摘要:

AbstractSynthesis and application of copolymers are not seldom connected with different phase equilibria. Their precise knowledge is of importance for industrial processing as well as it is a profound basis for a better understanding of the nature and thermodynamics of such systems. As a common situation today, enough experimental information is seldom available in the necessary or desired amount, and a lot of model calculation is, therefore, more or less unavoidable to cover the desired ranges of application. Different equations‐of‐state as well as lattice models are discussed with respect to their applicability for calculating liquid‐liquid and gas‐liquid phase equilibria in copolymer solutions and blends. Examples for high‐pressure phase equilibria in monomer/copolymer mixtures, liquid‐liquid demixing in copolymer blends and for the isotropicnematic phase equilibrium in systems with rigid rod‐like copolymers characterized by distributions of rigid and flexible chain parts are given. The effects of copolymer polydispersity are included by means of continuous thermodynamics. Literature references for original sources, earlier reviews and further applications round

ISSN:1022-1344    

DOI:10.1002/mats.1993.040020501

出版商:Hüthig&Wepf Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractWe check here numerically and establish the validity of a simple estimate for the polymer theta‐point on various pure and diluted lattices. Our study on two‐dimensional lattices supports a linear relationship of the θ‐point value with the average numberZeffof non‐bonded (nearest) neighbours on a random self‐avoiding walk (SAW). ThisZeffin turn can be estimated from the connectivity constant μ of SAWs of the correspond

ISSN:1022-1344    

DOI:10.1002/mats.1993.040020502

出版商:Hüthig&Wepf Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractRecently it has been shown that the creep of oriented high‐modulus fibers satisfies a logarithmic time law over very long time intervals. Moreover, the modulus of these fibers increases due to the creep. This was interpreted by the annihilation of conformation defects during creep. In structures with strong intermolecular interactions as in aramides, however, the direct annihilation of defects is difficult to explain. Moreover a direct annihilation leads to a false time law if no further assumption about the properties of the defects are made. In this paper a model for the transport of conformation defects in oriented polymer chains imbedded into an oriented fibrillary structure with strong intermolecular interactions is presented. This modified transport model leads directly to the experimentally observed time law without any further assumptions about the defect propertie

ISSN:1022-1344    

DOI:10.1002/mats.1993.040020503

出版商:Hüthig&Wepf Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractBy use of the pivot algorithm, star‐branched chains withF= 4, 8 and 12 arms of lengthnand linear chains (F= 2) are generated on a tetrahedral lattice (120 ⩽nF⩽ 3 840). By taking into account non‐bonded nearest‐neighbour interactions (each contact contributes an energy ϕ ·kTto the total energy of the configuration) a variation of the thermodynamic quality of the solvent is simulated by a variation of the energy parameter ϕ in the range −0,425 to −0,525. The energy parameter ϕ⊙= −0,475, characteristic of theta conditions, was evaluated by use of an intramolecular criterion (proportionality between mean‐square dimensions and total chain‐length) and confirmed by a crossover scaling analysis. Theta dimensions are found to be larger than those of nonreversal random walks, the deviation growing with

ISSN:1022-1344    

DOI:10.1002/mats.1993.040020504

出版商:Hüthig&Wepf Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractIt is the aim of this work to develop analytical force field expressions that can be rapidly evaluated by computers. The new expressions approximate the energy hypersurfaces as described by the usual force fields. The energies and the derivatives of the energy expressions, i. e. the forces acting on the atoms, in most cases can be very quickly calculated as functions of one squared distance of two atoms per interaction, avoiding slow operations like cosine, square root etc. Formulae and algorithms are given to calculate the parameters needed from those of the AMBER force field.

