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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

The mechanism given for cationic polymerization of isobutylene (Mechanism 26-2) shows that all the monomer molecules add with the same orientation, giving a polymer with methyl groups on alternate carbon atoms of the chain. Explain why no isobutylene molecules add with the opposite orientation.

. Poly (trimethylene carbamate) is used in high-quality synthetic leather. It has the structure shown.

(a) What type of polymer is poly (trimethylene carbamate)?

(b) Is this a chain-growth polymer or a step-growth polymer?

(c) Draw the products that would be formed if the polymer were completely hydrolyzed under acidic or basic conditions.

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.)

Give a mechanism, using Figure 26-1 as a guide, showing chain branching during the free-radical polymerization of styrene. There are two types of aliphatic hydrogens in the polystyrene chain. Which type is more likely to be abstracted?

Chain branching occurs in cationic polymerization much as it does in free-radical polymerization. Propose a mechanism to show how branching occurs in the cationic polymerization of styrene. Suggest why isobutylene might be a better monomer for cationic polymerization than styrene.

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