Polymers Flashcards
What are polymers?
Polymers are very large molecules that consist of thousands of small repetitive units (called monomers) linked by covalent bonds
What is the polymer structure?
covalent molecular substances composed of many small molecules joined together to forma long chain of atoms.
What are some examples of natural polymers?
proteins, starch, cellulose and DNA
What is an example of a synthetic polymer?
Bakelite
hard, brittle plastic used to make cases for items like telephones and electrical guitars
As polymer chain get longer…
the strength of the dispersion forces between neighbouring polymer chains increases.
The stronger the dispersion forces….
the harder and more rigid material of a polymer
What are the two different types of branching of polymer chains?
Linear fashion or with a degree of branching
What are branched polymers?
are formed when some monomers react with sites on the side of the polymer chain instead of the ends.
What straight chain polymer?
When monomer joins to the side of the polymer chain, it begins a new chain growing a different direction.
How does branching affect properties of polymers?
Branching can cause polymer molecules to be spaced further apart, resulting in less dense materials
The greater distance between the polymer chains
the intermolecular attraction between neighbouring chains is weakened, increasing flexibility of material.
What are the bonds between thermoplastic polymers?
bonds between long polymer chains are hydrogen, dipole-dipole bonds or weak dispersion forces, rather than covalent bonds.
Why are thermoplastic polymers soft when they are heated and can be remoulded and recycled?
when heated molecules in thermoplastic materials have enough energy to overcome intermolecular forces and become free to move and slip past one another.
When can straight chain and branched chain polymers exist as thermoplastic polymers?
as long as there are no covalent cross-links between polymers chains.
What are cross-linked polymers?
polymer branches are covalently bonded to neighbouring polymer chains
Why can’t cross-linked polymers become liquids?
bonding creates a polymer network, polymers like this cannot be liquids because of polymer chains are held inlace by cross-linking and are unable to flow.
What are thermosetting polymers?
thermosetting polymers decompose or burn when heated, rather than melting and are hard and rigid.
Why are cross-linked polymers usually thermosetting polymers? and why don’t they melt?
do not soften as bonds between chains are very strong therefore a high temp must be used to break the bonds, causing the polymer to decompose.
Why cant thermosetting polymers be recycled?
it is difficult to recycle thermosetting polymers as they cannot be remoulded into new shapes
How are elastomers formed?
when occasional cross-links are presents.
As chains move past each there when stretched, but cross-links return the chains to their original position once the foresee causing stretching is released.
What happens when elastomers are heated?
crosslinks stop them from completely melting when heated and makes recycling difficult.
What are low density polyethene?
eg. cling wrap
they are longer and frequent keeping chains further making it less dense.
What are high density polyethene?
eg. bottles
there arent a large number of branches so they pack together tightly, increasing the density and hardness of the polymer formed.
How does additional polymerisation occur?
Double bonds are broken and new covalent bonds are formed between carbon atoms on nearby monomers. Only unsaturated monomers.
What is polyethene/Polyethylene?
Non-polar molecule, that only exhibits dispersion forces between adjacent long polymer chains
dispersion forces are sufficiently strong to cause it to be a solid at room temperature
What are two different types of polyethene?
Low-density polyethene (LDPE)
High-density polyethene (HDPE)
How are low-density polyethene made?
Process called free-radical polymerisation: high temperatures around (300C) and extremely high pressures.
What are free-radicals?
Free radicals highly reactive atoms, molecules or ions with an unpaired electron. They break the double bonds in ethane monomers. They attack sides of the polymer chain, resulting in significant branching
How do branches affect properties of low density polyethene? (3)
Dispersion forces between molecules are weaker when molecules are further apart.
Arrangement of polymer molecules is describe as disordered or non-crystalline
Causing them to not be able to pack closely together
What are properties of low density polyethene?
soft and flexible, low density, low melting point, non-crystalline, non-conductor of electricity
What are examples of LDPE?
used in plastic bags, flexible containers and the waterproof layer in juice and milk cartons
Why do high-density polyethene not need high pressures?
low pressure and high transition metal catalyst are used to avoid the need for high pressures.
How are HDPE arranged?
Arrangement of polymer molecules are more ordered, resulting crystalline sections. (crystalline sections)
What are properties of HDPE?
relatively high melting point
non conductor of electricity
What is polytetrafluoroethene (PTFE)?
[—CF₂=CF₂] formed from the monomer tetrafluoroethene (more known as Teflon)
Give examples of high density polyethene. (4)
eg. plastic bottles, food storage containers, water pipes and fuel tanks
Give examples of polytetrafluoroethene (6)
plumber’s tape, non-stick cookware, artificial hips and vocal cords and machinery parts that require lubrication and pipes or containers designed to hold reactive or corrosive liquids
Is Telfon polar or non-polar?
non-polar, intermolecular forces present between polyethene and Teflon molecules are weak dispersion forces
What are 6 properties of Teflon?
