ISSN:0007-1641    

DOI:10.1002/pi.4980170201

出版商:John Wiley&Sons, Ltd    

年代:1985

数据来源: WILEY

摘要:

AbstractThe earliest investigations on rubber elasticity, commencing in the 19th century, were necessarily limited to phenomenological interpretations. The realisation that polymers consist of very long molecular chains. commencingc. 1930, gave impetus to the molecular theory of rubber elasticity (1932‐). according to which the high deformability of an elastomer, and the elastic force generated by deformation, stem from the configurations accessible to long molecular chains. Theories of rubber elasticity put forward from 1934‐1946 relied on the assumption that the junctions of the rubber network undergo displacements that are affine in macroscopic strain. The theory of James and Guth (1947) dispensed with this premise, and demonstrated instead that themeanpositions of the junctions of a ‘phantom’ network consisting of Gaussian chains devoid of material properties areaffine in the strain. The vital significance of the distinction between the actual distribution of chain vectors in a network and their distribution if the junctions would be fixed at their mean positions went unnoticed for nearly 30 years. Experimental investigations, commencing with the incisive work of Gee in 1946. revealed large departures from the relationship of stress to strain predicted by the theories cited. This discrepancy prompted extensive studies, theoretical and experimental, during succeeding years.Inquiry into the fundamentals of polymer networks, formed for example by interlinking very long polymer molecules, exposed the need to take account of network imperfections, typically consisting of chains attached at only one end to a network junction. Various means were advocated to make corrections for these imperfections. The cycle rank ζ of the network has been shown (1976) to be the fundamental measure of its connectivity, regardless of the junction functionality and pattern of imperfections.Often overlooked is the copious interpenetration of the chains comprising typical elastomeric networks. Theories that attempt to represent such networks on a lattice are incompatible with this universal feature. Moreover, the dense interpenetration of chains may limit the ability of junctions in real networks to accommodate the fluctuations envisaged in the theory of phantom networks.It was suggested in 1975 that departures from the form predicted for the elastic equation of state are due to constraints on the fluctuations of junctions whose effect diminishes with deformation and with dilation. Formulation of a self‐consistent theory based on this suggestion required recognition of the non‐affine connection between the chain vector distribution function and the macroscopic strain in a real network, which may partake of characteristics of a phantom network in some degree. Implementation of the idea was achieved through postulation of domains of constraint affecting the equilibrium distribution of fluctuations of network junctions from their mean positions. This led in due course to a theory that accounts for the relationship of stress to strain virtually throughout the ranges of strain accessible to measurement. The theory establishes connections between structure and elastic properties. This is achieved with utmost frugality in arbitrar

ISSN:0007-1641    

DOI:10.1002/pi.4980170202

出版商:John Wiley&Sons, Ltd    

年代:1985

数据来源: WILEY

摘要:

AbstractThe lineshape analysis of the2H nuclear magnetic resonance of uniaxially strained poly(1,4‐butadiene) networks deuterated homogeneously and selectively at network junctions shows that the orientation of chain segments attached to crosslinks is larger than the average segmental orientation. In addition, it is shown that the molecular effective extension ratio of all elastically effective chains is smaller than the macroscopic extension ratio, and short chains are stretched to a higher extent than long chains. The deviation from the affine deformation behaviour and the onset of inhomogeneous deformation of individual chains takes place at the transition from the Gaussian to the non‐Gaussian network. In the Gaussian regime the segmental orientation varies with the inverse of the molecular weight of elastically effective chains in agreement with molecular theories of rubber elasticity.2H n. m. r. spectra of a thermoplastic poly(styrene‐b‐butadiene‐b‐styrene) block copolymer carrying selectively deuterated butadiene segments at the block boundaries reveal an enhanced mobility of these segments under deformation.2H n. m. r. experiments on amorphous segmented polyurethanes selectively deuteratured in hard and soft segments, respectively, show that the elasticity in these samples is achieved by physical crosslinks formed by very small highly mobile aggregates of hard segments dispersed in the soft phase. Within the hard domains two processes for motion due to phenyl groups in 4. 4'‐methylenebis(phenylisocyanate) units and CH2groups in 1. 4‐butanediol units can b

ISSN:0007-1641    

DOI:10.1002/pi.4980170203

出版商:John Wiley&Sons, Ltd    

年代:1985

数据来源: WILEY

摘要:

