摘要:

AbstractThe kinetics of the reaction between ethylene oxide and diethyl phosphoric acid (diethyl hydrogen phosphate) was studied in order to elucidate the mechanism of addition of oxiranes to phosphoric acid, the first reaction leading to phosphorus‐containing polyols. It was shown that the reaction proceeds by addition of the activated ethylene oxide molecule to the POH bond. Due to the low ionisation constant of the acid, activation via formation of the secondary oxonium ion plays a minor role, and the reaction proceeds mainly with participation of hydrogen‐bonded comp

ISSN:0025-116X    

DOI:10.1002/macp.1991.021920301

出版商:Hüthig&Wepf Verlag    

年代:1991

数据来源: WILEY

摘要:

AbstractThe chemical modification of the surface of low‐density polyethylene films exposed to an atmosphere of fuming sulfuric acid for different periods of time has been investigated. The degree of surface sulfonation for each treated film was calculated as the weight‐increase per unit area. The correlation of the absorbance of infrared bands associated to the sulfonic group with the degree of sulfonation of the films allowed to determine the IR absorption coefficients, especially for the band at 1 040 c

ISSN:0025-116X    

DOI:10.1002/macp.1991.021920302

出版商:Hüthig&Wepf Verlag    

年代:1991

数据来源: WILEY

摘要:

AbstractBimodal elastomeric networks are unusually tough materials in that they generally show large increases in modulus at high elongations. In the present study such networks were prepared by end‐linking mixtures of very short and relatively long chains of poly(dimethylsiloxane) (PDMS) [Si(CH3)2O]n, which is known to have easily deformable SiOSi bonds. Their stress‐strain isotherms were then determined in order to locate the range of elongations over which the upturns were most pronounced. Raman and infrared spectra were then obtained in this range using both a double monochromator Raman spectrophotometer and a Fourier transform infrared spectrophotometer with attenuated total reflection. The elongations imposed were found to cause small but not negligible frequency shifts for the stretching and bending modes of the SiOSi backbone. These shifts are probably due to rotational isomerization of the PDMS skeletal bonds, but there could also be a small contribution from bond‐angle deformations. The results thus support the usual assumption that the increases in modulus observed for bimodal networks are primarily due to the very limited number of spatial configurations available to the short network chains, particularly in the case of chains having skeletal bonds that are less easily deformed t

ISSN:0025-116X    

DOI:10.1002/macp.1991.021920303

出版商:Hüthig&Wepf Verlag    

年代:1991

数据来源: WILEY

摘要:

AbstractAcrylic monomers containing a cyclic carbonate group in their structural unit have been shown to copolymerize very rapidly and extensively with urethane and phenoxy oligomers having two acrylic functional end groups. With the most reactive resin, 90% conversion was reached within 20 ms of UV exposure in the presence of air. The kinetics of these ultrafast polymerizations was studied by infrared spectroscopy and their actual profiles were recorded in real time by RTIR spectroscopy. The rate of polymerization and the amount of residual unsaturation were determined for the three monomers studied, and compared to the performance of the mono‐, diand triacrylates commonly used as reactive diluents in UV‐curable systems. Quantum yield measurements indicate a very efficient propagation reaction, with kinetic chain lengths in the order of 104mol per initiating radical, even in the presence of air. The crosslinked polymers obtained with these new monomers exhibit both a great hardness and a high flexibility, together with a good resistance to organic solvents, chemicals and UV radiation, which makes them well suited for applications as protective coati

ISSN:0025-116X    

DOI:10.1002/macp.1991.021920304

出版商:Hüthig&Wepf Verlag    

年代:1991

数据来源: WILEY

摘要:

AbstractThe differential radial distribution functions of a sample of amorphous (atactic) poly(propylene) and of an isotactic one were compared, showing the absence, in the former sample, of interatomic correlations beyond 8 Å (1 Å = 0,1 nm). The influence of the length of atactic and isotactic chain segments on the calculated X‐ray interference functions was investigated. A model based on the arrangement of atactic chains in close‐packed spheres fits well the experimental X‐ray diffraction pattern of the amorphous

ISSN:0025-116X    

DOI:10.1002/macp.1991.021920305

出版商:Hüthig&Wepf Verlag    

年代:1991

数据来源: WILEY

摘要:

AbstractDipole moments of poly(4‐methoxystyrene) (PMeOSt) and poly(4‐bromostyrene) (PBrSt) were determined from dielectric constant and density measurements on dilute solutions of the polymers in benzene, 1,4‐dioxane and toluene, over the range of temperatures from 25 to 55°C. The average dipole moments per constitutional repeating unit (μ) obtained in benzene (Bz), 1,4‐dioxane (Dox), and toluene (Tol) at 25°C are as follows: 1,219 D (Bz), 1,253 D (Dox) and 1,175 D (Tol) for PMeOSt, and 1,371 D (Bz) and 1,413 D (Dox) for PBrStIn SI units: 1 D ≈ 3,33564 · 10−30C · m.. The dipole moment ratio, Dr= 〈μ2〉2/μ20, was found to be 0,942 for PMeOSt and 0,467 for PBrSt in Bz at 25°C, for which the observed values of the dipole moments of 4‐methoxytoluene and 4‐bromoethylbenzene were used as μ0for the respective polymer. The variation of the dipole moment ratio with temperature was linear but very small, dDr/dTgiving a negative value for PMeOSt bu