Non-stick Heat resistance Chemical resistance Good mechanical properties Low friction coefficient Flame resistance
How is Teflon non-stick?
As Teflon repels all other substances, both hydrophobic (oil, fat) and hydrophilic (water and aqueous solutions)
How is Teflon Heat resistant?
The melting point of Teflon is 335C and its upper operating temperature is 260C
How is Teflon chemically resistant?
Because of the strength of the C-F bonds, Teflon is extremely resistant to all known chemicals. It is not attacked by strong acids and alkalis and is inert to all organic solvents.
How does Teflon have Good mechanical properties?
Strong and durable
How does Teflon have low friction coefficient?
Teflon is slippery to the touch. The friction coefficient between two pieces of Teflon is very low
How is Telfon flame resistant?
non-flammable
What is polyvinylchloride?
[CHCl=CH₂] Polymerisation of Chloroethene
Why is polyvinylchloride harder and more rigid than polyethene and Teflon?
Carbon—chlorine bonds are polar and allow dipole-dipole attractions to form between polymer chain, therefore there are stronger polar attractions holding it together
Give an example of polyvinylchloride
Drain pipe
What is a condensation polymerisation reaction?
Functional groups reacts chemically which functional groups on neighbouring monomers
What are is a difference between addition polymers and condensation polymers? (monomers)
Addition:Monomers must be unsaturated, containing a double bon or triple carbon-carbon bond
Condensation: Monomers must contain two functional groups that can react with those on neighbouring molecules
What are is a difference between addition polymers and condensation polymers? (By-Products)
Addition polymers: No by products are produced during the reactions
Condensation: Small molecules, often water are produced during the reaction.
What are is a difference between addition polymers and condensation polymers? (polymer backbone)
Addition: The polymer backbone is a long C-C chain
Condensation: The polymer backbone contains functional groups; for example, amides or esters
What are monomers to create polyesters? (2)
they are formed by reacting a dicarboxylic acid monomer with a diol monomer, it can also be formed between monomers that contain both a carboxyl and hydroxyl functional group within the same monomer.
What kind of force is formed between ester groups for polyesters?
dipole-dipole interactions with each other
What is polyethylene terephthalate?
used to make polyester fabric, recyclable drink bottles and food packaging
What are the monomers to create Polyethylene terephthalate?
reacting 1,4-benzenedicarboxylic acid monomers with ethane-1,2-diol monomers
Why is Polyethylene terephthalate a strong material?
strong material because ester groups are polar therefore there are dipole-dipole attractions between polymer chains
What are polyamides made of? (2)
dicarboxylic acid molecules react with diamine molecules.
Also form between monomers that contain both a carboxyl and amino functional group within the same molecule
Water is also produced.
Why are polyamides stronger than polyesters of similar structures?
Hydrogen bonds can form between amide groups on neighbouring polymer chains
What are 2 examples of polyamides?
nylon and kevlar
What are properties of nylon? (3)
- can be easily drawn into fibres with a high tensile strength
- fibres used produce strong, lightweight materials for clothes, parachutes, ropes, fishing line and even guitar strings.
- also used to make hard, rigid plastics that can be used in pipes and machinery
- group of polyamides which the monomers contain linear carbon chains.
Give an example of nylon.
nylon-6,6, dicarboxylic acid monomer has a chain of six carbons and the diamine monomer also has a chain of six carbon atoms.
What is kevlar?
a polyamide that replaces carbon chains in nylon with benzene rings
Why is kevlar extremely strong and lightweight? (2)
extremely strong material which is very lightweight due to its molecular structure, benzene rings make polymer chains rigid.
allows molecules to align closely together, as a result strong hydrogen bonding between amide groups in these molecules.
What are co-polymers?
Polymer made from at least two different monomers
both addition and condensation polymers can be copolymers
Give 2 examples of copolymers and their monomers?
ethene tetrafluoroethene (ETFE)
- ethene (CH₂=CH₂) and tetrafluoroethene (CF₂=CF₂) monomers
styrene-butadiene rubber (SBR)
- styrene (CH₂=CH(C₆H₅)) and buta-1,3-diene (CH₂=CHCH=CH₂)
Increasing the concentration of styrene monomers in styrene-butadiene rubber
increases the abrasion resistance of polymer and makes it suited for use in car tyres, it main application.
What is crystallinity?
long chains that twist around each other, with intermolecular forces from one chain to another
What are two regions that polymeric materials can contain, usually having both?
Crystalline and amorphous regions
Why is crystalline regions stronger?
the intermolecular forces between the closely packed chains are stronger and presence of crystalline regions strengthens the material overall.
What do crystalline regions in the polymer do to it when light hits it?
Crystalline regions in a polymer prevent the transmission of light through the material, making it appear opaque
What happens when you increase the percentage of crystallinity of material?
