bluuebunny/crossref_metadata_2025_split huggingface dataset:
Kinetik und mechanismus der kationischen polymerisation von trioxan: Ein katalysierter kristallwachstumsprozeß
Authors: Wegner Gerhard , Rodriguez‐Baeza Mario , Lücke Andreas , Lieser Günter 
Published: April 2003

AbstractThe kinetics of the cationic polymerization of trioxane initiated by perchloric acid is analyzed as a simultaneous polymerization and crystallization process. The details of the crystal growth such as nucleation, distribution of crystal sizes, development of growth spirals etc. have been investigated by electron and light microscopic techniques. The mechanism of polymerization can be understood as a catalyzed crystal growth. A well defined population of crystals is formed during a nucleation event at the start of the polymerization. An adsorption equilibrium with regard to the catalyst is then established in the presence of the rather large surface area of the growing polymer crystals. Assuming a Langmuir‐type adsorption behaviour, the observed growth features (growth spirals) can be quantitatively interpreted on the basis of the BCF‐theory of crystal growth. The current concepts on the molecular mechanism of cationic polymerization of cyclic formals have been modified such as to take into account that each chemical step of the polymerization is a building step of the crystal too.
A mesophasic polymer: Poly(oxydodecandioyloxy‐1,4‐phenylene‐2‐methylvinylene‐1,4‐phenylene)
Authors: Roviello Antonio , Sirigu Augusto 
Published: April 2003

AbstractPoly(oxydodecandioyloxy‐1,4‐phenylene‐2‐methylvinylene‐1,4‐phenylene) (1) was synthesized and partially characterized by differential scanning calorimetry and X‐ray diffraction methods. The polymer shows a thermotropic liquid crystalline behavior. The X‐ray diffraction spectrum of the anisotropic liquid is coherent with a nematic phase. Solid state polymorphism is also observed.
Application of the spin trapping technique to radical polymerization, 19. Reactions of the tert‐butoxyl radical with some N‐alkyl‐substituted acryl‐ and methacrylamides
Authors: Otsu Takayuki , Tanaka Hitoshi , Sato Tsuneyuki , Quach Loc 
Published: April 2003

AbstractThe reactions of tert‐butoxyl radical with some N‐alkyl‐substituted acryl‐ and methacrylamides were investigated at room temperature in benzene by means of the spin trapping technique. 2‐Methyl‐2‐nitrosopropane (BNO) was used as a spin trapping reagent. The tert‐butoxyl radical was found to undergo both hydrogen‐abstraction from N‐methyl groups and double bond addition in its reactions with N‐methylacrylamide (NMAm) and with N,N‐dimethylacrylamide. Contrary to this, the benzoylthio radical reacted exclusively with the double bond of NMAm. In the reaction of the tert‐butoxyl radical with N‐methylmethacrylamide (NMMAm), only double bond addition was observed. However, when the tert‐butoxyl radical reacted with N,N‐dimethylmethacrylamide (NDMMAm), it mainly attacked the N‐methyl group of NDMMAm. The tert‐butyl radical abstracted a hydrogen atom from the α‐methyl group of NMMAm and NDMMAm, keeping their N‐methyl group unreacted. Furthermore, in the reaction of the tert‐butoxyl radical with N‐propyldimethacryloylamine (NPDMAm) in the presence of BNO, both a methylene radical which was derived from intramolecular cyclopropagation giving a five‐membered ring and a radical derived from the addition to the double bond of NPDMAm were trapped as their aminyl radicals.
Metathetische spaltung von butadien‐styrol‐copolymeren; abbauprodukte
Authors: Thorn‐Csányi Emma , Abendroth Henning , Perner Helmut 
Published: April 2003

AbstractThe metathetical degradation of styrene(S)‐butadiene(B) copolymers gives a wide spectrum of fragments which are characteristic for the microstructure. We also determined degradation of products of S‐1, 2B‐ and 1,2B‐S‐sequences.
Polymere phthalocyanine und ihre vorstufen, 1. Reaktive oktafunktionelle phthalocyanine aus 1,2,4,5‐tetracyanbenzol
Authors: Wöhrle Dieter , Meyer Gunter , Wahl Bernd 
Published: April 2003

