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Question
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?
Solution
Low-density polythene: It is obtained by the polymerisation of ethene under high pressure of 1000 to 2000 atmospheres at a temperature of 350 K to 570 K in the presence of traces of dioxygen or a peroxide initiator (catalyst). The low-density polythene (LDP) is obtained through the free radical addition and H-atom abstraction has highly branched structure.
High-density polythene: It is formed when addition polymerisation of ethene takes place in a hydrocarbon solvent in the presence of a catalyst such as triethylaluminium and titanium tetrachloride (Ziegler-Natta catalyst) at a temperature of 333 K to 343 K and under a pressure of 6-7 atmospheres. High-density polythene (HDP) thus produced, consists of linear molecules as shown below and has a high density due to close packing. It is also chemically inert and more tougher and harder. It is used for manufacturing buckets, dustbins, bottles, pipes, etc.
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