Increasing the percentage crystallinity of material makes it stronger and less flexible. Making the material less transparent because the crystalline regions scatter light.
What are crystalline regions?
Where chains line up in a ordered fashion, they create crystalline regions
What are amorphous regions?
Where polymer chains are randomly tangled and unable to pack very closely, and have no orderly arrangement
What happens when a polymer material is entirely amorphous?
making it less rigid and weaker and often transparent
Are HDPE more crystalline or LDPE?
HDPE 95% while LDPE is more amorphous with a percentage crystallinity low as 65%
When extensive branching is present,
polymer chains are unable to pack together as closely when solid
less dense and more flexible material with far fewer crystalline regions
What are additives?
Additives improve or extend properties of the polymer
What are additives used for?
include pigments (to add colour), UV stabilisers (to prevent deterioration in sunlight), flame retardant and plasticisers
What are plasticisers? and what do they do?
- small molecule that can be added to polymers
- polymer molecules are forced slight further apart, weakening the forces between chains and making the material softer and more flexible
Give an example of plasticisers. (4)
Polar C-Cl bond in polyvinyl chloride (PVC) the polymer chains are held together strongly by dipole-dipole attractions. Pure PVC is quite rigid at room temp.
When plasticisers is added between chains, they can slide past each other making it softer and more flexible.
How are foamed polymers formed?
formed by blowing gas through melted polymer materials
introducing pentane into melting polystyrene beads the beads swell up to produce lightweight, insulating, shock absorbing foam.
What are two ways to recycle plastics?
Reprocessing and depolymerisation
What is reprocessing?
Reprocessing involving shredding, melting and reshaping used plastic into new products
only used with thermoplastic polymers
What is one issue of reprocessing for recycling plastics?
One of the issues is that different types of plastic need to be completely seperation before they melt
What is depolymerisation? (2)
Polymers are broken down into monomers, usually by heat.
Requires a large amount of energy and yield is usually is low, making this method less economically viable than reprocessing.
What is biodiesel made out of? (2)
mixture of organic compounds of esters
chemical reaction between vegetable oils or animal fats and an alcohol (methanol)
What is transesterfication? (3)
- triglyceride is converted into biodiesel by warming it with alcohol, usually methanol
- requires a base,(eg. KOH or lipase, which is an enzyme) to catalyse the reaction
- these can be known to be called fatty acid esters
How are triglycerides produced by animals such as tallow?
form saturated esters which have only carbon-carbon single bonds
What type of triglyceride is produced by plants?
unsaturated esters
What is Ultra-high-molecular-weight polyethylene (UHMWP)? What can it be used to make?
strongest and toughest polyethene
It is used as bearing material in hip and knee replacement joints. UHMWP fibres are used to make fabric for bulletproof vests
Identify the major type of bonding that would exist between the side chains of proline and leucine.
Dispersion forces
Identify the major type of bonding that would exist between the side chains of glutamic acid and lysine.
Ionic
Identify the major type of bonding that would exist between the side chains of glutamine and serine
Hydrogen bonding
Identify the major type of bonding that would exist between the side chains of cysteine and cysteine
Covalent bonding
Why is high density polyethylene (HDPE) less flexible than LDPE?
High density polyethylene is manufactured at a lower pressure than LDPE and uses a catalyst that produces polymer chains with much less branching. With fewer branches to get in the way, the polymer chains can approach much more closely and significant dispersion forces produce a material that takes on crystalline-like properties. HDPE is denser than LDPE and the structure is more rigid. This means that HDPE is not as flexible as LDPE.
What are the production conditions that favour longer polymer molecules?
thermoplastic with high melting temperature
What production conditions with affect the on-corporation of side groups with benzene rings (-C6H5)?
lower density/more transparent polymer
Explain how PVC’s structure allows it to be a good material for covering electrical cables. (4)
PVC has no free charged particles to conduct electricity.
It has strong inter-chain bonding due to dipoles, which increase its strength and raise its melting point.
PVC contains strong bonds that do not burn easily and it produces chemicals that extinguish flames when burnt.
PVC is plasticised to make it flexible
Why does polytetrafluoroethene have a higher melting point that polyethene? (dispersion forces)
It has stronger dispersion forces between polymer chains. Both polymers are non-polar, but the Teflon monomers have a higher molar mass compared to ethene. This means a greater number of electrons are present in the polymer hence dispersion forces are stronger.
How does fibre manufacturing process of cold drawing enhances their presence?
Fibres stretch the polyamide molecules untangle and become aligned. Due to the attractive forces of hydrogen bonding they will naturally align in such a way that maximises the amount of hydrogen bonding between adjacent polymer chains.
How are hydrogen bonds formed? (2)
Large difference between the electro negativity of hydrogen atom and fluorine, carbon and oxygen
Small size the hydrogen atom (allowing it to approach relatively closer to the fluorine than other atoms)
