摘要:

AbstractThis paper describes the use of evanescent light for the optical characterization of polymer thin films and interfaces. Firstly, a few basic concepts of evanescent wave phenomena, including total internal reflection, plasmon surface polaritons and guided optical modes, are reviewed. It is shown that the excitation of these waves allows for a sensitive determination of the optical architecture of the interface(s) involved. This “surface light” can then be used for the same broad range of optical techniques as it is known from experimental set‐ups designed for the investigation of various optical properties of polymer samples using plane electromagnetic waves, i.e. “normal” photons. This is demonstrated for diffraction experiments, microscopic investigations, inelastic scattering, e.g. Brillouin‐ or Raman‐spectroscopies, etc. The examples given include thin polymer films prepared by spin‐coating or by the Langmuir‐Blodgett‐Kuhn technique. It is shown that properties and processes at solid‐solution interfaces can be investigated equally well, and even surfaces of bulk samples

ISSN:0025-116X    

DOI:10.1002/macp.1991.021921201

出版商:Hüthig&Wepf Verlag    

年代:1991

数据来源: WILEY

摘要:

AbstractOur earlier work about alkoxysilanes as external donors in high‐activity Ziegler‐Natta catalysts is broadened with studies on the performance of some other oxygen‐containing silane compounds and with some studies on the effect of the structure of the hydrocarbon part of the alkoxysilane compounds: There are new informations about the optimum structure of an external silane‐type donor. The alkoxy group proved to be the best electron‐donating group, whereas the other oxygen‐containing electron‐donating groups tested worked less effectively. In some structures the oxygen atoms were sterically too hindered for effective deactivation. Some increase in the isotacticity was nevertheless observed even with the poor performance donors, which indicates that there could be a population of active centres that are very easy to deactivate. All the para‐substituted alkoxy phenyl silane donors tested gave polypropene with high isotacticity and activity. Therefore, we conclude that the nature of the substituent does not markedly affect the performance of the donor — at least as long as the substituent has not a sterically free electr

ISSN:0025-116X    

DOI:10.1002/macp.1991.021921202

出版商:Hüthig&Wepf Verlag    

年代:1991

数据来源: WILEY

摘要:

AbstractComonomer reactivity ratios (from kinetic and13C NMR data), compositional homogeneity of ethylene‐propene copolymers, and molecular structure of individual fractions of the copolymers obtained with supported Ti‐Mg catalysts of different compositions were determined. The copolymerization reactivity of these systems was found to increase upon introduction of ethyl benzoate and dibutyl phthalate to the catalyst system. It was found that both lowly stereospecific and highly stereospecific catalysts have a broad distribution of active sites with respect to copolymerization reactivity. The composition of the catalysts (titanium content and stereoregulating additives) was shown to influence the reactivity ratios of the comonomers and the microstructure of the copolym

ISSN:0025-116X    

DOI:10.1002/macp.1991.021921203

出版商:Hüthig&Wepf Verlag    

年代:1991

数据来源: WILEY

摘要:

AbstractA cationic polyacrylamide was examined using polarography, constant potential coulometry, photon correlation spectroscopy, electrocapillarity and potentiometric titrimetry. A polarographic response was found in differential‐pulse polarography (DPP), direct‐current and Kalousek modes at −1,7 V versus a silver/silver chloride electrode. In each case the magnitude of the response was a function of polymer concentration. However, it is thought that the response is not due to the polymer itself but impurities found with it. These were found to have a pK of 4,75. The polymer appears to develop a more open structure in LiCl solution (<0,0013 mol/L). The unwashed polymer was found to greatly increase the interfacial tension at the mercury drop, but this effect was considerably reduced on washing the polymer in 70% acetone solution. Hydrolysis of the polymer seems to occur at pH 10. The suppression of the negative tensammetric peak of poly(ethylene glycol) (PEG200) by a range of cationic polyacrylamides was used for their analysis in the determination of their adsorption onto the surface of woodpulp. The adsorption was found to be a function of both their cationicity and mean molar mass. The rate of hemicellulose desorption from the woodpulp appears to be pH dependent. The impurity is thought to be mainly adipamic acidSystematic name: 5‐carbamoylpentanoi

ISSN:0025-116X    

DOI:10.1002/macp.1991.021921204

出版商:Hüthig&Wepf Verlag    

年代:1991

数据来源: WILEY

摘要:

AbstractBy means of ESR (electron spin resonance) spectroscopic investigations it is shown, that in dithiol/diene‐mixtures, in the absence of daylight and oxygen, radicals are formed spontaneously. Using the spin trapping technique and nitrosodurene (ND) as the trapping agent the existence of sulfur and carbon radicals could be proved unambiguously. Oxygen has no significant influence on the reaction. Spin trapping experiments have shown, that the aliphatic dithiols investigated do not form any traceable quantity of RS.and.OOH radicals in the presence of air. Radicals are detected only after addition of an ene‐compo

ISSN:0025-116X    

DOI:10.1002/macp.1991.021921205

出版商:Hüthig&Wepf Verlag    

年代:1991

数据来源: WILEY

摘要:

