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Chem Y12 > Mod 7.6 - Polymers > Flashcards

Mod 7.6 - Polymers Flashcards

1
Q

What are polymers?

A

Polymers are large molecules composed of repeating units. These repeating unitss are linked by covalent bonds.

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2
Q

How are polymers formed?

A

They are formed via a reaction called polymerisation, which utilises small and simple molecules called monomers to react with each other to form polymer chains (these monomers form covalent bonds with other monomers to form polymers)

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3
Q

What are the different types of polymers based on how they are produced?

A

Natural vs synthetic polymers

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4
Q

What are natural polymers? Examples

A

These are synthesised in living organisms (or occur in nature

E.g. silk, cellulose, starch (edible part in potatoes, wheat and rice)

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5
Q

What are synthetic polymers?

A

These are human made materials obtained from the chemical reaction of monomers. They can be designed for specific uses.

E.g. polyethylene

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6
Q

How are polymers visualised?

A

By showing a repeating unit in square brackets with a subscript ‘n’ on the bottom right

the ‘n’ indicates that there is a large number of repeating units in the polymer chain

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7
Q

What is a homopolymer? How are they named?

A

These are polymers made of a single type of monomer.

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8
Q

How are homopolymers named?

A

These are named based on the monomers (reactants). The prefix ‘poly’ is followed by the name of the monomer

For example, the polymer derived from the monomer ethylene is called polyethylene

If the name of the monomer contains two words or starts with a number, we use brackets around the name of the monomer and the prefix ‘poly’

For example, a polymer made of vinyl chloride is named poly (vinyl chloride)

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9
Q

What are copolymers?

A

These are polymers made of two or more different types of monomersH

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10
Q

How are copolymers named?

A

The prefix ‘poly’ and brackets around the name are also used like the homopolymers

Unlike homopolymers, the monomer derived names in copolymers can be either the actual name of the reactant monomer or the name of the new unit derived form the monomer

For example, the copolymer derived from the monomer ethylene glycol and terephthalic acid is called:

Poly (ethylene terephthalate)

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11
Q

What are the ways of classifying a polymer based on structures?

A

Unbranched (linear)

Branched

Cross linked

Bulky side groups (attachment of an atom which is heavier than hydrogen such as Cl to a polymer chain)

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12
Q

What are linear polymers?

A

These contain repeating units attached only at the two ends of the chain.

It is a single flexible chain with continuous covalent bonds which join monomers together end to end

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13
Q

What are branched polymers?

A

These contain a large number of side chains (branches) connected to the main polymer chainW

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14
Q

What are cross linked polymers?

A

Cross links are atoms or functional groups that join polymer chians via covalent or ionic bonds

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15
Q

What is polymerisation?

A

It is any chemical reaction that causes monomers to join together to form a polymer. These can be classified into two reactions such as the addition and condensation reactions

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16
Q

What is addition polymerisation?

A

It is a polymer forming process in which monomers react without the formation of by products. This can occur through a variety of mechanisms, but the monomers all polymerise without the formation of by products

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17
Q

What are some examples of addition polymers?

A

Polyethylene (PE)
Poly (vinyl chloride) (PVC)
Polystyrene
Polytetrafluoroethylene (PTFE)

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18
Q

Explain the process of the synthesis of addition polymers

A

One of the bonds in the carbon-carbon double bond C=C breaks. The breaking of the C=C bond results in each carbon having an electron available to form a chemical bond with another monomeric unit

This repeats itself multiple times, resulting in polymer chains that are thousands of units long

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19
Q

What is the relationship between the weight of a polymer chain and monomer?

A

MM (Addition polymer) = MM (Monomer) * n(number of moles)

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20
Q

What is condensation polymerisation?

A

It is a polymer forming process where monomers react with the elimination of a small molecule (typically H2O).

If x monomers are condensed to form a condensation polymer, then (x-1) H2O molecules are eliminated

This is formed from monomers containing two functional groups (also known as difunctional monomers). For each newly formed covalent bond, an additional molecule is formed and released as a by product of the condensation polymerisation reaction. The by product molecules released are small molecules like water or methanol.

Natural condensation polymers include cellulose, starch, wool, silk and hair

Synthetic condensation polymers include polyesters (e.g. PET) and polyamides (e.g.nylons)

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21
Q

What are the 2 important condensation polymers?

A

Polyesters and polyamides (nylon)

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22
Q

What are polyesters? Example?

A

Polyesters contain repeating units joined by ester links -COO- ( R-C=O-O-) [kinda]. In this case, there will be either -COOH or -OH at the ends of monomers.

