Polymers

Latin: Plasticus, that which can be molded Polymer This name hints at how polymers are made Many + Parts PLASTICS Latin: Plasticus, that which can be molded

Polymer Polymers are made up of many many molecules Poly- means "many" and -mer means “unit”

Polymers: Introduction If a Monomer = A then Polymer = A-A-A-A-A-A-A-A-A-A-A-A-A-A-A- Ex: C=C + C=C + C=C    -C-C-C-C-C-C monomer monomer monomer polymer (plastic) Note: Only one product Occurs with alkenes

POLYMERISATION A process in which small molecules called monomers join together into a large molecule. There are 2 basic types ADDITION : made from alkenes using an Addition reaction. And all the atoms in the monomer are used to form the polymer We will do this in Grade 12 CONDENSATION monomers join up the with expulsion of Small molecules not all the original atoms are present in the polymer

POLYMERISATION OF ALKENES ADDITION POLYMERISATION The equation shows the original monomer and the repeating unit in the polymer ethene poly(ethene) MONOMER POLYMER n represents a large number

Polyethylene. Polyethylene. It is the most common plastic you see. It is used for bottles, buckets, jugs, containers, toys, even synthetic lumber, and many other things.

There are two types of polyethylene polymers (plastics). HDPE, called high density polyethylene, with long straight chains as long as 20,000 carbons (shown here). It is hard. The other LDPE has many branching chains and is soft

HDPE

Polymerisation of Ethene https://www.youtube.com/watch?v=sk6h4oaArE0

Another polymer, which is almost the same as polyethylene, is PolyVinyl Chloride or PVC. The difference is that every other hydrogen is replaced with a chlorine atom (green sphere).

POLYMERISATION OF ALKENES ADDITION POLYMERISATION Chemical Properties Fairly inert. This means it is resistant to chemical attack and 2) it is non-biodegradable. 3) VERY large molecules so they have a lot of INTERMOLECULAR forces…..what property does this give them?

POLYMER PROPERTIES Plastics are all solid at room temperature, why? These molecules are VERY large so intermolecular forces are huge. so polymers are solid at room temperature. The carbon–carbon covalent bonds are strong and there are so very many, so plastics are NOT chemically reactive. The physical properties come from weak intermolecular Forces, but here are many of these too, thus plastics melt but ay a fairly high temperatures Ex: 150 0C (polyethene). Unless they are cross bridged (we talk later) 2. Why do plastics melt rather than react?

DIFFERENT KINDS OF PLASTIC EXAMPLES OF ADDITION POLYMERISATION ETHENE POLY(ETHENE) PROPENE POLY(PROPENE) CHLOROETHENE POLY(CHLOROETHENE) POLYVINYLCHLORIDE PVC TETRAFLUOROETHENE POLY(TETRAFLUOROETHENE) PTFE “Teflon”

POLYMERISATION OF ALKENES SPOTTING THE MONOMER

POLYMERISATION OF ALKENES SPOTTING THE MONOMER

Polymerisation of Propene https://www.youtube.com/watch?v=nz1ucI6gCIg

Thermosetting V Thermosoftening Polymers Thermosetting Polymer Thermosoftening polymers cannot be reshaped. If heated it will burn, not re-melt polymer chains joined by cross-links  can be reshaped when heated up again. Polymer chains are not linked

NATURAL POLYMER Cellulose made of chains of the sugar, although not by addition reactions

Plastic can be bad

Plastics Uses and Problems https://www.youtube.com/watch?v=eZiBAkbCR0E

Disadvantages of Plastic Most plastics are non-biodegradable. 2) During combustion toxic fumes are released. 3) Plastics are made from fossil fuels which are non-renewable

Burning some plastics is bad (CH2CHCl)n + O2  CO2 + CO + HCl + H2O PVC pipes are safe until it burns. The chlorines in the PVC combine with the hydrogen atoms in the PVC to form hydrogen chloride gas (HCl). When this contacts water in lungs or mouth, it turns to hydrochloric acid (HCl(aq)).

They are cheap and easy to make. They don’t oxidize (rust). Advantages of Plastics They are cheap and easy to make. They don’t oxidize (rust). Plastics are resistant to chemical attack They are easy to mould into shape and colour They last a lot longer than many metals   .

Biodegradable Plastics Instead of using fossil fuel derived monomers for polymerization, Starch from foods (corn starch or potato starch can be used, they can polymerize and form plastics as well as ethene or propene. Advantage: pollution control as these will rot in less than a year Disadvantage: using food when the world still has hungry people is grossly unethical. These plastics do not work as well

Plastics How They are Made https://www.youtube.com/watch?v=JararyOXa0Q

Quiz http://www.bbc.co.uk/education/guides/zxm39j6/activity

STOPPING POLYMERIZATION REACTIONS How can the polymerization reaction end or be stopped? Run out or reactants (monomers) ii) 2 free radial monomers combine head to head iii) Addition of chain terminating agent such as nitro benzene INITIATION, free radical formation via a catalyst benzoyl peroxide PROPAGATION, the reaction keeps going when the ethene forms a free radical upon collision with benzoyl peroxide TERMINATION 3 ways