AbstractProcedures for the evaluation of quantitative orientation parameters using wide‐angle x‐ray scattering data are outlined. Data are presented for crosslinked natural rubber. a copolymer of polyethylene and polyvinylacetate and for polymethylmethacrylate. These quantitative orientation data are compared to the predictions of models of rubber elasticity. Critical comparisons are made with affine and phantom chain models and the variable network constraint model recently introduced by Erman and Flory. The effects of entanglements and segmental interactions are also considered. An approach is introduced which allows the evaluation of the level of intersegmental interaction contribution to the orientation‐strain beha

ISSN:0007-1641    

DOI:10.1002/pi.4980170204

出版商:John Wiley&Sons, Ltd    

年代:1985

数据来源: WILEY

摘要:

AbstractEquilibrium elastic behaviour of crosslinked polymers (networks) is analysed both from the macroscopic (phenomenological) and microscopic (molecular) points of view. Molecular mechanisms possibly responsible for non‐linear rubber elasticity are discussed. They include: conformational entropy of network chains at small and large extensions, hindered rotation of such chains and intra‐chain point interactions, dipole‐dipole interactions between asymmetric chain segments, and topological constraints leading to chain entangl

ISSN:0007-1641    

DOI:10.1002/pi.4980170205

出版商:John Wiley&Sons, Ltd    

年代:1985

数据来源: WILEY

摘要:

AbstractElasticity is discussed as an aspect of viscoelasticity, which is described by the tube model. The effects of both crosslinks and entanglements contribute to this model and a discussion of how these effects can be quantified is given. At high enough concentration, entanglements ensure the existence of elastic effects even without crosslinks, and a theory is presented on how this dynamical phase change comes about.

ISSN:0007-1641    

DOI:10.1002/pi.4980170206

出版商:John Wiley&Sons, Ltd    

年代:1985

数据来源: WILEY

摘要:

AbstractThe application of the continuous‐time random walk model to the description of the non‐equilibrium stress response of a crosslinked network is discussed. Different versions of the continuous‐time random walk model lead to the prediction of a stress relaxation function having either a fractional‐power law form or a fractional‐exponential law form. Both forms are tested against experimental data on the stress relaxation and loss modulus behaviours of crosslinked natur

ISSN:0007-1641    

DOI:10.1002/pi.4980170207

出版商:John Wiley&Sons, Ltd    

年代:1985

数据来源: WILEY

摘要:

AbstractA large number of specially prepared model networks with different types of network defects have been produced since de Gennes proposed the reptation motion for linear chains. The viscoelastic properties of these model networks show clearly that branched chains and dangling chains are the cause of the gradual and extremely slow relaxations in lightly crosslinked networks. These experimental results have been followed by theoretical developments that point towards a complete molecular theory for the non‐equilibrium properties of lightly crosslinked networks. It is proposed that the presence of dangling chains in endlinked networks may be revealed by measurements of the viscoelastic properties of such networks near the transition zon

ISSN:0007-1641    

DOI:10.1002/pi.4980170208

出版商:John Wiley&Sons, Ltd    

年代:1985

数据来源: WILEY

摘要:

AbstractIn this study two aspects of the thermoviscoelasticity of EPDM elastomers are discussed, namely their complex behaviour as a result of the presence of (micropara)crystallinity, and the dependence of the time‐temperature shift functions on the crosslink densit

ISSN:0007-1641    

DOI:10.1002/pi.4980170209

出版商:John Wiley&Sons, Ltd    

年代:1985

数据来源: WILEY

摘要:

AbstractPredictions of the theory of elasticity of real networks are compared with results of experiments. The shape of the stress‐strain curve for networks in the dry and swollen states and over wide ranges of strain, both in tension and compression, agrees with results of calculations based on the theory. The theory is also in close agreement with results of multiaxial stress‐strain experiments and with the predictions of the degree of crosslinking obtained from measurements of the modulus. The theory may additionally be applied to the analysis of birefringence. The assumption of the linear additivity of the elastic and mixing free energies in a swollen network leads to results which are in agreement with experimental findings on different crosslinked syst

ISSN:0007-1641    

DOI:10.1002/pi.4980170210

出版商:John Wiley&Sons, Ltd    

年代:1985

数据来源: WILEY