Polymers and gels

Question 1

Polymers are polydisperse. What does this mean in terms of chain length?

Answer 1

Chain length cannot be controlled

Question 2

Range of chain length is called _______

Answer 2

polydispersity

Question 3

Polymers cannot be chiral. True or false?

Answer 3

False - they can

Question 4

What does isotactic mean?

Answer 4

All groups in polymer point upwards

Question 5

What does syndiotactic mean?

Answer 5

Groups in a polymer alternate up and down

Question 6

What does atactic mean?

Answer 6

Groups randomly alternate up and down

Question 7

What is the name given to a polymer made of charged monomers?

Answer 7

A polyelectrolyte

Question 8

If an acid is placed in contact with a basic pH, what will happen to the chains?

Answer 8

At basic pH, the acid will be ionised so groups will repel each other as they have the same charge. As they are charged, they will attach to water molecules and therefore the chains will swell and extend.

Question 9

If an acid is placed in contact with a solvent that is not polar, what happens to the chain?

Answer 9

The chain will contract

Question 10

Do water soluble polymers increase or decrease viscosity?

Answer 10

Increase viscosity

Question 11

Soluble polymers are used to create films and coating materials. True or false?

Answer 11

False - insoluble polymers are

Question 12

What are the pharmaceutical uses of polymers?

Answer 12

Excipients for tableting
Coating applications
Controlled release of drugs
Controlled delivery following parenteral administration
Ion exchange resins 
Adhesive polymers for skin delivery
Excipients for semi-solid preparations

Question 13

Carboxypolymethylene (carbomer)
Cellulose derivatives e.g. HPMC
Natural gums e.g. gum arabic and tragacanth are examples of what water _________ polymers ?

Answer 13

soluble

Question 14

PVP and PEG are water insoluble polymers. True or false?

Answer 14

False - they are water soluble

Question 15

What are water insoluble polymers used for?

Answer 15

The making of membranes, tubing and containers

Question 16

Why is it important to consider the permeability to gases when using water insoluble polymers?

Answer 16

Important for packaging materials. Polar films are more ordered and less porous therefore less oxygen permeable - less likely to degrade

Question 17

Why is it important to consider the drug’s affinity to plastics when using water insoluble polymers?

Answer 17

Because some drugs e.g steroids may adsorb on polyethene tubing

Question 18

What are gels?

Answer 18

Gels are jelly like materials, they are made of a cross-linked network and do not flow when they are in a steady state

Question 19

What are gels called when the polymer is hydrophilic?

Answer 19

Hydrogels

Question 20

What forms the backbone of a gel?

Answer 20

A polymeric network

Question 21

Type 1 gels are __________ systems of covalent bonds between macromolecules: chains have been cross-linked

Answer 21

irreversible

Question 22

Type two gels are held together by __________ bonds such as H bonds. They are reversible (often heat reversible)

Answer 22

intermolecular bonds

Question 23

Gels that are prepared with polymers that have different properties are called ___________

Answer 23

heterogels

Question 24

What percentage of gels does the liquid phase represent?

Answer 24

90% (apart from in pHPMA used in contact lenses - the fraction of polymers is much higher)

Question 25

What is syneresis?

Answer 25

solvent binds to gel -> chains are hydrophilic so swell -> back force so contract -> solvent is released

Question 26

What are the most common polymers used in gels?

Answer 26

cellulose derivatives
polysaccharides
poly(acrylic acid)

Question 27

The majority of pharmaceutical gels are type 1. True or false?

Answer 27

False - majority are type 2