Notesale: Turn your study into money

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An intro into macromolecules and polymers
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Polymers: Large molecules made up of hundreds of small molecules called monomers
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Synthetic polymers: Man-made produced through the use of chemical substances or materials such as
PVC, PP and nylon
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Homo-polymer (same): [A-A-A-A-A-A]
2
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Alternating

A-B-A-B-A-B-A-B-A-B-A-B-A-B-A-B-A

2c
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A-A-B-A-B-A-A-B-B-A-B-B-A-B-A-B-B

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2b
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Graft
Side chains that have a different composition to the
main chain
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Linear

Single continuous chain
 Weak VDW forces exist between chains
 Good packing efficiency = easily crystallise
 High density
3
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 Stronger than branched, but more brittle

2
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Network

Tri-functional monomer units that have 3 active
covalent bonds, forming 3D networks
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There are several structural characteristics
that play a role in determining the properties:
(a)
(b)
(c)
(d)
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Degree of rigidity
Electrostatic VDW forces between chains
Degree of forming crystalline domains
Degree of cross-linking between chains (h-bonds, VDW): most prominent

Cross-links are chemical bonds between the
polymer chains other than at the ends
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If intermolecular forces between chains are sufficiently strong, they prevent motion of molecules moving
past one another and so the polymer will be solid at room temperature
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There are two types of cross-linked polymers:
Thermoplastic

No cross-linking:
 Weak attractive forces between chains are
broken by heat
 The polymer can change shape/be remoulded
 Weak forces reform in new shape upon cooling

Thermoset

Extensive cross-linking:
 Cross-links are covalently bonded and are
strong
 Bonds prevent chains moving relative to one
another

Polymerisation process
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Polymerisation: The process of forming high molecular mass macromolecules which consist of repeating
units derived from monomers
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The type of products produced can be classed as
 Addition polymerisation: ONLY the polymer is formed
 Condensation polymerisation: BOTH polymer and low molecular weight molecule such as water
is formed
The specific reaction mechanism can be classed as
 Step-growth polymerisation: Functional groups within the monomer units react
 Chain-growth polymerisation: Free radicals (molecule with no charge but has an unpaired
valence electron and so is highly reactive) or ions are generated

NOTE: BOTH addition and condensation polymerisation can occur by either step-growth or chain-growth
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Example: POLYSTYRENE
 Produced in an addition polymerisation reaction, monomer being ethenylbenzene
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 Gas can be added to polystyrene during manufacturing to make polystyrene foam (expanded
polystyrene) which has very low density and is used as heat insulation in coffee cups, as packaging
and floatation devices
 It is chemically inert, resistant to acids and bases but soluble in many chlorinates solvents
 It is a thermoplastic that softens on heating so it can be moulded into different shapes, then harden
on cooling… Hence why it is recyclable, though very slow to biodegrade

Exothermic reaction: 121 kJ mol-1 (at 25oC)
According to Le Chatelier’s principle, increasing the temperature would favour production of the
monomers, so this additional polymerisation is carried out at mild temperatures
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NOTE: A vast majority of addition reactions occur via chain-growth so we can loosely interchange
between the two terms “addition polymerisation”/”chain growth polymerisation” but for condensation
reactions, they occur equally by either step-growth or chain-growth
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Water/HCl/small molecules are
eliminated during the reaction
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Form when –OH functional group of one monomer reacts with –COOH of another
2
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Form when –COOH functional group of one monomer reacts with –NH2 of another
2
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Step-growth polymerisation:
Bi-functional or multifunctional monomers react to form first dimers, then trimers, then longer
oligomers and eventually long chain polymers
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The
process is then terminated once all the monomers are used up
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It’s a fast process compared
to step-growth
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Chain-growth occurs via 4 main steps:
1
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Example: POLYSTYRENE
Di(dodecanoyl) peroxide is used to form a free radical
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This is then used as the initiator for the next step…
2
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The active centre then
shifts
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For polystyrene, the free radical attacks the ethylenebenzene monomer
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This has resulted in a new free radical
being formed which goes on to react with additional styrene monomers
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Propagation (growth)
The chain continues to grow and build up as the active centre R-M* keeps attacking more monomers
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For polystyrene, the new radical produced during initiation reacts with a styrene molecule, opening up the
double bond and leaving an unpaired electron on a carbon atom
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4
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Any two of the radicals produced at ANY stage can
react and terminate the reaction (short chain-long chain, two long chains, any chain-radical, R)
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It’s a thermoplastic that softens when heated so when pressure is applied, you’re able to remould
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V containers
Applications: Due to being low cost, they are used as
 flooring in operation theatres and are easily sterilised with steam or radiation
 vehicle components as they’re light, reducing the weight, thus the fuel consumption but this also
allows room for other components such as airbags and fire retardant properties for safety
 outdoor uses such as window frames, mud flaps, water pipes and garden furniture as it resists
corrosion and weathering
 being shaped as fibre, foam or film as PVC is tough and doesn’t crack
PVC is produced via addition polymerisation using monomer chloroethene (vinyl chloride
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Dissociation
A substance is split into two with an unpaired electron on either side
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2
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The bond consists of an electron from the
radical, and an electron from the double bond
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3
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Then this process
repeats to form a large chain
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This formation allows
 close packing = reducing flexibility = rigid
 maximising intermolecular forces between chains = strong = rigid
(b) Syndiotactic (syndiotactic PVC said to be highly crystalline, but only little is produced in this
structure)

