Chemistry Reference
In-Depth Information
7-9 When an equilibrium step-growth polymerization is 99.5% complete what
fraction of the reaction mixture is still monomer
(a) on a mole basis?
(b) on a weight basis?
7-10 Ethylene glycol is polymerized with an impure sample of terephthalic
acid, which contains 1.0 mol% benzoic acid. How does this impurity affect
the limiting degree of polymerization at very high conversions?
7-11 Consider the following alkyd recipe:
Pentaerythriol
1.21 moles
Phthalic anhydride
0.54 moles
Tricarballylic acid
0.49 moles
Can the above reaction be carried out to complete conversion without
gelling? Explain why equations such as x
i
5
p)p
i-1
and w
i
5
p)
2
p
i-1
cannot be used to calculate the fractions of the monomers in the
above reaction mixture.
(1
i(1
7-12 Consider a step-growth polymerization using a bi-functional monomer
which contains two co-reactive sites, the so-called AB-type monomer.
(a) What is the average functionality of the monomer?
(b) Would the reaction mixture gel?
(c) At a given extent of reaction p, what are the respective probabilities
of finding the co-reactive sites reacted and un-reacted?
(d) What are the mole and weight fractions of the molecules containing
10 monomers in the reaction mixture when p
0.99?
(e) What are the most probable sizes of the molecules in the reaction mix-
ture in terms of mole and weight fractions when p
5
0.99 and what
5
are the corresponding mole and weight fractions?
(f) Given that GPC analysis shows that M
n
of the reaction mixture
described in part (d) is 12,000 g/mol, what are the polydispersity index
and standard deviation of the number molecular weight distribution of
the reaction mixture?
7-13 Given that the variance of the number distribution of the molecular weight
of a step-growth polymerization reaction mixture is given by the following
equation:
2
n
5
M
n
σ
M
w
M
n
2
(a) Show that the corresponding standard deviation is given by the follow-
ing equation:
