ABSTRACT
To studding of physical aging processes of amorphous polymers a significant number of proceedings is devoted. It is found, that the influence of aging on these polymers structure and properties is due to thermodynamical nonequilibrium of glassy state and aging process itself can be considered as a slow approach to system equilibrium with wide distribution of relaxation times [1]. The results of papers [2-4] assume, that as a result of amorphous polymers aging below their glass transition temperature Tg occurs the densification of liquid-like packing of these polymers, that approaches again their structure to equilibrium glassy state. About concrete ways of the mentioned approaching there are two main opinions. The first of them is [5] that, the aging causes polymers free volume changes. The second [6] is that aging effects are due to thermoreversible molecular reformations. The closer definition of these processes are given by the authors of paper [7]. They assumed, that at aging are occurred relatively subtle changes of conformations, occur than, for example, transition from weaker cis-to trans-conformation. They also assume, that the free volume decrease is the aging process display, but not the main cause of a polymer physical properties change. In paper [8] the results of PC thermal aging were described within the framework of cluster model and this allowed to demonstrate, that the present treatment is generalization of the mentioned points of view.In Fig. 3.1 the dependencies of cluster entanglements network density vci on testing temperature T for initial and annealed at 393 K during 6 hours PC are shown. One can see, that the value vci is larger for aged PC, i.e., for it the local order degree is larger. This tendency is fully corresponded to amorphous polymer structure approaching to equilibrium state since such state will be just ordered state [9]. Besides, the increase of segments number in clusters is agreed with paper [7] conclusions that the structural changes are due to relatively subtle conformational changes.Let’s consider further a relative fluctuational free volume f g changes at PC thermal aging. The dependencies of f g on testing temperature T are shown in Fig. 3.2, from which follows, that the value f g for initial PC is larger, than for the aged, in the entire considered temperature range. This is agreed with the paper [6] conclusions. Some more interesting conclusions
allow to make the dependencies f g(yd), adduced in the insertion of Fig. 3.2. These dependencies do not coincide for initial and aged PC and for the same value vc/ the values f g are found smaller for the aged polymer. Since entire fluctuational free volume concentrates in loosely packed matrix, this means, that at thermal aging its densification occurs. Such conclusion is fully agreed with the data for annealed below Tg PAr, obtained by positrons annihilation spectroscopy [10]. Further are dependencies f g(yd) extrapolations of interest to values f g=0 and vcf=0. It is obvious, that at f g=0 should be obtained densely packed structure of polymer, in essence, sole supercluster. The value vd for such structure can be estimated as Lllst (see the equations (1.7) and (1.8)), that for PC (initial or aged) gives the value vc/=7.04xl027 m"3. The extrapolation of plot f g(vd) in the insertion of Fig. 3.2 to f g=0 gives close magnitude vc/, equal about to 6.8xl027 m'3. The extrapolation to vc/=0 gives the value of fluctuational free volume at glass transition temperature Tg. This value distinguishes for initial (~ 0.150) and aged (~ 0.133) PC. Although these values exeed Simha-Boyer universal value f g (~ 0.113 [11]), but they are fully agree a with Sanchez calculations (0.105-0.159 [12]).
