Question

Which are true about polymers? (a) They all have a repeating structural unit. (b) They have high viscosity (c) They scatter light. (d) They have low molecular weights.

Short answer

True: (a), (b - conditionally), (c). False: (d).

Step-by-step solution

Identify True Statement: Repeating Unit

All polymers are composed of long chains of molecules with repeating structural units. This makes statement (a) true, as the repeating unit, often called a monomer, is a fundamental characteristic of polymers.

Analyze Statement: High Viscosity

Many polymers have high viscosity due to their large molecular size and entanglement of long chains. However, not all polymers exhibit high viscosity as it largely depends on the specific polymer and its state (liquid, solid, etc.). Therefore, statement (b) is conditionally true.

Evaluate Light Scattering Property

Polymers scatter light because their long chains create regions of density fluctuations that can cause light scattering. This feature is common, so statement (c) is often true for many polymers, especially in solutions or solid states.

Evaluate Statement: Molecular Weights

Polymers have high molecular weights because they consist of long chains with many repeating units. Consequently, statement (d) is false as it suggests polymers have low molecular weights, which contradicts their structural nature.

Key concepts

Molecular Structure

Polymers are fascinating materials primarily due to their unique molecular structures. A polymer consists of long chains made up of repeating units called monomers. These monomers link together through covalent bonds to form the extensive chain structure of a polymer.
This repetition creates a pattern that is essential for the material's stability and properties. The arrangement of these monomers can vary, allowing for different types of polymers, such as linear, branched, or cross-linked networks.

• Linear polymers: Consist of monomers linked end-to-end in single chains, similar to a string of pearls.
• Branched polymers: Feature side chains attached to the main chain, which can affect the properties of the material.
• Cross-linked polymers: Have chains that are interconnected, forming a three-dimensional network which can result in tougher materials.

The versatility of molecular structures is what allows polymers to be used in a wide variety of applications, from everyday products like plastic bottles to advanced materials like bulletproof vests.

Properties of Polymers

The properties of polymers are influenced by their molecular structure, as well as their chemical composition and environmental conditions. Polymers can exhibit a wide range of properties, such as viscosity, transparency, and flexibility. One intriguing property of polymers is viscosity. This refers to the thickness or flowability of the material. While many polymers indeed have high viscosity due to the entanglement of their long chains, others can be less viscous depending on their state or added components.
Another property is their ability to scatter light, which is often seen in polymer solutions or films. This occurs due to the fluctuations in density caused by the polymer's chains, allowing them to scatter light effectively.
Moreover, the physical and chemical characteristics of polymers, such as resistance to chemicals, heat stability, and durability, make them ideal for many applications. Understanding these properties allows scientists and engineers to tailor polymers for specific uses, enhancing their functionality in different environments.

Monomers

Monomers are the building blocks of polymers. They are small, simple molecules that bond with each other to form the long, repeating chains found in polymers. The type of monomers used directly affects the properties and characteristics of the resulting polymer. One of the most common examples is ethylene, which is used to create polyethylene, a widely used plastic found in shopping bags and containers.
Monomers can be natural, like amino acids, used in forming proteins, or synthetic, like styrene, used in creating polystyrene. The versatility and selection of monomers determine the range of polymers that can be produced and their potential applications.

• Monomers can form homopolymers: These are polymers consisting of only one type of monomer, like polyethylene.
• Conversely, they can form copolymers: Polymers that are made of two or more different types of monomers, resulting in tailored properties.

The science of monomers is pivotal to material science, where selecting the appropriate monomer is crucial to producing materials with desired properties and performance.