Abstract1,2,4,5‐Tetracyanobenzene reacts under mild conditions with anionic reagents not to polymer but to low molecular weight, high substituted phthalocyanines: 2,3,9,10,16,17,23,24‐octacyanophthalocyanine (3a) and tetrakis(1‐imino‐3‐propoxyisoindolo)porphyrazine (3b). 3a is saponified to the octacarboxyphthalocyanine 3c and converted with hydrazine to tetrakis(1,4‐diaminophthalazino)porphyrazine (3d). Low molecular metal chelates are synthesized starting from 3a and 3c. IR‐ and UV/VIS‐spectra are discussed.
Syntheses of N‐(nitrophenyl)amine substituted diacetylene alcohol monomers
Authors: Horner Charles J. , Garito Anthony F. 
Published: April 2003

AbstractA procedure for the preparation of a novel class of nitroaniline substituted diacetylene alcohols is reported. The polymerization behavior of one member of this class, 6‐(4‐nitro‐2‐trifluoromethylanilino)‐2,4‐hexadiyn‐1‐ol (11a), has been studied using X‐ray irradiation.
Polymers containing enzymatically degradable bonds, 1. Chymotrypsin catalyzed hydrolysis of p‐nitroanilides of phenylalanine and tyrosine attached to side‐chains of copolymers of N‐(2‐hydroxypropyl)methacrylamide
Authors: Kopeček Jindřich , Rejmanová Pavla , Chytrý Vladimír 
Published: April 2003

AbstractA series of copolymers of N‐(2‐hydroxypropyl)methacrylamide were prepared, which contained side chains of the general formula ‐Gly‐X‐Y‐NAp, where Gly ¨ glycine; X ¨ glycine, alanine, β‐alanine, valine, leucine, isoleucine, phenylalanine; Y ¨ phenylalanine or tyrosine; NAp ¨ p‐nitroanilide, the latter modelling biologically active compounds. The rates of chymotrypsin‐catalyzed hydrolysis of p‐nitroanilide groups at pH = 8,0 and 25°C were determined over a range of substrate concentrations to derive values for kcat and KM. The results allowed us to determine the influence of the structure of side chains on the rate of cleavage of Y‐NAp. The increase in the susceptibility to chymotrypsin attack with an increasing spacing of the Y‐NAp residue from the backbone of the polymer chains is demonstrated by comparing the kinetic data of copolymers containing ‐Gly‐Gly‐Phe‐Phe‐NAp, ‐Gly‐Gly‐Phe‐NAp and ‐Gly‐Phe‐NAp side chains. Results obtained with α‐chymotrypsin were compared with the cleavage of the above polymer substrates with chymotrypsin covalently bound to a copolymer of N‐(2‐hydroxypropyl)methacrylamide.
The counterion effect on the steric course of the cationic polymerization of tert‐butyl vinyl ether
Authors: Kunitake Toyoki , Takarabe Kunihide 
Published: April 2003

AbstractThe cationic polymerization of tert‐butyl vinyl ether was carried out at −76°C with a variety of triphenylmethyl salts as initiator. The microtacticity of the polymer was determined by 1H NMR spectroscopy after conversion to poly(vinyl alcohol). The fraction of isotactic units, Pm, increased with decreasing polarity of the polymerization medium, in consistence with the published data for metal halide initiators. The Pm value decreased gradually from 0,85 to 0,72–0,75 in 7 : 3 (v/v) CH2Cl2‐toluene by increasing the counteranion radius from 2,4 Å (BF−4) to ca. 4 Å (AlCl−4). A further increase in the counteranion size, however, did not notably influence the steric structure of the polymer. These structure variations are discussed in terms of the steric course of cationic propagation. In the case of pentacoordinate counteranions (SnCl−5 and ZrCl−5), the steric structure depended also on the counteranion concentration, as already reported for other monomers.
Investigation of the copolymerization of mono‐ and bifunctional monomers of methacrylic esters
Authors: Krakovyak Marc , Ananieva Tatiana , Anufrieva Elisaveta , Gotlib Yulii , Nekrasova Tatiana , Skorokhodov Serguei 
Published: April 2003

