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| Callulose |
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| A graphic representation of an alpha olefin hexene molecule |
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| Long chains |
| At about the same time a German scientist, Professor Hermann
Standinger, proposed that molecules were held together not in
blocks or networks, but formed long chains. That notion was
further developed by a compatriot, Professor Herman Mark.
Employed by IG Farbenindustrie as its director of research, he
came to realise that major differences in polymers (many
molecules joined together) would result from the degree to
which their chains were branched (explanation coming up
shortly). And different polymers would, of course, produce
different thermoplastics. |
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| We’ve seen that methane consists of one atom of carbon
attached to four of hydrogen. Next comes ethane: two carbon
atoms attached to each other, with each of their remaining
hooks connected to a hydrogen atom - hence the chemical
formula for ethane, C2H6. Now, if you use a high-temperature process to sever a hydrogen atom from each of the carbon
atoms - it’s called dehydrogenation - you get ethylene (C2H4).
To make use of the hooks that had connected them to those
now-missing hydrogen atoms, the carbon atoms create a
double-bond between themselves. The molecule, however, is
called "unsaturated" because that double bond, as noted in an
earlier chapter, is not a happy state of affairs; either of the
carbon atoms would much rather connect with an atom in
some other molecule. |
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| You can form long, merry chains in that way until
some spoilsport hydrocarbon molecule comes along
and effectively saturates the end of the chain |
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| Which, of course, they can quite easily if
you put many ethylene molecules into a
pot. The carbon atom in one ethylene
molecule will remove one of its hooks from
the other carbon atom in the same molecule and use
it to bond with a carbon atom in another ethylene
molecule. So you end up with a sort of Conga line of
carbon atoms, each joined by its belt to the one in front,
and holding out its arms sideways, with a hydrogen atom in
each hand. |
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| You can form long, merry chains in that way until some
spoilsport hydrocarbon molecule comes along and effectively
saturates the end of the chain. During the course of its growth,
the chain may have developed molecular branches. That
happens when a hydrogen atom at some point along the chain serves to link it with a shorter,
unsaturated chain of hydrocarbons
drifting around in the
neighbourhood. This can happen
many times along the length of
the main chain. |
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| But what has all that to do with plastics? |
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| Top of page |
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