摘要:

AbstractThe expression “stiffness” of a polymer chain is shown to be ambiguous, and the use of the word “rectilinearity” is proposed to replace it in certain contexts. The influence of non‐uniform curvature on Kuhn length and mean‐square end‐to‐end distance of (co)polymers is studied using the frameworks of the freely‐rotating‐chain model and the Porod‐Kratky model. It is shown that every fluctuation around the given mean curvature of a chain increases its overall rectilinearity. Specifically, it is concluded that the rectilinearity increases with increasing fluctuation magnitude and with increasing separation of the different curvatures along the chain, i. e., it becomes greater in the order: alternating, rando

ISSN:0025-116X    

DOI:10.1002/macp.1991.021920801

出版商:Hüthig&Wepf Verlag    

年代:1991

数据来源: WILEY

摘要:

AbstractThe chemical and electrochemical reductions of two series of oligo(p‐phenylene)s with different substitution patterns are investigated. The resulting anionic species are characterized on the one hand using NMR spectroscopy and quenching experiments obtaining dianions in the case of terphenyls and quaterphenyls. On the other hand, cyclic voltammetric experiments were carried out with the results that compounds with substitution only in the terminal rings behave as typical conjugated oligomers, and substituents in the middle rings disturb the conjugation and alter the mechanism of electron transfer. Further, the charge distribution, the stereodynamic behaviour and the redox potentials are examined as a function of chain length and substitution. The reduction of the title compounds shows that only the substitution of terminal phenyl rings leads to suitable model compounds for the doping of poly(p‐phenyle

ISSN:0025-116X    

DOI:10.1002/macp.1991.021920802

出版商:Hüthig&Wepf Verlag    

年代:1991

数据来源: WILEY

摘要:

AbstractLow‐temperature specimen preparation techniques, energy‐filtering electron microscopy, quantitative image analysis and elemental mapping are applied to an analysis of two macroporous, hydrated, polystyrene sorbents (XAD4® and PS50X2T) in order to determine whether or not minor differences in the apparent binding behaviour of Cephalosporin C to each hydrated sorbent can be related to specific determinants of polymer porosity. Mercury intrusion volume calculations suggest that each polymer has almost identical characteristics in the dry state. In contrast, electron microscopically‐derived pore profile measurements from the hydrated polymer suggest that XAD4® has a greater proportion of pore area associated with small (5–50 nm) diameter pores and a correspondingly smaller proportion of its pore area associated with the larger (80–150 nm) pore diameters as compared to PS50X2T, and that these differences are associated with changes in the local distribution of adsorbed Cephalosporin C within the polymer's por

ISSN:0025-116X    

DOI:10.1002/macp.1991.021920803

出版商:Hüthig&Wepf Verlag    

年代:1991

数据来源: WILEY

摘要:

AbstractIn order to render the surface of silicone hydrophilic without changing its bulk properties, acrylamide was grafted onto its surface. A silicone sheet was first treated with a corona discharge in air to introduce peroxides onto the surface. The concentration of peroxide introduced to the surface was determined using 2,2‐diphenyl‐1‐picrylhydrazyl and the maximum concentration was about 1,80 · 10−8mol/cm2when the corona discharge treatment was performed with 9 or 15 kV. Graft polymerization was allowed to proceed by heating the aqueous solution of the monomer together with the immersed silicone pretreated with the corona discharge. It was critical to throughly deaerate the silicone before and after the corona discharge treatment. Unless deaeration was sufficient, graft polymerization did not occur, irrespective of heating. The friction coefficient of the poly(acrylamide)‐grafted silicone decreased drastically, even if only a small amount of poly(acrylamide) was grafted onto the surface of the silicone. Collagen could be immobilized covalently using a water‐soluble carbodiimide, 3‐dimethylaminopropyl(ethyl)‐carbodiimide hydrochloride, when the grafted poly(acrylamide) chains were converted to poly(acrylic acid) by alkaline hydroysis, in order to introduce carboxyl groups. The maximum concentration of collagen immobilize

ISSN:0025-116X    

DOI:10.1002/macp.1991.021920804

出版商:Hüthig&Wepf Verlag    

年代:1991

数据来源: WILEY

摘要:

AbstractA polyester composed oftrans‐2,5‐linked tetrahydropyran rings (4t) was synthesized by direct polycondensation oftrans‐5‐hydroxytetrahydropyran‐2‐carboxylic acid (5t) usingN‐methyl‐2‐chloropyridinium iodide or triphenylphosphine and hexachloroethane as condensing agents in pyridine at 25 or 50°C. The hydroxycarboxylic acid5twas polymerized also with dibutyltin oxide, although longer reaction times were required. The polyester4tis soluble inm‐cresol and halogenated protic solvents such as 2,2,2‐trifluoroethanol, trifluoroacetic acids and dichloroacetic acid, but insoluble in chloroform and dichloromethane in which the correspondingcis‐isomer (4c) composed ofcis‐2,5‐linked tetrahydropyran rings is soluble. According to conformational energy calculations, the repeating unit exists predominantly as a conformer in which both the exocyclic oxygen and the carbonyl carbon in the backbone of the chain are located in the equatorial positions of the tetrahydropyran ring; in other words, the chain of4ttakes a linear conformation. On the other hand, the exocyclic oxygen in the repeating unit of4coccupies an axial position of the tetrahydropyran ring and the chain is winding. Conformational energies for dimer models for4cand4twere also estimated by means of force field calculations. These polyesters are partially crystalline according to their X‐ray diffraction patterns. Both polyesters show birefringence at or above 200°C. The polyesters4cand4tdecompose at 300°C in nitrogen atmosphere, approximately 150°C hi

