Properties in the Glassy State

Density, p, depends on atomic composition, which can be represented by a 

The CRU (constitutive repeating unit) can be considered as the monomer unit of the network. It has been defined in Chapter 2. 

The density of many linear, as well as tridimensional, polymers has been plotted against Ma in Fig. 10.2. One can estimate p from a power law  

This empirical relationship remains valid for light inorganic materials such as calcium carbonate, silica, aluminium, etc., and allows the density to be predicted with a maximum error of 10% in the range of most usual organic network densities (1100 p 1400 kg m ). In this range, density can be approximated by a linear relationship  

Typical density values for networks are 1150 1330 kg m for amine-crosslinked epoxies (Ma 7 1) 1120-1180 kg m for styrene-crosslinked vinyl esters (Ma 6.3-7.1) and 1170-1220 kg m for styrene-crosslinked 

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It thus seems that there is no direct link between volumetric and elastic properties in the glassy state and that the anomalous density variations cannot be attributed to a crosslink density effect, either direct (on molecular packing) or indirect (through internal antiplasticization as discussed below). It seems reasonable to correlate this behavior with the presence of unreacted epoxides. The density would be (in the systems under consideration) a continuously increasing function of the amine/epoxide ratio, owing to the... 

Cured epoxy resins are often used as structural materials and their performance is determined by their mechanical properties in the glassy state. However, as mentioned in Chapter 5, the mechanical properties of unfilled resins in the glassy state are almost equal and do not depend much on the chemical structure and degree of crosslinking. 

It has been mentioned in several previous chapters that below the glass transition temperature the convolutions of polymer chain backbones are largely immobilized. Thus, most viscoelastic properties in the glassy state must reflect limited local molecular motions. There are several possible types of these torsional oscillations, rotations around chain backbone bonds with short-range coordination, various configurational rearrangements of side chains, and rotations of terminal groups of side chains such as methyl which require very little cooperation from the environment. 

In the preparation and processing of ionomers, plasticizers may be added to reduce viscosity at elevated temperatures and to permit easier processing. These plasticizers have an effect, as well, on the mechanical properties, both in the rubbery state and in the glassy state these effects depend on the composition of the ionomer, the polar or nonpolar nature of the plasticizer and on the concentration. Many studies have been carried out on plasticized ionomers and on the influence of plasticizer on viscoelastic and relaxation behavior and a review of this subject has been given 119]. However, there is still relatively little information on effects of plasticizer type and concentration on specific mechanical properties of ionomers in the glassy state or solid state. 

Polycarbonate (PC) serves as a convenient example for both, the direct determination of the distribution of correlation times and the close connection of localized motions and mechanical properties. This material shows a pronounced P-relaxation in the glassy state, but the nature of the corresponding motional mechanism was not clear 76 80> before the advent of advanced NMR techniques. Meanwhile it has been shown both from 2H NMR 17) and later from 13C NMRSI) that only the phenyl groups exhibit major mobility, consisting in 180° flips augmented by substantial small angle fluctuations about the same axis, reaching an rms amplitude of 35° at 380 K, for details see Ref. 17). 

Oleinik, E. F. Epoxy-Aromatic Amine Networks in the Glassy State Structure and Properties. Vol. 80, pp. 49-99. 

The reaction of curing the epoxy-amine system occurring in the diffusion-controlled mode has little or no effect on the topological structure of the polymer 74> and on its properties in the rubbery state. However, the diffusion control has an effect on the properties of glassy polymers 76 78). 

Structure and Properties of Epoxy-Aromatic Amine Networks in the Glassy State... 

Thus, although some degree of local organization may indeed occur in amorphous systems, and may even have some effect on the mechanical properties of polymers in the glassy state, the influence on the mechanical properties of melts, concentrated solutions and networks appears to be negligible. 

Labana, S. S., Newman, S., Chompff, A. J. Chemical effects on the ultimate properties of polymer networks in the glassy state, pp. 453-477. In Polymer networks, structure and mechanical properties. See Ref. (260). 

Various authors have considered the glassy state behaviour, and in particular the sorption of gases and supercritical fluids. The main dificulty is to find a thermodynamic model suitable for the description of the properties of the glassy state. Also, the normal equations of state specially developed for polymeric systems are not directly applicable to the non-equilibrium conditions of this state. 

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