Polymers Flashcards
- Differentiate between polymeric molecule and polymeric material
A polymeric material is composed of polymeric molecules. There are natural (DNA) and synthetic polymers. A polymeric molecule is composed of up to millions of repeated units, the monomers
Polymeric material made of polymers of molecules. Polymeric molecules made of monomers.
Polymers are synthesized by polymerization when
monomers react to form the polymer molecules.
In Condensation Polymerization there is elimination of a smaller molecule when monomers react to form _____ bonds
covalent. (ex water or ethanol are releases in order for things to join)
common example - aminoacid rxn where -OH from the acid and H+ from the amine group form H2)
Examples of Condensation Polymerization:
Examples: amino acid reaction, nylon, polysulfides, and silicones with water, water, salt, and water, respectively, as condensation by-product. Note their use in dentistry.
Addition Polymerization: free radicals (unpaired electrons) react with _____ ______ to form the polymer
vinyl compounds
Example of addition polymers
Acrylics
Acrylic ______ is supplied as liquid monomer to the dentist and the final polymer is synthesized in the office or lab
resin
Acrylic _____ is supplied as a liquid polymer to the dentist ready to be used. Note applications in dentistry.
acid
Three steps/stages needed for addition polymerization:
Generation of radicals.
- activation (light/heat) - WE control
- initiation at molecular level
Propagation of reaction.
Termination of reaction.
NO more radicals available to react.
Generation of radicals is accomplished when activator (energy) works on the initiator (molecule) of the reaction. Give examples of activators:
heat, light and chemicals. Light is the most important of them in dentistry. Light is the activator that can be used more easily in the office.
Intermolecular forces between polymeric molecules to form a polymeric material ranked from less to more strong:
entanglement/friction, van der Waals forces, covalent bonds.
Intramolecular forces in polymeric molecules are strong because ______ bonds are formed while polymer polymerizes.
covalent
Condensation and Addition Polymerization defined in other words
–Condensation polymerization: elimination/release of a smaller molecule while forming covalent bonding between monomers (e.g., water, ethanol, etc) – Addition polymerization: without the elimination of a smaller molecule
Acrylic in Dentistry Examples
-
Degree of Polymerization
of repeating units
of monomers joined
Molecular Weight
Degree of Polymerization (# of units/monomers) x molecular weight of the repeating units
Higher the molecular weight =. higher the ____
higher the strength/rigidity
difficult to entangle
4 (I have 3?) States of Polymerization
Elastomers (rubber)
Hard amorphous (glass)
Hard semicrystalline
Define glass transition temperature
a temperature range at which the polymer changes from rigid to flexible (on heating) or flexible to rigid (on cooling). The molecular mobility changes as they lose intermolecular bonds.
Elastomers, such as rubbers, have Tg ____ room temperature. Hard polymers, such as PMMA, have Tg ____ room temperature.
below, above
Intermolecular forces from low to high
Molecular entanglement, van der waals, covalent
Where are intermolecular forces found and what do they create?
Molecular entanglement, van der waals, covalent
between polymeric molecules to creat polymeric materials
Polymers are viscoelastic.
Elastic depends on
the uncoiling and stretching of the molecules
Addition polymerization
without the elimination of a smaller molecule
if chain of C - organic polymer
Polysulfide - NaCl byproduct
Silicones - No C, look for Si and O. H2O byproduct
PMMA is an acrylic ____
acrylic resin, very rigid
Acrylic resin is ______/_____ and acrylic acid is an _____
acryllic resin is hard/rigid and acrylic acid is an adhesive
if you change ____, ____ or _____ they all affect one another
structure, properties and application
Polymers can be viscoelastic. Elastic component depends on ___
the uncoiling and stretching of the molecules
Polymers can be viscoelastic. Viscous/Plastic response depends on the ___
disentanglement of the molecules and breakage of intermolecular bonds.
If the polymer can not disentangle the molecules, the polymer will __ have viscous component.
will NOT have viscous component, the polymer will not be viscoelastic, it will be purely elastic.
Plasticizers are small molecules that act reducing friction BETWEEN the _____ ________ and thus, they soften the polymer and make it more flexible and more viscoelastic.
polymeric molecules. EX: water
Polymer may be more flexible. Relate this to Tg
lower Tg ?
Note to self - review glass transition temp
review
Describe the effect of cross-linking on polymer properties
Cross-linked polymers are usually more rigid, harder, stronger, and less viscoelastic (more purely elastic) because the mobility of the molecules is limited due to the strong covalent bonds that have between molecules. Uncoiling and disentanglement of molecules is much more difficult, if not impossible, in cross-linked molecules.
List the available types of co-polymer
different monomer arrangements lead to co polymers with different properties because if we change structure we change properties.
Uses of polymers in dentistry
SOFT
Agar, alginate impressions - hydrocolloids
Natural rubbers for root canal obturation
HARD
Nylon, PMMA (dentures), sealants/adhesive cements
