Polymers

Step 1: Understanding thermal insulation materials.
Thermal insulation materials are used to reduce heat transfer. Effective insulating materials generally have low thermal conductivity and often contain trapped air or gas within their structure.
Step 2: Properties of polyurethane foam.
Polyurethane foam has a cellular structure with numerous closed cells filled with gas. This structure significantly reduces heat flow, making it an excellent thermal insulator widely used in buildings, refrigerators, and cold storage.
Step 3: Analysis of options.
(A) Melamine resin: Mainly used for heat-resistant laminates and tableware.
(B) Polyurethane foam: Correct — Highly effective due to its low thermal conductivity.
(C) Polyethylene: Not commonly used as a thermal insulating foam.
(D) Polystyrene: Used mainly for packaging and cushioning; less effective compared to PU foam in insulation.
Step 4: Conclusion.
Polyurethane foam is widely used for thermal insulation, hence option (B) is correct.

Step 1: Understanding biodegradable polymers.
Biodegradable polymers are polymers that can be broken down into simpler substances by microorganisms such as bacteria and fungi under natural environmental conditions.
Step 2: Nature of given polymers.
Polylactic acid (PLA) is derived from renewable resources like corn starch and undergoes biodegradation through hydrolysis and microbial action. Other polymers listed are conventional synthetic polymers that resist biodegradation.
Step 3: Analysis of options.
(A) Polylactic acid: Correct — It is a biodegradable and bio-based polymer.
(B) Polybutylene terephthalate: A synthetic polyester, not biodegradable.
(C) Polystyrene: Highly resistant to biodegradation.
(D) Polypropylene: Non-biodegradable polyolefin.
Step 4: Conclusion.
Polylactic acid is the biodegradable polymer among the given options, hence option (A) is correct.

Step 1: Understanding molecular weight control.
Controlling molecular weight during polymerization is important to obtain polymers with desired mechanical and processing properties. This is achieved by regulating chain length.
Step 2: Role of chain transfer agents.
Chain transfer agents terminate growing polymer chains and initiate new ones, thereby controlling the average molecular weight of the polymer formed.
Step 3: Analysis of options.
(A) Antioxidant: Prevents oxidation, not molecular weight control.
(B) Antiozonant: Protects rubber from ozone degradation.
(C) Chain transfer agent: Correct — Directly controls polymer chain length.
(D) Plasticizers: Improve flexibility but do not affect molecular weight.
Step 4: Conclusion.
Chain transfer agents are added to control molecular weight during polymerization, making option (C) correct.

Step 1: Understanding glass transition temperature (T_g).
The glass transition temperature is the temperature at which a polymer changes from a rigid, glassy state to a flexible, rubbery state. It is a thermal property related to molecular mobility.
Step 2: Technique used for T_g measurement.
Differential Scanning Calorimetry (DSC) measures changes in heat flow associated with thermal transitions in polymers, making it ideal for determining T_g.
Step 3: Analysis of options.
(A) NMR: Used for structural analysis, not thermal transitions.
(B) TEM: Used for morphological studies.
(C) DSC: Correct — Directly measures glass transition temperature.
(D) TGA: Measures weight loss, not T_g.
Step 4: Conclusion.
The glass transition temperature of a polymer is determined using DSC, hence option (C) is correct.