The chlorine atoms alternate above and below the carbon backbone
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The large chlorine
atoms stick out,

 preventing the polymer chains from packing together closely
 expecting to be softer and more flexible, when actually atactic PVC is quite rigid due to
the chlorine atoms being more electronegative than the carbon atoms and so it obtains a
partial negative charge ( -) whilst the carbon has a partial positive charge ( +)
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4
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The
simplest reaction for making nylons is diamine + diacid
Nylon 6,6 is one of the most important nylons (polyamide)
Reaction for nylon 6,6:

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Reaction for nylon 6,10:

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The name of the polymer includes the word “nylon” with a number or two:
o If there’s one number then it’s only been made with one type of monomer
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g
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o If there’s two numbers then it was made with two types of monomers
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g
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Physical properties of nylon:
Intermolecular forces (h-bonding being the most important) gives rise to give good fibre properties
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Conducting polymers
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The process of making polymers conductive: insulating materials that have the ability to transmit or
carry charge
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The Ziegler-Natta catalyst was added 1,000 times in excess
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Exposure to halogens such as chlorine, bromine and iodine vapour during a process named
“doping” (oxidisation) had increased the conductivity of polyacetylene a billion fold
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It needs to imitate a metal, meaning the electrons have to be free to move and not bind to the
atoms
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Electrons can’t be fixed in their position – they need to be free to migrate from one end of the
polymer backbone to the other, and in doing so, electricity can be conducted
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Nearly all polymers that are considered conductive have a conjugated backbone structure
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The structure comprises of alternating double and single bonds
between the carbon atoms (=conjugation)
The pi-electrons are located around the double bonds and are delocalised over the entire chain
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Pi-orbitals overlap above and below the plane of the sigma orbitals which aids conductivity
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The sigma
orbitals provide strength to the chain
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Chemically: through the use of reagents as mentioned previously (halogens)
2
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Photochemical: least common method with use of light/photons to induce REDOX reactions
Electrochemical:
 Conjugated polymers can be doped and undoped by immersing the material as an electrode in an
organic electrolyte solution such as tetrafluoroborate dissolved in ACN or other non-aq
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 The nature of the doping produced (n- or p-) depends on the polarity of the applied voltage
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The conductivity can be further increased by choosing a different dopant – but this will affect
surface and bulk structure properties e
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colour, porosity, volume of the polymer
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An electrical potential can be applied through the polymer to cause the dopant to
leave, or re-enter, switching it between its conductive and insulating redox states
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Small e
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Cl-: Affect conductivity and structural properties
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Large e
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sodium polystyrenesulfonate: Affect conductivity and structural properties too
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Large dopants are more
integrated into the polymer and won’t leach out over time or with electrical stimulus = polymer has
greater electrochemical stability 

P-DOPING:
 A popular dopant is iodine (I2) which removes electrons to form I3-, but other halogens are commonly
used due to their ability to easily remove or add electrons
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This results in the double bond successively moving along the polymer
backbone and a charge begins to flow
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N-DOPING:
 Achieved by partial reduction of the pi-system backbone – dopant adds electron to the system
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Advantages of doping:
 Most polymers in natural state are either insulators or semiconductors… When subject to doping, the conductivity values are
comparable to metals such as silver and copper!
These conducting polymers are also
 More accessible
 Light weight
 Better resistance to pH and temperature, therefore, unlikely to
undergo degradation
 Good biocompatibility
 Ability to form networks and carrier molecules
(YouTube link on slide 28)

Applications:
 Conducting polymers are used in fuel cells (device that converts chemical energy from a fuel into
electricity through a chemical reaction of positively charged hydrogen ions with oxygen/other oxidising
agents), computer displays, microsurgical tools, and now finding applications in the field of biomaterials
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 Created to be biocompatible and biodegradable
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 Conductive nature allows cells/tissues to be cultures upon stimulation, physical properties can be
altered post-synthesis and the drugs bound in them can be released through the application of electrical
signals… Play an important role in biosensors, neural implants, drug delivery devices and tissue
engineering scaffolds
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 Good in vitro and in vivo biocompatibility
 Good chemical stability in air and water
 Reasonably high conductivity under physiological conditions
 Easily and flexibly synthesised in large quantities at RT in a wide range of solvents inc
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Fully oxidised pernigraniline base
2
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Fully reduced leucoemeraldine base
Advantages:
Ease of synthesis
Low cost
Good environmental stability
Ability to electrically switch between its conductive and resistive states

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Biological applications are limited due to
 Low process-ability
 Lack of flexibility
 Non-biodegradable
 Cause chronic inflammation once implanted
PANI is being investigated for biosensors, neural probes, controlled drug delivery and tissue engineering
applications

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