Chemistry Reference
In-Depth Information
Table 1.
Obtained copolymers.
in Figure 1.a and 1.b, with independent
particles distribution, for copolymers where
one of the monomers is the main compo-
nent in the backbone of the chain. How-
ever, when the percentage of both mono-
mers in the copolymer chain is similar, the
final product does not present a defined
morphology, as can be seen in the SEM
image corresponding to the EP59 sample
(Figure 1.c). This characteristic is typical
of polymers synthesized with a dissolved
catalytic system.
[23]
Such different behav-
iour could be related to the amorphous
character of the material: EP59 is elasto-
meric and the support particle can not
be broken when the polymerization takes
place.
The crystallinity of the synthesized
samples has been studied qualitatively by
XRD. The results are shown in Figure 2 for
all the copolymers. It is possible to check
how for copolymers EP99 and EP3 the
typical peaks for polyethylene and poly-
propylene, respectively, are obtained. When
the propylene is the monomer with higher
percentage (Figure 2, EP3), it is possible to
distinguish four fundamental signals in the
spectra for 2
% E molar
a)
Copolymer
C
2
/C
3
(mol/mol)
gas phase composition
EP3
0.010
3.4
EP6
0.013
5.8
EP13
0.029
12.7
EP21
0.126
20.5
EP31
0.390
30.4
EP59
0.970
59.0
EP81
5.046
80.7
EP87
6.740
86.7
EP94
19.000
93.8
EP99
107.69
99.0
a)
Copolymer composition obtained from triad distri-
bution as E
¼
EEE
þ
EEP
þ
PEP.
systems are used, it is expected that the
polymer particles replicates the shape of
the support.
[22]
This behaviour can be seen
values of 14.1, 16.9, 18.6, and
21.7, associated to the
u
a
or monoclinic
modification of iPP.
[24]
The peaks are wider when the ethylene
content increases because the second mono-
mer inclusion introduces higher disorder
into the lattice. The maximum disorder is
found for the EP59 copolymer, where it is
impossible to distinguish any characteristic
peak of the homopolymers.
[12]
On the other
composition limit, when the ethylene con-
tent is larger, two signals can be observed
which could be related with the orthor-
hombic
[25]
phase for 2
u
values of 21.5
8
and
23.9
8
, respectively.
Figure 3 shows the results obtained by
DSC for the glass transition temperature
(
T
m2
)in
function of the ethylene content. It is clear
that values for these temperatures are
lower for copolymers close to 50/50 ethy-
lene/propylene ratio. This is related to the
considerable decrease of crystallinity, since
the crystal domains which are being formed
T
g
) and the melting temperature (
Figure 1.
SEM micrographs for three different copolymers (a:
EP99, b: EP3, c: EP59).
