Week 2 - Polymers 2

Question 1

What are copolymers

Answer 1

A polymer which is form from 2 or more different types of monomers,

Question 2

What are comonomers

Answer 2

A minor component in a copolymer which bonds with the principal monomer to influence cross linking or change the viscosity

Question 3

What are the types of copolymers (2)

Answer 3

Block = where each monomer is clustered into blocks e.g. AAABBBAAABBB

Graft = linear backbone of one composition and randomly distributed branches of a different composition

Question 4

What are copolymers mainly used for

Answer 4

Used to achieve high degree of crosslinking and assist in making the uncured composite workable with respect to viscosity

Question 5

What is the influence of intermolecular forces on viscosity

Answer 5

• substances which can act as both Hydrogen bond donors and acceptors have a high viscosity
• Substances which are either only a donor or acceptor for h bonds have lower viscosities

Question 6

What are light cure resins

Answer 6

Resins which are photochemically activated

Question 7

How do light cure resins work

Answer 7

This material requires violet/blue light wave of around 440-480nm to produce the excited state of CQ molecules that then reacts with DMAEMA to produce an excited complex exiciplex which then falls apart to form 2 radicals which will subsequently be the initiators for polymerisation reactions.

Question 8

What is degree of conversion (DOC)

Answer 8

the measure of the percent of C=C bond in an acrylate resin which has been converted into single bonds during polymerisation - practically what percent of the material has reacted.
Ideally you want less unreacted monomers to be left behind as they are reactive and often cause allergic reactions.

Question 9

What is used to create images of polymers

Answer 9

atomic force microscope

Question 10

What are the different types of chiral polymers

Answer 10

• Atactic polymer - random configuration
• Syndiotactic polymer - alternating configurations
• Isotactic polymer - identical configurations

Atactic are more amorphous which pack less well

Isotactic polymers pack well together and tend to be more crystalline

Question 11

What is degree of polymerisation (DP)

Answer 11

average number of monomers per polymer

Question 12

What is the equation for DP

Answer 12

Question 13

What is the trend between molecular eight (degree of polymerisation) and the property of the polymer

Answer 13

The greater the molecular weight of the polymer the more hard and rigid the polymer becomes.

Question 14

What is an amorphous substance

Answer 14

substance will no no long-range order or repeating pattern in the arrangement of atoms or molecules
Most polymers are amorphous solids

Question 15

Answer 15

Tg - glass transition temperature

Question 16

Answer 16

Tcc - Cold Crystallization temperature

Question 17

Answer 17

Tm - melting temperature

Question 18

What is Tg

Answer 18

Glass transition temperature
the temperature at which the material turns from a glassy state to a more elastic state as particles are shuffling around more

This is the first small increase in endothermic energy

Question 19

What is Tg affected by (7)

Answer 19

• Flexibility of polymer chains

Steric hindrance - the more rigid the sidechains are which reduce the flexibility - increases Tg

• Intermolecular forces

Between sidechains reduces flexibility and hence increases Tg

• Molar mass polymer

Tg increases with Mn because Mn decreases flexibility

• Crosslinking/branching

Reduces chain mobility hence increasing Tg

• Plasticizer

Causes polymer chains to be held apart, increasing flexibility - hence decreasing Tg

• degree of crystallinity

Tg increases as crystallinity increases

• Copolymerization

Effects on Tg depend on copolymer

Question 20

What is Tcc

Answer 20

Cold crystallization temperature
this is the temperature at which a polymer particles are able to shuffle around and form a reasonably crystalline material that is amorphous regions at that point
Tcc appears as an exothermic peak on the curve because the crystallization process releases heat

Question 21

What is Tm

Answer 21

Melting Temperature
the temperature at which the crystalline region of a polymer melts and transitions into a disordered amorphous state.
*The higher the crystallinity the higher the melting point (Tm)

Tm is observed as an endothermic peak because the melting process requires the absorption of heat.

Question 22

What happens if the oral cavity temperature is close to the resin copolymer Tg

Answer 22

The resin will soften and fail in the patient mouth (very bad)
hence the copolymer temperature needs to exceed the Tg by a decent amount