CHME 435 – Mid Term Exam
Fall 2009/2010
SOLUTION
1. (2 pts) Plot qualitatively density versus temperature for a semicrystalline polymer. Show and name
any transition temperature (such as Tg and/or Tm) on the plot.
Density
Tg
Tm
T
2. (4 pts) In the following table, list four types of polymerization processes, list the
materials/chemicals involved in each, give the solubility information in case a solvent/water is used
(what is/are soluble in solvent/water and the level of solubility and what is/are not soluble) and
briefly give the advantages and disadvantages the process as compared with the others (especially
regarding heat removal and viscosity increase).
Polymerization
Processes
Materials/
Chemicals
Involved
Solubility
Information
Advantages/Disadvantages and
Comparison with Other Processes
Bulk
Polymerization
Monomer
Initiator
Polymer
Polymer might be
soluble in
monomer.
Heat removal to prevent boiling of monomer is
difficult.
Solution
Polymerization
Suspension
Polymerization
Emulsion
Polymerization
Monomer
Solvent
Initiator
Polymer
Monomer
Water
Suspending
agent
Initiator
Polymer
Monomer
Water
Emulsifier
(Surfactant)
Initiator
Polymer
Monomer is
soluble in solvent.
Initiator and
Polymer may or
may not be soluble
in solvent.
Monomer and
Polymer are not
soluble in water.
Suspending agent
is soluble in water.
Initiator is soluble
in monomer
Initiator is soluble
in water.
Viscosity build-up.
Removal of unreacted monomer is difficult.
Heat of polymerization is taken up by a greater
mass, thus easier temperature control.
Viscosity increase is minimized (lower
viscosity).
Heat removal to the reactor wall is efficient
(water better than an organic solvent because
of higher heat conductivity and heat capacity)
but temperature control is complicated (heat
build-up in the droplets).
Viscosity changes very little with conversion.
Best temperature control.
Viscosity changes very little with conversion.
Monomer is only
slightly soluble in
water.
3. (2 pts) What will be the effect of the following chain transfer on the polymerization rate and the
average degree of the polymerization if k3 ≈ k4 ≈ kp where kp is the rate constant for the propagation
step of the radical chain reaction polymerization.
k3
R′ + RM• Î RM + R′•
k4
R′• + M Î R′M•
&
The overall rate will not change.
Average degree of polymerization (i.e. ave. # of repeat units in the polymer chain) will decrease.
4. (3 pts)
σ
b
c
a
ε
List materials a, b and c from the most stiff to the least:
a
List materials a, b and c from the strongest to the weakest:
>
b
b
>
c
c
>
List materials a, b and c from the toughest to the most brittle:
c
>
>
a
a
>
b
5. (3 pts) Plot qualitatively strain versus time (from t = 0 to t → ∞) for a viscoelastic material for the
following loading.
d
σ
c
c>e>a=d>b
a
b
e
t
ε
d′
c′> e′> a′=d′> b′
c′
b′
e′
a′
t
6. (3 pts) Plot qualitatively strain versus time (from t = 0 to t → ∞) for a viscous material for the
following loading.
σ
t
ε
t
7 (4 pts) Two samples (A and B) with narrow-molecular-weight distributions (Mn≈Mw) are prepared
for a new polymer. Viscosity measurements in a solvent result in a solution viscosity of 1.43 poise
at a concentration of 0.30 g/dl for Sample A and a solution viscosity of 1.63 poise at the same
concentration for Sample B. Determine the molecular weight of sample B taking a=0.5, k ' = 0.5 ,
solvent viscosity = 1.1 poise and Molecular weight of Sample A = 8.50x104.
8. (4 pts) A polymer mixture ( M n =3.3×105, PDI=2.40) contains Polymer A (Mo=20, Mn=1.5×105,
PDI=3.8), Polymer B (Mo=30 Mn=5.5×105, PDI=1.6) and Polymer C (Mo=50, Mn=7.5×105,
PDI=1.0). Determine composition of the polymer mixture in weight fractions.