Polymerisation of Alkenes and CFCs and their effect on the environment

Research on the polymerisation of alkenes and the effect of CFCs on the environment including the mechanisms involved.

HideShow resource information
  • Created by: Olivia
  • Created on: 04-04-11 16:42
Preview of Polymerisation of Alkenes and CFCs and their effect on the environment

First 324 words of the document:

Polymerisation of alkenes
An addition reaction is one in which two or more molecules join together to give a single product. During the
polymerisation of ethene, thousands of ethene molecules join together to make poly(ethene) - commonly
called polythene.
nCH2=CH2 ==> -(-CH2-CH2-)-n ]
Polyalkenes such as low density poly(ethene) can be made by polymerising the alkene monomer with
oxygen or peroxide catalysts.
Temperature: about 200°C
Pressure: about 2000 atmospheres
Initiator: a small amount of oxygen as an impurity
Poly(propene) (polypropylene): PP
Poly(propene) is manufactured using Ziegler-Natta and other modern catalysts. There are three variants on
the structure of poly(propene) which you may need to know about, but we'll start from the beginning with a
general structure which fits all of them.
CFCs and their effect on the ozone
CFCs are chlorofluorocarbons - compounds containing carbon with chlorine and fluorine atoms
attached. CFCs are non-flammable and not very toxic. They therefore had a large number of uses.
They were used as refrigerants, propellants for aerosols, for generating foamed plastics like
expanded polystyrene or polyurethane foam, and as solvents for dry cleaning and for general
degreasing purposes.
Unfortunately, CFCs are largely responsible for destroying the ozone layer. In the high atmosphere,
the carbon-chlorine bonds break to give chlorine free radicals. It is these radicals which destroy
ozone. CFCs are now being replaced by less environmentally harmful compounds. Dr. Sherwood
Rowland and a post-doctoral research scientist, Mario Molina, at the University of California - Irvine in 1974,
speculated that the Cl radical so generated in the stratosphere could destroy O3 in a chain reaction. The
mechanism would be:
Cl + O3 --> ClO + O2
(from CFC photolysis)
O + ClO --> Cl + O2
(from O2 photolysis)

Other pages in this set

Page 2

Preview of page 2

Here's a taster:

Of course, there is other atmospheric chemistry which could remove the Cl radical, namely its reaction with
hydrocarbons, such as methane, or with water (H2O) to produce HCl:
CH4 + Cl --> HCl
H2O + Cl --> HCl
The HCl should be removed as hydrochloric acid (aqueous HCl) - acid rain.…read more


No comments have yet been made

Similar Chemistry resources:

See all Chemistry resources »See all resources »