Question 1

What is the difference between addition and condensation polymerisation?

Accepted Answer

Addition polymerisation involves monomers with a C=C double bond (alkenes) that join together without losing any atoms; the polymer is the only product. Condensation polymerisation involves monomers with two functional groups (e.g., -COOH and -OH) that react, eliminating a small molecule like water or HCl each time a bond forms. The polymer and the small molecule are both products.

Question 2

How do you draw the repeating unit of a polymer from a monomer?

Accepted Answer

For addition polymers, take the monomer (e.g., ethene CH₂=CH₂) and break the double bond, leaving single bonds on each carbon. The repeating unit is -CH₂-CH₂- (with bonds extending from the brackets). For condensation polymers, identify the linkage (e.g., ester or amide) and show the atoms that repeat, including the functional group. For example, from ethane-1,2-diol and hexanedioic acid, the repeating unit is -OCH₂CH₂OCO(CH₂)₄CO-.

Question 3

Why do some polymers have higher melting points than others?

Accepted Answer

Melting point depends on the strength of intermolecular forces between polymer chains. Longer chains have more points of contact, increasing van der Waals forces. Crystalline regions (where chains pack closely) also raise melting point. Branching reduces crystallinity, lowering melting point (e.g., LDPE vs HDPE). Cross-linking creates a network that prevents melting (thermosetting polymers).

Question 4

What are biodegradable polymers and how do they work?

Accepted Answer

Biodegradable polymers are designed to break down in the environment through hydrolysis or microbial action. Examples include poly(lactic acid) (PLA) and polyhydroxyalkanoates (PHAs). They contain ester linkages that are susceptible to hydrolysis in the presence of water and enzymes. However, many require specific conditions (e.g., industrial composting) to degrade effectively.

Question 5

How do you name polymers from their monomers?

Accepted Answer

For addition polymers, the name is 'poly(monomer name)'. For example, from ethene → poly(ethene); from chloroethene → poly(chloroethene). For condensation polymers, the name often reflects the linkage: polyesters from diols and dicarboxylic acids, polyamides from diamines and dicarboxylic acids (e.g., nylon-6,6 from hexane-1,6-diamine and hexanedioic acid).

Question 6

What is the difference between thermoplastic and thermosetting polymers?

Accepted Answer

Thermoplastic polymers (e.g., poly(ethene), nylon) have linear or branched chains that can be melted and reshaped repeatedly because intermolecular forces are weak enough to break upon heating. Thermosetting polymers (e.g., Bakelite, vulcanised rubber) have extensive cross-linking, forming a rigid 3D network that cannot be remelted; they decompose upon heating.

Polymers (A-level only)

Topic Overview

Key Concepts

What You Need to Demonstrate

Marking Points

Examiner Tips

Common Mistakes

Frequently Asked Questions

Before You Start

Key Terminology

Likely Command Words

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Related Topics in AQA A-Level Chemistry

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Alcohols

Aldehydes and ketones (A-level only)

Alkanes