The ester link is formed from a condensation reaction between hydroxyl and carboxyl groups

An example of polyesters is polyethylene terephthalate (PET)

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23
Q

How is PET synthesised?

A

Condensation polymerisation of terphthalic acid (benzene-1,4-dicarboxylic acid) and ethylene glycol (ethan-1,2-diol) (will have to look at image)

It is made from two monomers, each containg two hydroxyl groups and two carboxl groups. As such, PET is an example of a condensation copolymer.

The hydoxyl and carboxyl groups from each monomer react and produce water molecules as a by product for every ester bond (ester link) formed (n-1 rule = no. of water molecules formed)

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24
Q

What is the molecular weight relationship for a condensation homopolymer?

A

MM (Homopolymer) = MM (monomer) * n - MM (By product) * (n-1)

where n is the number of repeating units in the polymer chain, and by product is a small molecule produced in condensation reaction like water

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25
Q

What is the molecular weight relationship for a condensation copolymer?

A

MM (copolymer) = MM (Monomer 1) *n + MM (Monomer 2) * n - MM (By product) * (2n-1)

where n is the number of repeating units in the polymer chain, and by product is a small molecule produced in condensation reaction like water

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26
Q

What is a polyamide?

A

These contain repeating units joined by amide bonds (-CONH) (C double bonded to O and bonded to an NH)

The amide link is formed fro a condensation reaction between carboxyl and amino (-NH2) groups

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27
Q

What is a common example of a polyamide?

A

Nylon 6,6 (most commonly used nylon)

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28
Q

How is nylon 6,6 synthesised?

A

Condensation polymerisation of adipic acid (hexanoic acid) and hexamethylene diamine (1,6-diaminohexane) - will have to look at picture

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29
Q

How are nylons named?

A

Nylons are systematically named to reflect the monomers that compose the polymer chain. the numbers indicate the number of carbon atoms between each amide link

Single digits indicate that the nylon is made from a single monomer (homopolymer), whereas two digits indicate that the nylon is made from two types of monomers (copolymer)

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30
Q

What are the typical requirements considered when determining the suitability of a polymer for a given application?

A

Mechanical performance, chemical resistance, electric insulation, biocompatability, appearance and opacity 9transparency) and texture

Must also take into consideration; cost, complexity, availability and environmentla impact

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31
Q

What are the general properties of polymers?

A

Lightweight
Durable
Acid and base resistant
Non conductive of electricity
Flammable
impermeable to water

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32
Q

What are mechanical properties?

A

These are intended as the ability of the material to withstand an applied force without breaking or permanent deformation.

Polymers can exhibit tensile strength (resistant to pulling), flexural strength (resistant to bending) and toughness (resistance to impact)

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33
Q

WHat does brittle mean?

A

They break with minimal deformation. They break before change of shape

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34
Q

What does ductile mean?

A

When they deform extensively before breaking (in other words they can stretch)

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35
Q

What does tough mean?

A

When they resist breakdown. It is a measure of amount of energy a specimen can absorb before structure collapse

36
Q

WHat does strong mean?

A

When they resist deformation and breakdown. They arent deformed during the test but can absorb high levels of energy before breaking

37
Q

What does hard mean?

A

When they resist permanent changes under a compressive force. They can resit dents, scratches and abrasion

38
Q

How are the properties of a polymer determined? (which molecular indicators)

A

Crystallinity
Chain length
Bonds in polymer chain backbone
Side groups
Branching
Cross linking

Could also be influenced by manufacturing process and use of additives such as plasticisers

39
Q

What is crystallinity?

A

Refers to the degree of structural order in solid materials. It can be used to determine how rigid the material is.

The extent and shape of crystalline regions have a strong impact on the properties of polymers

Polymers can be regarded as crystalline, amorphous or semi crystalline

40
Q

What is a crystalline polymer?

A

It is comprised of polymer chains that are packed very closely and orderly organised. However, as polymers are large covalent chains with complex structures, it is hard to achieve perfect crystallinity

The regular arrangements brings the polymer chains closer together. The IMF between closely packed chains are stronger, and thus the presence of a crystalline polymer or crystalline regions strengthens the material overall

Crystalline regions in a polymer prevents the transmission of light through the material, making it appear cloudy or opaque

There re more crystalline regions in unbranched polymers

41
Q

What is an amorphous polymer? WHat are some characteristics?

A

This is when polymer chains are randomly tangled and are unable to pack very closely

These are comprised of polymer chains that are disordered. Most polymers have at least some part that isnt crystalline. The non crystalline parts of the polymer are called amorphous

Also, these are more flexible and weaker and are often transparent

42
Q

What is a semi crystalline polymer?

