摘要:

AbstractA tetrahedral lattice model for a polymer chain with three‐unit kinetic elements was used to find the correlation functions which describe the local dynamics of unit vectors oriented in the longitudinal or transverse directions with respect to the chain. These unit vectors can represent the dynamics of the emitting oscillator of the marker. It is shown that the spectra for longitudinal and transverse components of the emitting oscillator differ greatly. It is also shown that at short relaxation times the anisotropy of local relaxation properties of a kinetic chain fragment may be described by an equivalent ellipsoid with an axes ratio of ca. 1

ISSN:1022-1344    

DOI:10.1002/mats.1993.040020101

出版商:Hüthig&Wepf Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractThe expressions for the functions of spectral density at different orientations of the components of the internuclear vector with respect to the chain backbone, the frequency dependences of the spin‐lattice relaxation time of13C nuclei (T1C) and the values of the nuclear Overhauser effect (NOE) were obtained for the tetrahedral lattice model of a polymer chain with three‐unit kinetic elements. It was shown that peculiar features of the behavior ofT1Cand NOE reflect the characteristic properties of the spectra of relaxation (correlation) times for “longitudinal” and “transverse” components of the internuclear vector. It was established that in the range of relatively short times of the relaxation spectrum the dynamics of an anisotropic kinetic segment of the chain may be described with the aid of a simple model of an elongated ellipsoid of rotation with an axial ratio of about 10. It is shown that the equivalent‐ellipsoid model leads to significant differences from a more specific model of chain dynamics when a broad frequency range

ISSN:1022-1344    

DOI:10.1002/mats.1993.040020102

出版商:Hüthig&Wepf Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractThe conformations of thermotropic polyesters with alternating mesogens and poly(methylene) spacers in the main chain were investigated by conformational calculations using the data of linear‐dichroism IR‐spectroscopy, X‐ray analysis and differential scanning calorimetry. The conformations of monomeric units and of the macromolecules as a whole in different phase‐aggregated states were estimated. It is shown that in the liquid‐crystalline (LC) state the polymer chains are strongly extended. The results are compared with the data of various theories of LC

ISSN:1022-1344    

DOI:10.1002/mats.1993.040020103

出版商:Hüthig&Wepf Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractMelting‐point depression in miscible polymer blends is interpreted with Flory‐Prigogine's equation‐of‐state theory (FP theory) and Sanchez‐Lacombe's lattice fluid theory (LF theory). The equations for equilibrium melting point depression in polymer mixtures are proposed from both the FP and LF theories. For miscible poly(ether‐sulfone) (PES)/poly(ethylene oxide) (PEO) blends, the proposed equations are tested. The interaction parameters,X12in FP theory and ζ12in LF theory, can be determined with these equations. The theoretically predicted equilibrium melting‐point depression is subdivided into three terms, namely, the equation‐of‐state, the entropy and the contact interaction terms. When the estimated interaction parameters are converted to the heat of mixing by use of both theories, the composition dependence of the heat of mixing can be properly predicted. Using the interaction parameters obtained from the melting‐point depression in PES/PEO blends, the spinodal curves are simulated from both th

ISSN:1022-1344    

DOI:10.1002/mats.1993.040020104

出版商:Hüthig&Wepf Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractThe atomistic dynamics of the interaction of an atomic force microscopic (AFM) probe with a crystalline polyethylene surface was examined by using the molecular dynamics method. The results show that the internal dynamics of the polymer crystal is such that rapid relaxation occurs, providing for a large amount of structural reversibility and making it possible to perform nondestructive AFM experiments. However, surface and/or AFM tip defects or contaminants (such as those which can be induced by polar molecules adsorbed on the surface), can result in significant perturbations in the AFM images produced, causing large and sharp structures to appear on the surface topology. A rationale of the mechanisms responsible for the image distortions is presented, and a relationship to defects observed in AFM and STM experiments is given.

