Question

Draw the structure for the polymer that could be produced from each of the following monomers by the method stated. a. Addition \(\quad\) b. Condensation

Short answer

a. For the addition polymerization, using ethylene (\(C_2H_4\)), the resulting polymer is polyethylene with the structure: \(\cdots - CH_2 - CH_2 - CH_2 - CH_2 - \cdots\). b. For the condensation polymerization, using acetic acid (\(CH_3COOH\)) and ethylene glycol (\(HOCH_2CH_2OH\)), the resulting polymer is poly(ethylene terephthalate) or PET with the structure: \(\cdots - OCH_2CH_2OCOCH_3 - OCH_2CH_2OCOCH_3 - \cdots\).

Step-by-step solution

a. Addition Polymerization

For addition polymerization, we need a monomer with double bonds that can break and form new bonds with adjacent monomers. Let's use the example of ethylene, which has the formula \(C_2H_4\). In addition polymerization, the double bond in ethylene will break to form a single bond, and ethylene molecules will join together to form a long chain called polyethylene. The structure of polyethylene can be represented as: \[ \text{Polyethylene: } \cdots - CH_2 - CH_2 - CH_2 - CH_2 - \cdots \]

b. Condensation Polymerization

For condensation polymerization, we need two different monomers that can react together to form a covalent bond and release a small molecule, such as water or methanol. The most common example is the reaction between a carboxylic acid and an alcohol to form an ester and release water. Let's use the example of acetic acid (\(CH_3COOH\)) and ethylene glycol (\(HOCH_2CH_2OH\)). 1. Acetic acid: \[ CH_3COOH \] 2. Ethylene glycol: \[ HOCH_2CH_2OH \] In condensation polymerization, the hydroxyl (\(OH\)) group of acetic acid reacts with the hydroxyl group of ethylene glycol to form a covalent bond, creating an ester linkage and releasing water. The resulting polymer, called poly(ethylene terephthalate) or PET, has the following structure: \[ \text{PET: } \cdots - OCH_2CH_2OCOCH_3 - OCH_2CH_2OCOCH_3 - \cdots \]

Key concepts

Addition Polymerization

Addition Polymerization is a process where monomers with double bonds join together to form polymers. The double bonds in the monomers break, allowing new covalent bonds to form along the monomer chain. This results in a long and stable polymer. The entire process involves using catalysts to initiate the chain reaction, prompting the monomers to link up and form a polymer chain.
Addition polymerization is widely used in creating various synthetic materials due to its simplicity and efficiency. This method only involves monomers with unsaturated bonds, like alkenes, making it a specific approach suited to particular types of raw materials.

Condensation Polymerization

Condensation Polymerization is a technique that involves two different monomers reacting to form a polymer and a small molecule, typically water. This process usually happens with monomers that contain functional groups such as hydroxyl, carboxylic acids, or amines. The removal of the small molecule byproduct is crucial to the reaction's success.
This type of polymerization is essential for creating a variety of materials, including polyesters and polyamides. Unlike addition polymerization, the resulting polymer chain from condensation polymerization is usually more complex due to different monomers being used. The reaction might also require heat or pressure to proceed efficiently.

Monomer Structure

Monomers are the building blocks of polymers. They are small molecules with specific functional groups that allow them to link into large chain structures. Understanding the monomer structure is crucial, as it determines the kind of polymer produced and its properties.
Each monomer type has its characteristics, for instance:

• Alkenes often serve as monomers in addition polymerization due to their double bonds.
• Monomers like carboxylic acids and alcohols are frequently used in condensation polymerization due to their ability to release small molecules like water during the reaction.

Recognizing the structure helps in predicting how monomers will react and what type of polymer they will form.

Polyethylene

Polyethylene is one of the most common polymers and is created through addition polymerization of ethylene monomers. Ethylene, with the formula \(C_2H_4\), utilizes its double bonds in the process to link multiple ethylene molecules, forming polyethylene.
The structure of polyethylene is a straightforward repeating sequence of \(-CH_2-CH_2-\) units. This simplicity makes it an incredibly versatile material used in everyday products:

• Plastic bags
• Bottles
• Containers

Its lightweight and durable nature make it a favorite choice for many applications and industries.

Poly(ethylene terephthalate)

Poly(ethylene terephthalate), commonly known as PET, is produced through condensation polymerization. This process involves ethylene glycol and terephthalic acid as monomers, creating ester linkages by releasing water.
The resulting polymer has a repeating structure symbolized by ester bonds, \(-OCH_2CH_2OCOC_6H_4CO-\), throughout the chain. PET is known for its strength, thermal stability, and transparency. It is extensively used in:

• Plastic bottles for beverages
• Packaging materials
• Textile fibers

These properties rank PET as an essential material in various industrial and consumer applications.