Transcript Application of Polymers

PROPERTIES OF POLYMERS
K AU S A R AH M AD
K U L L I Y Y AH O F P H AR M AC Y , I I U M
H T T P : / / S T A F F . I I U . E D U . M Y / A K A U S A R
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CONTENTS
1. Polymerisation factors
2. Tg, Tm
3. Tensile strength
4. Diffusion coefficient
5. Permeability
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TOP MONOMERS
Ethylene
Propylene
Styrene
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TOP POLYMERS IN PHARMACEUTICALS?
Type
Application
Properties
Submit
through
LMS
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TYPES OF POLYMERS
Addition polymers:
break a double bond
to make a polymer
Condensation
polymers:
give by-product such
as water, methanol,
or hydrogen chloride
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REACTION MECHANISMS
• Addition->
• Chain-growth
• By free radical or
ion
e.g.
polyethylene
polypropylene
polystyrene
• Condensation->
• Step-growth
• By functional groups
e.g.
polyurethane
polyester
naturally occurring
polymers
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POLYMERISATION CONDITIONS
Bulk
polymerisation
Suspension
polymerisation
Emulsion
polymerisation
Seed
polymerisation
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DEGREE OF POLYMERIZATION
• (n)- the number of
monomer units that
have polymerized
together.
• Exercise: What are
the factors that
influence D.P.?
• D.P. values can be
as high as 10,000.
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Submit
through
LMS
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PHYSICAL PROPERTIES
Determined by:
flexibility of
the polymer
molecule
molecular
weight &
polydispersity
regularity of
the polymer
structure
strength of
intermolecular
forces
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PHYSICAL AND MECHANICAL
PROPERTIES
melting
point
boiling
point
solubility
melt
viscosity
tensile strength
tear strength
Tg
hardness/
crystallinity
puncture
strength
diffusion
coefficient
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POLYMER CRYSTALLINITY
Rigidity
The extent
of
crystallinity
in a
polymer
affects:
Fluidity
Resistance to diffusion of small molecules
in the polymer and solubility
Water/solvent uptake
Extent of leaching
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TENSILE STRENGTH
Tensile strength measures how difficult it is
to break a substance when stress is
applied to pull it apart.
Tensile strength generally increases with
molecular weight.
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[A] Stress at the Yield Point:
At this point the force of the
tensile pull is sufficient to
cause polymer chains to slip
past each other, and yield
occurs.
[C] Stress at Failure: At this level
of stress the polymer molecules
can no longer maintain cohesive
integrity and the sample breaks
[D]
Elongation
at Failure:
This is how
much the
sample can
stretch before
it breaks
stress
C
A
[B] Elongation
at the Yield
Point: Maximum
stretching before
yield failure takes
place
B
strain
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DIFFUSION IN A POLYMER
• J is the flux
• D is the diffusion
coefficient
• K is distribution
coefficient of the
permeant towards the
polymer
• C is the difference in
concentration at the
interface
• L is the thickness of the
polymer
The diffusion in a
solid although very
slow still obeys
Fick’s first law:
J = -DKC/L
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FACTORS INFLUENCING
DIFFUSION COEFFICIENT
Crystallinity
increases
Fillers
increase i.e.
reinforcing
filler
Crosslinking
increases
MW
increase
Diluent
decreases
Diffusion
coefficient
decreases
when:
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Size of drug
increases
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PERMEABILITY
describes the ability of molecules to diffuse
through a layer of polymer
for a tightly arranged polymer /high degree of
crystallinity, permeability is very low.
• The crystalline regions act as a barrier to
diffusing molecules
highest for a completely amorphous polymer
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NATURAL PERMEABILITY OF
POLYMERS
important in gas diffusion, water sorption, permeation &
dialysis.
Water-vapour permeability depends on polarity of
polymer
• Polar polymers are more ordered and less porous;
thus less permeable to oxygen
• Less polar polymers may allow oxygen to permeate
• However, less polar polymers have lesser affinity for
water.
Need to control hydrophilicity of polymer or use a
copolymer
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POLYMER FILM PREPARATION
The way a polymer film is prepared affects
the permeability
When a polymer film is prepared by casting,
gradual drying and the resultant shrinkage
gives a less porous film compared to a
polymer film prepared by ‘coacervation’
The difference would be in the number of
pores/voids, size and density of the film
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PHASE SEPARATION IN
POLYMER FILMS
Incompatibility
e.g. can be based
on solubility
parameter.
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Different polarity
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REFERENCES
Aulton, M. E. (1988). Pharmaceutics: The Science of dosage form
design. London: Churchill Livingstone.
Wise, D. L. (2000). Handbook of Pharmaceutical Controlled
Release Technology. New York: Marcel Dekker.
Chasin, M & Langer, R (1990). Biodegradable polymers as drug
delivery systems. New York: Marcel Dekker.
Vyas, S. P & Khar, R. K. (2002). Targeted and controlled drug
delivery. New Delhi: CBS.
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