ISSN:0025-116X    

DOI:10.1002/macp.1991.021920306

出版商:Hüthig&Wepf Verlag    

年代:1991

数据来源: WILEY

摘要:

AbstractThe real part of the relative permittivity ϵ′rof some cellulosic materials contaminated with commercial impurities and NaCl (determined as weight percent ash contents), and that of the purified fibres, as well as their hydrolysed residues, free of such contaminations, was measured in the frequency range 102Hz ≤f≤ 105Hz and in the temperature range 283,15 K ≤T≤ 333,15 K. Additional measurements of the imaginary part of relative permittivity ϵ″rhave been carried out in the same frequency and temperature ranges for hydrocellulose samples free of inorganic impurities and contaminated with NaCl. The results obtained show that the variation with temperature of the relative permittivity of the samples examined exhibits a change in slope in the vicinity of 303,15 K except for hydrocellulose samples free of impurities. They further show that the presence of inorganic contaminations has a significant effect on the magnitude of the relative permittivity and its variation with temperature, particularly at low frequency. In the case of samples contaminated with inorganic impurities, interfacial polarization is responsible for the anomalous dielectric behaviour observed with the exa

ISSN:0025-116X    

DOI:10.1002/macp.1991.021920307

出版商:Hüthig&Wepf Verlag    

年代:1991

数据来源: WILEY

摘要:

AbstractA novel technique is described for the investigation of polyanions by direct polyelectrolyte titration. In connection with a specially developed phototitrator, an extremely high sensitivity can be reached using 3,6‐ionene bromide as cationic titrant and eriochrome black T as metachromatic indicator for end‐point detection. This enables both the determination of charge densities for polymer characterization as well as the detection of polymers in aqueous solution down to trace concentrations of 10 μg/L. Monovalent salt ions do not interfere with the titration up to concentrations of about 0,1 mol/L. Potential interference of divalent metal ions can be prevented by adding ethylenediaminetetraacetic acid (EDTA) as chelating agent. The applicability of the method was proved by measuring charge densities of poly(sodium acrylate) (NaPAA) in the concentration range of 0,01 to 10 mg/L and of poly(potassium vinyl sulfate) (KPVS). As expected, the charge density of NaPAA decreases with a pH decrease from 11 to 7, whereas the charge density of KPVS is independent o

ISSN:0025-116X    

DOI:10.1002/macp.1991.021920308

出版商:Hüthig&Wepf Verlag    

年代:1991

数据来源: WILEY

摘要:

AbstractPolydimethylsiloxane chains were tetrafunctionally end‐linked with tetraethoxysilane in solution, with either a linear dimethylsiloxane oligomer or hexadecane as solvent. Stress‐strain isotherms for the networks thus prepared were obtained in the extracted but unswollen state, both in elongation and in compression (biaxial extension, which was achieved by inflation of sheets of the materials). Measurements were carried out to the rupture points in order to provide as large a range of deformation as possible. Comparison of the experimental and theoretical stress‐strain isotherms indicated that the experimental results were in good agreement with the constrained junction theory of rubberlike elasticity. The results showed that the constraint parameterkdecreases with decrease in the volume fractionv2cof polymer present during cross‐linking and incorporated into the network structure, which means that networks prepared at high dilutions have fewer chain‐junction entanglements, as expected. However, the experimental values of the phantom modulus [f ph*] are also a function of the weight fraction of soluble (uncross‐linked) polymer which had been present. This confirms the expectation that networks prepared at high dilutions have imperfections such as loops and dangling ends. There is an excellent agreement, however, between experiment and theory with respect to the relationships amongk, the Mooney‐Rivlin 2C1estimate of the phantom

ISSN:0025-116X    

DOI:10.1002/macp.1991.021920309

出版商:Hüthig&Wepf Verlag    

年代:1991

数据来源: WILEY

摘要:

AbstractThe concept of macro iniferter (MI) was applied to realize the synthesis of triblock copolymers of ethyl acrylate (EA) with styrene (St) or methyl methacrylate (MMA), with EA forming the end blocks. The syntheses involved 3 steps. Secondary amine terminated poly(ethyl acrylate) was synthesisted by polymerization of EA in presence of butyl‐(2‐mercaptoethyl)ammonium chloride as a functional chain‐transfer agent. The macroamine so obtained was converted to the macrothiuram disulfide by reaction with CS2and I2. Thermal polymerization of MMA or St in presence of this macroiniferter led to the respective triblock copolymers. The kinetics of polymerization of MMA and styrene using MI and two different chain lengths was done in limited concentration ranges. The kinetic parameters indicated that the iniferter action was not affected by the incorporation of the thiuram disulfide groups in the polymer backbone. Triblock copolymers of differing block lengths of hard and soft segments could be prepared by varying the chain length of the macroamine and the concentration of the iniferter in the reaction system. The copolymers were characterized by GPC analysis and spectral or elemental analyses. In the case of St, analysis showed formation of perfect triblocks, whereas for MMA, tendencies to form diblocks were observed on increasing the chain length of the iniferter‐forming block. DSC analyses showed demixing of the soft EA block and the hard central

ISSN:0025-116X    

DOI:10.1002/macp.1991.021920310

出版商:Hüthig&Wepf Verlag    

年代:1991

数据来源: WILEY