Lecture 19 - Polymers (A)

Question 1

Polymer Structure

Answer 1

• Can be amorphous, crystalline, or semi-crystalline

- Comprised of repeat units called mers

Question 2

Monomer

Answer 2

Molecule containing only one mer

Question 3

Oligomer

Answer 3

Molecule containing 2-10 mers

Question 4

Repeat Units

Answer 4

Can be saturated:
- Each carbon in mer bonded to 4 other atoms
Can be unsaturated:
- Two of carbons in mer bonded with double bonds

Question 5

Degree of Polymerization (n)

Answer 5

• Length of polymer chain

- Ex: [PP]14 where n=14

Question 6

Number-Average Molecular Weight (M_n)

Answer 6

• M_n = [sum]_i (x_i * M_i)
• x_i = N_i / ([sum]_i N_i)
• N_i = number of chains with the molecular weight M_i
• x_i = number fraction of molecular weight
• M_i = an average molecular weight for the chosen molecular weight range

Question 7

Weight-Average Molecular Weight (M_w)

Answer 7

• M_w = [sum]_i (w_i * M_i)
• w_i = W_i / ([sum]_i W_i)
• W_i = number of chains with the molecular weight W_i (also = N_i * W_i)
• w_i = mass fraction of molecular weight
• M_i = an average molecular weight for the chosen molecular weight range

Question 8

Polydispersity

Answer 8

• M_n treats all polymer chains equally
• M_w gives more emphasis to larger chains
• PI = M_w / M_n

Question 9

Size Exclusion Chromatography

Answer 9

Measures molecular weight and PI

Question 10

Mer Conformation

Answer 10

• Each macromolecule can take on a wide variety of different shapes
• C-C-C bonds in backbone are not strictly linear
• C can rotate along 109.5 bond allowing polymer to bend and fold back upon itself
• Chemistry of backbone and size of side groups affects conformation

Question 11

Isotactic

Answer 11

All side groups evenly spaced on the same side of polymer backbone

Question 12

Syndiotactic

Answer 12

Side groups uniformly spaced on either side of polymer backbone

Question 13

Atactic

Answer 13

Side groups arranged in random manner

Question 14

Cis

Answer 14

Side groups on same side of C/C double bond

Question 15

Trans

Answer 15

Side groups on opposite sides of C/C double bond

Question 16

Linear

Answer 16

Bifunctional mer

Question 17

Branched

Answer 17

Trifunctional mer

Question 18

Crystallinity

Answer 18

• Key physical properties of polymers

- Percent Crystallinity dependent on chemical structure of mer and polymer configuration

Question 19

Side Groups

Answer 19

Size:
- If large and bulky, prevents neighboring chains from coming close enough to form crystalline structure
Location:
- Prevents neighboring chains from folding in ordered fashion

Question 20

Percent Crystallinity

Answer 20

• Crystalline regions more dense (up to 20%)
• Calculate density of sample (ps)
• Known density in fully amorphous (pa)
• Known density in almost fully crystalline (pc)
• % crystallinity = [pc * (ps-pa) * 100] / [ps * (pc-pa)]

Question 21

Lamella

Answer 21

• Basic unit of crystal structure
• Larger than unit cell
• Polymer chains folded back on themselves
• Highly idealized

Question 22

Spherulite

Answer 22

• Crystallization from melt

- 3D aggregates of lamella

Question 23

Examples of Biomedical Spherulites

Answer 23

• Polycaprolactone (PCL)

- Polylactic Acid (PLA)

Question 24

Functionality

Answer 24

• Bifunctional —> may bond with mers on both ends

- Trifunctional —> possess three active bonds that can bind to other mers