Wednesday, September 19, 2007

Answers to Simple Questions Ch. 33 Polymers

1. What is a polymer?

Polymers are compounds of very high molecular masses formed by the combination of a large number of simple molecules. In Greek, poly means many and meros means units or parts.

2. Give two examples of natural polymers.

i) Starch ii) Celulose

3. What are homopolymers?

A polymer formed from one type of monomers is called homopolymer.

4. What are step-growth polymers?

Step growth is also called condensation polymerisation. In this type the monomers genrally contain two functional groups and the polymer is formed with the elimination of simple molecules like water, ammonia, hydrogen chloride, alcohol etc. IN this process each step is the same type of chemical reaction. Common examples are Nylon 66 and Bakelite.

5. What are chain growth polymers?

This is also called addition polymerisation. This polymerisation involves a series of reactions each of whichconsumes a reactive particles and produces anohter similar particle resulting in a chain reaction. Likeother chain reactions, this polymerisation reaction also involves an initiator whihc may be a free radical, a cation or anion.

6. What are elastomers?

The polymers that have elastic character like the rubber are called elastomers. The most important example of elastomer is natural rubber.

7. Give two examples of fibres.

Nylon 66, dacron

8. What is a thermoplastic?

These are polymers which can be easily softened repeatedly when heated and hardened when cooled with little change in their properties.

9. What is the monomer for polymer polyvinyl acetate?

Vinyl acetate

10. How do you get isomers of Poly(1,3-butadiene) from butadiene?

butadiene , colorless, gaseous hydrocarbon. There are two structural isomers of butadiene; they differ in the location of the two carbon-carbon double bonds in the butadiene molecule. One (1,2-butadiene) has the formula CH-2:C:CHCH-3 . The other (1,3-butadiene), often called simply butadiene, has the formula CH-2 :CHCH:CH-2 ; it is used in the manufacture of synthetic rubber, latex paints, and nylon and is obtained chiefly by dehydrogenation of butane and butene obtained by cracking petroleum.

11. Give two examples of copolymers.

Saran, Buna-S (a rubber)

12. What vulcanizatin of rubber?

Both natural and synthetic rubbers are soft. In vulcanisation, rubber is heated with a per cent by mass of sulphur. This results into the formation of sulphur bridges between polymer chains.

13. Give tow examples of step growth polymers.

Terylene or Dacron and Nylon-6.

14. How do you get nylon-66 polymer?

Hexamethylene diamine and Adipic acid polymerise to produce nylon-66 polymer.

15. How do you produce bakelite?

The starting materials are formaldehyde and phenol. IN the presence of a basic catalyst (OH) these two substances combine to give ortho and para hydroxymethylphenol. These materials undergo condensation to produce cross-linked polymer bakelite involving methylene bridges in ortho, para, or both ortho and para positions.

Polybutadiene can be formed from many 1,3-butadiene monomers undergoing free radical polymerization to make a much longer polymer chain molecule.

A chain propagating step in this chemical reaction involves a free radical near the end of a growing polymer chain forming a covalent bond with the #1 carbon in a 1,3-butadiene monomer molecule being added, resulting in a polymer chain intermediate with a substituted allyl free radical at the end of the chain. This allyl free radical, formed from the butadiene just added, can further bond to another monomer molecule at either the #2 or #4 carbons of the previous butadiene monomer. Most of the time, the new monomer bonds to the #4 or terminal carbon of the previous butadiene, resulting in a 1,4-addition of the previous butadiene unit. In a 1,4-addition, the two double bonds of the previous butadiene unit are turned into single bonds and a new double bond is formed between the #2 and #3 carbons. This new double bond may have either a cis or a trans configuration.

There are different catalysts available which can result in polymerization either in the cis or the trans configurations.

16. What are the monomers of Buna-S polymer?

Styrene(25%) + Butadiene (75%)

17. What do you get by polymerisation of caprolactum?

Nylon 6

18. What is monomer of teflon?


19. What is monomer of synthetic rubber?

2-methyl-1, 3-butadiene

20. What is the monomer of starch?


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