Question

Under which combination of conditions does the glass transition of a polymer increase?

• A. Increase in molecular weight and increase in plasticizer content
• B. Increase in plasticizer content and decrease in cross-linking
• C. Increase in branching and decrease in inter-chain interactions
• D. Increase in chain length and decrease in plasticizer content

Hint:

To increase the glass transition temperature of a polymer, focus on increasing the molecular weight and reducing the plasticizer content.

Answer 1

The Correct Option is D

The glass transition temperature (\(T_g\)) of a polymer is the temperature at which it transitions from a hard, glassy state to a more flexible, rubbery state. Several factors influence the \(T_g\), including molecular weight, plasticizer content, branching, and cross-linking.
- Molecular weight plays a crucial role in the \(T_g\). As molecular weight increases, the polymer chains become longer and more entangled, which increases the \(T_g\). However, an increase in plasticizer content generally decreases \(T_g\) because plasticizers act as lubricants, making it easier for the chains to move.
- Plasticizer content typically decreases the \(T_g\) because plasticizers reduce the intermolecular forces between polymer chains, making them more flexible.
- Cross-linking increases the rigidity of the polymer and typically increases \(T_g\).
- Branching can lower \(T_g\) because it reduces the packing density of the polymer chains, which decreases intermolecular forces.
- Chain length increases \(T_g\) because longer chains increase the entanglement and restrict the movement of the polymer chains, making it more rigid. Therefore, increasing chain length and decreasing plasticizer content will result in an increase in the glass transition temperature. Hence, the correct answer is (D) Increase in chain length and decrease in plasticizer content.