摘要:

AbstractA structural investigation was carried out on the product of the cationic oligomerization of propylene with the aim of identifying the main isomers present in the dimer and trimer fractions. BF3‐proton donor complexes were used as cationic catalysts. The different isomers, after hydrogenation, were separated by GLC analysis and identified by GC‐MS analysis after comparison with reference products. The structures of the obtained isomers give clear evidence that hydride and methanide shifts may be operative. The influence of the experimental conditions (temperature, type of catalyst) in obtaining the various isomers was evaluated. The number of isomers, mainly those due to methanide shift, increases with increasing reaction temperature. The identified oligomer structures give indications about the chemistry of the first steps of the cationic oligomerization of propyl

ISSN:0025-116X    

DOI:10.1002/macp.1988.021890111

出版商:Hüthig&Wepf Verlag    

年代:1988

数据来源: WILEY

摘要:

AbstractThe Heck reaction allows the synthesis of monomers in a one‐step reaction. Catalyzed by Pd, bromoarenes are reacted with ethylene to form substituted styrenes and symmetrical stilbenes. Unsymmetrical stilbenes are obtained from substituted bromoarenes and styrenes. Substituted hydroquinones and terephthalic acids are also available in high yields. Poly(1,4‐phenylenevinylene) is obtained starting from 4‐bromost

ISSN:0025-116X    

DOI:10.1002/macp.1988.021890112

出版商:Hüthig&Wepf Verlag    

年代:1988

数据来源: WILEY

摘要:

AbstractReactions of diisocyanatodiketenes, 3‐(ω‐isocyanatoalkyl)‐4‐(ω‐isocyanatoalkylidene)‐2‐oxetanones(3a–c), with oligomeric diols(4or5)as well as 1,4‐butanediol afforded linear polyurethanes containing reactive diketene moieties. From these poly(diketene‐urethane)s polymeranalogues products were prepared by reaction with ethanol, ammonia, water or acetic acid. The resulting polyurethanes containing ß‐ketoester, ß‐ketoamide or keton moieties were characterized by IR spectroscopy, viscosimetry, differential scanning calorimetry and size exclusion chromatography. The properties of the products based on diols4or5are mainly determined by the oligomeric diols, whereas the (modified) diisocyanate part has a great influence e.g. on the thermal beh

ISSN:0025-116X    

DOI:10.1002/macp.1988.021890113

出版商:Hüthig&Wepf Verlag    

年代:1988

数据来源: WILEY

摘要:

AbstractThe dielectric and viscometric behaviour of poly(dibenzyl itaconate) (1) in 1,4‐dioxane is studied as a function of temperature. The dipole moments at 25°C and at 33°C are determined by measuring the dielectric constant as a function of polymer concentration at fixed temperature. Also, the variation of the dielectric constant for a fixed concentration is determined at several temperatures in the temperature range between 15 and 39°C. The dipole moment is by 10% higher at 33°C than at 25°C, and the variation of the dielectric constant with temperature shows a stepwise increase between 25°C and 30°C. Viscosity measurements demonstrate an anomalous behaviour of1in 1, 4‐dioxane at approximately the same range of temperatures. At ca. 25°C the value of the Huggins constant drops to practically zero. By measuring samples with different molecular weights the unperturbed dimensions, interaction parameter, and Mark‐Houwink‐Kuhn‐Sakurada exponent are obtained. All of these parameters exhibit a discontinuity at ca. 25°C. The variations in the dielectric and viscometric behaviour with temperature are attributed to a conformational change of the macromolecules

ISSN:0025-116X    

DOI:10.1002/macp.1988.021890114

出版商:Hüthig&Wepf Verlag    

年代:1988

数据来源: WILEY

摘要:

AbstractThe1H NMR parameters (chemical shift and coupling constant) of ß(1→4)‐linked polysaccharides xylan, cellulose, and chitin are compared in solutions of aprotic solvents. The following NMR parameters are analyzed: (1) Chemical shifts of labile protons, (2) their variation with temperature, (3) coupling constants through the HCOH moiety — for monomers, dimers, and the corresponding polymers. It is observed that the OH‐3 hydroxyl group for cellulose and chitin oligomers and polymers present a particular behaviour, which is in agreement with the existence of an intramolecular hydrogen bond between this hydroxyl of one monomeric unit, and the heterocyclic oxygen atom of the adjacent monomeric unit. This kind of intramolecular hydrogen bond is not observed in case of the xylan series. It can be concluded that substitution of an equatorial hydrogen atom at the C‐5 position of the sugar ring by a CH2OH group — when passing from xylan to cellulose and chitin — induces a rotation restriction around the glycosidic bond. This places the OH‐3 hydroxyl group in a favourable position to be hydrogen‐bonded. The consequent implication on the respective conformations of the chains

ISSN:0025-116X    

DOI:10.1002/macp.1988.021890115

出版商:Hüthig&Wepf Verlag    

年代:1988

数据来源: WILEY

摘要:

