Polymers Flashcards
What is the base structure of a polymer?
Chain of molecules, backbone of carbon atoms covalently bonded together.
What is a mer unit?
Repeat unit.
What are the 2 types of polymerisation?
Addition polymerisation: Adding one monomer to another.
Condensation polymerisation: Reacting monomers together.
What are the 3 types of polymer materials?
Thermoplastics, Thermosets and elastomers.
Describe thermoplastics structure and what characteristics do they have?
Held together with secondary bonds. Can be formed and reformed many times (recyclable).
What is degree of polymerisation?
Average number of mer units in the polymer chain.
how does degree of polymerisation relate to molecular weight?
High DP = High MW
Which has the higher density, linear polymers or branched polymers?
Linear polymer.
Branched polymer has low density.
What are the 3 types of copolymer?
Regular pattern.
Random pattern.
Block pattern.
How would you achieve more crystallinity when forming a thermoplastic?
Cool it slowly.
If a thermoplastic has high crystallinity, what properties will it have?
Higher melting point, higher stiffness, higher resistance to solvents, reduced permeation of gases.
What happens to a thermoplastic when it is heated to above its glass transition temperature?
Becomes more ductile, less yield strength and lower elastic modulus.
During tensile testing of a thermoplastic what happens to the polymer structure once it reaches the necking stage?
The polymer chains become aligned in direction of stress.
Describe thermoset structure and properties.
Linked by covalent bonds. Low ductility, high strength stiffness and hardness.
Describe the affect of temperature change on thermosets.
Not much variation in properties.
