Polymers

Question 1

Definition of a polymer

Answer 1

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

Question 2

monomer

Answer 2

smallest repeating unit (molecule) in polymer chain

Question 3

polymerization

Answer 3

rxn of monomers to synthesize/form polymers

Question 4

condensation polymerization

Answer 4

elimination/release of a smaller molecule (water, ethanol) while forming covalent bonding between monomers

Question 5

addition polymerization

Answer 5

polymerization without the elimination of a smaller molecule

Question 6

Dental examples of condensation polymerization

Answer 6

flexible dentures - nylon
impressions - polysulfides, silicones
wax - silicones

Question 7

Free radical addition polymerization

Answer 7

free radical is a reactive chemical species with an unpaired electron

Can react with vinyl compounds (like acrylic resin - dentures, splints, cements)

Question 8

What is the difference between acrylic resin and acrylic acid? What are each used for in dentistry?

Answer 8

acrylic resin: hard rigid glass polymer - splints, dentures, cements

acrylic acid: adhesive water-soluble polymer - adhesives

Question 9

What are the stages of polymerization of vinyl compounds (addition polymerization)

Answer 9

1. Generation of free radicals (activation, initiation)
2. propagation of the rxn
3. termination of the rxn

Question 10

What is the difference between polymer molecules and polymeric materials?

Answer 10

Polymer molecules: composed of millions of repeated units (monomers)

Polymeric material: made up of polymeric molecules; natural and synthetic

Question 11

What INTRAmolecular forces are employed by polymer molecules?

Answer 11

covalent bonds

Question 12

What INTERmolecular forces are employed by polymeric materials?

Answer 12

Molecule entanglement - friction between mols
Secondary bonds - Van der Waals
Covalent bonds - crosslinking

Question 13

Degree of polymerization (DP)

Answer 13

number of repeating units in a polymer - the # of monomer units joined together

Avg length of the molecules

Question 14

Molecular weight of polymers

Answer 14

degree of polymerization x the molecule weight of the repeating units

avg mass of the mols

Question 15

The higher the molecular weight, the higher the _______ and _________

Answer 15

strength

rigidity

Question 16

higher degrees of polymerization provide ________ in dental polymeric materials

Answer 16

higher strength

Question 17

What are the three types of physical states of polymers?

Answer 17

Elastomers (rubbers)
Hard amorphous (glasses - transparent)
Hard semicrystalline (partially crystalline - translucent)

Question 18

What is the difference between flexible polymers (elastomers/rubbers) and rigid polymers?

Answer 18

Molecular flexibility depends on temp
Higher temps - more flexible, easier disentanglement
Lower temps - more rigid

Question 19

Glass transition temperature (Tg)

Answer 19

Each polymer has a temp range at which it changes from rigid to flexible (heating)/flexible to rigid (cooling)

Question 20

A polymer with a comparatively high Tg (78 degrees C) will be ______ at mouth temp

Answer 20

rigid

ex: denture base material

Question 21

a polymer with relatively low Tg (-22 degrees C) will be _______ at mouth temperature

Answer 21

flexible

Ex: impressions, denture linings

Question 22

Elastomers or rubbers have a ______ Tg, and work at temperatures ____ Tg

Answer 22

Have a low Tg

Work at temperatures above Tg

Question 23

Hard polymers have a ______ Tg and work at temperatures _____ Tg

Answer 23

high Tg

Work at temps below Tg

Question 24

Polymers show a combination of _____ and ____ behavior

Answer 24

elastic

viscous

Question 25

Viscous behavior in polymers

Answer 25

breaking of intermolecular bonds and disentanglement of molecules

Question 26

Elastic behavior in polymers

Answer 26

Uncoiling and stretching of molecules

Question 27

Plasticizers

Answer 27

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)

Question 28

How do plasticizers change polymers?

Answer 28

Soften them | May be more flexible (lower Tg)

Question 29

Resin composites are a _______ polymer

Answer 29

cross linked

Question 30

Cross linked polymers

Answer 30

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

Question 31

co-polymers

Answer 31

Same composition but different arrangement = different properties

Question 32

Hydrocolloids such as agar and alginate are _______ polymers

Answer 32

naturally occurring polymers

Question 33

Gutta percha, an isomer of rubber, is a __________ polymer

Answer 33

natural rubbers

Question 34

Nylon (sometimes used in dentures) is what kind of polymer?

Answer 34

Hard synthetic, condensation

Question 35

Poly(methyl methacrylate) (PMMA), used for dentures, is what kind of polymer?

Answer 35

hard synthetic | free radical addition (mostly linear structures)

Question 36

Dental composites, fissure sealants and some adhesive cements are what kind of polymer?

Answer 36

hard synthetic | Free radical addition (extensively cross linked)

Question 37

resin composites consist of polymer and ________ and are used in:

Answer 37

polymer and inorganic fillers pit and fissure sealants, luting cements, resin composite filling materials

Question 38

Impression materials (polysulfides, silicones, polyethers) and denture liners (silicone) are examples of...

Answer 38

flexible synthetic polymers | elastomers

Question 39

Resilient linings and tissue conditioners are examples of what kind of polymer?

Answer 39

Plasticized methacrylates | flexible synthetic polymers

Question 40

Poly(acrylic acid) and other acids (itaconic, aleic) are adhesive to tooth tissues by ionic attraction and are examples of what kinds of polymers?

Answer 40

water soluble synthetic polymers