W10 Polymer fundamentals and Polymers in Solution Flashcards
2 lectures
What are polymers used for? (8)
Drugs
Suspending agents
Tablets
Film coatings
Packaging
Adhesives
Implants
Dressings
What is a polymer?
What are they built up of?
- Polymers are a specific type of macromolecule – molecules composed of a large number of atoms with a high molecular weight
- Polymers are built up of repeating units called monomers
What does the molecular weight of a
polymer depend upon?
The polymerisation number
What is PDMS an example of?
An antifoaming agent. Used to help dissolve gases that build up in the GI tract.
What are the 5 different ways that monomers can be arranged?
Homopolymer
Alternating copolymer
Random copolymer
Block copolymer
Graft copolymer
Why do polymers have many pharmaceutical uses?
Their properties vary massively
What do the properties of polymers depend upon? (3)
– Properties of the monomer itself, e.g. what functional groups are present?
– Arrangement of the monomers (and the polymerisation number)
– How the polymer chains interact with each other and/or the environment
What can block polymers act as?
Emulsifying or suspending agents
They can have hydrophobic and hydrophilic portions
What is Dissolution of polymers is dependant upon? (4)
– Polar / non-polar (the same as for small molecules)
– Molecular weight
– Prescence of crosslinking
– Crystalline or amorphous form
Polymer solutions are typically much more viscous
How do polymers and small molecules differ?
- Small molecules have a fixed molecule weight whereas most polymers do not have an exact molecular weight—- polydisperse
- Molecular weight quoted for a polymer is usually an average
Can polymers be suspending agents?
Yes
e.g. Polysorbate, Methylcellulose, Povidone, Xanthan Gum, Carbomer
What are Water-soluble polymers potentially able to do?
– Increase the viscosity of solvents
– Swell / change shape (in solution)
– Adsorb at surfaces
These properties make water-soluble polymers useful as suspending agents, e.g. xanthan gum
What are Insoluble polymers capable of?
Forming thin films and are used in tablet coating, wound dressings, membranes etc.
How does polymer dissolution occur?
- Polymer dissolution is a slower process
- Swollen (gel) layer appears at the surface of the polymer and outside this is a diffusion layer
- Slow polymer dissolution rates + existence of these layers creates opportunities for developing modified release dosage forms
What factors have a big impact on the solubility of
polymers? (2)
- Polymer molecular weight
– Partially determines the rate of dissolution
– Inc Molecular weight causes dec in rate of dissolution - Polymer crystallinity
– Polymers can be crystalline or amorphous or somewhere in between
The more crystalline a polymer is…
Then the lower the dissolution rate
What is cellulose used in?
Is it soluble?
Is it branched?
Pharmaceutical packaging
No it is insoluble in water
No unlike starch
Cellulose uses in pharmaceutical science:
HPMC is also known as “Hypromellose” – used in eye drops for dry eyes
What is Dextran/dextrose?
What is it used as?
A branched polymer of α-d-glucose
* Active ingredient uses:
1. Artificial tears,
2. Emergency blood plasma expander
3. Anticoagulant
* Used as a protectant/ bulking agent in lyophilised (freeze dried) formulations
What is the ionisation of acidic/basic groups on a polymer dependent on?
What can the ionic charge on a polymer impact?
pH (Henderson-Hasselbalch)
Molecular shape
Unionised- polymer contracted; low viscosity
Ionised (charged) - groups repel; expanded structure; increased viscosity
pH-sensitive polymers:
How is Chitosan prepared?
Why is it useful?
-Chitosan is prepared by the deacetylation of chitin (from the shells of crustaceans such as crabs and shrimps)
-Amine group ionises at lower pH values and delivery
systems can make use of that
pH-sensitive polymers:
Why are they important?
They are important in enteric tablet coating
Polymethacrylates contain an acid functional group which only ionises at higher pH values
Higher pH in small intestines= unionised
Low pH in stomach= unionised
When a water-soluble polymer enters solution you can often observe some distinct layers around the polymer mass. What are these layers?
From external first;
1. Diffusion layer
2. Gel layer
3. Infiltration layer
4. Polymer mass
