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Chemistry - Polymers

Grade 9IGCSE

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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A polymer is a large molecule (macromolecule) built up from many smaller units called monomers. The process of joining monomers is called polymerization.

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Addition polymerization occurs when unsaturated monomers (alkenes) join together. The C=CC=C double bond breaks to form single bonds that link the monomers. For example, ethene monomers form poly(ethene): n(CH2=CH2)→−[CH2−CH2]n−n(CH_2=CH_2) \rightarrow -[CH_2-CH_2]_n-.

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Condensation polymerization involves the joining of monomers with the elimination of a small molecule, such as water (H2O)(H_2O). This usually requires monomers with two functional groups.

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Polyamides (e.g., Nylon) are formed from a diamine and a dicarboxylic acid, resulting in amide linkages −CONH−-CONH-.

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Polyesters (e.g., Terylene) are formed from a diol and a dicarboxylic acid, resulting in ester linkages −COO−-COO-.

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Natural polymers include proteins (polymers of amino acids), starch/cellulose (polymers of glucose), and DNA.

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Plastics are synthetic polymers. They are often non-biodegradable, leading to environmental issues like landfill accumulation and harm to marine life when disposed of improperly.

📐Formulae

n(CH2=CH2)→−[CH2−CH2]n−n(CH_2=CH_2) \rightarrow -[CH_2-CH_2]_n-

R−COOH+R′−NH2→R−CONH−R′+H2OR-COOH + R'-NH_2 \rightarrow R-CONH-R' + H_2O

R−COOH+R′−OH→R−COO−R′+H2OR-COOH + R'-OH \rightarrow R-COO-R' + H_2O

−Amide Linkage: −C(=O)−NH−-\text{Amide Linkage: } -C(=O)-NH-

−Ester Linkage: −C(=O)−O−-\text{Ester Linkage: } -C(=O)-O-

💡Examples

Problem 1:

Draw the repeat unit of the polymer formed from the monomer propene (CH2=CHCH3CH_2=CHCH_3).

Solution:

−[CH2−CH(CH3)]n−-[CH_2-CH(CH_3)]_n-

Explanation:

During addition polymerization, the double bond of the propene monomer opens up. The CH3CH_3 group remains as a side chain attached to one of the carbon atoms in the main polymer chain.

Problem 2:

Identify the type of polymerization and the small molecule released when a dicarboxylic acid reacts with a diol.

Solution:

Condensation polymerization; Water (H2OH_2O)

Explanation:

When a carboxylic acid group (−COOH-COOH) reacts with an alcohol group (−OH-OH), an ester linkage (−COO−-COO-) is formed and a molecule of water (H2OH_2O) is eliminated.

Problem 3:

A section of a polymer chain is shown as: −[CH2−CHCl−CH2−CHCl−CH2−CHCl]−-[CH_2-CHCl-CH_2-CHCl-CH_2-CHCl]-. Identify the monomer used.

Solution:

Chloroethene (CH2=CHClCH_2=CHCl)

Explanation:

The repeating unit is −[CH2−CHCl]−-[CH_2-CHCl]-. Since this is an addition polymer, the monomer must be the corresponding alkene where the single bond between the carbons is replaced by a double bond, which is CH2=CHClCH_2=CHCl (also known as vinyl chloride).