Basic polymer properties Flashcards
Macromolecules
Molecules made of a large number of atoms
Polymers
Substances of a high molecular weight with repeating monomer units
Pharmaceutical applications of polymers
Drugs Adhesives Hydrogels Suspending agents Film coatings Packaging Giving sets Tablet matrices
If the polymer is polydisperse,
It contains a range of molecular weights
Gel Electrophoresis
Separates polymers using charge + molecular weight
What polymer structure is simeticone
Homopolymer
Chemical reactivity of polymer depends on
Monomers
Physical properties of polymer depends on
Arrangement of monomers
How the polymer chains interact with each other and/or the environment
What polymers do not have an exact molecular weight + why
Synthetic + naturally occurring polymers
- because they are polydisperse.
Mn
Number average molecular weight
Mw
Weight average molecular weight
Degree of polydispersity
Mw / Mn
What can water-soluble polymers do
- increase viscosity of solvent
- swell / change shape
- adsorb at surfaces
which makes them useful as suspending agents (carbomer, acacia)
Use for insoluble polymers
Form thin films for use in tablet coating, wound dressings, membranes
Rate of dissolution of a water-soluble polymer is dependent on…
molecular weight
- high molecular weight means stronger forces keeping chains together
- therefore more energy needed to break them
Velocity of penetration
(of a solvent into the bulk polymer)
S = kM^-A
What are constants in velocity of penetration
k + A
What does M mean in velocity of penetration
Polymer molecular weight
What does a negative A mean in velocity of penetration
S (velocity of penetration) is inversely proportional to the molecular weight
Pharmaceutical uses of water-soluble polymer
Wound-dressings Contact lenses Bulk laxatives Nappies Vehicles for drug delivery
Crosslinked water-soluble polymers can be come ____
Swollen
- large quantities of water can be retained leading to increase volume
How can polymer gels form
Swelling of a highly cross-linked polymer
Making dissolved polymer less soluble
Relation between viscosity and concentraion
Viscosity increases with polymer concentration
Polymer gels will possess a…
critical gelation concentration
- gel cannot be formed below this polymer conc
- depends on molecular weight
Classification of Gels
Type 1 = irreversible systems contact lenses)
Type 2 = heat-reversible (gelatin / agar)
A greater solubility parameter…
A more polar substance
Increasing cross-linking speeds of water-soluble polymer speeds up…
Dissolution
What solvent has an expanded open structure
Good solvent
What solvent has ideal conditions
Theta solvent
Poor Solvent
High polymer-polymer interaction = compact cotacted structure
Example of a good solvent
Water
example of a poor solvent
THF = tetrahydrofuran
How can charge of a polymer affect molecular shape
Neutral = polymer contracted, low viscosity Ionised = groups repel; expanded structure; increased viscosity
What structure would the polymer sodium alginate be in a good solvent
Expanded open structure
e.g. water
What would the polymer sodium alginate structure be in a poor solvent
Contracted, compact structure
Solubility parameter
s = ( △Hv - RT / V ) ^1/2
Measure of cohesion between like molecules
- Used to predict polymer swelling
v in solubility parameter
Molar volume
T in solubility parameter
Absolute temperature
R in solubility parameter
Gas constant
△Hv in solubility parameter
molar enthalpy (heat) of vaporisation
The greater the solubility parameter…
more polar the substance
What solvent has the highest solubility parameter
Water
Polymer at Low concentration
Isolated polymer chains
Shape + volume determined by polymer-solvent + intra-polymer interactions
Mark Houwick
n=KM^a
n = intrinsic viscosity
K + a = constants
M = molecular weight
a in the mark houwick equation a reflection of
Shape of the polymer
Shape of polymer with an a value of 1.8
Rod
Shape of polymer with an a value of 0.5-0.8
Random coils
Shape of polymer with an a value of 0
Spheres
Light scattering techniques
measure polymer molecular weight + hydrodynamic radius
Viscosity Rheological Flow techniques
Examine flow properties + polymer shape
Analytical ultracentrifugation
Separates polymers according to molecular weight
Gel electrophoresis
Separates polymers according to charge + molecular weight
Nuclear magnetic resonance
Conformation in solvent, structure
Differential scanning calorimetry
Used to examine interactions between polymer chains
Gel permeation chromatography
Separate polymers according to molecular weight
