular characterization of gelatin by light scattering
Authors: Stejskal Jaroslav , Straková Dagmar , Kratochvíl Pavel 
Published: April 2003

AbstractIn aqueous KSCN solutions the salt is preferentially desorbed from the domain of gelatin molecules, similarly to synthetic polyelectrolytes. Light‐scattering measurements in gelatin solutions in 0,5 M KSCN and in a single solvent (formamide) show that both solvents are suited for the molecular characterization of gelatin at room temperature. Neglecting the effect of selective sorption in salt solutions does not cause any considerable error in the molar mass determination of gelatin.
NMR study of aggregation of heterotactic‐like poly(methyl methacrylate) in solution
Authors: Spěváček Jiří , Fernandez‐Pierola Inés 
Published: April 2003

AbstractThe aggregation of heterotactic‐like poly(methyl methacrylate) (PMMA) in some solutions was proved by NMR spectroscopy. It was found that the fraction of aggregated units depends on solvent, solution concentration and temperature; the aggregates are completely decomposed at 45°C. Aggregation occurs by intermolecular interactions of m‐diads with rrr‐tetrads, i. e. by interactions of the stereocomplex type. The formation of a stable aggregated structure is probably a consequence of the microstructure of the heterotactic‐like PMMA chain, with relatively long sequences of regularly repeating mrrr pentads or mrrr hexads. The aggregation in mixtures of heterotactic‐like PMMA solutions with isotactic or syndiotactic PMMA solutions was also studied.
Silicium‐29 kern‐relaxations‐messungen an kieselsäurederivaten
Authors: Marsmann Heinrich C. , Meyer Ehler 
Published: April 2003

AbstractDerivatives of silicic acid of the type Si6O5R18 and Si8O7R18 (R = Cl, OCH3, and OC2H5) as well as bicyclic Si8O9(OC2H5)14 were isolated and characterized by 29Si NMR. The spin‐lattice‐relaxation and the nuclear Overhauser enhancement factor of the esters were determined between 273 and 343 K. The temperature dependency of the dipolar contribution to the longitudinal relaxation time gave an energy of activation for the segmental motion of the siloxane skeleton of about 10 kJ/mol which is independent of the kind of building unit.
Resonance Raman spectroscopic studies on dehydrochlorinated stretched poly(vinyl chloride)
Authors: Bowley Heather J. , Gerrard Donald L. , Maddams William F. 
Published: April 2003

AbstractResonance Raman spectroscopy has been used to assess the effect of streching on the formation of conjugated polyenes during the thermal dehydrochlorination of poly(vinyl chloride). Two samples, a commerical mass polymer and a material prepared at −30°C, have been examined, unplasticised and plasticised, at different draw ratios. Stretching prior to dehydrochlorination leads to an increase in the length of the polyene sequences, the effect being more marked with the low temperature polymer and with increasing draw ratio. Stretching after dehydrochlorination has no significant effect on the polyene distribution. These observations are consistent with the occurrence of chain orientation and alignment during stretching; this reduces the incidence of cross‐linking between polyene sequences in adjacent chains and leads to an increase in the average sequence length.
Acid and base functionalization of ethylene‐propylene rubbers, 2. Influence of type and content of functional groups on the mechanical and thermal behaviour of elastomeric network
Authors: Greco Pietro , Laurienzo Paola , Maglio Giovanni , Malinconico Mario , Martuscelli Ezio 
Published: April 2003

AbstractThermal and mechanical properties of various functionalized ethylene‐propylene rubbers (EPR) were evaluated. The samples studied varied both in the type of functional groups and in the grafting degree. Grafted molecules included succinic anhydride, 2‐(dimethylamino)ethylsuccinimide and 2‐(dimethylamino)ethyl methacrylate. The insertion of these groups was found to influence deeply the elastic response of rubbers, leading to the formation of network whose properties were dependent upon the density of polar crosslinks introduced. On the other hand, the thermal properties were less influenced, i.e. the glass transition temperature Tg increased only slightly with increasing content of functional groups.
Photo‐oxydation des polyéther‐bloc‐polyamides, 2. Influence de la composition des polymères multiséquencés
Authors: Gauvin Pascal , Lemaire Jacques , Sallet Daniel 
Published: April 2003

