Polymers

Question 1

• Differentiate between polymeric molecule and polymeric material

Answer 1

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.

Question 2

Polymers are synthesized by polymerization when

Answer 2

monomers react to form the polymer molecules.

Question 3

In Condensation Polymerization there is elimination of a smaller molecule when monomers react to form _____ bonds

Answer 3

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)

Question 4

Examples of Condensation Polymerization:

Answer 4

Examples: amino acid reaction, nylon, polysulfides, and silicones with water, water, salt, and water, respectively, as condensation by-product. Note their use in dentistry.

Question 5

Addition Polymerization: free radicals (unpaired electrons) react with _____ ______ to form the polymer

Answer 5

vinyl compounds

Question 6

Example of addition polymers

Answer 6

Acrylics

Question 7

Acrylic ______ is supplied as liquid monomer to the dentist and the final polymer is synthesized in the office or lab

Answer 7

resin

Question 8

Acrylic _____ is supplied as a liquid polymer to the dentist ready to be used. Note applications in dentistry.

Answer 8

acid

Question 9

Three steps/stages needed for addition polymerization:

Answer 9

 Generation of radicals.

• activation (light/heat) - WE control
• initiation at molecular level

 Propagation of reaction.

 Termination of reaction.

NO more radicals available to react.

Question 10

Generation of radicals is accomplished when activator (energy) works on the initiator (molecule) of the reaction. Give examples of activators:

Answer 10

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.

Question 11

Intermolecular forces between polymeric molecules to form a polymeric material ranked from less to more strong:

Answer 11

entanglement/friction, van der Waals forces, covalent bonds.

Question 12

Intramolecular forces in polymeric molecules are strong because ______ bonds are formed while polymer polymerizes.

Answer 12

covalent

Question 13

Condensation and Addition Polymerization defined in other words

Answer 13

–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

Question 14

Acrylic in Dentistry Examples

Answer 14

-

Question 15

Degree of Polymerization

Answer 15

of repeating units

of monomers joined

Question 16

Molecular Weight

Answer 16

Degree of Polymerization (# of units/monomers) x molecular weight of the repeating units

Question 17

Higher the molecular weight =. higher the ____

Answer 17

higher the strength/rigidity

difficult to entangle

Question 18

4 (I have 3?) States of Polymerization

Answer 18

Elastomers (rubber)

Hard amorphous (glass)

Hard semicrystalline

Question 19

Define glass transition temperature

Answer 19

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.

Question 20

Elastomers, such as rubbers, have Tg ____ room temperature. Hard polymers, such as PMMA, have Tg ____ room temperature.

Answer 20

below, above

Question 21

Intermolecular forces from low to high

Answer 21

Molecular entanglement, van der waals, covalent

Question 22

Where are intermolecular forces found and what do they create?

Molecular entanglement, van der waals, covalent

Answer 22

between polymeric molecules to creat polymeric materials

Question 23

Polymers are viscoelastic.

Elastic depends on

Answer 23

the uncoiling and stretching of the molecules

Question 24

Addition polymerization

Answer 24

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

Question 25

PMMA is an acrylic ____

Answer 25

acrylic resin, very rigid

Question 26

Acrylic resin is ______/_____ and acrylic acid is an _____

Answer 26

acryllic resin is hard/rigid and acrylic acid is an adhesive

Question 28

if you change ____, ____ or _____ they all affect one another

Answer 28

structure, properties and application

Question 29

Polymers can be viscoelastic. Elastic component depends on ___

Answer 29

the uncoiling and stretching of the molecules

Question 30

Polymers can be viscoelastic. Viscous/Plastic response depends on the ___

Answer 30

disentanglement of the molecules and breakage of intermolecular bonds.

Question 31

If the polymer can not disentangle the molecules, the polymer will __ have viscous component.

Answer 31

will NOT have viscous component, the polymer will not be viscoelastic, it will be purely elastic.

Question 32

Plasticizers are small molecules that act reducing friction BETWEEN the _____ ________ and thus, they soften the polymer and make it more flexible and more viscoelastic.

Answer 32

polymeric molecules. EX: water

Question 33

Polymer may be more flexible. Relate this to Tg

Answer 33

lower Tg ?

Question 34

Note to self - review glass transition temp

Answer 34

review

Question 35

Describe the effect of cross-linking on polymer properties

Answer 35

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.

Question 36

List the available types of co-polymer

Answer 36

different monomer arrangements lead to co polymers with different properties because if we change structure we change properties.

Question 37

Uses of polymers in dentistry

Answer 37

SOFT

Agar, alginate impressions - hydrocolloids

Natural rubbers for root canal obturation

HARD

Nylon, PMMA (dentures), sealants/adhesive cements