Chemistry Reference
In-Depth Information
ΔHl
, determine
T
m
for the high-density poly-
ethylene containing lamella with an average thickness (
l
) of 12.0 nm. Take
γ
e
5
2
γe
T
m
1
Given that
T
m
5
2
0.0874 J/m
2
and
279 MJ/m
3
.
Δ
H
5
4-5 The Clausius
Clapeyron equation for the effects of pressure on an equi-
librium temperature is
dP
=
dT
5Δ
H
=
T
Δ
V
where
ΔV
is the volume change associated
with a phase change. Calculate the melting temperature for polyethylene
in an injection molding operation under a hydrostatic pressure of 80 MPa.
Take
ΔH
is the enthalpy change and
143
.
5
Cat
Δ
H
5
7
.
79 kJ/mol of ethylene repeat units and
T
m
5
1 atm.
4-6 Which of the following polymers would you expect to have a lower glass
transition temperature? Which would have a higher melting point? Explain
why. (Assume equal degrees of polymerization.)
(a)
(
(
)
C
)
OCH
2
CH
2
OC
CH
2
x
O
O
(b)
(
OCH
2
CH
2
OC
C
)
n
O
O
4-7 Estimate the glass transition temperature of a copolymer of vinyl chloride
and vinyl acetate containing 10 wt% vinyl acetate. The
T
g
's of the homo-
polymers are listed in
Table 4.2
.
4-8 According to the Arrhenius equation, ln
a
T
and temperature
T
are related
as follows:
E
R
1
T
2
1
T
0
ln
a
T
5
where
E
is the activation energy for the viscoelastic relaxation and
R
is
the gas constant (8.314 J/mol K).
(a) Obtain an analytical expression for the activation energy for materials
exhibiting viscoelastic behavior that can be described by the WLF
equation in terms of constants
C
1
and
C
2
and
T
0
5
T
g
.
