Understanding Polydimethylsiloxanes Formation

The question asks about modern materials formed specifically from the hydrolysis of chlorosilanes in the presence of water. Let's look at the options provided and understand which one fits this description.

Hydrolysis of Chlorosilanes

Chlorosilanes are compounds containing silicon-chlorine bonds. A common example is dimethyl dichlorosilane, \(\text{(CH}_3\text{)}_2\text{SiCl}_2\). Hydrolysis is a chemical reaction involving water. When chlorosilanes react with water, the chlorine atoms are replaced by hydroxyl (-OH) groups. For dimethyl dichlorosilane, the reaction is:

\(\text{(CH}_3\text{)}_2\text{SiCl}_2 \text{ + } 2\text{H}_2\text{O} \rightarrow \text{(CH}_3\text{)}_2\text{Si(OH)}_2 \text{ + } 2\text{HCl}\)

The resulting silanols (\(\text{(CH}_3\text{)}_2\text{Si(OH)}_2\)) are unstable and undergo condensation, where water molecules are eliminated between two silanol groups, forming Si-O-Si linkages (siloxane bonds):

\(n\text{(CH}_3\text{)}_2\text{Si(OH)}_2 \rightarrow \text{[-(CH}_3\text{)}_2\text{Si-O-]_n} \text{ + } n\text{H}_2\text{O}\)

This process leads to the formation of long chains or networks of silicon and oxygen atoms with organic groups (like methyl, -\(\text{CH}_3\)) attached to the silicon atoms. These polymers are known as polysiloxanes, commonly called silicones.

Identifying the Correct Material

Based on the reaction described, the product formed from the hydrolysis and condensation of chlorosilanes is a polysiloxane. Among the given options:

• Polydimethylsiloxanes: This name directly corresponds to a specific type of polysiloxane formed from dimethyl dichlorosilane hydrolysis and condensation. It has the repeating unit \(\text{[-(CH}_3\text{)}_2\text{Si-O-]_n}\). Polydimethylsiloxanes are the most common type of silicone and are modern materials used in various applications (oils, rubbers, resins).
• HDPE (High-Density Polyethylene): This is a thermoplastic polymer made from the monomer ethylene (\(\text{C}_2\text{H}_4\)). It is formed by the polymerization of ethylene, not by the hydrolysis of chlorosilanes.
• LDPE (Low-Density Polyethylene): Similar to HDPE, this is also a thermoplastic polymer made from ethylene. It differs in structure and properties from HDPE but is also not formed from chlorosilane hydrolysis.
• Carbosilanes: These are compounds containing carbon-silicon bonds. While they involve silicon, they are not the direct polymeric products formed from the hydrolysis of chlorosilanes. The primary chain in polysiloxanes contains Si-O bonds, not Si-C bonds in the backbone.

Therefore, the modern materials formed from the hydrolysis of chlorosilanes in the presence of water are Polydimethylsiloxanes (a type of polysiloxane).