Question

Among the following substituted silanes, the one which will give rise to cross-linked polymer on hydrolysis is:
(A) $R_{2}SiCl$
(B) $R_{4}Si$
(C) $RSiC{l}_3$
(D) $R_{2}SiC{l}_2$

Answer 1

Hint: Polymers are macromolecules built up by linking together a large number of small molecules. The repeating units in a polymer are linked through a strong covalent bond. Carbon and silicon are from group 14 in the periodic table that silicon also forms polymers with cross-linked structure. These polymers are synthesized by addition and condensation polymerization.

Complete step by step answer:
Polymers are classified based on the source are natural polymers and synthetic polymers.
Natural polymers: These polymers are available in nature such as plants and animals.
For example, proteins, cellulose, starch, and natural rubber
Synthetic polymers: these varieties of synthetic polymers as plastic fibers, and synthetic rubbers, silanes are the examples of man-made polymers prepared in daily life as well as in industries or laboratories.
Silanes: these are known as synthetic organic silicon polymers, which contained repeated $R_{2}SiO$ units by Si-O-Si linkages. Silanes general formula is ${(R_{2}SiO)}_n$ , where R = alkyl or aryl group.
Polymerization of silanes:
Step-1: when silicon reacts with alkyl chloride in presence of copper catalysts at 570 K, various types of alkyl-substituted chlorosilanes $R_{3}SiCl,R_{2}SiC{l}_2,R_{3}SiCl,R_{4}Si$ are formed.
Step-2: among the substituted alkyl chlorosilanes, trichloro alkyl silane will give cross-linked silicone polymer on hydrolysis.
On hydrolysis $RSiC{l}_3$ will give $RSi{(OH)}_3$ which will give a cross-linked polymer during the polymerization process.
$RSiC{l}_3+3H_{2}O\to RSi{(OH)}_3+3HCl$
$RSi{(OH)}_3\stackrel{polymerization}{\to }$ Cross-linked polymer.
Hence, among the all substituted silanes, the one which will give rise to cross-linked polymer on hydrolysis is: $RSiC{l}_3$
The correct answer is option C.

Note: Silanes are made up of short-chain molecules that are oily liquid, medium chains behave as viscous liquids, greases and very long chains behave as elastomers and resins. These are chemically inert and easily attacked by organic reactants. These silanes are heat resistant and have high dielectric strength.