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Polymers — Chemistry STD 12 Science — Question

Gujarat BoardEnglish MediumSTD 12 ScienceChemistryPolymers1 Mark
MCQ
What is not true regarding free radical polymerisation of propene?
  • A
    Without proper control, atactic polypropylene is formed.
  • B
    Use of Ziegler$-$Natta catalyst results in isotactic polypropylene.
  • ✓
    During polymerisation, a linear unbranched, crystalline polymer is usually obtained.
  • D
    During polymerisation, a secondary free radical is produced in every step.
✓

Answer

Correct option: C.
During polymerisation, a linear unbranched, crystalline polymer is usually obtained.
The statement $(C)$ is not true. During polymerization, a branched polymer is usually obtained. Chain branching always occur during olefenic polymerization due to abstraction of some $H-$radical from the growing polymer chain.
Note$:\ 1^\circ $ free radical forms $2^\circ $ free radical by abstracting hydrogen at middle of another chain, which further adds to propene and there is growing of the branch. Ziegler Natta catalyst is titanium chloride and triethyl aluminum $\left[\mathrm{TiCl}_4+\mathrm{Al}\left(\mathrm{C}_2 \mathrm{H}_5\right)_3\right]$

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