Polymers Flashcards
Polymers
Covalent molecular substances of non metals bonded into molecules made by joining a large number of small molecules called monomers
Bonds between monomers
Covalent bonds form between the monomer molecules to produce a polymer molecule
Elements commonly found in polymers
Hydrogen, oxygen, chlorine and nitrogen
Polymer advantages
all electrons are localised- will not conduct electricity therefore good electrical and thermal insulators
thermoplastics can be recyled
lightweight and easily moulded
corrosion resistant and chemically inert
Co-polymer
Polymer made from more than one type of monomer
Thermoplastic polymers
Generally quite soft and flexible- strong covalent bonds within monomer molecules but weak dispersion forces between the chains
soften when heated, allowing it to be reshaped and recycled
Thermosetting polymers
Rigid
Have a covalent network structure with strong covalent bonds throughout the solid and strong forces within monomers and between chains
do not melt, cannot be reshaped, recycling is limited
elastomer
cross-linking
Cross linking
joining the chains by covalent bonds
greater the number of cross-links, more rigid the polymer
Elastomers
Polymers with special cross links which allow the polymer to stretch
Polymerisation
Monomer molecules form polymer chains
Condensation polymerisation
step-growth polymers, thermosetting polymers
Each monomer has a functional group at each terminus. Reaction occurs between two di-fuctional molecules
Leads to the formation of a covalent bond between the two monomers and elimination of a small molecule as the other reaction product(usually H2O, HCl)
Addition polymerisation
Chain growth polymers
carbon-carbon double bonded monomers
empirical formula of polymer is same as monomer
Polyethene
Simplest of polymers because only Hydrogen atoms are bonded to the atoms in the chain
it is a thermoplastic polymer
Two different forms of polyethene
High density and low density
depends on the reaction conditions- temperature and pressure
High density polyethene
Monomers join in continuous chains without any branches
Unbranched chains pack together quite closely
Hard, stiff, strong, able to be sterilised
Plastic bottles and fuel tanks
Low density polyethene
Polymer chains are branched
Cannot pack together as closely as unbranched chain
Flexible and somewhat soft
Cling film and flexible water pipes
Factors affecting polymer physical properties
Polarity of groups type of polymer polymer chain length extent of branching arrangement of groups inclusion of additives like plasticisers
Plasticisers
organic molecules that soften the plastic, by weakening intermolecular attractions
Heteronuclear molecules
When the reactant (HX) is a heteronuclear molecule, the products are isomers.
Water is a heteronuclear molecule therefore the products are isomers
Polyvinyl chloride
polychloroethene
Cross linked polymer
Stiff, hard, strong, brittle, good electrical insulators, resists chemicals
tableware, knobs, handles and electrical insulation
Why molar mass of a polymer always given as an average?
Linear polymers rarely have chains that are the same length so degree of polymerisation varies from chain to chain. Therefore when the molar mass of a polymer is calculated it will be an average of the values for the various chains
Polymers disadvantages
made from non-renewable sources, aren’t biodegradable and cause evironmental risks
burn easily and give off toxic fumes
derived from crude oil which is a non renewable source
brittle at low temperatures
UV sensitive
deformed under mechanical load
