L1: Polymers

Question 1

Give a brief definition for RESIN materials.

Answer 1

A non-metallic material, synthesized from organic components, that is moldable when soft and is hardened for use.

Question 2

Polymer materials of these origin types fall under what classification category?

• Proteins & Nucleic acids
• Polyisoprenes eg. rubber & gutta percha
• Polysaccharides eg. starch, agar & alginates

Answer 2

Natural

Question 3

Polymer materials of these origin types fall under what classification category?

• PMMA
• Nylon
• Teflon

Answer 3

Synthetic

Question 4

What defines “Thermoplastic resins” based on their thermal behavior? 3 things…

Answer 4

1. Soften under heat and pressure and harden when cooled
2. No chemical reaction
3. Generally soluble in organic solvents

Question 5

What defines “Thermoset resins” based on their thermal behavior? 2 things…

Answer 5

1. Harden by a chemical reaction

2. Generally insoluble in organic solvents

Question 6

What type of condensation reaction is described below? Give an example.

• Repeating units are joined by functional groups
• Reaction is slow and giant molecules are difficult to form
• reaction b/t two molecules to form a larger molecule w/ the elimination of a smaller molecule

Answer 6

Condensation (step growth) plymerization
Eg. -Condensation silicon impression
-Polysulfide impression

Question 7

Define an addition polymerization. What is the major difference b/t condensation & addition polymerization reactions?

Answer 7

Successive reactions b/t monomer molecules to form a polymer w/o formation of volatile by-products. The lack of formation of volatile by-products is the biggest difference

Question 8

The 4 things listed below are features of what type of polymerization rxn?

1. The presence of an unsaturated group
2. Readily form giant molecules
3. Chain growth can continue indefinitely
4. Exothermic reaction

Answer 8

Addition Polymerization

Question 9

Acrylic is formed via what polymerization rxn?

Answer 9

Addition

Question 10

What are the 3 steps in an addition polymerization rxn?

Answer 10

1. Initiation - Activation/formation of a reactive free radical, then formation of an activated free radical monomer complex
2. Propagation - polymer free radicals react w/ monymers to continually grow chain
3. Termination - Reaction b/t 2 free radicals to form a non-reactive polymer chain.

Question 11

Give 3 examples of activators used in addition rxns to form the initial free radical.

Answer 11

1. Heat
2. Tertiary amine
3. Light (UV, Visible)
4. Microwave energy

Question 12

Give 2 examples of polymerization inhibitors. Why are they so important?

Answer 12

Polymerization inhibitors are important bc they delay start & slow down reaction. Generally any impurity will attach to free radical to reduce reactivity.

1. Impurities
2. Hydroquinone - Prevents spontaneous polymerization in Acrylic Resin
3. Oxygen - “Oxygen inhibitor layer” added to resins outer layer