Chapter 3

Question 1

Characteristics of an amorphous polymer

Answer 1

Glassy-like, rigid, brittle, transparent

Question 2

What is Tg

Answer 2

The temperature at which the polymer transitions from rubber to glass as it cools

Question 3

What occurs at Tg

Answer 3

Increase in stiffness, changes in physical but not chemical or structural properties (this means the chains are just as random before and after)

Question 4

Fast cooling effect on Tg

Answer 4

Fast cooling = higher Tg. Slow cooling = lower Tg

Question 5

Outline differential scanning calorimetry

Answer 5

Sample is heated to be kept at the same temperature as a reference. The difference in energy supplied to the sample relative to the reference is indicative of Tg, Tm or Tcc

Question 6

Factors effecting Tg

Answer 6

chain flexibility, nature of the side groups, molecular branching/crosslinking.
Generally speaking, more flexibility or movement means a lower Tg

Question 7

What is the total volume of a polymer made up of

Answer 7

Occupied volume + free volume

Question 8

Changes in Vf with temperature

Answer 8

Below Tg, Vf is constant. Beyond Tg, Vf increases rapidly

Question 9

characteristics of crystalline polymers

Answer 9

opaque or translucent

Question 10

Density of a polymer

Answer 10

Mass of a unit cell/volume of a unit cell
Mass is dependent on the number of monomer units per unit cell

Question 11

Melting temperature equation for crystalline species

Answer 11

Tm = DH/DS

Question 12

How do we know 2AC = n(lamda)?

Answer 12

Crystalline refractive patterns are a result fo constructive interference. The extra distance travelled by one of the waves must equal a whole phase in order for the waves to interfere constructively

Question 13

Degree of crystallinity equations

Answer 13

V = Vc + Va
W = Wa + Wc
pV = pcVc + paVa

Question 14

Factors affecting Tm

Answer 14

stiffness of the polymer backbone, type and size of substituents, hydrogen bonding, molar mass and branching

Question 15

Which are stronger, ester or amide linkages?

Answer 15

Amides linkages are stronger, buts esters offer more flexibility

Question 16

Drawing hydrogen bonding between branches

Answer 16

The functionalities need to match between the chains ‘down’ carbonyls match ‘up’ nitrogen or oxygen

Question 17

What is Tm and how is it characterized

Answer 17

Melting point that only occurs in crystalline or semi-crystalline structures. Characterised by volume change, phase change and a structure change (from crystalline to melt)

Question 18

Variation of Tm in co-polymers

Answer 18

Both individual homo-polymers will likely form different crystal lattice structures and so, the mixing in a co-polymer will disrupt the lattice structure, lowering Tm below that of the homo-polymer

Question 19

Variation of Tg in copolymers

Answer 19

changes relative to the inverse rule of mixtures, is dependent on the mass fractions of A and B and the Tg of A and B respectively

Question 20

Why do low molar mass crystalline polymers have lower Tm?

Answer 20

The chain ends will disrupt the crystalline structure, reducing strength and hence lowering Tm

Question 21

Which molecules are best for for crystalline formation in polymers

Answer 21

Linear, symmetrical monomers

Question 22

Polar groups and Tg

Answer 22

When considering the effects of substituents on Tg, polar substituents will increase Tg more than non-polar substituents because polar interactions further restrict rotation

Question 23

What does XRD let us measure?

Answer 23

Single crystal polymer = c = lattice parameter
Semi-crystalline = d = spacing of the lattice planes