Question

Identify the monomers required for the synthesis of these step-growth polymers.

Short answer

Answer: The primary monomers required for the synthesis of step-growth polymers are diols (with two hydroxyl groups), diamines (with two amine groups), and diacids (with two carboxylic acid groups). Examples of step-growth polymers and their corresponding monomers include: 1. Polyesters: Synthesized from diols and diacids, for example, Polyethylene terephthalate (PET) is synthesized from ethylene glycol (a diol) and terephthalic acid (a diacid). 2. Polyamides: Synthesized from diamines and diacids, for example, Nylon-6,6 is synthesized from adipic acid (a diacid) and hexamethylenediamine (a diamine). 3. Polyurethanes: Synthesized from diols and diisocyanates, for example, Polyurethane foam is synthesized from polyols (diols with multiple hydroxyl groups) and diisocyanates.

Step-by-step solution

Understand step-growth polymerization

Step-growth polymerization is a process where the functional groups of monomers react with one another to form larger molecules. This process involves the elimination of a small molecule, such as water or methanol, as a byproduct. The resulting polymers have a high molecular weight and can be classified as condensation polymers.

Identify monomers

In order to identify the monomers required for the synthesis of step-growth polymers, we need to analyze the functional groups that can undergo condensation reactions. Common monomers that may be involved in step-growth polymerizations are: 1. Diols: Molecules with two hydroxyl groups (-OH) that can condense with diacid molecules. 2. Diamines: Molecules with two amine groups (-NH2) that can condense with diacid molecules. 3. Diacids: Molecules with two carboxylic acid groups (-COOH) that can condense with diols or diamines. These monomers can pair up to form different types of step-growth polymers, such as polyesters, polyamides, or polyurethanes.

Examples of step-growth polymers and their monomers:

Here are some examples of step-growth polymers and the monomers required for their synthesis: 1. Polyesters: Synthesized from diols and diacids. Example: Polyethylene terephthalate (PET) is synthesized from ethylene glycol (a diol) and terephthalic acid (a diacid). 2. Polyamides: Synthesized from diamines and diacids. Example: Nylon-6,6 is synthesized from adipic acid (a diacid) and hexamethylenediamine (a diamine). 3. Polyurethanes: Synthesized from diols and diisocyanates. Example: Polyurethane foam is synthesized from polyols (diols with multiple hydroxyl groups) and diisocyanates. In summary, to identify the monomers required for the synthesis of step-growth polymers, we must recognize the functional groups that can undergo condensation reactions, which primarily involve diols, diamines, and diacids.

Key concepts

Monomers in Polymer Chemistry

In the world of polymer chemistry, monomers are the fundamental building blocks that combine to form polymers. Monomers are small molecules, usually organic, that can join with other identical or similar molecules to create a long chain or network. Think of them as the individual beads on a necklace that, when strung together, make up the entire piece.

There are different types of monomers, but for step-growth polymerization, the focus is primarily on monomers with two functional groups, such as diols, diamines, and diacids. These functional groups are reactive ends of the monomers that allow them to link with one another, forming long chains. When two different monomers have compatible reactive groups, they can bond through a process known as condensation reaction. For example, in synthesizing a polyester, a diol with two hydroxyl (-OH) groups would react with a diacid containing two carboxylic acid (-COOH) groups.

It's important to note that the existence of two functional groups on monomers is crucial for step-growth polymerization. This allows for a diversity of three-dimensional structures and polymeric materials with varying properties, because the two points of attachment allow for the creation of complex networks.

Condensation Reactions

A condensation reaction in polymer chemistry is a type of chemical reaction where two molecules or functional groups combine with the loss of a smaller molecule, typically water or an alcohol. This process is the core of step-growth polymerization.

During the condensation reaction, monomers with two reactive groups each link together to form dimers, which in turn can react with other monomers or dimers to form longer chains or three-dimensional networks. Each linkage results in the release of a small molecule - for instance, when a hydroxyl group (-OH) from a diol reacts with a carboxylic acid group (-COOH) from a diacid, the condensation reaction produces a molecule of water as the -OH and -H from the respective groups combine and depart the forming chain.

It's this characteristic of step-growth polymerization that distinguishes it from addition polymerization, where monomers add to a growing chain without the loss of molecules. The subtle but critical difference is what allows step-growth polymers to have a variety of material properties, making them useful for countless applications including textiles, plastics, and engineering materials.

Polymer Synthesis

The process of polymer synthesis can seem complex, but it's simply about connecting monomers in a repeating fashion to form larger structures, known as polymers. In step-growth polymerization, monomers with two functional groups react to form oligomers and eventually long polymer chains through condensation reactions.

During polymer synthesis, two key factors play crucial roles: the types of monomers and the conditions under which they react. Synthesizing a desired polymer involves carefully choosing monomers with the appropriate reactive groups and then controlling the reaction conditions such as temperature, pressure, and catalysts. These conditions can affect the rate of reaction and the molecular weight of the resulting polymer.

Let's take polyester synthesis as an instance: it requires a diol and a diacid, reacting in a controlled environment to lengthen the molecular chain and eventually form a polymer like polyethylene terephthalate (PET). Through polymer synthesis, we create a plethora of materials with various characteristics determined by the nature of the monomers used and the synthesis conditions, ranging from flexible to rigid, and from water-absorbent to water-resistant.