ISSN:1022-1344    

DOI:10.1002/mats.1993.040020505

出版商:Hüthig&Wepf Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractThe chain rigidity of poly(p‐hydroxybenzoate) was estimated through the theoretical evaluation of its persistence length (Lp). A non‐Brownian molecular dynamics (MD) simulation of an isolated chain with 20 monomeric units was performed. The sampled conformational population was analyzed and the orientational correlation function between monomeric units along the chain was calculated. An algorithm based on the worm‐like chain model was applied to evaluate the persistence length. The results were compared with those obtained from equilibrium models like the freely‐rotating‐chain and the rotational‐matrix method with fluctuations. Equilibrium models give different results depending on the degree of accuracy used in describing the monomeric unit. The inclusion of thermal fluctuations is crucial to obtain realistic results. These coincide with those given by MD simulation when only nearest‐neighbour orientational correlations are taken into account: inclusion of higher‐order correlation terms leads to lower values of the persistence length. The origin of this discrepancy was investigated. The MD simulation results are characterized by an overrepresentation of conformations with a short end‐to‐end distance resulting from an anomalous energy concentration in the first bending mode of the chain. In analogy with previous simulation results from systems characterized by a week coupling amoung their degrees of freedom, failure in the energy equipartition is proposed as a likely explanation of the anomalous

ISSN:1022-1344    

DOI:10.1002/mats.1993.040020506

出版商:Hüthig&Wepf Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractConformational energies as function of rotational angles over two consecutive skeletal bonds for bothmesoandracemicdiads of poly(Nvinyl‐2‐pyrrolidone) have been computed. The results of these calculations were used to formulate a statistical model that was then employed to calculate the unperturbed dimensions of this polymer. The conformational energies are sensitive to the Coulombic interactions, which are governed by the dielectric constant, of the solvent, and to the size of the solvent molecules. Consequently, the calculated values of the polymeric chain dimensions are strongly dependent on the nature of the solvent, as it was experimentally found bef

ISSN:1022-1344    

DOI:10.1002/mats.1993.040020507

出版商:Hüthig&Wepf Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractIn this work, a neural network was used to learn features in potential energy surfaces and relate those features to conformational properties of a series of polymers. Specifically, we modeled Monte Carlo simulations of 20 polymers in which we calculated the characteristic ratio and the temperature coefficient of the characteristic ratio for each polymer. We first created 20 rotational potential energy surfaces using MNDO procedures and then used these energy surfaces to produce 10000 chains, each chain 100 bonds long. From these results we calculated the mean‐square end‐to‐end distance, the characteristic ratio and its corresponding temperature coefficient. A neural network was then used to model the results of these Monte Carlo calculations. We found that artificial neural network simulations were highly accurate in predicting the outcome of the Monte Carlo calculations for polymers for which it was not trained. The overall average error for prediction of the characteristic ratio was 4,82%, and the overall average error for prediction of the temperature coefficient was

ISSN:1022-1344    

DOI:10.1002/mats.1993.040020508

出版商:Hüthig&Wepf Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractA method based on matrix algebra and on the rotational isomeric state scheme to study the configurational‐ conformational entropy of 1,4‐polydienes with geometrical isomerism has been developed. Bernoullian and first‐and second‐order Markovian statistics for the sequences ofcisandtransunits along the chains have been considered, and the explicit relation between entropy and mole fraction ofcisunits has been derived. Calculations performed by using available experimental data for the configurational parameters and the conformational partition functions of 1,4‐polybutadiene and 1,4‐polyisoprene show that entropy is a monotonic function of the geometrical isomer composition. While the entropy of polybutadiene increases with the content ofcisunits, the reverse is true for p

ISSN:1022-1344    

DOI:10.1002/mats.1993.040020509

出版商:Hüthig&Wepf Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractA computer program, MACO5, was developed which employs the Monte‐Carlo approach to simulate the time‐variation of the mass spectral peak intensities of a copolymer sample during the synthesis of an A/B copolyester via reactive blending of a mixture of homopolyesters A and B or when a copolymer undergoes partial degradation. The program was first used to simulate literature data consisting of a series of mass spectra of a butadiene/styrene copolymer subjected to partial ozonolysis. It was also used to investigate the role of terminal groups in reactive blending processes. Two models were developed: the first one describes inner‐group ester‐ester exchange reactions, the second describes the process in which and active terminal groups attacks an ester group. The predictions of the two models are compared with recent experimental mass spectral data concerning a poly(ethylene adipate‐co‐ethylene terephalate)

ISSN:1022-1344    

DOI:10.1002/mats.1993.040020510

出版商:Hüthig&Wepf Verlag    

年代:1993

数据来源: WILEY