AbstractThe relationships of free‐radical copolymerization of mono‐ and bifunctional monomers were investigated taking as an example a model system of monomers: methyl methacrylate (MMA) and 9,10‐dianthrylenedimethyl dimethacrylate (1). The copolymerization was carried out in toluene at 60°C at a 525: 1 mole ratio of MMA to 1, with AIBN as initiator. Chemical and luminescent methods for the quantitative determination of bridge bonds containing anthracene moieties in the polymer system and the method of their selective cleavage were developed. Experimental dependences of the concentration of monomers and single and double bonded monomeric units of 1 in the copolymers on the copolymerization time were established. It was found that during the copolymerization the activity of each monomer double bond and that of the pendent double bonds in the monomeric units of 1 in the copolymer are similar. It was shown that over a specific range of changes in the content of bridge bonds (the position of which depends on the length of the chains being crosslinked) the values of the intrinsic viscosity of the copolymer solutions increase cooperatively and gel fraction is formed subsequently.
The influence of molecular interaction on polymerization, 5. Copolymerization of benzyl methacrylate with maleic anhydride
Authors: Boudevska Hrissanta , Platchkova Svetla 
Published: April 2003

AbstractCopolymerization of benzyl methacrylate (BMA) with maleic anhydride (MA), initiated by 2,2′‐azoisobutyronitrile at 70°C in chloroform or acetonitrile, were investigated. The complex formation between the two monomers in chloroform was studied by 1H NMR spectroscopy. The stability constant of the complex was found to be 0,25 l.mol−1. The following copolymerization reactivity ratios were found: in chloroform: rBMA = 0,188 ± 0,035 and rMA = 0,003 ± 0,005, in acetonitrile: rBMA = 0,116 ± 0,093 and rMA = 0,231 ± 0,027. By 1H NMR investigations it could be shown that the results correlate with the changes of the reactivity ratios depending on the solvent used.
Interaction of human serum proteins with synthetic polymers in homogeneous systems
Authors: Ohno Hiroyuki , Abe Koji , Tsuchida Eishun 
Published: April 2003

AbstractHuman serum albumin and γ‐globulin form complexes with various synthetic polymers through some secondary binding forces. This complex formation between serum proteins and ionic or nonionic polymers is discussed. Polycations and polyanions interact with serum proteins through electrostatic interaction force mainly. There is strong pH dependence on the interaction, because these proteins show amphoteric properties. When ionic polymers interact strongly with proteins, the conformations of both proteins are changed by the complexation. In case of complexation with nonionic polymers, γ‐globulin tends to be precipitated at higher pH than 6. In addition, there exists suitable hydrophobicity of nonionic polymers for complex formation with high efficiency. On the contrary, albumin is easily precipitated by nonionic polymers in the lower pH region. There are little conformational changes of proteins through complexation with nonionic polymers except for the case of poly(N‐vinyl‐2‐pyrrolidone) treatment. Selective complexation is achieved by some nonionic polymers having less hydrophobicity such as poly(ethylene oxide). High efficiency of selective complexation is observed by control of the pH and the hydrophobic properties of the noionic polymers.
Time resolved small angle scattering during isothermal crystallization of unoriented poly(ethylene terephthalate) using synchrotron radiation
Authors: Elsner G. , Koch M. H. J. , Bordas J. , Zachmann H. G. 
Published: April 2003

AbstractThe time course of the small angle scattering pattern of amorphous poly(ethylene terephthalate), (PET), was measured during isothermal crystallization using synchrotron radiation. The samples were heated to temperatures between 117 and 145°C in an oven placed in the path of the X‐ray beam. The scattering curves were measured within 10 s at intervals of 1 s so as to follow the kinetics of the process continuously. It appears that the distance between the centres of mass of the crystallites decreases with increasing crystallization time as in oriented PET. The integrated small angle scattering follows approximately the same time course as the increase in the degree of crystallinity during an isothermal crystallization yielding Avrami exponents between 5 and 7. Guinier plots of the low angle region show that the scattering can be attributed to rod‐like particles.
Thermal decomposition of flame retardant acrylonitrile polymers, 2. Effect of red phosphorus
Authors: Ballistreri A. , Foti S. , Montaudo G. , Scamporrino E. , Arnesano A. , Calgari S. 
Published: April 2003

