HOME PAGE * KS3 SCIENCES * GCSE BIOLOGY  CHEMISTRY  PHYSICS * ADVANCED LEVEL CHEMISTRY

Advanced Level Organic Chemistry: The structure, properties and uses of poly(alkenes)

Part 2. The chemistry of ALKENES - unsaturated hydrocarbons

Doc Brown's Chemistry Advanced Level Pre-University Chemistry Revision Study Notes for UK KS5 A/AS GCE advanced level organic chemistry students US K12 grade 11 grade 12 organic chemistry

2.8 The reaction of alkenes to form addition polymers - structure, properties & uses of poly(alkene) polymers

Please note that I'd already written quite a bit about poly(alkenes) before reaching my Part 2. Alkenes, for my Advanced Level Organic Chemistry Notes, so I'm not repeating much of the material. Links will point to relevant pages, BUT extra notes are added where appropriate for advanced level organic chemistry students of alkene based addition polymers.

INDEX of ALKENE revision notes

Sub-index for this page

Introduction (links)  *  Individual addition polymer notes on poly(alkenes)

1. Poly(ethene) 2. Poly(propene)
3. Poly(chloroethene) 4. Poly(tetrafluoroethene)
5. Polyacrylonitrile 6. Poly(phenylethene)
7. Poly(methyl methacrylate) 8. Poly(ethenol)

The thermal stability of poly(alkene) plastics (this page)

AND on other pages

More on the uses of polymers - plastics

Problems with using, recycling, disposing of polymer plastics and pollution problems


INDEX of ALKENE revision notes

All Advanced A Level Organic Chemistry Notes

Index of GCSE/IGCSE Oil - Useful Products Chemistry Notes

[SEARCH BOX] ignore the adverts at the top



Introduction to the formation and structure of addition polymers formed from alkenes

doc b oil notes

General equation for the addition polymerisation of alkenes.

Introduction to the formation and structure addition polymers from alkenes

Free radical polymerisation to give poly(alkene) polymers e.g. ethene ==> poly(ethene)

Due to the large size of the molecule (Mr typically ?), strong C-C, C-O, C-F or C-F covalent bonds, addition polymers made for alkenes and very resistant to chemical or biological attack.

They are synthetic material not found in nature, so no enzymes have evolved to break them down.

Advantages

It is useful to have materials that resist corrosion and chemical attack, that can be used to make a variety of objects for many applications and can have a long useful life - the properties and uses are described eight different polymers.

Disadvantages

Unfortunately, the chemical stability and long life mean that when discarded into the environment they cause pollution effects, litter, bulk plastics in land-fill sites, plastics affect wild-life e.g. animals can be trapped in plastic mesh, plastic objects found in the stomachs of dead animals.

Toxic gases can be produced in incinerators.

 

Examples of poly(alkene) addition polymers - their structure and uses follow ...


TOP OF PAGE and sub-index


1. Poly(ethene)

polymerisation equation for ethene monomer to poly(ethene) polythene polymer advanced A level organic chemistry doc brown's revision notes

skeletal formula of poly(ethene) polythene polyethylene polymer advanced A level organic chemistry doc brown's revision notes

Simplified abbreviated structural formulae equation:  n CH2=CH2  ===>   (CH2CH2)n

Examples of poly(alkene) polymer molecules e.g. manufacture of poly(ethene)

Summary of the properties and uses of poly(ethene)

A few C-C cross-links put still plastic - pliable and low melting/softening temperature.

BUT not a with lots of C-C cross-links to give a rigid 3D network of bonds like the full cross-linked rigid thermoset structure like Melamine or the old brown Baekalite

See also comparison of thermoplastic addition polymers with thermoplastic synthetic fibres from condensation polymers and hard rigid thermoset plastics


TOP OF PAGE and sub-index


2. Poly(propene)

polymerisation equation for propene monomer to poly(propene) polypropylene polymer advanced A level organic chemistry doc brown's revision notes

skeletal formula of poly(propene) polypropene polypropylene polymer advanced A level organic chemistry doc brown's revision notes

Simplified abbreviated structural formulae equation:  n CH2=CHCH3  ===>   {CH2CH(CH3)}n

Poly(propene) - formation, structure, properties and uses

The stereoisomers of poly(propene)

See organic chemistry Part 14.6 Stereoregular polymers -  isotactic/atactic/syndiotactic poly(propene)


TOP OF PAGE and sub-index


3. Poly(chloroethene)

polymerisation equation for chloroethene monomer to poly(chloroethene) polyvinyl chloride PVC polymer polymer advanced A level organic chemistry doc brown's revision notes

skeletal formula of poly(chloroethene) polyvinyl chloride PVC polymer advanced A level organic chemistry doc brown's revision notes

