Chemistry Reference
In-Depth Information
cluster particles between these points. In common case
l
>
r
and equality
sign is achieved in that case, when the indicated chain piece is stretched
fully between points, that is, it has dimension
D
ch
= 1.0. The condition
l
=
r
assumes the equality
d
f
=
d
l
, that follows from the Eqs. (2.6) and (2.7) and
according to Ref. [31] achieves for DLA only. Therefore, polymers structure
quasiequilibrium state realization at
D
ch
= 1.0 within the frameworks of DLA
model assumes also polymer chains straightening also (
l
=
r
) and impossibil-
ity of j
cl
further enhancement (
d
f
reduction).
For semicrystalline polymers it has been shown [32, 33] that their mo-
lecular mobility is realized in noncrystalline regions. For polyethylenes at
relatively small temperatures (> 240 K [34]) noncrystalline regions are de-
vitrificated. In Refs. [35, 36] the hypothesis was proposed, that the indicated
regions have peculiar conformational structure, which cannot be described
by interpenetrating chaotically tangled macromolecular coils model (“felt”
model [37]). Therefore, the question arises about influence of one or another
structural organization on their chains molecular mobility. Proceeding from
this authors of Ref. [38] studied the influence of molecular and structural
characteristics of high density polyethylene (HDPE) noncrystalline regions
on the fractal dimension
D
ch
value and, hence, on molecular mobility level
in these regions.
Apart from the Eq. (2.5), at present there are a number of methodics,
which allow to estimate the value
D
ch
. One from them was proposed in Ref.
[20]:
(
)
,
(2.8)
2
D
-
1
cos
q
=-
1
2
ch
where q is an angle between chain neighboring segments (Fig. 2.2).
FIGURE 2.2
The schematic picture of macromolecule fragment and angles, used for
D
ch
calculation according to the Eq. (2.8) [20].
