transition in polymers Flashcards
name the natural polymers
collagen silk natural rubber DNA protein
Synthetic polymers
polystyrene
polyamide
low density polyethee
applications of polymers in dentisrty
prosthodontics operative dentistry orthodontics endodontics equipment
performance criteria for dental resins
mechanically strong physcially stable easily manipulated good aesthetic qualities chemically stable biocompatible reaosnable cost
dental resins use
bone cements
screw fixation in bone
filler for bone cavities
properties of dental resins
acceptable cost for properties good mechanical properties biocompatible suitable for manipulation aesthetics
problems with dental resins
colour stability
shrinking problems
adhesion probelsm
how can shrinking of polymer resin be reduece
by adding MMA
polymer defifniton
large chain like molecule made up of monomers which are small molecules joined by covalent bonds
main polymer materials
metals
ceramics
polymers
composites
structures of polymers
linear
cyclic
branched
cross linked
molecular forces in polymers
thermoplastic
thermosetting
elastomers
What do the physical properties of polymers depend on
how their molecules are arranged (polymer structure)
the strength of the forces between the molecules
covalent bonds
strong
join atoms to each other in individual polymer molecules
intermolecular forces
weak
attract polymer molecules towards each other
Strength and flexibility of the polymer depends on
chain length
side groups
branching
cross linking
chain length effect
longer the chain stronger the polyner
side groups effect
intramolecular forces give stronger attraction between polymer chains making the polymer stronger
branching effects
straight unbranched chains can pack together more closely than highly branched chains
higher density = more crystalline =stronger
crystallinity
degree of structure order
types of polymers in terms of crystallinity
amorphous
crystalline
amorphous polymer
chains of polymers in random structure
crystalline polymer
crystal like order
what does crystallinity affect
optical mechanical thermal chemical properties
thermoplastic polymers (structure, under heat, properties)
linear/branched structure
flow when heated and can be reshaped upon heating
easily moulded and extruded into films?
Thermosetting polymers(structure, under heat, properties)
cross linked structures
cannot be reshaped upon heating
hard and durable
elastomers(structure, under heat, properties)
rubbery polymers
can be stretched easily
return to original form when stress is released
glass transition temperature
temperature at which the polymer chains begin to flow past each other
Tg (transition temp) is always lower than..
the melting temperature
the weaker the secondary bonds the ..
lower the TG
below the Tg
the polymer is solid
above the Tg
the polymer can flow
polymerisation mechanisms
chemical reaction in which monomers of a low molecualar weight are converted into chains of polymers with a high molecular weigh
types of polymerisation
addition
condensation
addition polymerisation
reaction between 2 molecules producing a large molecule without elimination of a smaller molecules
steps of addition polymerisation
activation
initiation
propagation
termination
activators in addition pm
heat
chemical compounds (tertiary amines)
loght
what is a radical
has one free e-
where does a radical go to
a double bond (High density of e-)
acrylate groups
look on Internet or word document for it
condensation polymerisation
when a reaction between two molecules produces a larger molecule with elimination of a smaller molecules
what is a blend used for
mixing polymer prior to moulding
moderate changed to mechanical properties
copolymer
two different types of monomers are joined in the same polymer chain
more noticeable changes in the mechanical properties
plasticizer
small molecules added to the polymer
reduced attraction forces between polymerchains
big effect in mechanical properites
effect of a plasticiser on polymer
lowers Tg and elastic modulus(e.g. therefore good for brittle polymers)
composite
combination of material with different mechanical properties in which the combination material offers superior properties comparing them to the individual components
resin based composites
highly cross linked resin reinforced by a dispersion of amorphous silica or organic resin filler particles and or fibres bonded to the polymer matrix by a coupling agent
