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Organic Chemistry - Polymers (Addition and Condensation)

Grade 12IGCSEChemistry

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

🔑Concepts

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Polymers are macromolecules made by linking many small units called monomers together.

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Addition polymerization occurs when unsaturated monomers (alkenes) join without the loss of any atoms. The C=CC=C double bond breaks to form C−CC-C single bonds.

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In addition polymers, the repeat unit has the same atoms as the monomer. For example, nn molecules of ethene (C2H4C_2H_4) form poly(ethene) −[CH2−CH2]n−-[CH_2-CH_2]_n-.

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Condensation polymerization involves monomers with two functional groups. When they react, a small molecule (usually H2OH_2O or HClHCl) is eliminated.

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Polyesters are formed from a dicarboxylic acid and a diol, creating ester linkages (−COO−-COO-). An example is Terylene.

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Polyamides are formed from a dicarboxylic acid and a diamine (or amino acids), creating amide linkages (−CONH−-CONH-). An example is Nylon.

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Proteins are natural polyamides formed from amino acid monomers, where the linkage is specifically called a peptide bond.

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Plastics pose environmental challenges because most addition polymers are non-biodegradable and chemically inert due to strong C−CC-C bonds.

📐Formulae

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

n(HO−R−OH)+n(HOOC−R′−COOH)→−[O−R−O−CO−R′−CO]n−+2nH2On(HO-R-OH) + n(HOOC-R'-COOH) \rightarrow -[O-R-O-CO-R'-CO]_n- + 2n H_2O

n(H2N−R−NH2)+n(HOOC−R′−COOH)→−[NH−R−NH−CO−R′−CO]n−+2nH2On(H_2N-R-NH_2) + n(HOOC-R'-COOH) \rightarrow -[NH-R-NH-CO-R'-CO]_n- + 2n H_2O

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

💡Examples

Problem 1:

Identify the monomer used to create the addition polymer poly(propene) and draw its repeat unit.

Solution:

Monomer: Propene (CH3CH=CH2CH_3CH=CH_2). Repeat unit: −[CH(CH3)−CH2]n−-[CH(CH_3)-CH_2]_n-.

Explanation:

In addition polymerization, the double bond of the monomer CH3CH=CH2CH_3CH=CH_2 opens up. The CH3CH_3 group remains as a side chain on one of the carbon atoms in the polymer backbone.

Problem 2:

A polyester is formed from ethane-1,2-diol (HO−CH2−CH2−OHHO-CH_2-CH_2-OH) and benzene-1,4-dicarboxylic acid (HOOC−C6H4−COOHHOOC-C_6H_4-COOH). Draw the structure of the ester linkage and identify the byproduct.

Solution:

Linkage: −O−CO−-O-CO-. Byproduct: H2OH_2O.

Explanation:

The hydroxyl group (−OH-OH) from the diol reacts with the carboxyl group (−COOH-COOH) from the acid. A molecule of H2OH_2O is removed, and the remaining oxygen from the diol bonds to the carbonyl carbon of the acid.

Problem 3:

Compare the biodegradability of poly(ethene) and Nylon.

Solution:

Poly(ethene) is non-biodegradable; Nylon is potentially biodegradable over long periods via hydrolysis.

Explanation:

Poly(ethene) consists of strong, non-polar C−CC-C bonds that bacteria cannot easily break. Nylon contains amide linkages (−CONH−-CONH-) which are polar and can be broken down by hydrolysis (the reverse of condensation) or enzymatic action.

Polymers (Addition and Condensation) Revision - Grade 12 Chemistry IGCSE