Question

Which of the following is not a characteristic of thermosetting polymers?
A. Linear or slightly branched long chain polymers.
B. Heavily branched and cross-linked polymers.
C. Become infusible on moulding.
D. Cannot be remoulded or reused on heating.

Answer 1

Hint: polymers are the macromolecules in which the intermolecular forces of attraction like van der Waals forces and hydrogen bonds are of much significance. Many of their applications are the outcome of their unique mechanical properties such as tensile strength, elasticity, toughness, etc. which in turn is related to the magnitude of these intermolecular forces. The magnitude of these forces depends upon the size of the polymer and the number of functional groups along the polymer chain. Longer the polymer chain, the greater the magnitude of intermolecular forces. Depending upon the magnitude of intermolecular forces, polymers have been classified into the following four categories
1.Elastomers.
2.Fibers.
3.Thermoplastics.
4.Thermosetting plastics.
The magnitude of the intermolecular forces has the order:
Fibres \[ > \] Thermosetting \[ > \] Thermoplastics \[ > \] Elastomers

Complete step by step answer:
Thermosetting plastics are three-dimensional polymers which are insoluble in any kind of solvent. These are normally prepared from relatively low molecular semi- fluid polymers which become infusible (or permanently hard) and insoluble hard mass on heating. The formation of infusible hard mass is due to extensive cross-linking between different polymer chains to give a three-dimensional network solid. This means the thermostatic plastics can be heated once before their formation, after which heating again results in chemical decomposition. Hence, they cannot be reworked.
Some typical thermosetting plastics are Bakelite (phenol-formaldehyde), Melamine- formaldehyde, Urea-formaldehyde, Silicones, etc.

After discussing it we can conclude that a linear or slightly branched long chain is not the characteristic of thermosetting polymers or plastics.

So, the correct answer is Option A .

Note: Polymers are the high molecular mass compounds obtained by regularly joining repeating structural units. The simple reactive molecules from which the repeating structural units are derived are called monomers. The use of polymers in the manufacture of toys, synthetic clothing materials, packaging bags, automobile tires, plastic buckets, cups, and saucers, etc. has completely revolutionized the daily as well as the industrial scenario. The giant molecules like DNA, chlorophyll, proteins, carbohydrates, etc. are regarded as macromolecules.Chlorophyll is a macromolecule but is not regarded as a polymer because it does not contain a repeating unit.