ORGANIC CHEMISTRY: POLY(CHLOROETHENE)
The characteristic reaction of an alkene is addition across the carbon
double bond, as exemplified by addition polymerization. A particularly
versatile addition polymer is poly(chloroethene), commonly known as PVC
(polyvinylchloride), which is formed from the monomer chloroethene.

1.  The monomer chloroethene is manufactured in two steps from ethene:
    C2H4 —————————————————————® C2H4Cl2 ——————————————————————® C2H3Cl
(a) Name the product eliminated when 1,2-dichlorethane is converted to
chloroethene. _________________________________________________________
                                                                    [1]
(b) Suggest one physical method which could determine whether a sample
of chloroethene contained either ethene or 1,2-dichloroethane. ________
_______________________________________________________________________
                                                                    [1]
(c) Determine the general formula of the homologous series to which
chloroethene belongs. _________________________________________________
                                                                    [1]
2.  The addition polymerization of alkenes occurs under a variety of 
reaction conditions. Broadly speaking, high temperatures and pressures 
are used to obtain low-density polymers, whereas catalysts are used to 
obtain high-density polymers. The equation below summarizes two sets of
typical reaction conditions used to polymerize chloroethene.

(a) Complete and label the energy level diagram for the polymerization
of chloroethene.
   
            Energy               ___
                                     
   
   
   
                                 
                                 ___
                                     
            _____________ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
            _____________
                                                   
                                            _________________
                                            _________________
            _________________________________________________
                          Path of reaction
                                                                    [4]
(b) Carefully explain one advantage in using high pressures to obtain 
(low-density) poly(chloroethene), apart from increasing the speed of
reaction. _____________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
                                                                    [2]
(c) Carefully explain one disadvantage in using higher temperatures to 
obtain (high-density) poly(chloroethene), apart from reasons of safety 
and cost. _____________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
                                                                    [2]

3.  The following description of addition polymerization only refers to 
that of chloroethene under conditions of high temperature.
When thousands of molecules of the monomer are heated, the double bonds

break to produce 'free radicals' (•); these bond inter-molecularly,

but randomly, to form one polymer molecule:

[Polymers with the functional groups arranged randomly along the chain
are known as 'atactic polymers'.]
(a) How many unpaired electrons are there in each free radical? _______
                                                                    [1]
(b) Suggest what is formed when a free radical bonds intra-molecularly.
_______________________________________________________________________
                                                                    [1]
4.  Aside from conserving non-renewable resources, the recycling of
addition polymers, followed by catalytic cracking and fractional 
distillation, should be better for the environment than their disposal: 
certainly, present methods cause serious problems. Thus, these plastics 
are usually neither bio- nor photo-degradable and, when burnt, produce 
gases which are often serious pollutants.
(a) Biodegradable substances are broken down enzymically by which group 
of living organisms? __________________________________________________
                                                                    [1]
(b) What type of energy is involved with photodegradability? __________
                                                                    [1]
(c) Name one acidic and one toxic gas produced when poly(chloroethene) 
is burnt. _____________________________________________________________
                                                                    [2]
5.  The addition reaction of fluorine with chloroethene produces a CFC
(i.e., a chlorofluorocarbon). 
(a) Draw the structural formula of this addition product. _____________
_______________________________________________________________________
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_______________________________________________________________________
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                                                                    [2]
(b) State two environmental effects of CFCs. __________________________
_______________________________________________________________________
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                                                                    [2]

Dr. R. Peters                   Next                     Contents' List