A

A polymer can contain both crystalline and amorphous regions (called domains). This is referred to as semi crystalline.

Most polymers are semi crystalline, with the extent of crystalline domains depending on molecular properties and of the manufacturing methods

43
Q

What are the bulk properties of amorphous polymers?

A

Low melting energy
Soft
Transparent
Low chemical reisistance
Low, even expansion when heated
Permeable to gas

44
Q

What are the bulk properties of crystalline polymers?

A

High melting energy
Hard
Opaque
high chemical resistance
High, uneven expansion when heated
Low permeability to gas

45
Q

How is the extent of crystallinity in polymers determined?

A

Determined by the molecular structure of the material. the factors that favour high crystallinity are:

Linear polymer chains
Long polymer chains
Rigid chain backbone
Strong IMF

These factors above allow for an ordered arrangement of the polymer chains –> increased crystallinity

46
Q

Compare linear vs branched polymers in terms of crystallinity

A

Linear polymers have a higher degree of crystallinity, whereas branched polymers have a lower degree of crystallinity as they are more bulky and dont allow for the chains to pack densely

47
Q

What is the effect of temperature on amorphous polymers? (extension)

A

At low temps, an amorphous polymer is typically rigid and brittle

Upon heating, atoms gain kinetic energy (vibrate) giving the molecules mobility and softening the polymer.

Due to the disordered and tangled nature of amorphous polymers, some molecules will reuire relatively low energy to soften while other molecules will require more energy to soften

Therefore the change in mechanical proeprties is gradual (no sharp melting point) as the energy required to mobilise varies between molecules

48
Q

What is the effect of temperature on semi crystalline polymers? (extension)

A

Highly crystalline polymers can preserve their solid properties at higher temps

To mobilise molecules in crystalline polymers, relatively high energy is required

The molecules in crystalline polymers require similar energy levels to mobilise.

Once a certain temp is reached, all of the molecules gain mobility. At the macroscopic level, the polymer changes from solid to liquid (melting)

Therefore, the melting happens over a small temp range. In other words, we observe a defined melting point

49
Q

What do key features of polymers (such as strength and flexibility), depend on?

A

Chain length
Bonds in polymer chain backbone
Side groups
Branching
Cross linking

50
Q

How does chain length impact key features of polymers?

A

Generally, the longer the chains, the stronger the polymer is because longer chains can become more tangled and requires more energy to stretch and untangle

Also, Because polymers are extremely large covalent molecules, the dominant intermolecular force is dispersion forces, which will increase as chain length increases–> higher crystallinity

Thus, as chain length increases the MELTING POINT, RIGIDITY AND HARDNESS of a polymer increases

51
Q

How does bonds in polymer chain backbone impact key features of polymers?

A

Chain flexibility depends on the types of bonds on the polymer backbone and the groups directly attached to it.

Single covalent bonds such as C-C and C-O bonds make the polymer chains quite flexible. Thus, polymer chains can move easily, and the material is soft at relatively low temps

Meanwhile, ringed groups result in rigidity to the chain, and makes the polymer stronger. Chains are stiffer and rigid even at higher temps

52
Q

How do side groups impact key features of polymers?

A

The side groups that give stronger attraction between polymer chains (e.g. intermolecular forces such as hydrogen bonding) make the polymer stronger.

Side groups can be introduced to make a material more rigid and brittle –> harder polymer

53
Q

How can branching impact key features of polymers?

A

Polymer chains that are close to each other can thus be held together by stronger interactions such as dispersion forces.

Polymers are able to form branched and unbranched chains. Unbranched chains are able to pack more closely in an orderly fashion, forming a rigid crystalline solid

Meanwhile, branched polymer chains are unable to align with each other, forming an amorphous solid that has weak IMF between the chain

As a result, linear polymers can have higher density and crystallinity than their branched counterparts and are therefore stronger

54
Q

How can cross linking impact key features of polymers?

A

Cross links join together polymer chains by covalent chemical bonds. Thus, they prevent the polymer chains from moving from each other. If cross linking is extensive, the polymer is harder and more difficult to melt

This causes the polymer to be more rigid, hard and heat resistant. They also cant be remoulded

Impacts thermosetting polymers

55
Q

What is a thermoplastic polymer?

A

These are polymers with only intermolecular forces between their chains. They soften when heated as the IMF are relatively weak and easily broken to allow the chains to move between one another. This property allows polymers to be remoulded

56
Q

What is a thermosetting polymer?

A

Polymers with cross links are called thermosetting polymers. Since covalent bonds are very strong, cross links limit movement between polymer chains, making it more rigid, hard and heat resistant. These cant be remoulded

57
Q

How do u structure a response to link polymer structure with properties?