ISSN:0025-116X    

DOI:10.1002/macp.1991.021920805

出版商:Hüthig&Wepf Verlag    

年代:1991

数据来源: WILEY

摘要:

AbstractThe catalyst systems Mg(OC2H5)2/benzoyl chloride (BC)/TiCl4and Mg(OC2H5)2/ethyl benzoate (EB)/TiCl4were prepared for the polymerization of propene. In case of the Mg(OC2H5)2/BC/TiCl4catalyst, BC changes into the internal donor EB during the in situ preparation of the catalyst and the unchanged BC acts as additional donor after reaction with triethylaluminium (TEA). Catalyst activity and isospecificity were also studied for the two catalysts by changing the amounts of BC or EB in the polymerization of propene cocatalyzed with TEA.

ISSN:0025-116X    

DOI:10.1002/macp.1991.021920806

出版商:Hüthig&Wepf Verlag    

年代:1991

数据来源: WILEY

摘要:

AbstractThe modification reaction of poly(vinyl alcohol) with diethyl chlorophosphate and ethyl dichlorophosphate is studied in homogeneous phase using tertiary amines as catalysts. The structure of the modified polymers was determined by means of1H and31P{1H} nuclear magnetic resonance (NMR) spectroscopy as well as by chemical analysis. The structure of the polymers resulting from the reaction with diethyl chlorophosphate greatly depends on the reaction temperature as well as the catalyst. For lower reaction temperatures (≤25°C) only acyclic phosphate ester groups were observed. The activation energy was found to be 24,9 kJ/mol. The presence of cyclic phosphate ester groups was found, when higher reaction temperatures (>25°C) were used. These results can be interpreted considering the existence of transesterification reactions. Crosslinking structures were obtained in case ethyl dichlorophosphate was used instead of diethyl chlorophosph

ISSN:0025-116X    

DOI:10.1002/macp.1991.021920807

出版商:Hüthig&Wepf Verlag    

年代:1991

数据来源: WILEY

摘要:

AbstractA technique using buffer capacity has been developed for evaluating the approximate pKvalues of the stability constantK, of polyelectrolytes. The technique has been applied to hemicellulose extracted from woodpulp (pK≈ 3,9 (0,1MNaCl)) and dextran (pK= 13,55 ± 0,2 (2MNaCl)). Verification of the method has been obtained by applying it to acetic acid (pK= 4,55 ± 0,02 (0,1MNaCl), pK= 4,70 ± 0,02 (0,001MNaCl)) and glucose (pK= 12,00 ± 0,05 (2MNaCl)). Glucose was found to turn peppermint green in NaOH solutions. At least 50% of the surface charge of woodpulp was found to originate from its hemicellulose co

ISSN:0025-116X    

DOI:10.1002/macp.1991.021920808

出版商:Hüthig&Wepf Verlag    

年代:1991

数据来源: WILEY

摘要:

AbstractThe living cationic polymerization of isobutyl vinyl ether (IBVE) with 1‐(isobutoxy)ethyl acetate (1)/C2H5AlCl2as initiating system in hexane at +40°C in the presence of carboxylates was investigated in regard to the effect of the basicity and the steric hindrance of the added esters on the rate and living nature of the polymerization. The effect of the basicity was evaluated by use of fourp‐substituted ethyl benzoates (XC6H4COOC2H5; X: CH3O, CH3, H, Cl). Despite of the difference in basicity, all the benzoates gave living polymers with narrow molecular‐weight distributions (ratios of weight‐ to number‐average molecular weightsMw/Mn≤ 1,1), whereas the polymerization rate depends on thep‐substituents as follows: CH3O

ISSN:0025-116X    

DOI:10.1002/macp.1991.021920809

出版商:Hüthig&Wepf Verlag    

年代:1991

数据来源: WILEY

摘要:

AbstractFast living cationic polymerization of isobutyl vinyl ether (IBVE) was examined using the initiating system 1‐(isobutoxy)ethyl acetate (1)/C2H5AlCl2in the presence of various esters in hexane between 0°C and +40°C. Methyl chloroacetate as added ester turned out to be effective: the apparent polymerization rate constantkwas larger by a factor of 400 – 500 than that in the presence of methyl acetate. The rate difference was explained on the basis of the basicity of the esters and their nucleophilic interaction with the propagating species. The polymers obtained in the presence of both esters had a narrow molecular‐weight distribution (MWD) (Mw/Mn≤ 1,1), andMnwas directly proportional to monomer conversion. As low reactive monomers, 2‐chloroethyl vinyl ether (CEVE) andtert‐butyldimethylsilyl vinyl ether (SiVE) were polymerized under similar conditions. By selecting methyl chloroacetate as an additive, in the case of CEVE, fast living polymerization was achieved to give quantitative conversion within 10 min at 0°C; in the case of SiVE, polymers with a narrow MWD were obtained even at −20°C in high yield, whereas hardly any polymerization of SiVE occurred in the presence

ISSN:0025-116X    

DOI:10.1002/macp.1991.021920810

出版商:Hüthig&Wepf Verlag    

年代:1991

数据来源: WILEY