For glassy polymers

For glassy polymers, sorption isotherms are more complex and hysteresis oetween the pressurization and depressurization steps may... 

Largest for glassy polymers like acrylonitrile which are not highly swollen by monomer. (Living macroradicals can be obtained in heterogeneous acrylonitrile polymerization.)... 

Annealing can reduce the creep of crystalline polymers in the same manner as for glassy polymers (89,94,102). For example, the properties of a quenched specimen of low-density polyethylene will still be changing a month after it is made. The creep decreases with time, while the density and modulus increase with time of aging at room temperature. However, for crystalline polymers such as polyethylene and polypropylene, both the annealing temperature and the test temperatures are generally between... 

Studies at higher guest concentration have been performed for glassy polymer hosts at room temperature. Pyrene has been dispersed in PMMA82 and PS83 at... 

Microhardness (MH), has been shown to be a convenient additional technique to detect accurately the ferro to paraelectric phase changes in these copolymers. The increase of MH as a function of VF2 polar sequences observed at room temperature is correlated with the contraction of the p-all-trans unit cell On the other hand, the fast exponential decrease of MH with increasing temperature, observed above Tc, is similar to that obtained for glassy polymers above Tg and suggests the existence of a liquid crystalline state in the high temperature paraelectric phase. This phase is characterized by a disordered sequence of conformational isomers (tg-, tg+, tt) as discussed for Condis crystals [109]. 

While in rubbery polymers differences in the segmental mobility can be more important than differences in the free-volume distribution for glassy polymers often certain basic correlations can be found between the permeability of small molecules and free-volume distribution. Other important factors are the molecular mobility of chain segments and the local chemical composition. 

In contrast, for glassy" polymers, i.e. when T < Tg, the motion of the polymer chains is not sufficiently rapid to completely homogenize the penetrant s environment. Therefore, below Tg the polymer is not in a true equilibrium within the time scale of a conventional diffusion or sorption experiment, (6,9,11,13,15). From these considerations one may state that ... 

One possible solution to this problem is to develop microscopic diffusion models for glassy polymers, similar to those already presented for rubbery polymers. Ref. (90) combines some of the results obtained with the statistical model of penetrant diffusion in rubbery polymers, presented in the first part of Section 5.1.1, with simple statistical mechanical arguments to devise a model for sorption of simple penetrants into glassy polymers. This new statistical model is claimed to be applicable at temperatures both above and below Tg. The model encompasses dual sorption modes for the glassy polymer and it has been assumed that hole"-filling is an important sorption mode above as well as below Tg. The sites of the holes are assumed to be fixed within the matrix... 

The average value of Tg = 90 °C for PS is used from Table 2-2. Using Table 9-4 and Eq. (9-19) for glassy polymers one can immediately calculate the solubility coefficients ... 

Since the stiffness of the bonds transfers to the stiffness of the whole filler network, the small strain elastic modulus of highly filled composites is expected to reflect the specific properties of the filler-filler bonds. In particular, the small strain modulus increases with decreasing gap size during heat treatment as observed in Fig. 32a. Furthermore, it exhibits the same temperature dependence as that of the bonds, i.e., the characteristic Arrhenius behavior typical for glassy polymers. Note however that the stiffness of the filler network is also strongly affected by its global structure on mesoscopic length scales. This will be considered in more detail in the next section. 

Table 2 The set of parameters used in the thermal part of the analysis from [9] and standard for glassy polymers...

For T > Tg, most studies of the mechanical response found in the literature focus on the description of the molten state [8] due to its practical importance while no constitutive law for glassy polymers in the rubbery state is available. The mechanical response of the molten material is non-Newtonian for most polymers and described by t = tit", where q and m are material parameters. We will assume that this non-Newtonian response prevails as soon as Tg is exceeded. Hence, within the same framework as used below Tg, the equivalent plastic strain rate is taken as... 

Natural silk has a high value of 7 x 10 spins/cm. From these data it is clear that very similar amounts of molecular fracture can be obtained in polymers with widely different chemical structures, values approaching 10 spins/g being recorded for CIS PI, CIS PBD, nylon 6 and natural silk under appropriate conditions. Secondly, the lower values obtained for other polymers seem to relate more to their morfdiolo-gy or state rather than their chemical structure e.g. the very low figures for glassy polymers). 

An additional complication for glassy polymers is their spontaneous i ing for many years following vitrification. Linear elastic fracture mechanics can only treat the crack propagation parameters that currently prermil in the test specimens. 

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