AbstractAnalytical and kinetical aspects of the photooxidation in the solid state of two polyether‐block‐polyamides 1c and 1d are described. The block copolymers studied contain different polyether sequences at different percentages. In copolymer 1d as well as in copolymers 1a and 1b, previously studied, the photooxidation concerns mainly the ether groups. High maximal concentrations of hydroperoxy groups, CH(OOH)OCH2, are observed (0,12 mol.kg−1). These hydroperoxides are converted into hemi‐acetals, CH(OH)OCH2, saturated esters and formate through photolysis or thermolysis above 60°C. The hemi‐acetal groups are thermo‐unstable too and decompose into alcohol and aldehyde groups. The photooxidation of copolymer 1c presents different features. At long wavelengths, low stationary concentration of hydroperoxy groups are observed (0,02 mol.kg−1). Hydroperoxidation of the polyamide 6 sequences is revealed by the formation of imide groups. Hydroperoxidation of the poly(propylene glycol) sequences are surprisingly located on the ether methylene groups. Excitation of polyamide 6 sequences at short wavelength (254 nm) induces the formation of crotonized aldehyde groups.
Photo‐oxydation et photolyse de copolymères d'éthylène et d'acétate de vinyle à courte et grandes longueurs d'onde
Authors: Glikman Jean‐François , Arnaud René , Lemaire Jacques , Seinera Henri 
Published: April 2003

AbstractAnalytical and kinetic aspects of the photooxidation and photolysis in the solid state of various ethylene‐vinyl acetate (EVA) copolymers (0 < VA (in mol‐%) < 26) are described. At long wavelengths (λ > 300 nm), the photooxidation is independent of the vinyl acetate content. The acetate groups, which are not preferential sites for the photo‐induced hydroperoxidation, are photoconverted into chain ketones similar to those formed in the photooxidation of low density polyethylene (LDPE). As the content of monomeric units of vinyl acetate increases, associations between alcohols formed and the acetate groups are observed, based on the appearance of the 3530 cm−1 absorption band. The rate of the formation of vinyl‐type insaturations is a decreasing function of the content of monomeric units of vinyl acetate. At short wavelength (λ = 254 nm) direct photolysis of the acetate groups is observed through the formation of alcohols and ketones again similar to those found in LDPE photooxidation. The rate of the EVA photolysis varies linearly with the vinyl acetate content. Oxygen reacts with the primary radicals formed at 254 nm. Alcohols and ketones are formed faster than through photolysis, although no stoichiometry change is observed.
Functional polymers and sequential copolymers by phase transfer catalysis, 27. Synthesis of aromatic‐aliphatic polyformals by polyetherification of 1,4‐bis(chloromethoxy)butane with 4,4′‐isopropylidenediphenol
Authors: Shaffer Timothy D. , Antolin Katherine , Percec Virgil 
Published: April 2003

AbstractThe first examples of aromatic‐aliphatic polyformals were synthesized from 4,4′‐isopropylidenediphenol (2) and 1,4‐bis(chloromethoxy)butane (1) by a two‐phase (aqueous NaOH/toluene), phase transfer catalyzed (PTC) polyetherification. The influence of the reaction conditions upon the polymerization was studied by varying the phase transfer catalyst concentration, NaOH concentration and nucleophile to electrophile ratio. Changes in these parameters and their effects upon the microstructure of these polymers were also examined by 1H NMR (200 MHz) spectroscopy. The reactivity of 1 has permitted, according to our knowledge, the first examples of interfacial polyetherification. Further, this reactivity has also permitted the homopolymerization of 1 through its hydrolysis byproducts under PTC conditions.
Synthèse de composées photoréticulables, 7. Télomères des acides acrylique et méthacrylique gréffés par méthacrylate d'époxy‐2,3 propyle
Authors: Bauduin Gérard , Boutevin Bernard , Mistral Jean‐Pierre , Parisi Jean‐Pierre , Piétrasanta Yves 
Published: April 2003

AbstractTelomers were prepared from acrylic or methacrylic acid and CCl3Br, C12H25SH, C18H37SH or C8F17C2H4SH by initiation with 2,2'‐azoisobutyronitrile. The transfer constant of CCl3Br and the thiols, which are about 0,03 and 0,5, respectively, were determined. These telomers were used as supports of photopolymerizable functions, which were introduced by grafting of 2,3‐epoxypropyl methacrylate, catalysed with dodecyldimethylamine. The reactions were followed by 1H NMR, elemental analyses, tonometrie, and especially by GPC and titration of the acid functions. The grafting telomers, holding many acrylic functions which react upon UV and electron irradiation, give photoreticulated varnish coatings with very interesting properties.
Effect of a grafted chain as spacer of an insoluble polymeric ligand on the adsorption behaviour and the influence on the catalytic activity of the Cu(II) complex
Authors: Arai Kenichiro , Ogiwara Yoshitaka 
Published: April 2003

AbstractIn order to investigate the effect of a grafted chain as spacer of an insoluble polymeric ligand on the adsorption behavior of metal ions, acrylonitrile was copolymerized with cross‐linked polystyrene beads, and the nitrile groups in the grafted polyacrylonitrile chain were reduced to amino groups which were substituted by reaction with chloroacetic acid. It was found that the conversion of the nitrile groups into amino groups decreases with increasing percentage of grafting. The adsorption behavior of Cu(II) by the polymeric ligand was examined and found to be improved by the introduction of the grafted chain as spacer. The catalytic activity of the complex of the polymeric ligand with Cu(II) in the decomposition of hydrogen peroxide was also examined and found to increase with increasing percentage of grafting.