Chapter 26: Q20P (page 1337)
Give the structure of the polyurethane formed by the reaction of toluene diisocyanate
with bisphenol A.
Chapter 26: Q20P (page 1337)
Give the structure of the polyurethane formed by the reaction of toluene diisocyanate
with bisphenol A.
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Get started for free. (a) Draw the structure of gutta-percha, a natural rubber with all its double bonds in the trans configuration.
(b) Suggest why gutta-percha is not very elastic, even after it is vulcanized.
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.)
The polyester named LactomerRis an alternating copolymer of lactic acid and glycolic acid. Lactomer is used for absorbable suture material because stitches of Lactomer hydrolyze slowly over a two-week period and do not have to be removed. The hydrolysis products, lactic acid and glycolic acid, are normal metabolites and do not provoke an inflammatory response. Draw the structure of the Lactomer polymer.
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.)
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