[13.5] polymerisation in alkenes Flashcards
what is the definition of a monomer?
a small molecule that combines with many other monomers to form a polymer
what is the definition of a repeating unit?
the arrangement of atoms that occurs in a polymer structure over and over again
which molecules undergo addition polymerisation?
unsaturated alkene molecules undergo addition polymerisation
how is industrial polymerisation carried out?
at high temperatures and pressures using catalysts
draw the general equation for an addition polymerisation equation
- monomer unit goes to a repeating unit of a polymer
- n (signifies many units)
- double bond broken, outside bonds crossing the square brackets etc.
environmental concerns: disposing of waste polymers
- polymers are readily available, cheap to purchase and it is more convenient for our throwaway society
- many alkene-based polymers are non-biodegradable
- the amount of growing polymer waste has serious environmental impacts eg. killing marine life
environmental concerns: recycling
- recycling polymers reduces their environmental impact by conserving finite fossil fuels and decreasing the amount of waste going to landfill
- discarded polymers have to be sorted by type. if the polymers are mixed the recycling process does not work
- once sorted, polymers are chopped into flakes, washed, dried, and melted
- the recycled polymer is cut into pellets and used by manufacturers to make new products
environmental concerns: PVC recyling
- disposal and recycling of PVC is hazardous due to the high chlorine content and range of additive present in the polymer
- dumping in landfill is not sustainable
- when burnt, PVC released hydrogen chloride, a corrosive gas, and other pollutants like toxic dioxins
- new technology uses solvents to dissolve the polymer. high-grade PVC is recovered by precipitation from the solvent, and the solvent can be used again
environmental concerns: using waste polymers as fuel
- some polymers are difficult to recycle
- as they are derived from petroleum or natural gas, they have a high stored energy value
- waste polymers can be incinerated to produce heat, generating steam to drive a turbine producing electricity
environmental concerns: feedstock recycling
- describes the chemical or thermal processes that can reclaim monomers, gases or oil from waste polymers
- products from feedstock recycling resemble those produced from crude oil refineries
- theses materials can be used as raw materials for the production of new polymers
- advantage is that it is able to handle unsorted and unwashed polymers
environmental concerns: bioplastics
- produced from plant starch, cellulose, plant oils and proteins
- offer a renewable and sustainable alternative to oil-based products
- products our environment and also conserved valuable oil reserves
environmental concerns: biodegradable polymers
- broken down by microorganisms into water, carbon dioxide and biological compounds
- usually made from starch or cellulose, or contain additives that alter the structure of traditional polymers so microorganisms can break them down
environmental concerns: compostable polymers
- degrade and leave no visible toxic residues
- based on poly(lactic acid)
- becoming more common as an alternative to alkene-based polymers
- supermarket bags made from plant starch can be used as bin liners for food waste so that the waste and the bag can be composted together
environmental concerns: photodegradable polymers
- where the use of plant-based polymers is not possible, photodegradable oil-based polymers are being developed
- these polymers contain bonds that are weakened by absorbing light to start the degradation
- light-absorbing additive can also be added
