Flashcards in Polymer 3: Polymers in solution Deck (20):
Explain the stages of dissolution that occur in a polymer?
1. Diffusion of solvent molecules into polymer to form a gel
Macromolecules of polymer get surrounded (solvated)
2. Dissolution of gel
Water molecules start dissolving it
What happens to a cross linked polymer?
1. The macromolecule has strong covalent bonds so it'll only absorb the water slightly but cannot dissolve in water
2. Expands and swells a little to form a gel
3. Leads to no dissolution though
4. Strong crystallinity
What does solubility occur?
When the Delta G in the free energy equation is negative
What are the factors in the gibbs free energy equation that affect solubility?
Delta H= Enthalpy of mixing
Delta S= entropy of mixing
What is gibbs free energy equation?
Delta G = Delta H - T Delta S
What are the four factors that affect solubility?1
1. Polymer to solvent interactions (chemical nature of both solvent and polymer)
2. Cross linking or strong intramolecular interactions
4. Molecular weight of the molecules
Describe how polymer and solvent interactions work?
1. Polar polymers are soluble in polar solvents
2. Non polar polymers are soluble in non polar solvents
How does molecular weight play a role in solubility?
Smaller molecular weight means that polymer can dissolve more easily since solvate molecules can pick them up more easily
How does temperature play a role in solubility?
1. As you increase the temperature, each polymer reaches a single phase
2. As it hits this phase, it becomes more soluble
3. Can go from single to double phase
4. Or double to single phase
What is temperature induced phased separation?
1. When the molecule is completely soluble at a temperature such as 15 degrees in water
2. As temperature increases, the macromolecule forms hydrogen bonds
3. Macromolecule collapses to form nanoparticles to create precipitate
Give an example of pharmaceutical appliances of temperate sensitive polymers?
1. Thrombolytic enzyme in the blood stream can dissolve thrombus
2. If you heat the enzyme in the leg region, you can cause it to work better on thrombus
3. Due to at 38 degrees it precipitates to work better
If a molecule is more charged, what does that mean in terms of water? Give examples?
1. More soluble
- COO- , NH3+ or OH- are very hydrophilic
What functional group makes hydrophobic molecules so hydrophobic?
CH3 group makes molecule quite hydrophobic
How do you turn a hydrophobic molecule into more soluble hydrophilic molecules?
1. Changing the CH3 group into an OH group
2. Changing CH3 group on the repeating unit into a H group
If a molecule has low critical solution temperature, what does that mean?
Soluble in cold water, when you heat it, causes it to precipitate
What are some important synthetic water soluble non ionic polymers?
1. Poly (ethylene oxide)
2. Poly (vinyl alcohol)
3. Poly (acrylamide)
What are the mains reasons of insolubility in cellulose?
1. Strong intramolecular bonds
2. Strong hydrogen bonds
3. Crystalline domains
4. Swells slightly in water
What can be done to cellulose to make it hydrophilic? Give some examples of some newly formed soluble cellulose compounds?
1. Change the CH3 groups with hydrophilic groups
- Hydroxypropylmethylcellulose: Tablets and solutions
- Sodium carboxymethylcellulose (ether)
What does the solubility of the cellulose ethers depend on?
1. DS (degree of substitution): average substituted hydroxyl groups
2. MS (molar substitution): average molecules of reagent (alkylene oxide)