AbstractElemental red phosphorus was found to be an efficient flame retardant for poly(acrylonitrile) homopolymer (PAN) and, to a lesser extent, also for a modified acrylic resin containing 36 wt.‐% of vinylidene chloride (VC2) as comonomer. The data collected show that condensedphase and gas‐phase mechanisms are both responsible for the flame inhibition effect of red phosphorus on PAN. On the contrary, a gas‐phase mechanism seems to be responsible for the flame inhibition effect of red phosphorus on the AN‐VC2 copolymer. Flash‐pyrolysis GC data, with pyrolysis products MS identification, are reported for both polymers studied.
The anionic polymerization of 2‐pyrrolidone in bulk and in suspension
Authors: Costa Giovanna , Nencioni Macro , Russo Saverio , Semeghini Gian Luigi 
Published: April 2003

AbstractA study on the anionic polymerization of 2‐pyrrolidone in bulk and suspension under isothermal conditions is described. After a discussion about the disadvantages of the bulk process carried out by using N‐potassium‐2‐pyrrolidone as initiator and N‐acetyl‐ε‐caprolactam as activator, a possible alternative way is proposed on the basis of the suspension polymerization initiated by N‐potassium‐2‐pyrrolidone and activated by silicon tetrachloride. The ultraviolet absorption spectra of the polymer samples obtained by the above methods reveal that undesiderable side reactions leading to degradation of the keto amide groups, are almost negligible under the aforementioned conditions.
Thermally initiated emulsion polymerization of styrene
Authors: Kast Hans , Funke Werner 
Published: April 2003

AbstractThe thermal polymerization of styrene in emulsion was studied by determination of the number of particles, the rate of polymerization, and the average molecular weight of the polymer formed as a function of the emulsifier concentration. For the number of particles the relation N ∼ [E]1,4 was found, whereas the rate of polymerization showed a dependence of vbr ∼ [E]0,7, only up to an emulsifier content of 0,2 mol. dm−3, but remained constant at higher concentrations. A transfer of low molecular weight radical species from the organic to the aqueous phase is discussed as a prerequisite of polymerization in the latex particles. The deviations from the Smith‐Ewart theory are explained by the low rate of radical formation, which does not provide a constant radical concentration per particle.
Polymerization of L‐leucineN‐carboxyanhydride with 1,6‐hexanediamine as initiator
Authors: El‐Sabbah Mohamed M. B. , Elias Hans‐G. 
Published: April 2003

AbstractL‐Leucine N‐carboxyanhydride was polymerized in N,N‐dimethylformamide (DMF) or 1,4‐dioxane (DIO) at 25°C with either 1,6‐hexanediamine (1) or its monocarbamate 2 using a constant volume apparatus, initially filled with nitrogen or carbon dioxide. Number average molar masses from amino end group titrations on one hand and from initial monomer/initiator ratios and conversions on the other were practically identical for monomer conversions between 25 and 79%, indicating both the living nature of the polymerization and a participation of all initially present amino groups, despite the fact that polymer precipitation was observed at higher conversions for all systems and an additional precipitation of the carbonate 2 for the system 1/DIO/CO2 at low conversions. Two kinetic stages were observed for the latter system, but three kinetic stages for all other ones. The absence of a rapid initial polymerization period for the system, 1/DIO/CO2 as contrasted to the high initial rates for the systems 1/DMF/CO2 or 1/DMF/N2 points towards a carbamate mechanism in the first case and an amine mechanism in the second. The relation between intrinsic viscosities and number average molar masses of poly(L‐leucine) in trifluoroacetic acid at 25°C was found as [η] = 0,0169 〈Mn0,86 ± 0,04 ml/g.
Structural change of amorphous cellulose by water‐ and heat‐treatment
Authors: Hatakeyama Hyoe , Hatakeyama Tatsuko 
Published: April 2003

