Problem 27 - A Complete Resource Book in Chemistry for JEE Main

Question

Glyptal polymer is obtained from glycerol by reacting with (a) malonic acid (b) phthalic acid (c) maleic acid (d) acetic acid

Step-by-Step Solution

Answer

(b) phthalic acid

Step 1: Understanding the Reaction

Glyptal polymer is a type of alkyd resin. Alkyd resins are formed by the condensation polymerization of polyols with polybasic acids. In this case, glycerol acts as the polyol.

Step 2: Identifying the Correct Acid

Among the given options, identify the polybasic acid that reacts with glycerol to form glyptal polymer. Glyptal polymer is commonly known to form from the reaction between glycerol and phthalic acid, which contains two carboxylic groups that facilitate cross-linking.

Step 3: Selecting the Correct Option

Based on our understanding of how glyptal polymer is formed, the correct choice among the options provided is (b) phthalic acid.

Key Concepts

Alkyd Resin

Alkyd resins are a group of polymers that are widely used in the formulation of paints and coatings. They are known for providing excellent adhesion and durability, making them a popular choice in industrial and decorative finishes. These resins are primarily composed of three main components.

• Polyols: These are compounds with multiple hydroxyl (OH) groups, such as glycerol, that react to form the backbone of the resin.
• Polybasic acids: These acids contain multiple acid groups, which contribute to the formation of strong networks within the polymer matrix.
• Fatty acids or oils: These are often used to modify the properties of the resin, such as adding flexibility or enhancing drying characteristics.

Alkyd resins are typically synthesized through a process called condensation polymerization, which is characterized by the elimination of small molecules, like water or methanol, during the reaction. This process results in the formation of long chains or networks, which give the resulting material its desirable properties.

Condensation Polymerization

Condensation polymerization, also known as step-growth polymerization, is a method used to create polymers, like alkyd resins, by combining monomers with multifunctional groups in a stepwise fashion. This process is named for the water or other small molecules (like methanol) that are "condensed out" while the polymer is being formed.
Key characteristics of condensation polymerization include:

• Stepwise reaction: Monomers react slowly to form dimers, trimers, and eventually long polymeric chains.
• By-products: The reaction typically results in the production of small molecules as by-products, which are removed from the system.
• Reversible: Since the reaction is reversible, the removal of by-products, like water, is crucial to drive the reaction forward.

This polymerization mechanism is employed to create various types of polymers, like glyptal, due to its ability to form strong, three-dimensional networks when the appropriate multi-functional monomers, such as polyols and polybasic acids, are used.

Polyols

Polyols, also referred to as polyhydric alcohols, serve as one of the foundational components in the formation of polymers like alkyd resins. Polyols are distinguished by their chemical structure, which includes multiple hydroxyl (OH) groups, enabling them to participate actively in polymerization reactions.
Notable features of polyols include:

• Versatility: Common polyols like glycerol and pentaerythritol can form complex, branched structures due to their multiple reactive sites.
• Role in synthesis: They react with acid groups in polybasic acids to form ester linkages, contributing to the cross-linking and rigidity of the polymer.
• Importance in industry: Polyols are essential in producing not only resins but also in polyurethane products due to their reactive nature.

Understanding the role of polyols in polymer chemistry helps in comprehending how different polymer properties can be tailored by altering the type and structure of the polyol used in the synthesis.

Polybasic Acids

Polybasic acids are crucial components in the synthesis of various polymers, such as alkyd resins like glyptal. These are organic acids that possess more than one carboxyl group (-COOH), allowing them to react with polyols and form extensive polymer networks.
Key aspects of polybasic acids include:

• Multiple reactive sites: These allow the acids to form multiple bonds, leading to the creation of complex and strong polymeric structures.
• Types: Common examples include phthalic acid and maleic acid. Phthalic acid is especially significant in creating the strong cross-linked structure seen in glyptal polymers.
• Functionality: The number of carboxyl groups determines the possible cross-linking capacity, affecting the polymer's thermal and mechanical properties.

These acids are integral in determining the end-uses of a polymer due to their impact on the material's structural integrity and overall characteristics.