Saved Bookmarks
| 1. |
(a) What are polyolefins ? (b) Name two polyolefins and give their preparation and uses. |
|
Answer» Solution :(a) Polyolefins. They are addition polymers formed by the polymerisation of molecules containing carbon-carbon double bonds. Their formation can be represented in GENERAL as : `n(CH_2 =underset(G)underset(|)CH) to (-CH_2 - underset(G)underset(|)CH-)_n` where G may be H, `-CH_3, -C_6H_5`, halogen etc. (b) Polythene `(-CH_2-CH_2 -)_n` . When ethylene is heated under a high pressure in the presence of traces of oxygen, ethylene forms a long chain addition polymer having a molecular mass of about 20,000. `underset("Ethylene")(nCH_2=CH_2) underset("Traces of oxygen")overset("Heat, pressures")to underset("Polythene")(-CH_2-CH_2-)_n` Uses. It is used : (i) in the manufacture of polythene pipes , buckets squeeze bottles and toys. (ii) for packaging , coating for ELECTRICAL wires , cables and other materials. 2. Polypropylene`({:(-CHCH_2-),(" "|),(" "CH_3):})_n` When propylene is heated inthe presence of Zeigler Natta catalyst a MIXTURE of triethylaluminium and titanium tetrachloride, it results in the formation of polypropylene. `nCH_3 - underset("Propylene")(CH)=CH_2 underset("Zeigler Natta Catalyst")overset(Heat")to` Uses. It is used : `(underset("Polypropylene"){:(-CH-CH_2-),(" "|),(" "CH_3):})_n` (i) in packing of textiles and foods. (ii) for seat covers , CARPET fibres , ropes etc. (iii) for making unshrinking WRAPS for records and other articles and making liners for bags. |
|