chapter 15. INTRODUCTION TO POLYMER CHEMISTRY Class 12 Chemistry Textbook Solution

5. Answer the following.

i. How is polythene manufactured ? Give their properties and uses.

Answer:- i. Low-Density Polyethylene (LDP) is produced through the polymerization of ethylene under high pressure (1000 – 2000 atm) and temperature (350 – 570 K) in the presence of trace amounts of O₂ or peroxide as an initiator.
\[\ce{{n} CH2 = CH2->[Traces of O2 or][peroxide at 350-570 K, 1000 – 2000 atm] LDP}\]
ii. The mechanism behind this reaction involves free radical addition and H-atom abstraction, leading to branching within the polymer structure. iii. LDP possesses loosely held polymeric chains due to branching, resulting in its low density. iv. Properties of Low-Density Polyethylene: a. LDP films exhibit extreme flexibility, toughness, chemical inertness, and moisture resistance. b. LDP is a poor conductor of electricity and has a melting point of approximately 110°C. v. Uses of Low-Density Polyethylene: a. It is primarily used in the manufacture of pipes for applications such as agriculture, irrigation, and domestic water lines, as well as for insulation in electric cables. b. LDP is also utilized in submarine cable insulation. c. Additionally, it is employed in the production of extruded films and sheets, mainly for packaging and household items like squeeze bottles and attractive containers. vi. High-Density Polyethylene (HDP) is a linear polymer with high density due to close packing. vii. It is obtained through the polymerization of ethene in the presence of a Zieglar-Natta catalyst, which is a combination of triethyl aluminium and titanium tetrachloride. viii. Polymerization of ethene for HDP production occurs at a temperature of 333 K to 343 K and a pressure of 6-7 atm. ix. Properties of High-Density Polyethylene: a. HDP is crystalline, with a melting point in the range of 144 – 150°C. b. It is significantly stiffer than LDP, exhibiting high tensile strength and hardness. c. HDP offers better resistance to chemicals compared to LDP. x. Uses of High-Density Polyethylene: a. HDP finds applications in the manufacturing of toys and various household articles such as buckets, dustbins, bottles, and pipes. b. It is also employed in the production of laboratory wares and other objects where high tensile strength and stiffness are required.

chapter 15. INTRODUCTION TO POLYMER CHEMISTRY Class 12 Chemistry Textbook Solution page 339