Problem 43 - Chemistry: The Central Science

Question

Draw the structure of the monomer(s) employed to form each of the following polymers shown in Table \(12.5\) (a) polyvinyl chloride, (b) nylon 6,6, (c) polyethylene terephthalate.

Step-by-Step Solution

Answer

The monomers for the given polymers can be represented as follows: (a) Polyvinyl chloride (PVC): Vinyl chloride monomer with the structure \(H_2C=CH-Cl\) (b) Nylon 6,6: Hexamethylenediamine (\(H_2N(CH_2)_6NH_2\)) and adipic acid (\(HOOC(CH_2)_4COOH\)) (c) Polyethylene terephthalate (PET): Ethylene glycol (\(HOCH_2CH_2OH\)) and terephthalic acid (\(HOOC-C_6H_4-COOH\))

Step 1: Polyvinyl Chloride (PVC)

Polyvinyl chloride (PVC) is a polymer that is synthesized from the monomer vinyl chloride. Vinyl chloride is an organic compound with the molecular formula C2H3Cl, which consists of a carbon double bond (C=C) and a chlorine atom attached to one of the carbon atoms. The structure of the vinyl chloride monomer can be drawn as follows: ``` H2C=CH-Cl ```

Step 2: Nylon 6,6

Nylon 6,6 is a polymer synthesized from two monomers: hexamethylenediamine and adipic acid. Hexamethylenediamine is an organic compound with the molecular formula C6H16N2. Its structure consists of a six-carbon chain (C6), with an amine group (-NH2) at each end: ``` H2N-(CH2)6-NH2 ``` Adipic acid is an organic compound with the molecular formula C6H10O4. Its structure consists of a six-carbon chain (C6), with a carboxylic acid group (-COOH) at each end: ``` HOOC-(CH2)4-COOH ```

Step 3: Polyethylene Terephthalate (PET)

Polyethylene Terephthalate (PET) is a polymer synthesized from two monomers: ethylene glycol and terephthalic acid. Ethylene glycol is an organic compound with the molecular formula C2H6O2. Its structure consists of a two-carbon chain (C2), with a hydroxyl group (-OH) at each end: ``` HO-CH2-CH2-OH ``` Terephthalic acid is an organic compound with the molecular formula C8H6O4. Its structure consists of a benzene ring with a carboxylic acid group (-COOH) attached to the carbon atoms in the 1,4 positions: ``` HOOC-C6H4-COOH ``` In the above structure, the 1,4 positions refer to the carbon atoms bonded to the carboxylic acid groups on the benzene ring.

Key Concepts

Polyvinyl Chloride (PVC)

Polyvinyl chloride, also known as PVC, is a widely used plastic found in many applications ranging from pipes to credit cards. But before it comes into these forms, it exists as a simple monomer called vinyl chloride. Vinyl chloride has the chemical formula (C₂H₃Cl), and when drawn, it features a carbon-carbon double bond ((C=C)) alongside a chlorine atom bonded to one of these carbons.
Like linking hands in a chain, the vinyl chloride monomers undergo a process called polymerization, where the double bonds open up and connect, creating a long molecule—or polymer—that we recognize as PVC. This transformation is key to understanding how small organic molecules can create vast and diverse materials with practical uses.

Nylon 6,6 Synthesis

Nylon 6,6, a type of synthetic polymer, is a staple of the textile industry, known for its durability and resilience. Its creation is an excellent example of a condensation polymerization, which involves combining two types of monomers: hexamethylenediamine and adipic acid.
Hexamethylenediamine has the molecular structure ((C₆H₁₆N₂)), featuring a chain of six carbon atoms terminated by amine groups ((-NH₂)). Adipic acid, on the other hand, is organized as a six-carbon chain ((C₆H₁₀O₄)), and comes with a carboxylic acid group ((-COOH)) on each end. When these monomers react, they form the sturdy polymer chains of nylon 6,6, shedding water molecules as they link, which underscores the importance of understanding reactions between organic compounds.

Polyethylene Terephthalate (PET)

Think of the transparent plastic bottles that hold your favorite beverages, and you have encountered polyethylene terephthalate, better known as PET. This polymer is the result of the chemical bonding between two monomers: ethylene glycol and terephthalic acid.
Ethylene glycol has a simple structure, (C₂H₆O₂), two carbon atoms connected by a single bond, with hydroxyl groups ((-OH)) capping both ends. Terephthalic acid is slightly more complex, comprising a benzene ring joined to carboxylic acids ((-COOH)) at the first and fourth carbon atoms—this is denoted as the 1,4 positions on the ring. Their reaction to form PET is a fine display of organic chemistry, highlighting how seemingly small molecules can join to create sturdy, usable materials.

Organic Compound Structures

Understanding the organic compound structures is essential in chemistry, particularly when studying polymers like PVC, nylon 6,6, and PET. These structures consist of carbon-based backbones with various functional groups attached.

The structural formulas of these organic molecules reveal the arrangements of atoms and the types of bonds—single, double, or triple—that hold the atoms together. This information helps in predicting the physical and chemical properties of the materials. For example, the presence of a benzene ring in terephthalic acid indicates a level of rigidity which translates to the durability of PET.
By grasping the basics of these organic structures and how they combine, students can better conceptualize the transition from small monomers to large, functional polymers with diverse applications.