Additional Problems

Additional Problems

31 • Additional Problems

31 • Additional Problems

Visualizing Chemistry

Problem 31-13

Identify the structural class to which the following polymer belongs, and show the structure of the monomer units used to make it:

A ball-and-stick model of a polymer showing two benzene rings and connecting substituents. Wavy lines indicate boundaries of the repeating unit.
Problem 31-14
Show the structures of the polymers that could be made from the following monomers (green = Cl):
(a)
A ball-and-stick model of a monomer showing five-carbon chain with nitrogen, carbonyl, and alkene bond. Carbon, hydrogen, oxygen, and nitrogen are denoted using black, gray, red, and blue spheres, respectively.
(b)
Ball-and-stick model of 2-chloro-1,3-butadiene. Carbon, hydrogen, and halogen are denoted using black, gray, and green spheres, respectively.

Mechanism Problems

Problem 31-15

Poly(ethylene glycol), or Carbowax, is made by anionic polymerization of ethylene oxide using NaOH as catalyst. Propose a mechanism.

The structure of polyethylene glycol. Oxygen is connected to two methylene units and its structure is inside parentheses with n as the subscript.
Problem 31-16

The polyurethane foam used for home insulation uses methanediphenyldiisocyanate (MDI) as monomer. The MDI is prepared by acid-catalyzed reaction of aniline with formaldehyde, followed by treatment with phosgene, COCl2. Propose mechanisms for both steps.

The formation of methanediphenyldidisocyanate. Aniline reacts with formaldehyde to form a polymer. This polymer reacts with phosgene to produce the polymer, M D I.
Problem 31-17
Write the structure of a representative segment of polyurethane prepared by reaction of ethylene glycol with MDI (Problem 31-16).
Problem 31-18

The polymeric resin used for Merrifield solid-phase peptide synthesis (Section 26.8) is prepared by treating polystyrene with N-(hydroxymethyl)phthalimide and trifluoromethanesulfonic acid, followed by reaction with hydrazine. Propose a mechanism for both steps.

Polystyrene reacts with N-(hydroxymethyl)phthalimide and trifluoromethanesulfonic acid to form an intermediate that further reacts with hydrazine to form resin. The product's structure is inside parentheses with n as the subscript.
Problem 31-19

Polydicyclopentadiene (PDCPD), marketed as Telene or Metton, is a highly cross-linked thermosetting resin used for molding such impact-resistant parts as cabs for large trucks and earth-moving equipment. PDCPD is prepared by ring-opening metathesis polymerization of dicyclopentadiene, which is itself prepared from 1,3-cyclopentadiene. The polymerization occurs by initial metathesis of the more highly strained double bond in the bicyclo[2.2.1]heptane part of the molecule (Section 4.9) to give a linear polymer, followed by cross-linking of different chains in a second metathesis of the remaining cyclopentene double bond.

Two molecules of cyclopentadiene react with heat to form dicyclopentadiene. This further undergoes ring-opening metathesis polymerization to form polydicyclopentadiene. Wavy lines denote the bond extensions.
(a)
Show the mechanism of the formation of dicyclopentadiene from cyclopentadiene.
(b)
Draw the structure of a representative sample of the initially formed linear polymer containing three monomer units.
(c)
Draw the structure of a representative sample of PDCPD that shows how cross-linking of the linear chains takes place.

General Problems

Problem 31-20
Identify the monomer units from which each of the following polymers is made, and tell whether each is a chain-growth or a step-growth polymer:
(a)
The structure of a polymer whose repeating unit is C H 2 O. The unit is inside parentheses with bonds extending out and has a subscript n.
(b)
The structure of a polymer whose repeating unit is C F 2 C F Cl. The unit is inside parentheses with bonds extending out and has a subscript n.
(c)
The structure of a polymer comprising N H connected to three methylene units that is linked to a carbonyl. The structure is inside the parentheses and has a subscript n.
(d)
The structure of a polymer comprising oxygen linked to a benzene ring with a carbonyl group. The structure is inside the parentheses and has a subscript n.
(e)
The structure of a polymer comprising oxygen linked to cyclohexane further bonded to another oxygen and carbonyl group. The structure is inside the parentheses and has a subscript n.
Problem 31-21

Draw a three-dimensional representation of segments of the following polymers:

(a)
Syndiotactic polyacrylonitrile
(b)
Atactic poly(methyl methacrylate)
(c)
Isotactic poly(vinyl chloride)
Problem 31-22

Draw the structure of Kodel, a polyester prepared by heating dimethyl 1,4-benzenedicarboxylate with 1,4-bis(hydroxymethyl)cyclohexane.

