homogeneous meaning
same phase
heterogeneous meaning
different phases
alkene polymerisation reactions can be what
they can be homogeneous or heterogeneous
when polymerisation reactions occur what do we want to be able to control
we want to be able to control
polymer stereochemistry
the moelcular weight
the reaction rates
we want to control it in order to have the same product every time
whats PE and PP
polyethylene and polypropene
whats ethylene
ethene
ethene // ethylene turns into what when we polymerise it
turns into ethane with an n
aka -(-ethane-)-n
do we line linear or branched structures when we have polymers
we like linear structures
bc these have more vdw between them bc theyre not branched u can kinda pack lots of them together ans this allows lots of vdw
how do we get a hard polymer
make sure its linear and not branched
these can then be packed close and have lots of vdw between them
making them strong and hard
how do we get a soft polymer
we make sure the poymer is branched bc these prevent packing and prevent lots of vdw between the lengths
this gives u a softer polymer
what conditions do we need for free radical polymerisation of ethylene aka ethene
high temp
high pressure
low mw
what product does free radical polymerisation of ethylene aka ethene gives us
it gives us the branched products
why is free radical polymerisation of ethylene bad
no control over stereochemistry
poor mechanical properties bc branched polymer means less vdw means softer material
whats propene
propane with a double bond
=- or -=
when we polymerise propene what do we get
-(-propane-)- n
but u get it branched bc u need the propane inside the acc bracket
whats special about propene polymer when we compare it with the ethylene one
the propene one is branchedddddd
the ethylene one isnt
so we need to think about the branching bc that C will be chiral meaning we can get dashed branching or wedged branching
meso form of polypropene
this is where theyre both the same config
aka both wedged or both dashed
rac // racemic form of polypropene
this is where the branched bit is alternating between dashed and wedged
whats isotactic
this is where all the R groups on a polymer are on the same side
whats atactic
where the polymer has random stereochemistry
it doesnt pack well at all
whats syndiotactic
this is when the polymer has alternating stereochem all the way through
meso and isotactic
all on the same side
aka all R groups in the polymer are pointing in the same direction
rac // racial and syndiotactical
this is where the polymer R groups are alternating between wedge and dash
whats special about isotactic
bc the R groups are on the same side they will repel eachother
this leads to the chain twisting to reduce strain
they form a spiral // a helix
these give a long stick that can be packed rlly well with other sticks
it therefore is very strong
