polymer chem Flashcards
what do entanglements do
help hold the material together
when does entanglement occur
high molecular weight
polydispersity
weight average/number average
weight average equals number average
PDI=1 so monodisperse
if PDI = 2
polydispersed
which is larger? weight or number average
weight average
two things that chain branching and crosslinking do
- increase MW
- change bulk properties
3 factors affecting polymer properties
chain length, branching, and crosslinking
plasticizers do what?
- spread polymer chains apart
- facilitate slippage between chains (lubricant effect)
properties that can be manipulated to improve dental resins
- mechanical
- rheometric
- thermal
- solvation
factors affecting mechanical properties
- interpolymer interactions
- cross linking
- cross branching
rheometric properties are about what
flow behaviour
rheometric properties can include what types of recovery
- elastic
- viscoelastic
solvation properties: long chains dissolve fast or slow?
slow
what can affect polymer dissolution
Mw, pdi, crosslinking, crystallinity, chain branching, adsorbed molecules
polymers can be molded above what?
Tg (glass transition temperature)
temp at which an amorphous polymer goes from hard to soft
glass transition temp (Tg)
temp at which an amorphous polymer goes from disordered to ordered
crystallization temp (Tc)
temp at which a crystalline polymer goes from ordered to disordered
melting temp (Tm)
what transitions are seen in completely amorphous polymers?
only Tg
what transitions are seen in semicrystalline polymers?
Tg, Tc, and Tm
polymers that are heated above Tg to be reshaped many times?
thermoplastic
are thermoplastic polymers reversible or irreversible?
thermoplastic = reversible
polymers that undergo chemical change above Tg and dont become soft again
thermoset
are thermoset polymers reversible or irreversible?
thermoset = irreversible
fatigue can be caused by 2 things?
1) cyclic loading
2) steady loading + chemically active agent
cyclic loading is due to what?
crack growth
stress intensity factor (K) is based on what?
- applied stress
- crack length
- geometry
first part of cyclic loading is what?
initiation, due to shear forces, needs to pass a threshold
second part of cyclic loading is what?
growth, due to tension, propagation of the crack
third part of cyclic loading is what?
unstable growth, very rapid crack leading to failure
coupling reactions equation
carboxylic acid + alcohol => ester + water
polymer used in invisalign
polyurethane
synthesis of polyurethane?
alcohol and isocyanate
another name for chain growth poly
addition poly
another name for step growth poly
condensation poly
monomer chemical structure of chain growth poly
strained 3 member ring and double bond
monomer chemical structure for step growth poly
di-functional monomers
rate of initiation, propagation, and termination for chain growth
slow initiation
fast propagation
rate of initiation, propagation, and termination for step growth
all the same rate (depends on concentration)
increase in MW for chain growth
quick
increase in MW for step growth
slow (and random)
loss of a water molecule is observed in what type of polymerization?
water
part of the initiation in a chain growth poly is what
induction to form the reactive species
two types of chain growth poly
1) free radical polymerization
2) ring opening polymerization
monomer and RS for free radical poly
monomer: double bond with vinyl group
RS: free radical (acts as the initiator that becomes 2 R) I->2R, process required heat or light
monomer and RS for ring opening poly
monomer: 3 membered ring
RS: carbocation
free radical sources for composite curing
1) auto-cute
2) light-cure
3) UV cure
4) dual cure
what is required for auto-cure
benzoyl peroxide (BPO) (initiator) and tertiary amine
what is required for light cure
camphorquinone (CQ) - absorbs light
amine (initiator) called DMAEMA
what happens with light curing
light excites electrons to form a free radical
how does free radical poly terminate?
2 free radicals react with another
transfer of hydrogen
acrylate resins such as methyl methacrylate use what type of poly?
free radical poly
example of dentistry use for free radical poly
resins
example of dentistry use for ring opening poly
impression materials (polyether)