The structure of 1,4-bis(hydroxymethyl)cyclohexane.
Problem 31-23

Show the structure of the polymer that results from heating the following diepoxide and diamine:

Diepoxide comprises benzene bonded to two O-atoms on both sides. Further bonded to methylene and epoxide ring. It reacts with diamine to give unknown product, shown as a question mark.
Problem 31-24
Nomex, a polyamide used in such applications as fire-retardant clothing, is prepared by reaction of 1,3-benzenediamine with 1,3-benzenedicarbonyl chloride. Show the structure of Nomex.
Problem 31-25
Nylon 10,10 is an extremely tough, strong polymer used to make reinforcing rods for concrete. Draw a segment of nylon 10,10, and show its monomer units.
Problem 31-26
1,3-Cyclopentadiene undergoes thermal polymerization to yield a polymer that has no double bonds in the chain. Upon strong heating, the polymer breaks down to regenerate cyclopentadiene. Propose a structure for the polymer.
Problem 31-27
When styrene, C6H5CH ═ CH2, is copolymerized in the presence of a few percent p-divinylbenzene, a hard, insoluble, cross-linked polymer is obtained. Show how this cross-linking of polystyrene chains occurs.
Problem 31-28
Nitroethylene, H2C ═ CHNO2, is a sensitive compound that must be prepared with great care. Attempted purification of nitroethylene by distillation often results in low recovery of product and a white coating on the inner walls of the distillation apparatus. Explain.
Problem 31-29

Poly(vinyl butyral) is used as the plastic laminate in the preparation of automobile windshield safety glass. How would you synthesize this polymer?

The structure of poly(vinyl butyral). It comprises eleven-carbon chain with oxygen connected at C 3, C 5, C 7, and C 9. The oxygen is linked to the propyl group.
Problem 31-30

What is the structure of the polymer produced by anionic polymerization of β-propiolactone using NaOH as catalyst?

The structure of beta-propiolactone, a four-membered cyclic ester.
Problem 31-31
Glyptal is a highly cross-linked thermosetting resin produced by heating glycerol and phthalic anhydride (1,2-benzenedicarboxylic acid anhydride). Show the structure of a representative segment of glyptal.
Problem 31-32

Melmac, a thermosetting resin often used to make plastic dishes, is prepared by heating melamine with formaldehyde. Look at the structure of Bakelite shown in Section 31.7, and then propose a structure for Melmac.

The structure of melamine. It is a six-membered ring with alternating C and N, and alternating single and double bonds. Each C has an N H 2 substituent.
Problem 31-33

Epoxy adhesives are cross-linked resins prepared in two steps. The first step involves SN2 reaction of the disodium salt of bisphenol A with epichlorohydrin to form a low-molecular-weight prepolymer. This prepolymer is then “cured” into a cross-linked resin by treatment with a triamine such as H2NCH2CH2NHCH2CH2NH2.

The structures of Bisphenol A and Epichlorohydrin.
(a)
What is the structure of the prepolymer?
(b)
How does addition of the triamine to the prepolymer result in cross-linking?
Problem 31-34

The smoking salons of the Hindenburg and other hydrogen-filled dirigibles of the 1930s were insulated with urea–formaldehyde polymer foams. The structure of this polymer is highly cross-linked, like that of Bakelite (Section 31.7). Propose a structure.

An incomplete reaction in which urea reacts with formaldehyde to form unknown product(s) indicated by a question mark.
Problem 31-35
2-Ethyl-1-hexanol, used in the synthesis of di(2-ethylhexyl) phthalate plasticizer, is made commercially from butanal. Show the likely synthesis route.