A

Identify the chemical structure of the polymer

Determine the packing arrangement of the polymer

Determine the strength of the IMF of the polymer

Explain the properties and uses of polymer

58
Q

What are the common addition polymers we study?

A

Polyethylene (PE)
Poly (vinyl chloride) (PVC)
Polystyrene (PS)
Polytetrafluoroethylene (PTFE)

59
Q

What are common condensation polymers we study?

A

Poly (ethylene terephthalate) - (PET) or poly (ethyl benzene-1,4-dicarboxylate)

Nylon 6,6 or poly [imino (1,6-dioxohexamethylene)iminohexamethylene]

They are common types of polyester and nylon (a type of polyamide) respectively

60
Q

What is polyethylene? (polyethene)

A

It is the most popular plastic in the world and has a very simple structure.

Ethene is an unsaturated molecule because of the c=c bond. When ethene polymerases, the double bond breaks and new covalent bonds are formed between carbon atoms on nearby monomers. The polyethene formed does not contain any double bonds

It typically manifests as low density polyethylene (LDPE) or High Density polyethylene (HDPE)

61
Q

What is the difference between HDPE and LDPE?

A

Mainly it is the extent of branching. HDPE is mostly linear: chains can be packed closely, whereas LDPE is branched: chains cannot pack closely together

LDPE is produced under high temps and pressures –> formed too rapidly –> lots more branching

whereas HDPE utilise catalysts to avoid need for higher pressure –> more mild conditions –> fewer branching

62
Q

What are the properties of LDPE, and give reasons for them

A

Reasons: no stiffening side groups, no cross linking, and has extensive chain branching

Properties: Low MP, Low BP, flexible, soft, , lightweight, waterproof

63
Q

What are the uses of LDPE?

A

Agricultural films, cling wrap, part of multilayer packaging, disposable shopping bags, flexible toys, milk bottles

64
Q

What are the properties of LDPE, and give reasons for them

A

Reasons: Virtually no chain branching –> molecules pack closely in orderly fashion, no cross linking

Properties: Harder/more rigid than LDPE, strong, higher MP/BP than LDPE

65
Q

What are the uses of HDPE?

A

Plastic containers
Water pipes
Toys
Kitchen utensils
‘Wheely’ Bins

66
Q

What is poly (vinyl chloride) - PVC?

A

PVC is made out of vinyl chloride monomers which is chloroethene

The polymer is given by [chlorethane]n

PVC can be manufactured as flexible PVC (by adding plasticizers to the polymer) or there could be pure PVC

67
Q

What are the properties of pure PVC?

A

Thermoplastic, very hard, rigid, brittle.

This is because it has chlorine side groups which introduce dipoles into long molecules –> increased IMF –> harder, rigid etc

68
Q

What are the uses of pure PVC?

A

pipes, credit cards

69
Q

What are the properties of flexible PVCs?

A

Flexible, flame retardant, resistant to chemical corrosion

70
Q

What are the uses of flexible PVCs?

A

Raincoats, shower curtains, electrical insulation on wires

71
Q

What is polystyrene (PS)?

A

It is the product of the addition polymerisation of styrene

It involves a benzene ring which is covalently bonded on every second carbon in the polymer chain

It is typically manufactured as a foam. Foamed polymers are formed by blowing a gas through melted polymer materials. This can drastically change the physical properties of a polymer material

72
Q

Explain the properties of PS and the reasons behind it

A

Reasons:
Because of benzene rings covalently bonded in the polymer chain –> increases rigidity and causes it to be hard but quite brittle plastic with a low density. Also because of minimal chain branching, it is therefore very crystalline

Properties:
As a result, polystyrene is a hard but quite brittle plastic with a low density. Can form clear objects, It is also quite rigid because of the reasons listed above. It is sensitive to high temps

73
Q

What are the uses of polystrene?

A

Foam drinking cups
Bean bag fillers
Foam packing material
CD cases

74
Q

What is polytetrafluoroethylene (PTFE)

A

In this case, the monomer is tetrafluoroethene (C=C, with 2 F bonds on each C). It is formed when all hydrogen atoms in ethene is replaced by highly electronegative F atoms

These fluorine side groups repel each other. PTFE chains assume an elongated configuration because of the repulsion.

PTFE is linear and can form crystalline structures

75
Q

What are the properties of PTFE and why?

A

Reasons:

Electronegative fluorine atoms reduce strength of IMF with other substances –> non stick

PTFE is linear and can form crystalline structures –> contributes to it being hard and rigid

Properties:

Hard, rigid, high MP, high chemical resistance, low coefficient of friction, flame resistant, heat resistant, strong anti adhesion properties, flexible

76
Q

What are the uses of PTFE?

