BIOM-polymers Flashcards
(26 cards)
what are the 2 types of polymerization reactions?
condensation and addition
what happens in condensation reactions
elimination of a smaller molecule when monomers react to form covalent bonds - example: AA’s , nylon (flexible dentures - water by-product), polysulfides (impression materials - salt by product), silicones (impression and wax - water byproduct)
what happens in addition polymerization
free radicals form to react with vinyl compounds to form the polymer. vinyl compounds [CH2=CH-]. ex: ethylene to polyethylene
acrylic resin vs acrylic acid
hard rigid glass polymer (splints/dentures/cements) vs. adhesive water soluble polymer (bonding)
what are the 3 (4) steps needed for addition polymerization?
1) generation of radicals (activation and initiation) 2) propagation of reaction 3) termination (no more radicals available to react)
how is generation of radicals accomplished
when energy (activator) works on the initiator molecule - can be heat, light, or chemical
material structure affects….
material properties
intrAmolecular forces in polymeric molecules
covalent bonds - strong
intErmolecular forcesbtw polymeric molecules to form a polymeric molecules can be less to more strong. give examples
entanglement/friction, van der waals, covalent (crosslinking)
degree of polymerization vs molecular weight
average length of molecules (# of repeating units) vs. average mass of the molecules (Degree of polymerization multiplied by the molecular weight of the repeating units.
true/false: the higher the molecular, the higher the strength and rigidity of the polymer
true b/c more difficult to uncoil and disentangle
elastomers have a glass transition temperature that is __________ (above or below) room temp
below
hard polymers have a glass transition temperature that is ________ (above or below) room temperature
above
polymers can be viscoelastic. the elastic component depends on:
the uncoiling and stretching of the molecules
polymers can be viscoelastic. the viscous/plastic component depends on:
the disentanglement of the molecules and the breakage of intermolecular bonds
if the polymer can not disentangle its molecules then the polymer will not have a ________ component
viscous: therefore, the polymer will not be viscoelastic it will be purely elastic
small molecules that act to reduce friction
plasticizers - soften the polymer and make it more flexible (water is a common example) - lower the modulous of elasticity???
cross-linked polymers
more purely elastic (less viscoelastic) - they are more rigid, harder, stronger bc the mobility of the molecules is limited due to the strong covalent bonds that they have btw molecules - untangling is more difficult (or impossible)
how are co-polymers obtained
by combining different monomers in different sequential arrangements…. bcif we change strx then we change fx
true/false: composition by itself does not define the properties of a material
true
example of condensation polymers
nylon (dentures)
ex of free radical addition polymers that are very linear
PMMA (denture base and repair)
ex free radical addition polymer that is extensively crossed linked
composites, sealants, adhesive cements
what are the components of resin composites
polymer + inorganic fillers
