Question

Among the following substituted silanes the one which will give rise to cross linked silicone polymer on hydrolysis is (a) \(\mathrm{R}_{4} \mathrm{Si}\) (b) \(\mathrm{RSiCl}_{3}\) (c) \(\mathrm{R}_{2} \mathrm{SiCl}_{2}\) (d) \(\mathrm{R}_{3} \mathrm{SiCl}\)

Short answer

(b) \(\mathrm{RSiCl}_{3}\) forms a cross-linked polymer on hydrolysis.

Step-by-step solution

Understanding Cross-Linked Silicone Polymer Formation

Cross-linked silicone polymers are formed when monomers with the potential to form multiple bonds leading into a three-dimensional network. We need to analyze the ability of each compound to undergo such a reaction.

Analyzing \\(\mathrm{R}_{4} \mathrm{Si}\\)

This compound consists of silicon bonded to four alkyl groups. It cannot undergo hydrolysis or further polymerization as there are no reactive groups that can form bonds with other silicon atoms. Therefore, it cannot form a cross-linked structure.

Analyzing \\(\mathrm{RSiCl}_{3}\\)

This compound has one organic group and three chlorines attached to silicon. Upon hydrolysis, the chlorines are replaced by hydroxyl groups (OH), which can further undergo condensation to form Si-O-Si bonds with other silicon atoms, allowing for a three-dimensional and cross-linked polymer network.

Analyzing \\(\mathrm{R}_{2} \mathrm{SiCl}_{2}\\)

This compound has two organic groups and two chlorines attached to silicon. After hydrolysis, two OH groups are formed. These can intermingle and form Si-O-Si linkages, creating a linear or branched polymer, but this is less likely to lead to extensive cross-linking as compared to (b).

Analyzing \\(\mathrm{R}_{3} \mathrm{SiCl}\\)

This compound consists of three organic groups and one chlorine, leading to the formation of only one OH group upon hydrolysis. This limits bond formation to only one direction or linear links, prohibiting significant cross-linking.

Key concepts

Cross-linked Polymers

Cross-linked polymers are an essential concept in material science, offering unique structural characteristics that make them indispensable in various applications. These polymers form when monomers create multiple covalent bonds, interlinking chains into a three-dimensional network. This structure grants the polymer enhanced physical properties, such as increased mechanical strength, elasticity, and thermal stability.
Unlike linear polymers, where chains are arranged parallel and have limited interactions with each other, cross-linked polymers possess a robust and interconnected network. This structure prevents the polymer chains from sliding past one another, making the material more rigid and resistant to deformation.

• Enhanced strength and durability
• Increased resistance to solvents
• Greater thermal stability

In the context of silicone polymers, the cross-linking often occurs through Si-O-Si bonds, a reaction capable of supporting further network formation. This makes them particularly useful in creating durable, flexible materials such as elastomers and sealants.

Hydrolysis Reaction in Polymers

Hydrolysis reactions play a critical role in the formation and understanding of silicone polymers. In these reactions, chemical bonds are broken by the addition of water. For silicones, this usually involves the substitution of chlorine atoms with hydroxyl groups (OH) in silanes, which can subsequently lead to network formation through condensation polymerization.
During hydrolysis, the silicon-chlorine bonds in compounds like RSiCl extsubscript{3} are replaced by Si-OH bonds. This transformation is vital because once hydroxyl groups are present, they can undergo further reactions to enable the formation of siloxane bonds (Si-O-Si). This forms the basis of a three-dimensional polymer network, contributing to the cross-linking process crucial for silicone polymer structure development.
For example, in the compound RSiCl extsubscript{3}, the presence of three chlorine atoms allows for the formation of three hydroxyl groups upon hydrolysis. This setup facilitates extensive cross-linking when condensed into Si-O-Si bonds, leading to a robust and stable polymer.

Silane Chemistry

Silane compounds are organic derivatives of silicones and are pivotal in the formation of silicone polymers. Understanding silane chemistry is crucial because it underpins the creation of cross-linked silicone structures through hydrolysis.
Silanes possess a silicon atom bonded to one or more substituents, typically alkyl or halide groups. The reactivity of silanes, particularly those with halogens like chlorine, is fundamental to their ability to participate in substitution reactions during polymer synthesis. This reactivity facilitates their role in hydrolysis, where halogens are replaced by hydroxyl groups, eventually leading to the formation of Si-O-Si bonds.

• Substitution allows cross-linking potential
• Crucial in forming three-dimensional networks

Silane chemistry, therefore, is not only essential for polymer synthesis but also dictates the properties and applications of the resulting silicone materials. The number and arrangement of these substituents, such as in RSiCl extsubscript{3}, determine the polymer's potential to form rigid, robust networks.

Three-Dimensional Polymer Networks

Three-dimensional polymer networks are integral to the stability and functionality of high-performance materials, including silicone polymers. These networks arise from chains of molecules that are interconnected to form a strong, spatial lattice.
In silicone chemistry, this is often achieved by reactions forming Si-O-Si linkages, enabling three-dimensional cross-linking. This interconnectivity imparts the polymer with characteristics like heat resistance, elasticity, and tensile strength, making such materials ideal for various industrial applications.
The extent of this cross-linking and the resultant material properties are significantly influenced by the composition of the silicon compound used. For instance, RSiCl extsubscript{3} can form tri-functional networks due to its three chlorine atoms, allowing higher degrees of cross-linking compared to other configurations. This results in a more tightly packed network and superior material properties.

• The robustness of the network influences durability
• High degrees of linkage improve material stability

These three-dimensional networks are pivotal in applications where material durability and resistance are of paramount importance, such as in the automotive and construction industries.