BME213 Sem 3 Flashcards
Compare the two synthesis methods. Give an example of polymer synthesized via each method.
- Addition Polymerization (Chain-Growth):
• Monomers with double bonds join without forming by-products.
• Uses free radicals or ions to start the chain reaction.
• Fast growth, typically one type of monomer.
• Example: Polyethylene (from ethene) - Condensation Polymerization (Step-Growth):
• Monomers with two functional groups react step-by-step.
• Produces small by-products (like water or HCl).
• Slower build-up, often involves two types of monomers.
• Example: Nylon-6,6 (from hexamethylene diamine and adipic acid)
What key marker would you use to decide which polymerization mechanism a monomer would use?
The type of functional group or bond present in the monomer is the key marker.
If the monomer has:
• A carbon-carbon double bond (C=C) → It will likely undergo addition polymerization.
• Example: Ethene → Polyethylene
• Two or more reactive functional groups (e.g., –OH, –COOH, –NH₂) → It will undergo condensation polymerization.
• Example: Adipic acid + Hexamethylene diamine → Nylon-6,6
Addition polymerization has 3 steps. Briefly explain each stepusing ethene as the monomer.
- Initiation:
• A free radical (e.g. from a peroxide) attacks ethene’s double bond, breaking it and creating a reactive chain-starting radical.
• Example:
R + CH2 = CH2 -> RCH2CH2 - Propagation:
• The active chain end reacts with more ethene monomers, growing the polymer.
• Example:
RCH2CH2 + CH2 = CH2 -> RCH2CH2CH2CH2 - Termination:
• Two growing chains (radicals) combine, ending the chain reaction.
• polymerization comes to a stop via 2 principle mechanisms:
- recombination : joining of 2 radial molecules to form a non-reactive molecule
- occlusion : “frozen mobility” caused by decrease mobility of free radicals, macro-radicals and monomers due to entrapment within the increasingly dense polymer structure
• Example:
CH2CH2 + CH2CH2 -> CH2CH2CH2CH2
Draw the reaction mechanism for the polymerization of Nylon 6,6. Are there any by-products produced?
Reaction Mechanism (in words):
• Hexamethylene diamine (H₂N–(CH₂)₆–NH₂) reacts with adipic acid (HOOC–(CH₂)₄–COOH).
• An amide bond (–CO–NH–) is formed between the –NH₂ and –COOH groups.
• This repeats to form a long-chain polymer:
–NH–(CH₂)₆–NH–CO–(CH₂)₄–CO– \text{ (repeating unit)}
By-Product:
• Yes — water (H₂O) is released each time a bond forms.
• This is typical of condensation polymerization.
What are the classification of polymers by structure?
- Linear Polymers
• Long, straight chains (no branches or cross-links)
• Example: Polyethylene, PVC - Branched Polymers
• Main chain with short side branches
• Example: Low-Density Polyethylene (LDPE) - Cross-linked Polymers
• Chains connected by covalent bonds (cross-links)
• Rigid and thermosetting
• Example: Bakelite, vulcanized rubber - Network Polymers
• Extensive 3D bonding between monomers
• Very hard and brittle
• Example: Epoxy resin, phenol-formaldehyde
What are the different between thermoplastics and thermosets polymers?
Thermoplastics
• Soften when heated, can be remolded repeatedly
• Have linear or branched structures
• No cross-links between chains
• Recyclable
• Example: Polyethylene, PVC, Polystyrene
Thermosets (Thermosetting Polymers)
• Harden permanently when heated — cannot be remelted
• Have extensive cross-linking between chains
• Rigid and heat-resistant
• Not recyclable
• Example: Bakelite, Epoxy resin, Melamine
Describe the 2 types of bonding found in polymers
- Primary Bonding (Covalent Bonds)
• Strong bonds that hold atoms together within each polymer chain
• Formed during polymerization
• Provide backbone strength to the polymer
• Example: Carbon-carbon bonds in polyethylene - Secondary Bonding (Intermolecular Forces)
• Weaker forces between different polymer chains
• Include van der Waals forces, hydrogen bonds, or dipole interactions
• Influence properties like flexibility, melting point, and solubility
• Example: Hydrogen bonding between chains in nylon
What are 5 Advantages of Polymers
- Lower material cost compared to other biomaterials.
- Ease of manufacturability to produce various shapes
including complex shapes, e.g bulk, film, sheet, fibres, etc - Wide range of physical and mechanical properties (variety
of density and molecular weight). - Easily shaped or modified by the surgeon in-situ to obtain
better fitting. - Polymer is organic, higher biocompatibility compared to
other class of materials and low thrombocytes
What is a “polymer”?
A long chain macromolecule made up of many repeating units. Can often contain as many 45,000 repeating units.
What is a “monomer”?
The small repeating unit used to make up the polymer. E.g. ethene in polyethene
What is a “biopolymer”?
A biopolymer is a polymer that can be used for creating biomedical devices that come into contact with human biological
tissue or fluids.
What is a monomer’s functionality?
The number of bonding sites a monomer has with other monomer.
