W10 Polymer fundamentals and Polymers in Solution

Question 1

What are polymers used for? (8)

Answer 1

Drugs
Suspending agents
Tablets
Film coatings
Packaging
Adhesives
Implants
Dressings

Question 2

What is a polymer?
What are they built up of?

Answer 2

• 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

Question 3

What does the molecular weight of a
polymer depend upon?

Answer 3

The polymerisation number

Question 4

What is PDMS an example of?

Answer 4

An antifoaming agent. Used to help dissolve gases that build up in the GI tract.

Question 5

What are the 5 different ways that monomers can be arranged?

Answer 5

Homopolymer
Alternating copolymer
Random copolymer
Block copolymer
Graft copolymer

Question 6

Why do polymers have many pharmaceutical uses?

Answer 6

Their properties vary massively

Question 7

What do the properties of polymers depend upon? (3)

Answer 7

– 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

Question 8

What can block polymers act as?

Answer 8

Emulsifying or suspending agents
They can have hydrophobic and hydrophilic portions

Question 9

What is Dissolution of polymers is dependant upon? (4)

Answer 9

– 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

Question 10

How do polymers and small molecules differ?

Answer 10

• 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

Question 11

Can polymers be suspending agents?

Answer 11

Yes
e.g. Polysorbate, Methylcellulose, Povidone, Xanthan Gum, Carbomer

Question 12

What are Water-soluble polymers potentially able to do?

Answer 12

– 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

Question 13

What are Insoluble polymers capable of?

Answer 13

Forming thin films and are used in tablet coating, wound dressings, membranes etc.

Question 14

How does polymer dissolution occur?

Answer 14

• 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

Question 15

What factors have a big impact on the solubility of
polymers? (2)

Answer 15

• 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

Question 16

The more crystalline a polymer is…

Answer 16

Then the lower the dissolution rate

Question 17

What is cellulose used in?
Is it soluble?
Is it branched?

Answer 17

Pharmaceutical packaging
No it is insoluble in water
No unlike starch

Question 18

Cellulose uses in pharmaceutical science:

Answer 18

HPMC is also known as “Hypromellose” – used in eye drops for dry eyes

Question 19

What is Dextran/dextrose?
What is it used as?

Answer 19

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

Question 20

What is the ionisation of acidic/basic groups on a polymer dependent on?
What can the ionic charge on a polymer impact?

Answer 20

pH (Henderson-Hasselbalch)
Molecular shape

Unionised- polymer contracted; low viscosity
Ionised (charged) - groups repel; expanded structure; increased viscosity

Question 21

pH-sensitive polymers:
How is Chitosan prepared?
Why is it useful?

Answer 21

-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

Question 22

pH-sensitive polymers:
Why are they important?

Answer 22

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

Question 23

When a water-soluble polymer enters solution you can often observe some distinct layers around the polymer mass. What are these layers?

Answer 23

From external first;
1. Diffusion layer
2. Gel layer
3. Infiltration layer
4. Polymer mass