Simplified abbreviated structural formulae equation:  n CH2=CHCl  ===>   (CH2CHCl)n

Poly(chloroethene) - formation, structure, properties and uses


TOP OF PAGE and sub-index


4. Poly(tetrafluoroethene)

polymerisation equation for tetrafluoroethene monomer to poly(tetrafluoroethene) PTFE polymer advanced A level organic chemistry doc brown's revision notes

skeletal formula of poly(tetrafluoroethene) PTFE polytetrafluoethene polymer advanced A level organic chemistry doc brown's revision notes

Simplified abbreviated structural formulae equation:  n CF2=CF2  ===>   (CF2CF2)n

Poly(tetrafluoroethene) or PTFE - formation, structure, properties and uses


TOP OF PAGE and sub-index


5. Polyacrylonitrile

polymerisation equation for propenenitrile acrylonitrile monomer to poly(propenenitrile) polyacrylonitrile polymer advanced A level organic chemistry doc brown's revision notes

skeletal formula of poly(propenenitrile) polyacrylonitrile polymer advanced A level organic chemistry doc brown's revision notes

Simplified abbreviated structural formulae equation:  n CH2=CHCN  ===>   {CH2CH(CN)}n

Poly(acrylonitrile) fibres used for clothing fabrics. The polymer is stretched and extruded so that the molecules line up alongside each other to maximise the intermolecular forces between them - so increasing and maximising the strength of the fibres.

It has a low density and good thermal stability and chemical stability.


TOP OF PAGE and sub-index


6. Poly(phenylethene)

polymerisation equation for phenylethene styrene to poly(phenylethene) polystyrene polymer advanced A level organic chemistry doc brown's revision notes

skeletal formula of poly(phenylethene) polystyrene polyphenylethene poly(styrene) polymer advanced A level organic chemistry doc brown's revision notes

Simplified abbreviated structural formulae equation:  n CH2=CHC6H5  ===>   {CH2CH(C6H5)}n

Polystyrene - formation, structure, properties and uses


TOP OF PAGE and sub-index


7. Poly(methyl methacrylate)   PMMA

polymerisation equation for methyl methacrylate monomer to poly(methyl methacrylate) polymethylmethacrylate PMMA Perspex polymer advanced A level organic chemistry doc brown's revision notes

skeletal formula of poly(methyl methacrylate) polymethylmethacrylate PMMA polymer advanced A level organic chemistry doc brown's revision notes

Simplified abbreviated structural formulae equation: 

n CH2=C(CH3)COOCH3  ===>   {CH2C(CH3)(COOCH3)}n

The monomer is called methyl prop-2-enoic acid {methyl ester of prop-2-enoic acid (acrylic acid)}

PMMA is a transparent rigid plastic often encountered under the trade name Perspex.


TOP OF PAGE and sub-index


8. Poly(ethenol)

polymerisation equation for ethenol vinyl alcohol monomer to poly(ethenol) polyvinyl alcohol polymer advanced A level organic chemistry doc brown's revision notes

skeletal formula of poly(ethenol) polyvinyl alcohol polyethanol polyvinylalcohol polymer advanced A level organic chemistry doc brown's revision notes

Simplified abbreviated structural formulae equation:  n CH2=CHOH  ===>   {CH2CH(OH)}n

Sometimes incorrectly written as polyethanol

hydrogen bonding between poly(ethenol) PVA polyvinyl alcohol molecules and water advanced A level organic chemistry doc brown's revision notes

Used for 'disposable' laundry bags - because the polymer dissolves away leaving the laundry clothing to be washed.

Used for detergent capsules in washing machines, the pod/pouch dissolves away releasing the detergent for washing clothes.


The thermal stability of poly(alkene) plastics

When poly(alkene) polymers are heated, they initially soften and at higher temperatures they melt.

At higher temperatures still, undergo thermal decomposition giving off hydrocarbon molecules of low molecular mass e.g. alkanes and alkenes such as methane, ethene, ethane, propene and pentene, but only a small % of the products are the original monomer - not easy to recycle plastics by this particular mode, which is why a lot of waste plastic is burned to generate electrical power!

Melting temperatures: poly(ethene) 180 to 270oC;  poly(propene) 200 to 280oC;  poly(styrene) 170 to 280oC.

There is no sharp melting point for polymers because they are not pure compounds in the sense the molecules are not identical.

For poly(alkenes) like everyday 'polythene', there is a wide distribution of molecular masses and each size of molecule has its own melting point.

Matters are further complicated by a little bit of cross-linking in them too (you probably didn't know that!).

