13.5 Polymerisation in alkenes
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Who is believed to have been among the first to find an application for polymers
The Mayan civilisation in Central America 16th century Playing ball games using rubber collected from local trees
What are polymers
Extremely large molecules formed from many thousands of repeat units of smaller molecules known as monomers
What type of polymerisation do unsaturated alkene molecules undergo
Addition polymerisation Produce long saturated chains containing no double bonds
Roughly what conditions are used for industrial polymerisation
High temperature and pressure using catalysts
Addition polymers have high ______ masses. Synthetic polymers are usually named after the ______ that reacts to form their giant molecules, prefixed by ‘_____’.
Molecular Monomer Poly
What is a repeat unit
The specific arrangement of atoms in the polymer molecule that repeats over and over again Always written in square brackets After bracket, place letter n to show there is a large number of repeats
What are addition polymers usually made from
One type of monomer unit
How was poly(ethene) made
By accident Carrying out high pressure experiments with ethene, test vessel leaked allowing trace of oxygen to contaminate fresh sample Next day, white waxy residue had been produced
What properties does a polymer with linear chains have
HIGH DENSITY POLYETHENE Some strength making it ideal for toys, detergent bottles and water pipes
What properties does a polymer with branched chains have
LOW DENSITY POLYETHENE Little strength but is flexible making it ideal for plastic films and bags
What is PVC short for
Poly(chloroethene)
Common uses for PVC
Pipes Films and sheeting Ducts and profiles Insulation and cable sheathing Bottles Flooring
Economically - Polymers are:
Readily available Cheap to purchase More convenient for out throwaway society than alternatives (eg. paper bags and glass bottles)
Why are polymers suitable for storing food and chemicals safely
Their lack of reactivity
What are the negative effects of using polymers
Many alkene-based polymers are non-biodegradable Killing marine life
Recycling polymers:
Reduces environmental impact, conserving finite fossil fuels Decreases amt. of waste to landfill Polymers must be sorted by type Chopped into flakes, washed, dried, melted
PVC recycling:
Disposal and recycling of PVC is hazardous, high chlorine content and additives Not sustainable in landfill Solvents used to dissolve High grade PVC recovered by precipitation from solvent
Using waste polymers as fuel:
Some difficult to recycle From petroleum or natural gas, high stored energy value Can be incinerated to produce heat, generating steam to drive turbine producing electricity
Feedstock recycling:
Chemical and thermal processes that can reclaim monomers, gases or oil from waste polymers Materials produced can be used as raw materials for new polymers
What is a major advantage of feedstock recycling
It is able to handle unsorted and unwashed polymers
What are bioplastics produced from
Plant starch, cellulose, plant oils and proteins
Why is the use of bioplastics good
Protects the environment Conserves valuable oil reserves
Biodegradable polymers:
Broken down by microorganisms into water, CO2 and biological compounds Usually made from starch or cellulose or contain additives that alter the structure of traditional polymers so can be broken down Compostable - degrade and leave no visible or toxic residues
Photodegradable polymers
Oil based Bonds that are weakened by absorbing light to start the degradation