Polymers

Question 1

What does thermoplastic mean

Answer 1

Shaped by heat and hardened by cooling

Mechanical properties are sensitive to heat

Question 2

Are thermoplastic materials soluble

Answer 2

Dissolve in organic solvents

Question 3

How are thermoplastic polymer chains bonded together

Answer 3

Polymer chains are bonded to each other by secondary bonds

Question 4

What does thermosetting mean

Answer 4

Material is set to a permanent shape when it cools, chemical reaction involved

Question 5

How are thermosetting polymers bonded to each other

Answer 5

Primary covalent bonds (cross links)

Question 6

Which elastic impression material types polymerise via condensation and what are the by products

Answer 6

Polysulphides and condensation silicones

By products are water and lead sulfide

Question 7

What is a problem with condensation polymerisation reaction

Answer 7

Produces water as a by product. Water will weaken polymer and make it prone to degradation

Question 8

Is addition or condensation faster

Answer 8

Addition is the faster reaction

Question 9

What are the 3 main steps in addition reaction

Answer 9

1. Activation and initiation
2. Propagation
3. Termination

Question 10

What happens at initiation step of addition reaction

Answer 10

Catalyst benzoyl peroxide is initiated by heat or light or chemical releases free radicals

Question 11

What is cr polymerisation shrinkage

Answer 11

1.2-2%

Question 12

What is the average degree of polymerisation in addition reactions

Answer 12

60-64%

Question 13

Effects of increased chain length in polymers on physical properties

Answer 13

Increased viscosity

Increased strength

Increased glass transition temperature (higher softening point)

Increased rigidity (harder to distort)

Question 14

Effect of increasing filler load on polymer

Answer 14

Increased strength

Question 15

Effect of increased cross linking on polymer

Answer 15

Increase strength, increase glass transition temperature, increase hardness and rigidity, increase resistance to solvent action. Decrease water sorption

But extensive crosslinking can cause brittleness

Question 16

How do plasticisers work

Answer 16

Neutralise secondary bonds that prevent resin molecules from slipping past one another. Increases plasticity and decreases viscosity, make more flexible, decrease friction during handling

Question 17

How do external plasticisers neutralise secondary forces

Answer 17

Penetrate between polymer chains and increase the distance between them, thereby decreasing the forces

Question 18

How do internal plasticisers work

Answer 18

Plasticiser is part of polymer main chain and copolymerise

Question 19

How can strength of polymers be increased

Answer 19

Increase degree of polymerisation hence increasing molecular weight

Cross linking

Copolymerisation (different monomers)

Addition of inorganic fillers (inorganic fillers increase strength, rigidity and hardness)