L1: Intro and Solid State Flashcards
Define polymer
Many units of monomers covalently bonded together to form a long chain (a macromolecule)
Give the 3 conventional classifications of polymer
- Natural
- Semi-synthetic
- Synthetic
What are the subdivisions of natural polymers?
Organic and inorganic
What are semi-synthetic polymers? Give an example
Naturally occurring polymers chemically modified to make their properties desirable
Vulcanisation of rubber
What are synthetic polymers?
Human made polymers, made from monomers derived from petroleum
Give the key characteristic of organic synthetic polymers. How do inorganic synthetic polymers differ?
Backbones have C-C bonds
No C in backbone
What are the two main categories of polymerisation reaction and the sub-types for each?
Chain-growth -Free radical -Coordination -Cationic -Anionic Step-growth -Polycondensation -Polyaddition
When are brackets used in nomenclature?
When the monomer name consists of more than one word - eg poly(vinyl chloride)
What feature must monomers have in order to carry out chain-growth polymerisation?
What must happen to ethylene to create this feature?
Carbon-carbon double bonds ( C=C )
One or more hydrogen atoms in the ethylene monomer must be replaced by other elements or organic groups
Give an overview of free-radical polymerisation
- Initiation. A free radical initiator reacts with the monomer, opening the C=C bond. One electron from the double bond is left alone - a larger free radical has been made
- Propagation. Monomers are added to the chain one at a time
- Termination. Two large free radical chains meet to form dead chains. Dead chain length is random
What is the requirement for monomers used in step-growth polymerisation?
Monomers must have 2 different functional groups (can have 2 different monomers or 1 monomer with 2 different groups)
Give an overview of step-growth polymerisation
Difunctional group monomers react, potentially forming H2O as a byproduct.
Intermediate medium-sized oligomers form
Give an overview of condensation polymerisation
An ester linkage is formed between two monomers when the -COOH and -OH groups react (can have two different monomers or a difunctional monomer). A water molecule is produced as a by-product
Chain grows from both ends of the chain
What does an ester linkage look like?
O
ll
- O - C -
Give an overview of condensation polymerisation
The hydrogen from an amine group reacts with the hydroxyl group from another monomer to form a water molecule as a by-product, linking the two monomers by an amide bond
What does an amide bond look like?
H O
l ll
N - C
What are the key features of polyaddition polymerisation?
- Difunctional groups are required
- No small molecules are formed as byproducts
Describe the change when a thermoplastic polymer is heated
It melts into a viscous liquid. This is a reversible change
Describe how heat affects liquid thermoset polymers
They are ‘cured’ into a hard solid. They become hard and rigid due to inter-chain cross-linking reactions
What is the result of polymers being polydispersed, and what must therefore be measured?
No unique molecular weight
Need to measure Molar Mass Distribution
Give the formula relating mass, moles and molecular mass
Mass = moles x molecular mass
Define degree of polymerisation (both words and equation)
- Mean number of monomer units per polymer chain
- (Molar mass of chain)/(Molar mass of monomer)
Why is molar mass important?
- Higher MM gives better mechanical properties due to increased chain entanglement and interaction
- More difficult to process due to increased melt viscosity
Give names for polymer architecture with the following structures (2 is the group of i, ii, iii):
- -A-A-A-A-A-A
- i) -A-B-A-B-A-B-A-
ii) -A-A-A-A-B-B-B-B-
iii) -A-B-A-A-A-B-B-A-B
- Homopolymer
- Copolymer
i) Alternating
ii) Block
iii) Statistical
Give the names for polymers:
- Consisting of identical monomers
- Consisting of different monomers
- Homopolymer
2. Copolymer
Describe branched polymers
Long chains of identical monomers with shorter branching chains of identical monomers
Describe graft polymers and give their nomenclature
Long chains of identical monomers with shorter branching chains of
different identical monomers
poly(A-g-B)
Describe cross-linked polymers
A 3D network of polymer chains
Give the 3 spatial arrangements of tacticity and a basic description
- Isotactic - same orientation
- Syndiotactic - Alternating orientation
- Atactic - No regularity
Why can’t atactic polymers crystallise?
There are steric clashes so the molecules cannot arrange themselves in an ordered fashion
How do synthetic polymers crystallise?
They form regular helices, which are straight and periodic
What are lamellar stacks?
Alternating crystallise and amorphous layers
How does pinning work in lamellar stacks?
Macromolecules pass from one phase to another many times. The longer the chains, the more effective the pinning
Describe spherulites
Spherical aggregates, 1micrometer to 1mm in size.
They crystallise from a nucleation point & grow radially in 3D until impinged on
What effect do spherulites have on mechanical strength?
They degrade it, as cracks appear along their boundaries
How does density change with crystallinity?
More dense with higher crystallinity
How does young’s modulus change with crystallinity?
Increases linearly with degree of crystallinity
How does strength change with crystallinity and molar mass?
Increases
How does toughness change with crystallinity and molar mass?
Increases with molar mass, decreases with crystallinity
What is changing in the ductile-brittle transition?
Molar mass and density (ie crystallinity)
