Chemistry Reference
In-Depth Information
uniform feature and a planar direction without a second phase. It indicates
that the four samples have an order of phase separation extent of
(a)4(b)4(d)4(c), which agrees well with the transparency analysis.
The phase separation in solution or matrix can be attributed to the in-
compatibility of the maleinated oil-based resins and styrene. The acid
number of TOPERMA was above 200 mg KOH g
1
,
17
which is much higher
than general-purpose UPEs (about 30 mg KOH g
1
). As a consequence, the
maleate half-esters have a much higher polarity compared to styrene, lead-
ing to the incompatibility between them. Similar results for the mixtures of
soybean oil pentaerythritol glyceride maleates (SOPERMA) and styrene were
reported.
8
As the styrene content increases, the phase separation extent
should decrease gradually due to better solubilization of the maleinated
glycerides in styrene. Therefore, why did the TOPERMA67-ST33 matrix show
the minimum phase-separation extent after curing? One possible effect is
that the high curing temperature improves the collision chance between
TOPERMA and styrene, thus accelerating their diffusion to each other. An-
other effect that may result in this minimum extent of phase separation is
the reactivity ratios of the reactive monomers. It is known that each propa-
gation reaction has a characteristic rate constant, K
mn
, where the first sub-
script refers to the active center and the second refers to the monomer.
Defining the propagation rate constant ratio k
11
/k
12
and k
22
/k
21
as r
1
and r
2
,
respectively, one finally obtains:
26
d M
1
½
¼
M
1
½
r
1
M
1
½
þ
M
2
½
(2)
d M
2
½
½
M
2
r
2
M
2
½
þ
M
1
½
where [M
1
]/[M
2
] and d[M
1
]/d[M
2
] denote the initial feed ratio of mono-
mers and the mole fraction ratio of monomer units in the co-polymer,
respectively. Here styrene and TOPERMA were designated the 1
st
and 2
nd
monomers, respectively. When d[M
1
]/d[M
2
]
¼
[M
1
]/[M
2
], an azeotropic
co-polymerization between them is established. As a result eqn (2) can be
written as
½
M
1
¼
r
2
1
(3)
½
M
2
r
1
1
The reactivity ratios of styrene and monoethyl maleate were reported
as r
1
¼
0.13 and r
2
¼
0.035, respectively.
25
If these values are utilized for
the TOPERMA/styrene system, the molar ratio [M
1
]/[M
2
] is about 1.11, i.e.,
the weight fraction of styrene is about 32 wt%. This value is almost equal
to the styrene content in the TOPERMA67-ST33 feed. Normally, when
the feed ratio of two monomers reaches the ratio for an azeotropic co-
polymerization, the resulting polymer has a tendency to form a homo-
geneous system.
6,27
Otherwise matrices appear as complex heterogeneous
systems composed of styrene-rich phases (hard domains) and oil-rich phases
(soft domains).
5
