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e1
QUESTIONS
1. This question is related to your knowledge of how
chemical structure affects a polymer’s glass transition
temperature. For each pair below draw the repeat unit
of the polymers, select which polymer you believe has
a higher glass transition temperature, and explain
2. You have polymerized a product containing seven
PMMA molecules: three of the molecules have a
degree of polymerization of 150; two of the molecules
have a degree of polymerization of 400; one has a
degree of polymerization of 500; and the last has a
degree of polymerization of 1000. Calculate the num-
ber average and weight average molecular weights
of the polymer product and the polydispersity index.
Ignore the presence of initiator fragments.
ANSWERS
1. Please see Figure I.2.2.9.
CHAPTER I.2.2
Polymers: Basic Principles
H
H
H
CI
H
CI
Poly(hydroxyethyl methacrylate) Poly(propyl methacrylate)
CH3
CH3
Poly(hydroxyethyl methacrylate) will
have a higher Tg for the same reason
Poly(vinyl chloride) will have a higher
Tg due to a symmetry argument.
e2
2. In the problem statement, you are supplied with the
number of molecules with “i” repeat units (Ni). With
this information, the molecular weight of each mole-
Number of
Molecules
(Ni)
Degree of
Polymerization
(i)
Molecular Weight
of Molecule
(Mi)
3 150 15,000
3. Tooth enamel is a hard tissue that will be exposed
to many stresses, especially compressive stresses.
Furthermore, the material must be biostable and not
wear resistance. It should be relatively hydrophobic
or so highly cross-linked that it will not absorb water.
It should also exhibit a negligible rate of degradation
in vivo.
