Breaking Apart Polymers

Overview

• Identify monomers of condensation polymers (polyesters and polyamides) from diagrams of repeating units.
• Importance of the asymmetrical nature of ester and amide bonds to determine which part of the backbone was linked to carboxylic acid and which to alcohol or amine group.
  • Ester group: part linked to carboxylic acid and another part to alcohol.
  • Amine group: part linked to carboxylic acid and another part to amine.

Polyesters

• Single bonded O indicates the break between monomers.
• Side with carbon double bonded O (
  • Side with carbon double bonded O is the carboxylic acid side.
  • Side with O is the alcohol side.
• Monomers Identification:
  • Polymers can arise from either one or two monomers.
  • Determine by checking the direction of the ester groups.
    • If all face the same way: one monomer.
    • If they alternate directions: two monomers.
• Alcohols with two functional groups may be on non-terminal carbons, necessitating consideration of side groups relative to the molecule.
• Include side chains of the backbone in diagrams.

Example 1: Diagram Identification

• Cut at O bond locations.
• Observe ester group directions:
  • Alternating directions suggest two monomers.
  • Identify monomers by their recurring patterns:
    • Carboxylic acid side with 4 carbons.
    • Alcohol side with 2 carbons.
• Resulting monomers:
  • Butane dioic acid.
  • Ethan-1,2-diol.

Polyamides

• N indicates the break between monomers.
• Carboxylic acid and amine sides distinguished similarly to polyesters.
• Monomers can originate from one or two sources:
  • Check direction of amide groups:
    • Same direction: one monomer.
    • Alternate directions: two monomers.
• Side chains must be included in the diagrams.

Example 2: Diagram Identification

• Cut at N bond locations.
• Observe amide group directions:
  • Alternating directions indicate two monomers.
  • Identify monomers by their recurring patterns:
    • Di-carboxylic acid (3 carbons in chain).
    • Cyclobutane with two amine groups.
• Resulting monomers:
  • Propan-dioic acid.
  • 1,3-cyclobutane diamine.

Example 3: Single Monomer Polyamide

• Cut at N bond locations.
• Amide groups in the same direction:
  • Single monomer identified.
• Identify by recurring pattern:
  • Benzene ring with the amino group and carboxyl group at the opposite positions.
• Resulting monomer:
  • 1,4-amino benzoic acid.

Practice

• Recommended to try questions on provided platform for better understanding.