AbstractStrips of amorphous cellulose film were conditioned under wet atmospheres of 80 and 100% relative humidity or heated at 393 K in vacuo for different time intervals. The structural change of these samples was investigated using differential scanning calorimetry (DSC), IR spectrometry, x‐ray diffractometry (x‐ray), and the density‐gradient column method. In the initial stage of conditioning of cellulose samples at a wet atmosphere, it was found that the thermally determined relative volume fraction (α) of the amorphous part of cellulose stays constant while the diffusion coefficient (Dod), calculated from the rate of H → D exchange of OH groups observed in IR, decreases rapidly. This fact seems to show that the rearrangement of cellulose molecules does not occur as a whole but only partly in the vicinity of the OH groups which affect the process of H → D exchange. If large amounts of water are supplied, however, cellulose molecules rearrange freely and provide a crystalline structure, as observed clearly by x‐ray. On the other hand, during the heat‐treatment of amorphous cellulose, the decrease of α and Dod can be clearly observed by DSC and IR from the initial stage of treatment. Judging from the change of α and Dod, it was inferred that the hydrogen bond formation occurs step by step simultaneously with the rearrangement of cellulose molecules by heat‐treatment.
Solubilization of homopolymers and copolymers by block copolymer micelles in dilute solutions
Authors: Tuzar Zdeněk , Bahadur Pratap , Kratochvíl Pavel 
Published: April 2003

AbstractSolubilization by micelles of a three‐block copolymer poly(styrene‐butadiene‐styrene) with a polybutadiene core was studied by the light scattering method on three types of solubilizate: polybutadiene with (a) low and (b) high molar mass (with respect to the polybutadiene block of the copolymer), and (c) a block copolymer poly(styrene‐butadiene‐styrene) with a high content of butadiene. True solubilization of polybutadiene into the cores of spherical micelles occurs in case (a); in case (b) polybutadiene forms partially stabilized, emulsion‐like large droplets. In case (c) stable mixed micelles are formed having either lower or higher molar mass with respect to that of the original micelles, depending on the ratio of molar masses and on the composition of both copolymers. A similarity between solubilization of hydrocarbons by micelles of soaps or surfactants in aqueous solutions and solubilization of polymers by copolymer micelles in selective solvents is pointed out.
Comportement de copolymères greffés en milieu solvant sélectif des greffons. Cas des copolymères poly(styrène‐g‐bromure de vinyl‐4 N‐éthylpyridinium)
Authors: Selb Joseph , Gallot Yves 
Published: April 2003

AbstractThe dilute solution properties of amphiphilic graft copolymers with an “insoluble” polystyrene backbone (PS) bearing “soluble” poly(4‐vinyl N‐ethylpyridinium bromide) grafts (PVPQ), were studied in water‐methanol‐LiBr (0,1 mol/l) mixtures. In contrast to block copolymers with an identical chemical nature and in the same solvents, graft copolymers do not present intermolecular association. Viscometric data clearly show that a single graft molecule (or “monomolecular pseudo‐micelle”), has a structure similar to that of a “plurimolecular micelle” of a block copolymer, and exhibits a compact star‐like structure.
Polymers containing enzymatically degradable bonds, 3. Poly[N‐(2‐hydroxypropyl)methacrylamide] chains connected by oligopeptide sequences cleavable by trypsin
Authors: Ulbrich Karel , Strohalm Jiří , Kopeček Jindřich 
Published: April 2003

AbstractCopolymers (12–20) of N‐(2‐hydroxypropyl)methacrylamide (1) with p‐nitrophenyl esters of N‐methacryloylated oligopeptides (2–10) were prepared. These copolymers were crosslinked below the gel‐point with N,N′‐bis(Nε‐Boc‐lysine)hexamethylenediamine (11). The crosslinks connecting poly[N‐(2‐hydroxypropyl)methacrylamide] chains contained an oligopeptide sequence of 2–4 amino acids: ‐Gly‐Nε‐Boc‐Lys‐; ‐Gly‐X‐Nε‐Boc‐Lys‐ (X…Gly, Val, Leu, Phe, D‐Phe); ‐Ala‐Gly‐Val‐Nε‐Boc‐Lys; ‐Gly‐Gly‐Y‐Nε‐Boc‐Lys‐(Y…Phe, Val). After removal of the Boc blockade of lysine, copolymers degradable by trypsin were obtained. Changes in the molecular weight distribution of the polymers studied after incubation with trypsin allowed us to evaluate the influence of steric effects and of subsite interactions on the degradability of polymeric substrates.
Linear oligopeptides, 77. The effect of the insertion of a proline residue on the solid‐state conformation of host peptides
Authors: Toniolo Claudio , Bonora Gian Maria , Mutter Manfred , Pillai V. N. Rajasekharan 
Published: April 2003

