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Chapter 26: Q11P (page 1332)

. (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.

Short Answer

Expert verified

b)Due to more trans double bonds in gutta-percha, there occurs higher degree of crystallinity and lesser elasticity.

Step by step solution

01

Step-1. Structure of gutta-percha:

Gutta-percha is a natural polymer and is same as natural rubber with respect to its chemical properties. It is trans-polyisoprene and has all trans double bonds. On heating, it becomes plastic and is resistant to water.

Gutta-percha

All double bonds are trans

02

Step-2. Reason for low elasticity of gutta-percha:

Trans double bonds in gutta-percha allows for more ordered packing of the chains. Due to the ordered packing of the chains, there exists higher degree of crystallinity and less elasticity in gutta-percha. More crystalline the polymer, less elastic will it be.

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Most popular questions from this chapter

Give the structure of the polyurethane formed by the reaction of toluene diisocyanate

with bisphenol A.

Polypropylene is used in making polymer banknotes and textiles.

  1. Give the structure of polypropylene.
  2. Is this an addition polymer or a condensation polymer?
  3. What conditions (cationic, anionic, free-radical) would be the most appropriate for polymerization of propylene? Explain your answer.

One of the earliest commercial plastics was BakeliteR, formed by the reaction of phenol with a little more than one equivalent of formaldehyde under acidic or basic conditions. Bayer first discovered this reaction in 1872, and practical methods for casting and molding. Bakelite were developed around 1909. Phenol-formaldehyde plastics and resins (also called phenolics) are highly cross-linked because each phenol ring has three sites (two ortho and one para) that can be linked by condensation with formaldehyde. Suggest a general structure for a phenol-formaldehyde resin, and propose a mechanism for its formation under acidic conditions. (Hint: Condensation of phenol with formaldehyde resembles the condensation of phenol with acetone, used in Problem 26-17, to make bisphenol A.)

(a) Propose a mechanism for the reaction of bisphenol A with phosgene.

(b) Diethyl carbonate serves as a less-toxic alternative to phosgene for making Lexan. Propose a mechanism for the transesterification of diethyl carbonate with bisphenol A, catalyzed by a trace of sodium ethoxide. What small molecule is given off in this condensation?

In reference to cloth or fiber, the term acetate usually means cellulose acetate, a semisynthetic polymer made by treating cellulose with acetic anhydride. Cellulose acetate is spun into yarn by dissolving it in acetone or methylene chloride and forcing the solution through spinnerets into warm air, where the solvent evaporates.

(a) Draw the structure of cellulose acetate.

(b) Explain why cellulose acetate is soluble in organic solvents, even though cellulose is not.

(c) (A true story) An organic chemistry student wore a long-sleeved blouse to the laboratory. She was rinsing a warm separatory funnel with acetone when the pressure rose and blew out the stopper. Her right arm was drenched with acetone, but she was unconcerned because acetone is not very toxic. About ten minutes later, the right arm of the student’s blouse disintegrated into a pile of white fluff, leaving her with a ragged short sleeve and the tatters of a cuff remaining around her wrist. Explain how a substance as innocuous as acetone ruined the student’s blouse.

(d) Predict what usually happens when students wear polyvinyl chloride shoes to the organic laboratory.
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