Polymers Flashcards
Definition of a polymer
any of numerous natural and synthetic compounds of usually high molecular weight consisting of up to millions of repeated linked units, each a relatively light and simple molecule
aka long chain molecules with many repeating units
monomer
smallest repeating unit (molecule) in polymer chain
polymerization
rxn of monomers to synthesize/form polymers
condensation polymerization
elimination/release of a smaller molecule (water, ethanol) while forming covalent bonding between monomers
addition polymerization
polymerization without the elimination of a smaller molecule
Dental examples of condensation polymerization
flexible dentures - nylon
impressions - polysulfides, silicones
wax - silicones
Free radical addition polymerization
free radical is a reactive chemical species with an unpaired electron
Can react with vinyl compounds (like acrylic resin - dentures, splints, cements)
What is the difference between acrylic resin and acrylic acid? What are each used for in dentistry?
acrylic resin: hard rigid glass polymer - splints, dentures, cements
acrylic acid: adhesive water-soluble polymer - adhesives
What are the stages of polymerization of vinyl compounds (addition polymerization)
- Generation of free radicals (activation, initiation)
- propagation of the rxn
- termination of the rxn
What is the difference between polymer molecules and polymeric materials?
Polymer molecules: composed of millions of repeated units (monomers)
Polymeric material: made up of polymeric molecules; natural and synthetic
What INTRAmolecular forces are employed by polymer molecules?
covalent bonds
What INTERmolecular forces are employed by polymeric materials?
Molecule entanglement - friction between mols
Secondary bonds - Van der Waals
Covalent bonds - crosslinking
Degree of polymerization (DP)
number of repeating units in a polymer - the # of monomer units joined together
Avg length of the molecules
Molecular weight of polymers
degree of polymerization x the molecule weight of the repeating units
avg mass of the mols
The higher the molecular weight, the higher the _______ and _________
strength
rigidity
higher degrees of polymerization provide ________ in dental polymeric materials
higher strength
What are the three types of physical states of polymers?
Elastomers (rubbers) Hard amorphous (glasses - transparent) Hard semicrystalline (partially crystalline - translucent)
What is the difference between flexible polymers (elastomers/rubbers) and rigid polymers?
Molecular flexibility depends on temp
Higher temps - more flexible, easier disentanglement
Lower temps - more rigid
Glass transition temperature (Tg)
Each polymer has a temp range at which it changes from rigid to flexible (heating)/flexible to rigid (cooling)
A polymer with a comparatively high Tg (78 degrees C) will be ______ at mouth temp
rigid
ex: denture base material
a polymer with relatively low Tg (-22 degrees C) will be _______ at mouth temperature
flexible
Ex: impressions, denture linings
Elastomers or rubbers have a ______ Tg, and work at temperatures ____ Tg
Have a low Tg
Work at temperatures above Tg
Hard polymers have a ______ Tg and work at temperatures _____ Tg
high Tg
Work at temps below Tg
Polymers show a combination of _____ and ____ behavior
elastic
viscous
Viscous behavior in polymers
breaking of intermolecular bonds and disentanglement of molecules
Elastic behavior in polymers
Uncoiling and stretching of molecules
Plasticizers
Liquids that are able to penetrate between the randomly oriented chains of a polymer (eg. water)
Reduce frictional forces between mols
Result in a softened polymer
Polymer may be more flexible (lower Tg)
How do plasticizers change polymers?
Soften them
May be more flexible (lower Tg)
Resin composites are a _______ polymer
cross linked
Cross linked polymers
More purely elastic, less viscous because mobility of mols is limited
May have higher Tg
Harder, more brittle
More resistant to action of solvents/plasticizers
Uncoiling/disentanglement harder/impossible
co-polymers
Same composition but different arrangement = different properties
Hydrocolloids such as agar and alginate are _______ polymers
naturally occurring polymers
Gutta percha, an isomer of rubber, is a __________ polymer
natural rubbers
Nylon (sometimes used in dentures) is what kind of polymer?
Hard synthetic, condensation
Poly(methyl methacrylate) (PMMA), used for dentures, is what kind of polymer?
hard synthetic
free radical addition (mostly linear structures)
Dental composites, fissure sealants and some adhesive cements are what kind of polymer?
hard synthetic
Free radical addition (extensively cross linked)
resin composites consist of polymer and ________ and are used in:
polymer and inorganic fillers
pit and fissure sealants, luting cements, resin composite filling materials
Impression materials (polysulfides, silicones, polyethers) and denture liners (silicone) are examples of…
flexible synthetic polymers
elastomers
Resilient linings and tissue conditioners are examples of what kind of polymer?
Plasticized methacrylates
flexible synthetic polymers
Poly(acrylic acid) and other acids (itaconic, aleic) are adhesive to tooth tissues by ionic attraction and are examples of what kinds of polymers?
water soluble synthetic polymers
