A216 Polymer Chemistry - Lesson 6

Step-Growth Polymerization - Part 2

Overview

• Characteristics of step-growth polymerization.
• Polymers from condensation polymerization.
• Polymers from non-condensation polymerization.
• Functional groups and functionality of monomers.

Step-Growth Polymerization of Polyamide

• Monomer with di-amine functional group.
• Monomer with dioic acid functional group.
• Polyamide products: Umbrella, Rope, Anti-cut glove, Gears.
• Nylon is the first polyamide product, invented to replace expensive silk.
• Nylon is called the "wonder material" due to its heat and water resistance.
• Polyamide is often linked to Nylon.

Polyamide Formation

• Temperature range: 20°C - 350°C
• Water is a by-product: (2n-1) H_2O
• Reactants: Hexanedioic acid (Adipic acid) and Hexane-1,6-diamine (1,6-Diaminohexane).
• Hexanedioic acid itself can catalyze the reaction, besides the presence of an acidic catalyst.

Polyamide Reaction Mechanism

• Carbonyl oxygen of hexanedioic acid undergoes protonation, with the proton donated by a neighboring dioic acid.
• The carbonyl carbon is attacked by the amine group, forming an ammonium intermediate.
• Amide linkage is formed after water elimination.
• Resulting product: Polyamide 6,6 (Nylon 6,6).

General Process Setup for Polyamidation

• Components: Reflux condenser, monomers, reactor, heating jacket, main condenser, vent, vacuum pump, receiver, rotating mixer, cool water inlets.
• Cool water inlets remove by-product.
• Polymerization happens within the reactor.

Non-Condensation Polymerization

• Typical non-condensation polymers do not involve the elimination of small molecules during the polymerization process.

Step-Growth Polymerization of Polyurethane

• Monomer with diol functional group.
• Monomer with di-isocyanate functional group.
• Polyurethane products: Floor coating, Bedding, Insulation panel.

Polyurethane Formation Mechanism

1. Nucleophile (Oxygen) from diol compound is attracted to carbon from diisocyanate.
2. Active hydrogen shuffles to the negatively charged nitrogen, giving rise to urethane linkage.

• Urethane linkage forms via the reaction of alcohol with isocyanate.

Polyurethane Reaction Conditions

• Temperature range: 20°C - 25°C
• No by-product.
• Urethane link is formed repeatedly.

Step-Growth Polymerization of Polyurea

• Monomer with diamine functional group.
• Monomer with di-isocyanate functional group.
• Polyurea products: Floor coating, Roof coating.
• Polyurea is typically applied as a coating due to its fast reactivity and cure rate.
• Temperature range: 20°C - 25°C
• No by-product.

Polyurea Chemical Reaction

nH2N — (CH2)n—NH2 + nO=C=N-(CH2)6-N=C=0

• Reactants: hexamethylenediamine and hexamethylene diisocyanate
• Product: polyurea

Functional Groups and Functionality of Monomers

• The reaction between two monomers is determined by the functionality of the monomers.
• Reaction between an acid and alcohol to form an ester is incapable of further esterification, so no long-chain polymers are formed.
• The functionality of a molecule is its interlinking capacity or the number of sites it has for bonding with other molecules under specific polymerization conditions.

Monomer Functionality

• A molecule may be classified as monofunctional, difunctional, trifunctional, or polyfunctional depending on whether it has one, two, three, or multiple sites available for linking with other molecules.
• Reaction between di-acid and diol forms an ester that can undergo esterification indefinitely, forming long polymer chains.
• Reaction between two monomers ___ __ (incomplete in original slides).

Branched/Cross-Linked Polymers

• Reaction between tri/poly-functional molecules results in structural units that may be linked to form complex structures, leading to branched, cross-linked, or network polymer systems.

Phenoplasts

• Formaldehyde and Phenol.
• Trade name: Bakelite
• Example of network step-growth polymer.
• During polymerization, mono-, di-, and trimethylphenols are formed, allowing macromolecules to branch out and connect, forming a three-dimensional network structure.

Reaction Outcomes Based on Monomer Functionality

L3 Experiment

• Polyamide (Nylon) is produced.
• Several meters of nylon are collected.

Interfacial Polymerization

• Polymerization happens at the interface.
• 1,6-hexanediamine has (incomplete in original slides) than sebacoyl chloride and floats on top, forming a uniform contact between the layers (isotropic interface).
• Nylon is formed at the interface.
• 1,6-Hexanediamine in 3% NaOH solution.
• Sebacoyl chloride in hexane.
• Density info:
  • 1,6-Hexanediamine – 0.84 g/mL
  • Sebacoyl chloride – 1.12 g/mL

Interfacial Polymerization Process

• Interfacial polymerization occurs at the interface between the aqueous phase (1,6-hexanediamine) and the organic phase (sebacoyl chloride), resulting in a polymer constrained to the interface, which can be pulled out as nylon-6,10.