Molecular Structure and Properties

Question 1

What are 2 common ways of measuring average molecular weight of a polymer?

Answer 1

1. Number average
2. Weight average

(Mw is often skewed to the right of Mn since it looks give the heavier chains greater weight in the average)

Question 2

What does it mean when Polydispersity is close to 1?

Answer 2

That the polymers in solution are closer to all being the same chain

Question 3

What is Degree of Polymerization?

Answer 3

• calculation of the number of links in a polymer chain (ex. number of monomers in a chain)

X = Mn/M0

Question 4

Example: What is the degree of polymerization of a polypropylene chain with a number average molecular weight of 105,700 g/mol?

Answer 4

A. 2054.7

Question 5

Example:
for a sample of polytetrafloride:
- 10 chains of 100 unit sin length
- 30 chains of 500 units in length
- 5 chains of 1500 units in length

calculate Mn, Mw, and D

Answer 5

Mn = 52 222.22 g/mol

Mw = 80 212.77 g/mol

D = 1.54

Question 6

What types of properties does molecular weight impact?

Answer 6

• viscosity
• relaxation properties
• melting temp
• glass transition temp
• tensile strength, ductility, toughness
• optical properties
• melt strength

Question 7

What is hydrodynamic volume?

Answer 7

The random space that a single polymer floating in a liquid will occupy (the larger the hydrodynamic space, the more likely for the chain to run into other chains)

Question 8

What test can we use to find intrinsic viscosity experimentally?

Answer 8

• the capillary tube + fluid flow test
• measure the time for a volume of polymer solution to flow through the a capillary - do this for different concentrations of the polymer
• find the relative and inherent viscosities - where these two overlap is the intrinsic viscosity

Question 9

Inter vs Intra molecular forces

Answer 9

Intra = strong bonds and interactions holding single chains together (covalent, ionic bonds, ect.)

inter = weak interactions between neighbrouring chains and chain segments (excludes Van der Waals forces and hydrogen bonding)

(intermolecular bonds could be between 2 different chains or with itself after being folded on itself)

intra&raquo_space; inter