p-Block Elements-I 2 Question 9
9. Correct statements among (I) to (IV) regarding silicones are:
(2019 Main, 9 Jan I)
I. They are polymers with hydrophobic character.
II. They are biocompatible.
III. In general, they have high thermal stability and low dielectric strength.
IV. Usually, they are resistant to oxidation and used as greases.
(a) I and II only
(b) I, II, III only
(c) I, II, III and IV
(d) I, II and IV only
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Solution:
- Silicones are polysiloxanes with general chemical formula, $\left[R_{2} \mathrm{SiO}\right]_{n}$, where $R$ is an organic group such as:
$$ -\mathrm{CH}{3},-\mathrm{C}{2} \mathrm{H}{5},-\mathrm{C}{6} \mathrm{H}_{5} \text { etc. } $$
Silicones have many useful properties:
(i) They repel water and form watertight seals.
(ii) They are heat resistant because of constancy of properties over a wide range of temperature $\left(-100^{\circ}\right.$ to $\left.250^{\circ} \mathrm{C}\right)$.
(iii) Silicones are non-toxic.
(iv) Silicones are biocompatible because these do not support microbiological growth and these have high gas permeability at room temperature.
(v) They are resistant to $\mathrm{O}{2}, \mathrm{O}{3}$ and UV-radiation.
(vi) Silicones are formulated to be electrically insulative.
(vii) Silicone grease is typically used as a lubricant for brake components in automobiles, since it is stable at high temperature, is not water soluble and is a odourless viscous liquid.
