intro to polymers e lec Flashcards
definitions polymerisation properties such as shrinkage molecular mass structure thermal
what is alginate
a hydrocolloid
give an example of a natural polymer
collagen
what is a denture material made out of
the vulcanisation of rubber
when did we see alginate impressions
since the second world war
what did we see since the second world war
the poly methylmethacrylate and alginate impressions and acrylic base denture resin
what language does the world polymer come from
greek
what does polymer mean in greek
many parts
how many carbons does ethene have
it has 2 carbons
how many hydrogens does ethene have
it has 4 Hs
what is in the ethene molecule which makes it special
a double bond which is relatively easy to break
how can we write a repeated unit of a mer
by adding a bracket and a n outside the bracket
the n is called the
degree of polymerisation
how can we calculate the molecular mass of the polymer
by the degree of polymerisation and the product of the molecular mass
what are the three types of co polymer
block
graft
random co polymer
what can co polymers do
tailor the properties of the final material
what is a straight polymer called
a linear polymer- a simple polymer
if the chain is branched off the main backbone it can resemble a
graft co polymer
if the branched polymer attaches to another it can form
a 3D structure which is said to be cross linked
what is an example of cross linking in dentistry
a alginate impression material
which type of polymer can be melted and remodelled
linear or branched- and they are called thermoplastic
what type of waxes do we use in dentistry
thermoplastic
which type of polymer does not melt and rest
cross linked
in dentistry which example do we have of a thermoset polymer
poly methylmetacrylate(PMAA)/acrylic
what is polymerisation
the act of reacting the monomers or comonomers into a polymer
what are the two main branches of polymerisation
condensation polymer
addition polymer
what is condensation polymerisation
it is where the monomer reacts to form a polymer and a small by product is produced
what is addition polymerisation
it is when monomers great together but no by product is produced
condensation polymers grow by
step growth
what is the most common by product
water
what can also be a by product
low molecular weight alcohols
how does addition polymerisation occur
by a chain reaction
name the four steps of the chain reaction
activation
initiation
propagation
termination
what chemical is added to the monomer
the initiator
what is the initiator sensitive to
heat
light
additional chemicals
what does activation do
split the initiator molecule so that there are very reactive free radicals
what does the initiation stage have
the very reactive free radicals which hone into the weaker points in the monomer
what happens in the propagation step
the free radical binds and then gets passed on to the other monomer
during termination
the free radical must either meet another free radical or join to a hydrogen
what is it called when two free radicals join in the termination step
combination
what is it called when the free radical binds to a hydrogen in the termination step
disproportionation
what happens when a double bond is broken
heat is given out exothermic
what are the clinical considerations for breaking a double bond
it can become uncomfortable for the patient
the conversation from methyl methacrylate to polymathy methacrylate
can reduce in volume by 30%
how do we reduce the volume lost
by using filler particles of a material that doesn’t change volume
which particle is used in PMAA
particles that have been previously polymerised polymer
what does Mm stand for
mean molecular mass
what is different amount the graph
the graph is skewed so the mean lies funny
how can this be fixed that the graph is skewed
this can be rectified by taking the “number average molecular mass” this calculates what length chain the average (mean) monomer resides in.
what structures can polymers form
crystalline or amorphous
what structure is crystalline
a highly ordered structure
what structure is amorphous
random loose net work which is toucher
what structure are most polymers
a mixture of the two structures
this can depend on
chemistry and processing
what does Tg mean
gasses transition temperature
what is the temp of tg
lower than the melting point
polymers below Tg are said to be
glassy
polymers above Tg are said to be
rubbery
the longer the chain group the
lower the Tg
why does the tg become lower in the longer chain group
as they push the pendants far apart
