Polymer Structure and Properties Flashcards
(25 cards)
What is a Polymer?
- Chains of repeating units made from monomers
What can polymers be classified as?
- Synthetic polymers (plastics)
- Natural biopolymers
- What do polymers have relative to small molecules?
- What do polymers form?
- What properties do polymers exhibit?
- Polymers have large molecular mass relative to small molecules - exhibit long-range interactions
- Polymers form amorphous glasses and semicrystalline structures rather than crystals (small molecules)
- Unique physical properties, including toughness, viscoelasticity and permeability
What do long range interactions allow for?
- Allow polymers to be used in different ways
- Fibre formation
- Film formation
- Molding
The bulk properties of polymers which are observable to us with the naked eye are dependent on?
- The ordering of the polymer chains on the microscale
- Polymer morphology:
- Amorphous, crystalline, semi-crystalline
Polymer morphology is dependent on?
- Chemical composition and structure of the polymer at the nanoscale
What are the Properties of Spider Silk?
- Spiders can modify properties of fibre it produces by controlling polymer morphology
- Within fibre, it is made of proteins which are organised to give us amorphous and crystalline regions
- The ordering of the polymer chains results from the amino acid structure and sequence of the protein
The physical properties of polymers are dictacted by their ________?
- The physical properties of polymers are dictacted by their chemical properties
- Composition
- Sequence
- Stereochemistry
- Chain Length
- Architecture
The physical properties of polymers are dictacted by their chemical properties
- Composition
- Sequence
- Stereochemistry
- Chain Length
- Architecture
Elaborate on each of these
- Composition
- The molecular structure of the individual monomer unit(s)
- Sequence
- The ordering of the repeat units with respect to each other
- Stereochemistry (tacticity)
- The spatial arrangement of the repeat units with respect to each other
- Chain Length
- How long the polymer chains are
- Architecture
- The 3D structure of the polymer
Chemical Properties: Composition
- Elaborate
- By changing the composition slightly?
- Identity of the constituent monomer; the chemical structure of repeat unit
- By changing composition slightly, can drastically change characteristics of polymer
Chemical Properties: Composition
- What is polymer nomenclature based upon?
- What are the 2 types?
- Polymer nomenclature is based upon the type of monomer residues
- Homopolymers - single type of repeat unit
- e.g Polyethylene
- Copolymers - > 1 type of repeat unit
- Homopolymers - single type of repeat unit
Chemical Properties: Sequence
- Simplest copolymer based on?
- Various copolymer sequences possible?
- Simplest copolymer based on two monomers
- Sequences include:
- Random
- Alternating
- Di-block
- Tri-block
- Multi-block
Chemical Properties: Stereochemistry
- What is it?
- What are the types?
- Arrangement of pendent (side) groups with respect to each other
- Three types
- Isotactic
- All methyl groups same side
- Syndiotactic
- Methyl groups alternating sides
- Atactic
- Methyl groups random arrangement
- Isotactic
Chemical Properties: Molecular Weight
Elaborate
- Molecular weight = chain length
- Molar mass of individual polymer chains are rarely identical, therefore, we average the mass of each polymer chain to get the average molecular weight (AMW)
Chemical Properties: Architecture
What are the types?
- Linear
- Branched
- Have polymer backbone then have other branches coming off that forming new backbone
- Cross-linked
- Lots of branches joined together in infinite network
What is the Difference between Ultra-High MW and Low-density AMW and Branching?
- Ultra-high MW
- Strong intermolecular interactions
- No branches
- Super hard and dense
- Low-density
- Weak intermolecular interactions
- Short chains of PE and lots of branches
- Lots of branches stop the polymer chain packing together so well = lots of amorphous regions
What is Thermoplastics?
- The morphology of many polymers consists of semi-crystalline and amorphous regions
- Process:
- Start with hard material
- Heat causes intermolecular forces between chains and crystalline regions to start to weaken and brak
- Get to a point where we’ve broken crystalline regions up and form amorphous polymer netwrok
- Cool and crystalline regions reform
When the chains don’t interact strongly, the polymers posssess what?
- Amorphous morphology
- Although the chains can entangle, the weak intermolcular forces between the chains mean they can easily move around
- They are able to ‘flow’
How do we modify the properties of amorphous polymers to give us new materials?
- Cross link the polymer chains together with covalent linkages
- Form an infinite polymer network
- Polymer chains can’t flow over one another
What can the cross-linked polymers be referred to?
- Elastomers
- Can be stretched but will return to its original shapes
What elastomer do you always carry with you?
Skin
- Elastomers are?
- Hydrogels are?
- Elastomers are hydrophobic and the polymer chains extend and stretch under tension
- Hydrogels are hydrophilic, therefore absorb water and swell (but don’t dissolve)
In contrast to amorphous polymers we have?
- In contrast to amorphous polymers we have polymers that consist predominantly of crystalline regions
- Very hard and tough materials
- Intermolecular forces between chains are very strong
How can we improve the mechanical properties and ‘flexibility’ of crystalline polymers so that they aren’t so fragile?
- Add a plasticiser
- Small molecules that interfere and block interactions between the chains
- Breakup the crystalline regions
- Allows chains to easily move under deformable load