Therefore thermoplastic polymers soften, and eventually melt, over a wide temperature range - you see the same effect in animal fats, butter (derived from milk fats) or margarine (derived from vegetable oils) where there is a range of glyceride esters.

The activation energies for these thermal decompositions are high because it involves breaking strong carbon-carbon or carbon-hydrogen bonds in the polymer chain.

The activation energies (Ea) for purely thermal degradation in an inert nitrogen atmosphere are quoted below and the lowest temperature at appreciable thermal decomposition begins.

For poly(styrene): Ea ~150-200 kJ/mol for thermal decomposition >400oC,

For poly(ethene): Ea ~150-240 kJ/mol for thermal decomposition >400oC,

For poly(propene): Ea ~250 kJ/mol for thermal decomposition >400oC.

Very reactive free radicals (species with an unpaired electron), are initially formed by the weakest C-C bonds breaking.

After that, a whole series of complex free radical reactions breakdown the plastic to give stable hydrocarbon products with no free electrons.

The activation energies (Ea) for thermooxidative degradation in air are quoted below and the lowest temperature at appreciable thermal decomposition begins. All the values are lower than in nitrogen because the oxygen from air allows the easier formation of the highly reactive free radicals.

For poly(styrene): Ea ~125 kJ/mol for thermal decomposition >250oC,

For poly(ethene): Ea ~80 kJ/mol for thermal decomposition >250oC,

For poly(propene): Ea ~90 kJ/mol for thermal decomposition >200oC.

Some examples of the free radical reactions are quoted below ( = unpaired electron on the reactive free radical):

initiation stepsR-H  ===> R  +  H  (R = alkyl)

or  R-R  ===> 2R  (heterolytic bond fission in the carbon chain to give two free radicals)

R  +  O2  ==> ROO  (peroxide radical formed with oxygen, chain propagation step)

ROO  +  RH  ===>  ROOH  + R  (chain propagation step)

ROOH  ===> RO  +  RO  (further initiation step via heterolytic bond fission of the weak O-O peroxide bond)

After that, a whole series of complex free radical reactions breakdown the plastic to give stable hydrocarbon products with no free electrons, but the free radicals are more easily formed at lower temperatures than in inert nitrogen, hence the lower decomposition temperatures.

 

This sort of research is important when considering the high temperature thermal degradation and combustion (incineration) of large of poly(alkene) polymers e.g. trying to recycle the original monomer or ensuring complete combustion.

The data for this section was obtained from:

http://www.sci.utah.edu/publications/Pet2001a/2001_Peterson_Vyazovkin_Wight_Polystyrene_Polyethylene_and_Polypropylene.pdf

The poly(propene) used in this study had an average molecular mass of 12,000

The poly(styrene) used in this study had an average molecular mass of 128,000

See also Section (3) The vapourisation and thermal decomposition of alkanes

x-ref with dfalkanes12


Doc Brown's Advanced Level Chemistry Revision Notes

TOP OF PAGE and sub-index


 What next?

Index of all the ALKENE revision notes

All Advanced Level Organic Chemistry Notes

Index of GCSE/IGCSE Oil - Useful Products Chemistry Revision Notes

[SEARCH BOX] ignore the adverts at the top


TOP OF PAGE and sub-index

 

KS3 BIOLOGY QUIZZES ~US grades 6-8 KS3 CHEMISTRY QUIZZES ~US grades 6-8 KS3 PHYSICS QUIZZES ~US grades 6-8 HOMEPAGE of Doc Brown's Science Website EMAIL Doc Brown's Science Website
GCSE 9-1 BIOLOGY NOTES GCSE 9-1 CHEMISTRY NOTES and QUIZZES GCSE 9-1 PHYSICS NOTES GCSE 9-1 SCIENCES syllabus-specification help links for biology chemistry physics courses IGCSE & O Level SCIENCES syllabus-specification help links for biology chemistry physics courses
Advanced A/AS Level ORGANIC Chemistry Revision Notes US K12 ~grades 11-12 Advanced A/AS Level INORGANIC Chemistry Revision Notes US K12 ~grades 11-12 Advanced A/AS Level PHYSICAL-THEORETICAL Chemistry Revision Notes US K12 ~grades 11-12 Advanced A/AS Level CHEMISTRY syllabus-specificatio HELP LINKS of my site Doc Brown's Travel Pictures
Website content Dr Phil Brown 2000+. All copyrights reserved on revision notes, images, quizzes, worksheets etc. Copying of website material is NOT permitted. Exam revision summaries & references to science course specifications are unofficial.

 Doc Brown's Chemistry 

*

TOP OF PAGE and sub-index