26.381 – Polymer Science for Engineers I – QUIZ 2
1. (8 points) Fill in the blanks:
C=O, also known as a carbonyl , is a common part of many reactive groups used
in step polymerizations. The carbon in the C=O has a partial positive charge and is
attacked by groups like –OH, –NH2 and –SH, which are described collectively as
nucleophiles . Small molecules produced in such reactions, often referred to as
condensation products, are removed or reacted away to enhance the reaction rate.
The isocyanate group is the one type of C=O containing group whose reaction
does not generate a small molecule byproduct under most circumstances.
Grading: Correct entry in blank 2 points each
2. (6 points) Draw and label amide, ester, and urethane linkages, using dangling bonds to
indicate where the polymer chain attaches. For example, –O– would be the way to indicate
an ether linkage.
O O O
C N C O O C N
________________ ________________ H
Amide Ester Urethane
Grading: Correct drawings of linkages 2 points each
3. (2 points) Rank the amide, ester, and urethane linkages in order of acid resistance:
______Ester______ > ____Urethane____ > ______Amide______
(most acid resistant) (least acid resistant)
Grading: Correct order of acid resistance 2 points
4. (4 points) Show the first (electrophilic attack) step in the polymerization of a formaldehyde
resin (i.e. formaldehyde reacting with something).
Phenol Formaldehyde Monomethylol phenol
Grading: Correct starting molecules 1 point each
Correct product 2 points
BONUS (4 points) If vinyl amine (CH2=CH–NH2) cannot be directly polymerized because of
the amine group, how would you propose to make poly(vinyl amine)? (use back as needed)
If we cannot polymerize poly(vinyl amine) directly, we need to find another way of generating
an amine group after the fact. We know from previous discussions that amide groups can be
hydrolyzed to form amines plus carboxylic acids. Therefore, a logical means of forming
poly(vinyl amine) would be to polymerize a vinyl amide monomer to form a poly(vinyl amide):
H2C C (free radical polymerization) CH2 C
O C O C
We can then hydrolyze the amide linkage in this polymer – something that would work best
under acidic conditions (low pH) – to produce the desired poly(vinyl amine) plus a carboxylic
H H OH
CH2 C (acid hydrolysis) CH2 C + O C
NH NH2 R
In fact, this is exactly how poly(vinyl amine) is produced industrially; the poly(vinyl amide) used
in practice is poly(vinyl formamide) (R = H), and the byproduct of its hydrolysis is formic acid –
the same compound that causes the bites of fire ants to be painful (hence the name, which is
derived from the Latin word for ant, formica).
One potential alternative to the above would be to perform a free-radical polymerization of
vinyl isocyanate to form poly(vinyl isocyanate), followed by the reaction of this polymer with
water to produce carbon dioxide and poly(vinyl amine), as shown on the following page.
H 2C C (free radical polymerization) CH2 C
CH2 C + H2O CH2 C + CO2
There are two major disadvantages to this route. First, vinyl isocyanate is significantly more
volatile and flammable than vinyl formamide, in addition to being toxic, and is also sufficiently
moisture sensitive that it must be stored cold under dry inert gas. Second, poly(vinyl
isocyanate) will also be highly moisture sensitive and will be prone to self-crosslinking upon
exposure to moisture either accidentally or in an effort to form poly(vinyl amine) unless the
polymer is kept in very dilute solution. With that said, this approach is nevertheless possible,
and would be accepted as an alternate answer.