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 覧覧覧覧覧覧覧覧覧覧 C2H4Cl2 覧覧覧覧覧覧覧覧覧覧覧 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. _____________________________________________________________
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                                                                    [2]
(c) Carefully explain one disadvantage in using higher temperatures to 
obtain (high-density) poly(chloroethene), apart from reasons of safety 
and cost. _____________________________________________________________
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                                                                    [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.
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                                                                    [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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                                                                    [2]
(b) State two environmental effects of CFCs. __________________________
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                                                                    [2]
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