Chemistry Reference
In-Depth Information
FIGURE 1.4
The dependences of macromolecular entanglements cluster network density
n
cl
on testing temperature
T
for PC(1) and PAr (2) [28].
Earlier within the frameworks of local order concepts it has been shown
that temperature
T
'
g
is associated with segmental mobility releasing in poly-
mer loosely packed regions. This means, that within the frameworks of clus-
ter model
T
'
g
can be associated with loosely packed matrix devitrification.
Two main models, describing local order structure in polymers (with
folded [34] and stretched [28] chains) allows to make common conclusion:
local order regions in polymer matrices play role of macromolecular entan-
glements physical network nodes [28, 34]. However, their reaction on me-
chanical deformation should be distinguished essentially, it at large strains
regions with folded chains (“bundles”) are capable to unfolding of folds in
straightened conformations, then clusters have no such possibility and poly-
mer matrix deformation can occur by “tie” chains (connecting only clusters)
straightening, that is, by their orientation in the applied stress direction.
Turning to analogy about mediums with crystalline morphology of poly-
mer matrices, let us note, that semicrystalline polymers (e.g., high-molecular
polyethylenes) large strains, making 1000 ÷ 2000%, are realized owing to
crystallites folds unfolding [35].