ISSN:1022-1344    

DOI:10.1002/mats.1993.040020105

出版商:Hüthig&Wepf Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractRealistic, atomistic models of liquid tridecane in broad slits (>3 nm) and in narrow slits of thickness 1,2 nm and 1,0 nm have been obtained using the Monte Carlo technique. The setup of the models is such that the molecules in the slits are in equilibrium with the bulk liquid. The surfaces of the plates are modelled as two‐dimensional arrays of hexagonally packed units having the same size and interaction parameters of a methylene group. The regions adjacent to the plates in slits with thickness>3 nm are characterized by a well defined tendency to form partially ordered layer structures, while molecules at a distance from the plates larger than 1,5 nm are unperturbed. The simultaneous presence of two plates increases the tendency to form layer structures when their distance is 1,2 nm, while this tendency is almost totally destroyed when the slit is squeezed down to a thickness of 1,0 nm. This is also associated with a 10% decrease of the density in the latter sli

ISSN:1022-1344    

DOI:10.1002/mats.1993.040020106

出版商:Hüthig&Wepf Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractThe formation of ring and chain molecules during an irreversible step‐growth polymerization has been modelled on a three‐dimensional twenty six choice cubic lattice, and examined by the Monte‐Carlo method. Movements were not allowed in the system in this preliminary study. The limiting value of the extent of reaction was found to bep= 0,9837 (±0,0003), and the number fraction of molecules found to be rings was 0,300 (±0,045), but the weight fraction was much smaller, 0,056 (

ISSN:1022-1344    

DOI:10.1002/mats.1993.040020107

出版商:Hüthig&Wepf Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractThe Smoluchowski equation is used to derive equations for predicting the values of diffusion controlled propagation and termination rate coefficients in copolymerization. None of the resulting expressions are any more complicated than the analogous homopolymerization results. Diffusion controlled propagation rate coefficients in copolymerization are predicated to depend only very weakly on chain end type, and thus the propagation kinetics of high conversion copolymerizations are expected to be considerably simpler than those of low conversions. In considering termination, expressions for the rate coefficient for termination by ‘reaction diffusion’ are first of all derived. It is possible that under some conditions (for example, high conversions) these expressions describe the overall rate of termination, but in general, overall rates of termination will be determined by rates of center of mass diffusion, which are chain length dependent. For this reason the reaction diffusion results are incorporated into a more general treatment of termination in which chain end motion is both by translational and reaction diffusion; this treatment is envisaged as applying from intermediate conversions onward. Considerable effort is subsequently invested in developing simple descriptions of copolymerization in which rate coefficients (and in particular those for termination) are allowed to be chain length dependent. An important feature of this paper is that for every parameter usilized, a means of associating to it a value appropriate for a real system is discussed; in most cases this association is readily carried

ISSN:1022-1344    

DOI:10.1002/mats.1993.040020108

出版商:Hüthig&Wepf Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractA kinetic model with non‐constant propagation and termination rate constants is given for a sort of anionic polymerization. The expression of molecular weight distribution and other molecular parameters are derived by a non‐steady state procedure. The effect of the reaction conditions on the molecular parameters are illustrated by numerical examples. The theoretical curves of molecular weight distribution with two or three peaks are similar to those of polymers generated in the anionic polymerization of polar monomers in nonpolar solve

ISSN:1022-1344    

DOI:10.1002/mats.1993.040020109

出版商:Hüthig&Wepf Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractEquations for the calculation of the degree of polymerization in 'modified' living polymerizations (living polymerizations in the presence of deliberately added terminating and transfer agents) are developed from a mechanistic/kinetic model. It is shown that a modifier, acting by the mechanism discussed, would cause more chain transfer in a continuous stirred tank reactor (CSTR) than in a batch. This is found to be the case in the living polymerization of 1,3‐butadiene initiated by butyllithium in nonpolar solvents, such as cyclohexane, when 1,2‐butadiene was used as a modifier. Under similar conditions no chain transfer was detected in batch polymerizations, while ≈ 20% transfer was found in a CSTR. The equations developed can be used to calculate the ratio of the rates of propagation and termination,kp/kt. CSTR data yieldedkp/kt≈ 480 at 90°C; re‐evaluation of batch data published earlier by Adams et al. for the same system in hexane solvent yieldskp/kt≈ 1250 and 670 at 50° C and 70°C

ISSN:1022-1344    

DOI:10.1002/mats.1993.040020110

出版商:Hüthig&Wepf Verlag    

年代:1993

数据来源: WILEY