Question

Among cellulose, poly(vinyl chloride), nylon and natural rubber, the polymer in which the intermolecular force of attraction is weakest is (A) Nylon (B) Poly(vinyl chloride) (C) Cellulose (D) Natural Rubber

Short answer

Natural Rubber (D) has the weakest intermolecular forces of attraction.

Step-by-step solution

Understand the Types of Intermolecular Forces

Different polymers have varied intermolecular forces such as hydrogen bonding, dipole-dipole interactions, and London dispersion forces. Hydrogen bonds are generally stronger than dipole-dipole interactions, which are stronger than London dispersion forces.

Identify the Intermolecular Forces in Each Polymer

Cellulose has extensive hydrogen bonding. Poly(vinyl chloride) has dipole-dipole interactions because of its polar C-Cl bonds. Nylon has strong intermolecular hydrogen bonding between its chains. Natural rubber (polyisoprene) primarily exhibits weaker London dispersion forces due to its non-polar nature.

Determine the Polymer with Weakest Intermolecular Force

Since natural rubber has non-polar molecules, the intermolecular forces are mainly London dispersion forces, which are the weakest type of intermolecular forces.

Key concepts

Hydrogen Bonding in Polymers

Hydrogen bonding is a specific type of dipolar interaction characterized by a strong attraction between a hydrogen atom and a highly electronegative atom such as nitrogen, oxygen, or fluorine. This kind of intermolecular force significantly contributes to the mechanical properties of polymers.
For example, in cellulose, the abundant hydroxyl (OH) groups allow for extensive hydrogen bonding, giving the polymer high tensile strength and making it resistant to being pulled apart. Such bonding is directional and adds rigidity to the polymer chains, affecting their behavior and applications.

Dipole-Dipole Interactions

Dipole-dipole interactions occur when the positive end of a polar molecule is attracted to the negative end of another. In the context of polymers, these forces are present in materials like poly(vinyl chloride) (PVC).

Dipole Nature of PVC

Each repeating unit of PVC contains a polar covalent bond between carbon and chlorine, creating a molecular dipole. When numerous PVC chains come in contact, the electronegative chlorine atoms attract the partially positive hydrogens of adjacent chains, leading to overall cohesion in the material. This influence on properties like the glass transition temperature makes dipole-dipole interactions crucial for understanding polymer behavior.

London Dispersion Forces in Polymers

London dispersion forces, also known as Van der Waals forces, are the weakest form of intermolecular attraction. They arise from the temporary, random fluctuations in the electron distribution around atoms or molecules, which create instantaneous dipoles.

Role in Natural Rubber

In polymers such as natural rubber, the chains are composed of non-polar isoprene units that do not exhibit permanent dipoles. Therefore, the cohesion in natural rubber primarily relies on these fleeting attractions. The flexibility and elasticity of natural rubber can be attributed to the ease with which its chains can slip past one another, a direct consequence of the weakness of London dispersion forces.

Polymer Chemistry Fundamentals

Polymer chemistry is the science behind the creation and behavior of polymers, which are large molecules composed of repeating structural units called monomers. The physical properties of polymers, such as strength, flexibility, and heat resistance, are deeply influenced by the type and strength of intermolecular forces between their chains.

Polymers can be designed to have specific properties by manipulating the chemical structure of the monomers and the processing conditions. The variations in polymer types, like thermoplastics, thermosets, and elastomers, relate directly to the nature of their intermolecular forces, whether they are Van der Waals, hydrogen bonding, or ionic interactions.

Natural Rubber Properties

Natural rubber is a polymer with distinct properties that stem from its molecular structure and weak intermolecular forces. Known for its high elasticity and resilience, natural rubber is an elastomer composed primarily of the polymer polyisoprene.

Its ability to repeatedly stretch and return to its original shape is due to the coiled structure of polyisoprene chains and their non-polar nature, which results in predominantly London dispersion forces. Unlike polymers with stronger intermolecular forces, such as nylon with hydrogen bonding, natural rubber can deform under stress and quickly recover, making it ideal for products like tires and elastic bands.