A

Non stick coating for cooking pans, anti corrosion container, pipes, medical equipment coatings, medical implants, gears, clothing, Teflon,

It is a cost-effective solution for industries ranging from oil and gas, chemical processing, industrial to electrical/electronic and construction sector as
an insulator for electrical wiring

77
Q

What is polyethylene terephthalate (PET)?

A

It is a type of polyester formed through the process of condensation polymerisation. PET is synthesised by reacting benzene-1,4-dioic acid monomers with ethane-1,2-diol monomers

78
Q

What are the properties of PET, and what are the reasons for these?

A

Reasons:

The benzene ring from the terephthalic acid monomer unit in PET causes it to make chains rigid and gives the polymer its stiffness

Ester groups in the structure can be hydrolysed upon heating by water, acids or bases.

Properties:

High strength
Resistant to impact
PET fabrics are wrinkle resistant
Amorphous forms are transparent, lightweight and less rigid
Low chemical resistance
Semi-rigid to rigid (depending on degree of crystallinity)
Thermoplastic

79
Q

What are the uses of PET?

A

In textiles as heat insulation layers, sportswear, workwear, automotive upholstery, plastic bottles, component in multilayer packaging

It is used in everyday items, especially in packaging, owing to its lightweight and good resistance to impact. Most common applications include rigid and flexible packaging as it is very lightweight

80
Q

What are the properties of a polyester?

A

Polyester fabrics and fibers are extremely strong.

Polyester is very durable: resistant to most chemicals, stretching and shrinking, wrinkle
resistant, mildew and abrasion resistant.

Polyester is hydrophobic in nature and quick drying. It can be used for insulation by
manufacturing hollow fibres.

Polyester retains its shape and hence is good for making outdoor clothing for harsh
climates.

It is easily washed and dried.

81
Q

What is the uses of polyesters in fabric?

A

Polyester is used in the manufacturing of all kinds of clothes and home furnishings like
bedspreads, sheets, pillows, furniture, carpets and even curtains

HYDROPHOBIC NATURE - High tenacity and good durability makes polyester the choice of fabric for high stress outdoors use. Polyester is also a strong fiber that is hydrophobic in nature. It is thus ideal for clothing to be used in wet and damp environments. The fabric is also coated with a water-resistant finish and further
intensifies the hydrophobic nature.

CREATING INSULATION - By creating hollow fibers it is also possible to build insulation into the polyester fiber. Air is trapped inside the fiber, which is then warmed by the heat of the body. This keeps the body warm in cold weather.

WRINKLE RESISTANT - It assists in resisting formation of wrinkles

82
Q

What are the uses of polyesters in industry?

A

While clothing used to be the most popular use of polyester and which made it a household
name worldwide, there are many other uses polyester is put to.

PET − The most common use of polyester today is to make the plastic bottles that store
our much beloved beverages. Shatterproof and cheap these bottles are an absolute boon
to the beverages industry.

Mylar − An unusual and little known use of polyester is in the manufacturing of
balloons. Not the rubber kind that you use for water balloons but the really pretty
decorated ones that are gifted on special occasions.

Polyester is also used to manufacture high strength ropes, thread, hoses, sails, power
belting and much more in industries.

Polyester is hydrophobic in nature and quick drying. It can be used for insulation by
manufacturing hollow fibres.

83
Q

What is Nylon 6,6?

A

A nylon is a type of polyamide with linear carbon chains. The most commonly used nylon is Nylon 6,6 which is manufactured by the polymerisation of adipic acid and hexamethylene diamine

84
Q

What are the properties of Nylon 6,6 and the reasons for it?

A

Reasons:

Strong attractive forces (hydrogen bonds) established between polymer chains –> high crystallinity and thus greater strength

Properties:

Thermoplastic
Strong
Abrasion resistant
High thermal stability
Spun into fibres
High tensile strength (ability to stretch)

85
Q

What are the uses of nylon 6,6?

A

Mechanical parts for vehicles and machinery (e.g. screws, gears)

Seat belts

Rope

Fishing line

Guitar strings

Fire hoses

Parachute material

Clothing (socks, stockings)

86
Q

What are the general uses of nylon?

A

Nylon fiber is produced in two general product types: the regular type for textile use and the
high-strength type for industrial uses. Therefore it is often used for the manufacture of:

  • Carpets
  • Tire cords
  • Apparel
  • Hosiery
  • Upholstery
  • Seat belts
  • Parachutes
  • Ropes
  • Industrial cords
  • Guitar strings

Chem Y12 (16 decks)

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