Molecular theory, amorphous polymers

In addition to temperature and concentration, diffusion in polymers can be influenced by the penetrant size, polymer molecular weight, and polymer morphology factors such as crystallinity and cross-linking density. These factors render the prediction of the penetrant diffusion coefficient a rather complex task. However, in simpler systems such as non-cross-linked amorphous polymers, theories have been developed to predict the mutual diffusion coefficient with various degrees of success [12-19], Among these, the most notable are the free volume theories [12,17], In the following subsection, these free volume based theories are introduced to illustrate the principles involved. 

At the high polymer concentration used in plasticized systems the viscosity of amorphous polymer is given by the modified Rouse theory at low molecular weight, M - 2Mr [from equation (47)] and by the modified Doi-Edwards equation at high molecular weight. In the first case... 

Contents Chain Configuration in Amorphous Polymer Systems. Material Properties of Viscoelastic Liquids. Molecular Models in Polymer Rheology. Experimental Results on Linear Viscoelastic Behavior. Molecular Entan-lement Theories of Linear iscoelastic Behavior. Entanglement in Cross-linked Systems. Non-linear Viscoelastic-Properties. 

Despite its plausibility and the apparent absence of driving forces to produce other large scale arrangements, the random coil configuration has been questioned on various grounds. It seems worthwhile to review the evidence at this point, since most molecular theories for amorphous polymers are based on the random coil picture. 

Graessley.W.M. Molecular entanglement theory of flow behavior in amorphous polymers. J. Chem. Phys. 43, 2696-2703 (1965). 

The theory is not limited in its application to the transient properties of amorphous polymers it can be used to make molecular interpretation and prediction of the dynamic viscoelastic properties of crosslinked polymers [24] as well. According to the Fourier-Laplace transformation, the complex tensile modulus can be separated into the real and imaginary parts... 

The current interest is the examination of the consequences of fiee-volume theory on the effect of the solvent size on diffusional behavior, and the behavior of the diffusion process near the glass transition. Clearly, these two problems are interrelated. The experimental data needed to investigate both are accurate diffu-sivity-temperature data for a series of solvents that covers a wide range of molecular sizes. The series of solvents used should include solvents of large molecular size, incapable of segmental motion. Some recent work is reported hoe using polymethyl methacrylate, an amorphous polymer that can be studied over a wide temperature range. 

The purpose of our study was a rheological evaluation of the effect of composition on the properties of ABS resins in the molten state. Steady-state viscosity was determined over a wide range of temperatures and shear rates. The shear modulus in the molten state was determined by measurement of the diameter of the extrudate. ABS resins in the molten state behaved as an amorphous homophase polymer. The effect of the elastomer phase on the viscoelastic properties which characterize the behavior of the continuous matrix, i.e. monomer friction coefficient and molecular weight between entanglements (Me), was calculated by the application of the molecular theories. The significance of these properties in heterophase systems is discussed. 

Non-Newtonian viscosity, 77, is expressed in molecular theories for amorphous one-phase polymer as... 

Conventional models or theories consider only the segmental relaxation of amorphous polymers and the primary relaxation of nonpolymeric glass-formers in the change of molecular mobility with temperature and pressure (and concomitant changes in free volume and/or configurational entropy) leading to vitrification. Here we wish to recognise two different kinds of secondary relaxation processes. There... 

While there are many sophisticated theories of the equation of state for amorphous polymer liquids, a simple free-voliune equation of state has been found to be useful for many problems. The viscosity of bulk amorphous macromolecules is developed and discussed as a function of molecular... 

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