Question

The repeating structural units in silicone is:
(i) $\left( {{R_2}SiO - } \right)$
(ii) $Si{O_2}$
(iii) $R - O - Si - OR -$
(iv) $\left( { - {R_2}Si - O - O - R} \right)$

Answer 1

Silicones are organo-silicon polymers, any of diverse class of fluids, resins, or elastomers based on polymerized siloxanes. They are high-performance materials that include reactive silanes, silicone fluids and silicone polymers, which are widely used in a variety of consumer and industrial products.

Complete step-by-step answer: Silicone or polysiloxane are polymers made up of siloxane substances whose molecules consist of chains made of alternating silicon and oxygen atoms. Hence silicones have $\left( {{R_2}SiO - } \right)$ group as the unit building block, where $R$is typically methyl, but other groups particularly phenyl are also involved.
Hence the correct answer is (i) $\left( {{R_2}SiO - } \right)$.
Additional Information: The wide range of chain, cyclic and cross linked silicone polymers are based on structural patterns similar to those of silicates. For example, ${O^ - }$ in silicates have been replaced by the formally isoelectronic $C{H_3}$ groups in the dimethyl silicones. Both silicones and silicates are formed due to reluctance of silicon to form silicon to oxygen double bonds. But the silicates are all solids while the silicones may be oils, greases, rubbers or resins depending upon extent of polymerization.
The wide range of silicone polymers are marked by a combination of certain highly desirable properties like: good resistance to heat, oxidation and attack by most chemicals, excellent water repelling character, good electrical insulation at high and low temperatures, non-sticky property and physiological inertness.

Note: Many students have the tendency to get confused with the building block of silicones. Moreover the options provided are more or less the same in structure so chances of error increases. So read the question and options properly before answering in order to avoid errors.