AbstractUnsaturated liquid‐crystalline polymers are synthesized with the aim to fix the liquid‐crystalline state which causes the favourable polymer properties by means of subsequent crosslinking. The elucidation of the influence of crosslinking on the liquid‐crystalline properties of such polyesters is possible using the determination of the double‐bond content in the polymer. Because the CC bonds of fumaric acid units are determined analytically by electrochemical reduction, a polarographic determination of the double‐bond content appears to be a favourable method. The treatment of the polymeric material and the choice of a solvent system which is suitable both in respect to electroanalytical use and sufficient solvent power are of first

ISSN:0025-116X    

DOI:10.1002/macp.1991.021921206

出版商:Hüthig&Wepf Verlag    

年代:1991

数据来源: WILEY

摘要:

AbstractPolymerization of dialkyl itaconates with dimethyl azoisobutyrate (5) was studied in benzene at 50°C by means of electron spin resonance (ESR). The monomers used are dimethyl (1), diethyl (2), dibutyl (3) and di‐2‐ethylhexyl (4) itaconates. All the polymerization systems involve ESR‐observable propagating polymer radicals under the actual polymerization conditions. The polymerization rate (Rp) and degree of polymerization of the resulting polymer increase in going from shorter to longer alkyl groups. The ESR‐determined rate constants of propagation (kp) and termination (kt) decrease as the alkyl chain becomes longer.kpof1is 3,3 times higher than that of4, whilektof1is 590 times higher than that of4. Thus, the steric effect due to the alkyl group suppresses much more termination than propagation, leading to the fact thatRpincreases as the alkyl group become

ISSN:0025-116X    

DOI:10.1002/macp.1991.021921207

出版商:Hüthig&Wepf Verlag    

年代:1991

数据来源: WILEY

摘要:

AbstractPolyallylamine‐graft‐poly(N‐isopropylacrylamide) was prepared by coupling polyallylamine with poly(N‐isopropylacrylamide) (the latter with an end‐standing carboxyl group). The graft polymer obtained showed a temperature‐responsive phase transition under alkaline conditions, whereas the starting poly(N‐isopropylacrylamide) with end‐standing carboxyl group showed temperature‐sensitivity under acidic conditions. With an increase in the degree of grafting the temperature‐sensitivity of the polymer under weakly alkaline conditions increases. Microspheres were prepared by cross‐linking the graft polymers with glutaraldehyde in water‐in‐oil emulsion. Trypsin immobilized to the microspheres showed temperature‐responsiveness in its catalytic activity. The graft polymer can be used as a component of temperature‐sensi

ISSN:0025-116X    

DOI:10.1002/macp.1991.021921208

出版商:Hüthig&Wepf Verlag    

年代:1991

数据来源: WILEY

摘要:

AbstractSoluble macromolecular conjugates for the controlled delivery of the strongly hydrophobic antitumor drug adriamycin (ADR) were prepared. The association behaviour of two types of these amphiphilic conjugates consisting of ADR bound to poly(L‐glutamic acid) (PGA) in aqueous solution was investigated using absorbance and fluorescence spectroscopy as well as GPC and lowangle laser light scattering (LALLS) measurements. ADR was bound via the aminoribosyl moiety either directly with PGA side‐chain groups or via oligopeptide spacer groups. UV/VIS, GPC and LALLS data showed that in buffer solution both ADR conjugates associate intermolecularly. The data of the directly bound ADR conjugates are consistent with the presence of multimers of different degrees of association in equilibrium with single polymer chains. In contrast, spacer‐containing ADR conjugates associate to give stable uniform multimers. UV/VIS and fluorescence spectroscopy performed at very low conjugate concentration show that polymer‐bound ADR residues associate intramolecularly as well. The degree of intra‐ and intermolecular association of the conjugate‐bound ADR molecules depends on the type of conjugate, ADR load and conjugate concentration as well as on ionic strength of the solvent, the presence of organic cosolvents and temperature. The data indicate that hydrophobic domains in spacer‐containing conjugates are more stable compared with directly bound conjugates, probably due to enhanced flexibility and the presence of hydrophobic leucine residues. It is concluded that spacer‐containing conjugates of ADR may have a potential for effective drug delivery under in vivo conditions due to their solution properties in addition to the biodegradability of the dr

ISSN:0025-116X    

DOI:10.1002/macp.1991.021921209

出版商:Hüthig&Wepf Verlag    

年代:1991

数据来源: WILEY

摘要:

AbstractThe equilibrium copolymerization of 1,3‐dioxolane with 1,3‐dioxepane in CH2Cl2solution and with 1,3‐dioxane without solvent is analyzed, and the equilibrium constants of homo‐ and cross‐propagations are estimated and discussed. The corresponding thermodynamic parameters are calculated. The reported thermodynamic parameters of homopolymerization of 1,3‐dioxane (ΔHss= −3,1 kJ · mol−1, ΔSss= −35,5 J · mol−1· K−1), were determined on the basis of the copolymerization data. Predictions of comonomer concentrations and microstructure of copolymers in the equilibrium copolymerization system are presented for any initial composition, on the basis of the determ

ISSN:0025-116X    

DOI:10.1002/macp.1991.021921210

出版商:Hüthig&Wepf Verlag    

年代:1991

数据来源: WILEY