AbstractA novel synthetic route to (2E,4E)‐6‐amino‐2,4‐hexadienoic acid (1) and related ω‐aminodiene compounds is reported. These substances form layer perovskites, CdCl4(NH3—R)2, that furnish stereoregular 1,4‐polybutadienes upon γ‐irradiation in a topochemical solid state reaction. The synthesis of a chiral derivative is also described, that can be crystallized in a perovskite structure and polymerized by γ‐rays. An ambivalent solid state reactivity is observed for the hydrochloride of1: γ‐rays induce a chain reaction leading to a polymer of identical chemical structure and stereochemistry as reported for the perovskite, but with higher molecular weight. Upon UV‐irradiation, however, the hydrochloride undergoes a stereoselective (2+2)‐cycloaddition to a cyclobutanoic dimer as main product and oligomers after prolonged irradiation. In the case of γ‐irradiation at 273 or 300K significant contributions from postpolymerization are found both for the hydroc

ISSN:0025-116X    

DOI:10.1002/macp.1988.021890116

出版商:Hüthig&Wepf Verlag    

年代:1988

数据来源: WILEY

摘要:

AbstractThe photoinitiated polymerization of 4‐biphenylyl 4‐(6‐acryloyloxyhexyloxy)benzoate (1) in its oriented liquid‐crystalline state was studied. Monomer1has a thermotropic nematic phase between 88°C and 98°C, a monotropic nematic phase between 76°C and 88°C, and a monotropic smectic phase below 76°C. The orientation of1was established in a glass cell provided with a rubber polyimide coating and characterized by birefringence measurements. During polymerization both the birefringence and the liquid‐crystalline transition temperatures increase, indicating that the orientation was maintained. The oriented poly(1) is polycrystalline at room temperature, becomes smectic at 90°C, nematic at 172°C, and isotropic at 190°C. The order parameter of the nematic poly(1) is lower than that of the nematic monomer1at equal red

ISSN:0025-116X    

DOI:10.1002/macp.1988.021890117

出版商:Hüthig&Wepf Verlag    

年代:1988

数据来源: WILEY

摘要:

AbstractViscosity‐average relative molecular masses have been determined for a series of chitosans having the same relative molecular mass and relative molecular mass distribution but differing extents of N‐acetylation. The results obtained show that the same viscometric constants in the Mark‐Houwink equation [η] = Km·Maare applicable to chitosans over the range between 0 and 40%N‐acetylation Comparison of literature values for number‐ and weight‐avepge rela‐tive molecular massesMn, andMw, with the viscosity‐average relative molecular mass M, values calculated using the related viscosity data and each of the three sets of viscometric constants that have been proposed for chitosan, confirms that the most accurate values currently available arekm= 1,81 · cm−3· 10−1and a = 0,93, using 0,l M acetic ac

ISSN:0025-116X    

DOI:10.1002/macp.1988.021890118

出版商:Hüthig&Wepf Verlag    

年代:1988

数据来源: WILEY

摘要:

AbstractTemperature depenences of the pitch of cholesteric helix in solutions of poly(y‐benzyl‐L‐glutamate) inN,N‐dimethylformamide andN‐methyl‐2‐pyrrolidone were measured for various molar masses of poly(γ‐benzyl‐L‐glutamate). It was found that inN‐methyl‐2‐pyrrolidone inversion of the cholesteric helix takes place, i. e., that the right‐handed helix changes to the lefthanded one. By using an equation derived by Kimura, the temperatures at which the system has a nematic order were determined. The results obtained allow the statement that an important role in the inversion of the cholesteric helix in poly(γ‐benzyl‐L‐glutamate) solutions is played by conformational changes in side

ISSN:0025-116X    

DOI:10.1002/macp.1988.021890119

出版商:Hüthig&Wepf Verlag    

年代:1988

数据来源: WILEY

摘要:

AbstractNew conformational data for members of the series Boc‐(D‐Val)m‐(L‐Val‐D‐Val)(n‐m)/2‐OMe (m= 0 or 1;n= total number of residues) are presented and used together with earlier results to formulate general conclusions regarding types and relative stabilities of ß‐helices formed by D,L‐alternating valine peptides. The helices, single‐ or double‐stranded, are of the tightest geometry, the single‐stranded helices having only 4,4 residues per turn(ß4,4‐helices) and the double‐stranded ones only about 5,6 residues per turn (↑↓ß5,6‐and ↑↑ß5,6‐helices). The double‐stranded helices are of the type with the highest possible number of interstrand H‐bonds [2(n‐1)] and the antiparallel ones are always strongly preferred. In chloroform solution right‐and left‐handed ß4,4‐helices and left‐handed ↑↓ß5,6and ↑↑szlig;5,6‐helices are formed by the oligovalines studied with different preferences depending on the peptide chain length and on the parity of the number (od

ISSN:0025-116X    

DOI:10.1002/macp.1988.021890120

出版商:Hüthig&Wepf Verlag    

年代:1988

数据来源: WILEY