摘要:

AbstractPlasticization of the polycarbonate of bisphenol A (1) by dibutyl 4,4′‐ethylenedibenzoate (2) and dibutyl 4,4′‐stilbenedicarboxylate (3) was studied in order to establish the influence of the molecular rigidity on the antiplasticization phenomenon. UV spectroscopy, dielectric and mechanical properties proved that a rigid trans‐configuration of the “plasticizer” molecules and a strong interaction enhance antip

ISSN:0025-116X    

DOI:10.1002/macp.1990.021910501

出版商:Hüthig&Wepf Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractThe reactions of 3‐pyridinecarboxylic acid (nicotinic acid, NA) and 4‐pyridinecarboxylic acid (isonicotinic acid, ISNA) with 2,3‐epoxypropyl phenyl either (glycidyl phenyl ether, GPE) were studied by means of high performance liquid chromatography (HPLC). It is found that both reactions involve two‐step mechanisms and have induction periods. Two products, pyridinium salt and ester, are obtained in each study. The formation of pyridinium salt is the cause of the occurrence of the induction period. After the induction period, the kinetics of the reaction is second order. Pyridinium ions do not form complexes with carboxylate ions of pyridinecarboxylates but form activated complexes with the hydrogen‐bonded complexes of pyridinecarboxylic acids and GPE to activate the esterification reactions. The mechanisms of the reactions are discussed

ISSN:0025-116X    

DOI:10.1002/macp.1990.021910502

出版商:Hüthig&Wepf Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractIsotactic polystyrene samples crystallized from concentrated solutions (>10% by weight) in the thermodynamically good solvent toluene display a lamellar thicknessL= (170 ± 15) Å at room temperature, as determined by neutron scattering investigation. This thickness is about twice the value reported for samples crystallized in poor solvents. The results may be interpreted in terms of a substantially smaller melting enthalpy of the polymer in toluene, producing a proportionally inverse increase of the thickness L̄cof the central, crystalline portion of the lamellae. In turn, we suggest that the overall thicknessLof the lamellae increases more than proportionally with L̄c, due to the need of accomodating in the amorphous zone increasing amounts of polymer containing steric defects. The decrease of the melting enthalpy is also qualitatively consistent with growth rate results. The half‐peak width of the Bragg diffraction peaks suggests that the crystalline fraction of the lamellar thickness is about 50%, in approximate agreement with results obtained by Overbergh, Berghmans and Reynaers (J. Polym. Sci., Polym. Phys. Ed.14, 1177 (1976)) from bulk‐crystallized samples showing about the same values ofLand L̄cas observ

ISSN:0025-116X    

DOI:10.1002/macp.1990.021910503

出版商:Hüthig&Wepf Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractCrosslinkable liquid‐crystalline main‐chain polymers were prepared by high temperature polycondensation in solution. The polymers have reactive double bonds in the flexible spacer. Orientation of chains in the liquid‐crystalline state was not changed by crosslinking. Crosslinked polymers exhibit a high increase of the mesophase range and a higherE‐modulus than the uncrosslink

ISSN:0025-116X    

DOI:10.1002/macp.1990.021910504

出版商:Hüthig&Wepf Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractThe photodegradation of poly(tert‐butyl methacrylate) films under 100 ppm sulfur dioxide in air or 100 ppm nitrogen dioxide in air and in mixtures of the gases in air, at constant temperature (30°C) and humidity (30%), was studied. In the presence of sulfur dioxide and nitrogen dioxide under irradiation the polymer shows a rapid degradation, while the thermal degradation is very small, as well as the photodegradation in air. The measured effect of photodegradation of thin films was stronger than that of thicker films. An equation was derived to characterize the degradation by an autoacceleration and a linear part. FTIR spectroscopy shows the formation of carboxylic aci

ISSN:0025-116X    

DOI:10.1002/macp.1990.021910505

出版商:Hüthig&Wepf Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractSide reactions which have been proposed during the last 20 years to occur during the polymerization and oligomerization of vinylpyridine were reviewed, and some of them evidenced by experiments. The occurrence of ring substitution at the pyridine ring was demonstrated by model reactions. In addition, chain rearrangement in solution was observed. From the experimental results conclusions are drawn for the choice of the appropriate conditions for preparation and handling of polymers and oligomers of vinylpyridine.

ISSN:0025-116X    

DOI:10.1002/macp.1990.021910506

出版商:Hüthig&Wepf Verlag    

年代:1990

数据来源: WILEY

摘要:

Abstract3‐Chloro‐2‐hydroxypropyl ether of dextran (3a) and succinyldextran (4a) were prepared and used for coupling the anticancer agents 6‐purinethiol and 5‐fluorouracil. The “in vitro” drug liberation was measured at pH 7,2 and 8,8. The release rate from the dextran conjugates was compared with that of the poly(1‐vinyl‐2‐pyrrolidone‐co‐maleic acid) derivatives of these drugs. The effect of the macromolecular chain on the hydrolytic behaviour of the polymer‐bound d

ISSN:0025-116X    

DOI:10.1002/macp.1990.021910507

出版商:Hüthig&Wepf Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractThe anionic polymerization of L‐lactide was studied with four potential initiators of different basicity: potassium benzoate, potassium phenoxide, potassiumtert‐butoxide and butyllithium. Regardless of the solvent, only the two most basic initiators proved to be reactive enough to initiate and maintain the polymerization. This result and the formation of benzyloxy end‐groups upon addition of benzyl bromide prove that the polymerizations proceed via alkoxide chain ends. Absence of initiator fragments in the isolated polylactide chains suggests that initiation mainly involves deprotonation of L‐lactide, whereas nucleophilic substitution only occurs to a minor extent. Furthermore, optical rotation measurements indicate that both the initiator and the alkoxide chain end cause partial racemization regardless of solvent and temperature. Furthermore, it was found that reagents such as triethylamine, pyridine or potassium benzoate which are not reactive enough to initiate polymerization, are basic enough to cause partial racemization ofL‐lactide by depr

ISSN:0025-116X    

DOI:10.1002/macp.1990.021910508

出版商:Hüthig&Wepf Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractA selective method using polarography was developed for the determination of the degree of adsorption of anionic polyacrylamides onto Kaolinite. Four polymers of the same anionic character but different molar mass were studied. Limiting adsorption of the polyacrylamides onto the clay increased with their molar mass.

ISSN:0025-116X    

DOI:10.1002/macp.1990.021910509

出版商:Hüthig&Wepf Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractThe increasing exchange of 2,5‐dipentyloxyterephthaloyl units by terephthaloyl units, studied up to 60 mole‐%, influences the chemical and physical behaviour of the corresponding copolyesters. The copolyesters with an exchange of 30 mole‐% and more become insoluble in chloroform and dichloromethane. The decomposition temperatures increase and the copolyesters show a better long‐time thermal stability. The melting and clearing intervals shift to higher temperatures. The low temperature liquid‐crystalline (LC) phase, which can be seen very well in the HT05‐100 samples, disappears continuously with the increase of the terephthaloyl content. The solid to LC (high temperature phase) transition enthalpies decrease linearly with increasing terephthal

ISSN:0025-116X    

DOI:10.1002/macp.1990.021910510

出版商:Hüthig&Wepf Verlag    

年代:1990

数据来源: WILEY