Chapter 26: Q14P (page 1335)
Kodel® polyester is formed by transesterification of dimethyl terephthalate with 1,4-di(hydroxymethyl)cyclohexane. Draw the structure of Kodel.
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Zytel®finds extensive use in the automotive and electronics industries. Zytel® has the structure shown.
Bisphenol A is made on a large scale by a condensation of phenol with acetone. Suggest an appropriate catalyst, and propose a mechanism for this reaction. (Hint: This is a condensation because three molecules are joined with loss of water. The mechanism belongs to another class of reactions though.)
Propose a mechanism for reaction of the first three propylene units in the polymerization of propylene in the presence of benzoyl peroxide.
Plywood and particle board are often glued with cheap, waterproof urea-formaldehyde resins. Two to three moles of formaldehyde are mixed with one mole of urea and a little ammonia as a basic catalyst. The reaction is allowed to proceed until the mixture becomes syrupy, and then it is applied to the wood surface. The wood surfaces are held together under heat and pressure, while polymerization continues and cross-linking takes place. Propose a mechanism for the base-catalyzed condensation of urea with formaldehyde to give a linear polymer, and then show how further condensation leads to cross-linking. (Hint: The carbonyl group lends acidity to the N - Hprotons of urea. A first condensation with formaldehyde leads to an imine, which is weakly electrophilic and reacts with another deprotonated urea.)
Poly (vinyl alcohol), a hydrophilic polymer used in aqueous adhesives, is made by polymerizing vinyl acetate and then hydrolyzing the ester linkages.
(a) Give the structures of poly (vinyl acetate) and poly (vinyl alcohol).
(b) Vinyl acetate is an ester. Is poly (vinyl acetate) therefore a polyester? Explain.
(c) We have seen that basic hydrolysis destroys the Dacron polymer. Poly (vinyl acetate) is converted to poly (vinyl alcohol) by a basic hydrolysis of the ester groups. Why doesn’t the hydrolysis destroy the poly (vinyl alcohol) polymer?
(d) Why is poly (vinyl alcohol) made by this circuitous route? Why not just polymerize vinyl alcohol?
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