Problem 84 - Chemistry The Central Science In Si Units

Question

Indicate whether the following statement is true or false: For an addition polymerization, there are no by-products of the reaction (assuming \(100 \%\) yield).

Step-by-Step Solution

Answer

True, addition polymerization produces no by-products.

Step 1: Understanding Addition Polymerization

In addition polymerization, monomers add to one another without the loss of any small molecules. The process involves the rapid joining of monomers to form a polymer, commonly via a chain-growth mechanism.

Step 2: Identifying By-products in Polymerization

In chemical reactions, by-products are small molecules generated during the reaction other than the main product. For some polymerizations, like condensation polymerization, small molecules such as water or methanol are by-products. However, in addition polymerization, such as in the formation of polyethylene, no small molecules are released.

Step 3: Assessing the Statement

The statement claims that there are no by-products in an addition polymerization. Given the understanding that addition polymerizations do not involve the loss of small molecules during the process, the statement is consistent with this description of addition polymerization.

Key Concepts

Chain-growth Mechanism

In addition polymerization, the chain-growth mechanism plays a vital role in forming polymers. This mechanism works when a single monomer forms a reactive intermediate, usually a free radical, ion, or another molecule. Once this intermediate is formed, it reacts with another monomer to create a bond and form a longer chain. The chain reaction continues in a rapid sequence, adding more monomers to the growing polymer chain.

• The process begins with the initiation phase, where interactions generate the reactive intermediate.
• Next is the propagation phase, where monomers continue to add to the chain, making it longer and longer.
• Finally, there's a termination phase, where the chain stops growing due to a combination of various factors like exhaustion of monomers or the combination of growing chains.

This method ensures that all monomers contribute directly to the polymer, without needing to discard any by-products.

Monomers

Monomers are the building blocks of polymers. In the process of polymerization, these individual small molecules link together to form large, complex structures known as polymers. Every monomer involved in an addition polymerization process must possess at least one reactive site. This site enables the monomer to connect to its neighboring monomers in a repeating pattern. Common monomers include:

• Ethylene (forming polyethylene)
• Propylene (resulting in polypropylene)
• Vinyl chloride (leading to polyvinyl chloride or PVC)

Each monomer's structure determines the properties and functionality of the resulting polymer, making the choice of monomer crucial in creating specific materials.

By-products

A by-product is any secondary product derived from a chemical reaction, aside from the desired primary product. In the context of polymerization, by-products are small molecules released during the reaction. Addition polymerization stands out due to its ability to produce polymers without generating by-products, provided there is a 100% yield. This is because all monomers directly become part of the final polymer chain. In contrast, reactions like condensation polymerization generate small molecules such as:

• Water
• Methanol

These are considered by-products because they are released during the formation of the polymer. This distinction is crucial for applications where purity and the absence of by-products are essential.

Condensation Polymerization

Unlike addition polymerization, condensation polymerization involves two monomers reacting to form a polymer while simultaneously releasing small molecules as by-products. The released molecules can include water, alcohol, or gases, depending on the specific monomers used. Key characteristics of condensation polymerization:

• It often results in step-growth polymerization, which differs from chain-growth polymerization in addition polymerization.
• The process requires monomers with two functional groups to interact and release by-products.
• Production of common materials such as nylon, polyester, and certain types of adhesives relies on this method.

The requirement to manage potentially unwanted by-products is a notable aspect of this polymerization type, affecting both the environment and the purity of the finished product.