Condensation polymerisation generally involves a repetitive condensation reaction between two bi-functional or trifunctional monomeric units. These polycondensation reactions may result in the loss of some simple molecules as water, alcohol, hydrogen chloride, etc., and lead to the formation of high molecular mass condensation polymers. In these reactions, the product of each step is again a bi-functional species and the sequence of condensation goes on. Since, each step produces a distinct functionalised species and is independent of each other, this process is also called as step growth polymerisation.

What is the cross linked polymer formed when formaldehyde and phenol undergoes condensation?

Bakelite

The correct answer is option 2. Bakelite.

When formaldehyde and phenol undergo condensation polymerization, the resulting cross-linked polymer is Bakelite.

The initial reaction between phenol and formaldehyde produces a linear polymer called Novolac when the reaction is carried out under acidic conditions and with a lower ratio of formaldehyde to phenol. When the reaction is carried out under basic conditions and with an excess of formaldehyde, the linear chains of Novolac undergo further reaction to form a heavily cross-linked polymer network known as Bakelite. This process involves the formation of methylene \((–CH_2–)\) bridges that link the phenol units together.

Properties of Bakelite:

Thermosetting: Once formed, Bakelite cannot be remelted or reshaped, due to its extensive cross-linking.

Heat Resistance: It is highly resistant to heat and is used in electrical insulators and heat-resistant objects.

Durability: Bakelite is strong, rigid, and durable.

Applications:

Electrical Components: Used in the manufacturing of electrical insulators, switches, and other components due to its excellent insulating properties.

Household Items: Used to make kitchenware, radio and telephone casings, and various other household items.

Automotive: Used in car parts such as distributor caps and other components that require high heat resistance.

The cross-linked polymer formed when formaldehyde and phenol undergo condensation is Bakelite. Therefore, the correct answer is Bakelite.