Amorphous polymers physical structure

In the case of an amorphous polymer the glass transition temperature will define whether or not a material is glass-like or rubbery at a given temperature. If, however, the polymer will crystallise, rubbery behaviour may be limited since the orderly arrangement of molecules in the crystalline structure by necessity limits the chain mobility. In these circumstances the transition temperature is of less consequence in assessing the physical properties of the polymer. 

The physical origin for this difference is indicated in Fig. 5.21 amorphous polymers below Tg exhibit a constant modulus, since they are single-phase, rigid-chain structures, while semicrystalline, two-phase structures in the range Tg < T < Tm become weaker with increasing temperature, due to the increased mobility of the amorphous chains. 

It is known that in the glassy state below the glass transition temperature the physical properties of epoxy resin as well as other amorphous polymers are generally little dependent on temperature and structure 1,28). Also, the modulus of elasticity (E) does only weakly depend on the crosslinking density. 

For glassy amorphous polymers analogous expressions could be derived from the experimental data in the literature. The numerical values of the constants in the equations are somewhat lower, and also the accuracy is lower (this is probably due to the fact that the physical structure of the glassy state strongly depends on the processing of the polymer). 

Early fundamental studies of gas transport in polymers were almost entirely confined to hydrocarbon materials above their glass transition temperatures. The essentially nonpolar structures of the elastomers led to a number of reasonably successful attempts to correlate gas transport parameters with various physical characteristics of the gases and the polymers. These have been summarized and discussed in a number of papers In addition to studies with hydrocarbon elastomers a few studies of other amorphous polymers above their glass transition temperatures have dealt with polyvinyl acetate silicones and fluorocarbon polymers Recent studies have also dealt with poly(methyl aciylate) poly-(vinyl methyl ether) and poly(vinyl methyl ketone) With these more... 

Floes pack in a space-filling, Euclidean fashion hence, at the floe level of structure, the material can be considered as an orthodox amorphous substance. Within the floes, however, particles pack in a non-Euclidean, fractal fashion. For such a structural arrangement, the volume fraction of particles in a floe (O ) is equivalent to the volume fraction of particles in the entire system (O), namely = O. This well-known relation of polymer physics (11) has been experimentally shown to also apply to colloidal aggregates above their gelation threshold (12). 

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