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Polymers — Chemistry STD 12 Science — Question

Gujarat BoardEnglish MediumSTD 12 ScienceChemistryPolymers2 Marks
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?
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Answer

Low density polythene: It is obtained by the polymerisation of ethane under high pressure of 1000 to 2000 atmospheres at a temperature of 350K to 570K in the presence of traces of dioxygen or a peroxide initiator (catalyst). The low-density polythene (LDP) obtained through the free radical addition and H-atom abstraction has highly branched structure.
High density polythene: It is formed when addition polymerisation of ethane 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 333K to 343K and under a pressure of 6-7 atmospheres. High density polythene (HDP) thus produced, consists of linear molecules 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.

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