Chemistry Reference
In-Depth Information
Figure 3.
Glass transition and second melting temperatures for the copolymers in function of the ethylene content
(% E molar).
Figure 4 shows the results obtained by TREF
as a function of the ethylene comonomer
content and Figure 5 shows the TREF
profiles for these copolymers.
This technique was limited to copoly-
mers with very different comonomer con-
tents, since in the middle range of como-
nomer content an amorphous copolymer
was reached. In this case, the limit is lower
than 10% molar of ethylene and higher
than 80% molar of ethylene. For copoly-
mers with low ethylene content (EP3 to
EP13), values for T
e
decreases faster with
%Emolar than in the high ethylene content
(EP81 to EP99). This should be due to the
fact that the crystallinity of copolymers
with high propylene content is influenced
by the composition and sequence distribu-
tion, besides tacticity. This make the study
of the chemical composition distribution
of polypropylene copolymers more com-
plicated. The study of both tacticity and
composition distribution should be com-
pleted with other techniques like FTIR. For
low and high comonomer contents, the
is
low too, while for intermediate comonomer
contents the
SF
is very high, as expected.
In Ta
ble
3 the weight average molecular
wei
gh
t (
M
w
) and the polydispersity index
(
M
w
=
M
n
) of the copolymers by GPC and
G
PC-
MALS
ar
e
sho
wn.
M
w
and
M
w
=
M
n
values obtained by
GPC are higher tha
n t
he ones obtained by
GPC-MALS. The
M
w
values are depen-
dent on comonomer content, showing the
lowest values from 20 to 60%E molar. The
polydispersity index is approximately con-
stant, as expected for
SF
Table 2.
Crystallinity and n
E
and n
P
values for the copolymers.
Crystallinity (%)
a)
Copolymer
n
E
n
P
EP3
38.9
1.05
30.06
EP6
35.3
1.20
20.42
EP13
19.0
1.15
7.88
EP21
-
1.14
4.51
this
single-site
EP31
-
1.25
2.85
catalyst.
[28]
The use of a multiangle light scattering
detector allows the evaluation of both the
molecular weight and the mean radius of
gyration (R
g
), for each slice of the size
exclusion chromatogram. The dependence
EP59
-
2.07
1.41
EP81
18.1
4.64
1.14
EP87
28.2
6.67
1.12
EP94
37.5
15.00
1.10
EP99
51.1
81.84
1.00
a)
Calculated from the second melting point.
