Polymers: In Solutions

Question 1

List the stages of dissolution of a polymer

Answer 1

1. Water will penetrate sample
2. Tg lowers plasticisation stage
3. Swelling = each macromolecule surrounded/solvated by water molecules (micromolecules)
4. Full solvation - sample extremely flexible
5. Polymer starts dissolving and forming solution

Question 2

What can prevent a polymer undergoing dissolution?

Answer 2

If it is crosslinked
Covalent linkages will not allow macromolecules to separate
Polymer will still swell and form gel (pull apart slightly) but will not dissolve

Question 3

When does solubility occur?

Answer 3

When the free energy (ΔG) of mixing is negative
ΔG(mixing) = ΔH(mixing) - TΔS(mixing)
Therefore temperature affects the solubility of polymers

Question 4

What do the symbols in the ΔG equation represent?

Answer 4

ΔG(mixing) = free energy
ΔH(mixing) = enthalpy of mixing
ΔS(mixing) = entropy of mixing
T = temperature

Question 5

What does entropy describe?

Answer 5

The effect of MW

MW affects solubility - how big/small the macromolecule is

Question 6

What are crystallites?

Answer 6

Zones where macromolecules are heavily packed together

Question 7

List 4 factors which affect the solubility of polymers

Answer 7

1. Polymer-solvent interactions (chemical nature of both polymer & solvent)
2. Presence of cross-links or strong intermolecular interactions
3. Molecular weight of macromolecules
4. Temperature

Question 8

How do polymer-solvent interactions affect solubility?

Answer 8

Strong polymer-solvent interactions (good affinity) favours solubility
Polar polymers are soluble in polar solvents
Non-polar polymers are soluble in non-polar solvents

Question 9

How does molecular weight affect the solubility of the polymer?

Answer 9

Larger molecule = larger MW = more difficult to dissolve

Question 10

What is the upper critical solution temperature (UCST)?

Answer 10

The critical temperature above which the components of the polymer are miscible in all proportions
Increasing temperature (to a point) increases polymer concentration

Question 11

What is the lower critical solution temperature (LSCT)?

Answer 11

The critical temperature below which the components of the polymer are miscible for all compositions
Decreasing temperature (to a point) increases polymer solubility

Question 12

Name 2 hydrophobic (and water-insoluble) polymers

Answer 12

Poly(ethyl vinyl ether)

Poly(ethylene gylcol)

Question 13

Name 2 hydrophilic (and water-soluble) polymers

Answer 13

Poly(vinyl alcohol)

Poly(methyl vinyl ethher)

Question 14

What is the degree of substitution (DS)?

Answer 14

The average number of substituted hydroxyl groups (modified cellulose)

Question 15

What is molar substitution (MS)?

Answer 15

The average number of molecules of reagent reacted with cellulose units

Question 16

What does the MS/DS ratio represent?

Answer 16

The average length of the pendant change

Question 17

List 3 water-soluble but non-ionic polysaccharides

Answer 17

1. Cellulose ethers
2. Dextran
3. Starch