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Practice each question, then open the answer or worked solution.
To have practical applications why are cross-links required in rubber?
Ans: A vulcanisation process is used to improve the physical properties of natural rubber. This process consists of heating a mixture of raw rubber with sulphur and an appropriate additive at a temperature range between 373 K to 415 k. Sulphur forms cross links at the reactive sites of double bonds during vulcanization, stiffening the rubber.
Why does cis-polyisoprene possess elastic property?
Ans: Cis-polyisoprene has a coiled structure which consists of various chains held together by weak Van der Waals force of attraction. It can be stretched like a spring and thus, has elastic properties.
What is the structural difference between HDP and LDP? How does the structure account for different behaviour and nature, hence the use of a polymer?
Ans: LDP: The polymerization of ethene under high pressure and temperature in the presence of peroxide catalyst gives low-density polythene. It is obtained through free radical addition and has a high branched structure. It is chemically inert and is a poor conductor of electricity. It is used for manufacturing toys, bottles.
HDP: When addition polymerization of ethene takes place in a hydrocarbon solvent in the presence of a catalyst such as triethylaluminium and Ziegler-Natta catalyst at high temperature and pressure then high-density polythene is formed. It consists of linear molecules. It is also chemically inert. It is used for manufacturing buckets, dustbins.
What is the role of benzoyl peroxide in addition polymerisation of alkenes? Explain its mode of action with the help of an example.
Ans: Free radicals are generated from benzoyl peroxide. Alkanes, dienes are polymerized in the presence of free radical inhibitors like benzoyl peroxide, acetyl peroxide. For example, benzoyl peroxide inhibitor is used for the polymerization of ethene to polythene. First, phenyl peroxide radicals are formed which are added to the double bond of ethene generating a new and larger free radical.
Which factor imparts crystalline nature to a polymer like nylon?
Ans: Polymers that possess amide linkage are termed as nylon. Fibers have a strong intermolecular force of attraction like hydrogen bonding. It leads to the close packing of the structure which imparts the crystalline nature.
Name the polymers used in laminated sheets and give the name of monomeric units involved in its formation.
Ans: Urea-formaldehyde resin is used in laminated sheets. The monomer involved in the formation of urea formaldehyde resin is urea and formaldehyde.
Which type of biomolecules have some structural similarity with synthetic polyamides? What is this similarity?
Ans: Proteins have some similar structural similarities with synthetic polyamides. Proteins and polyamides both contain amide linkage.
Why should the monomers used in addition to polymerization through free radical pathway be very pure?
Ans: Monomers used in addition to polymerization through free radical pathway should be very pure because even the traces of impurities acts like inhibitors. It leads to the formation of polymers with a shorter chain lengths.
Match the polymer of column I with the correct monomer of column II.
Column I | Column II | |
i. High density polythene | a. Isoprene | |
ii. Neoprene | b. Tetrafluoroethene | |
iii. Natural Rubber | c. Chloroprene | |
iv. Teflon | d. Acrylonitrile | |
v. Acrilan | e. Ethene | |
Ans: (i) When addition polymerisation of ethene takes place in a hydrocarbon solvent in the presence of a catalyst such as triethylaluminium and Ziegler-Natta catalyst at high temperature and pressure then high density polythene is formed.
Thus, option (i) from column I is matched with (e) from column II.
(ii) Neoprene is formed by the free radical polymerization of chloroprene.
Thus, option (ii) from column I is matched with (c) from column II.
(iii) Natural rubber is a linear polymer of isoprene units.
Thus, option (iii) from column I is matched with (a) from column II.
(iv) Teflon is formed by heating tetrafluoroethylene at high pressure in the presence of free radical polymerization like persulfate catalyst.
Thus, option (iv) from column I is matched with (b) from column II.
(v) Acrilan is formed by the addition polymerization of acrylonitrile in the presence of a peroxide catalyst.
Thus, option (v) from a column I is matched with (d) from column II.
Match the polymers given in Column I with their chemical names given in Column II.
Column I | Column II |
i. Nylon-6 | a. Polyvinyl chloride |
ii. PVC | b. Polyacrylonitrile |
iii. Acrilan | c. Polycaprolactum |
iv. Natural Rubber | d. Low density polythene |
v. LDP | e. cis-polyisoprene |
Ans: (i) Nylon-6 is obtained by heating caprolactam with water at a high temperature.
Thus, option (i) from column I is matched with (c) from column II.
(ii).The chemical name of PVC is polyvinyl chloride.
Thus, option (ii) from column I is matched with (a) from column II.
(iii) Acrilan is formed by the addition polymerization of acrylonitrile in the presence of a peroxide catalyst.
Thus, option (iii) from column I is matched with (b) from column II.
(iv). Natural rubber is a linear polymer of isoprene units. It is also known as cis-polyisoprene.
Thus, option (iv) from column I is matched with (e) from column II.
(v) LDP is known as low density polythene. It is obtained through a free radical addition reaction.
Thus, option (v) from column I is matched with (d) from column II.