AbstractThe conformational properties of two series of monodispersed, chemically and optically pure, PEGThe following abbreviations have been used in the text: PEG, poly(ethylene glycol); ‐NHPEG, “amino‐PEG”; ‐NHPEG‐M, “amino‐PEG” monomethyl ether; NPS, o‐nitrophenylsulfenyl; t‐Boc, tert‐butoxycarbonyl; Z, benzyloxycarbonyl; Met, methionine; Pro, proline; OBzl, benzyloxy; OMe, methoxy; OEt, ethoxy; NHEt, ethylamino; Glu, glutamic acid; IR, infrared; MeOH, methanol; TFE, 2,2,2‐trifluoroethanol.
‐bound linear host oligopeptides of the general formula \documentclass{article}\pagestyle{empty}\begin{document}$ t{\rm - Boc\rlap{--} (L - Met\rlap{--} )}_n {\rm NHPEG} $\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$ t{\rm - Boc\rlap{--} [L - Glu(OBl)\rlap{--} ]}_n {\rm NHPEG - M} $\end{document} containing a single guest L‐Pro residue at different positions in the main chain have been investigated in the solid state using IR absorption. The corresponding N‐deblocked peptides have also been examined. The incorporation of a L‐Pro residue in a central position of a β‐conformation appears to induce the onset of a structural irregularity characterized by IR absorption bands in the vicinity of 3 325 cm−1 and 1 575 cm−1.
Linear oligopeptides, 78. The effect of the insertion of the proline residue on the solution conformation of host peptides
Authors: Toniolo Claudio , Bonora Gian Maria , Mutter Manfred , Pillai V. N. Rajasekharan 
Published: April 2003

AbstractThe conformational properties of three series of monodispersed, chemically and optically pure, PEGThe following abbreviations have been used in the text: PEG, poly(ethylene glycol); ‐NHPEG, “amino‐PEG”; ‐NHPEG‐M, “amino‐PEG” ‐monomethyl ether; t‐Boc, tert‐butyloxycarbonyl; Z, benzyloxycarbonyl; Ala, alanine; Met, methionine; Gly, glycine; Glu, glutamic acid; Pro, proline; OBzl, benzyloxy; OEt, ethoxy; CD, circular dichroism; MeOH, methanol; TFE, 2,2,2‐trifluoroethanol; HFIP, 1,1,1,3,3,3‐hexafluoro‐2‐propanol.
‐bound linear host oligopeptides of the general formula \documentclass{article}\pagestyle{empty}\begin{document}$ t{\rm - Boc\rlap{--} (L - Met\rlap{--} )}_n {\rm NHPEG} $\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$ t{\rm - Boc\rlap{--} (L - X\rlap{--} )}_n {\rm NHPEG - M} $\end{document} [X = Ala, Glu(OBzl)] containing a single guest L‐Pro residue at different positions in the main chain have been investigated in aqueous and alcoholic solutions as a function of concentration, temperature, and added salts using CD. The corresponding N‐deblocked peptides have also been examined. The incorporation of the L‐Pro residue into a host petide chain blocks the extension of the α‐helical conformation at the level of the segment containing the guest residue at its N‐terminal end. The investigations reveal asymmetric helixnucleation properties of the L‐Pro residue as predicted by theory. In β‐structure‐forming oligopeptides, the insertion of a L‐Pro residue results in a significant destabilization of the ordered conformation. Thus, aggregation of peptide chains is less pronounced in these co‐oligopeptides.