introduction to polymers
DESCRIPTION
Introduction to Polymers. Kausar Ahmad Kulliyyah of Pharmacy, IIUM http://staff.iiu.edu.my/akausar. Contents. Polymers in drug delivery. Polymers in delivery systems: Examples. BLOCK COPOLYMERS. Consisting of block of two or more polymers - PowerPoint PPT PresentationTRANSCRIPT
Physical Pharmacy 2
1K A U S A R A H M A D
K U L L I Y Y A H O F P H A R M A C Y , I I U MH T T P : / / S T A F F . I I U . E D U . M Y / A K A U S A R
INTRODUCTION TO POLYMERS
CONTENTS
Polymers in drug delivery• Copolymer• Polysaccharides
Properties of polymers• Crosslink density• Molecular weight
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POLYMERS IN DRUG DELIVERY
use in drug delivery due to
Surface activity efficient stabilisers for colloidal drug delivery system
Gel forming capacity
rheological control
Formation of self-assembly structure
analogous to simple surfactants: solubilisation of sparingly-soluble drugs
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POLYMERS IN DELIVERY SYSTEMS:EXAMPLES
Polyurethane• elasticity• catheter
Polysiloxane/silicone• inert• implants
Polymethyl methacrylate• physical strength & transparency
Polyvinylalcohol• hydrophilicity & strength
Polyethylene• toughness & lack of swelling
Polyvinyl pyrrolidone• suspension capabilities
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BLOCK COPOLYMERS
• Consisting of block of two or more polymers
• Example is poly(ethylene oxide)-poly(propylene oxide) block copolymers:
H-OCH2CH2)a(OCH2CHCH3)b(OCH2CH2)cOH
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ADVANTAGE OF BLOCK COPOLYMERS
• degradation rate of polymers can be
controlled.
• can obtain controlled drug release
• protect compound from harsh environment • e.g. in stomach – in particular polymers containing
poly(lactic) acid or poly(glycolic) acid
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EXAMPLE OF BLOCK COPOLYMERS
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Poly(lactic) acid
Poly(glycolic) acid
POLYSACCHARIDES
• Mainly due to formation of gels in aqueous solutions
• Examples: • carrageenans• alginates• starch
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CHEMICAL STRUCTURE OF SOME POLYSACCHARIDES USED IN DRUG DELIVERY
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PROPERTIES OF POLYMERS
• High molecular weight
• Repeating units
• Exist as linear or branched
• Can be crosslinked
• Properties depend on the polymerisation of the
monomers
• Can be divided into homopolymers or copolymers
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TYPES OF COPOLYMERS
These can be further divided into:
1. Alternating
2. Block
3. Graft or branched
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NATURAL POLYMERS
• Chemical modification can be carried out
to change the properties
• Example: Crosslinking
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RIGIDITY
In decreasing order:
• Plastics• Rubbers• Elastomers
Can be related to the glass transition temperature
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STRUCTURE OF POLYMER
Linear Branched Crosslinked
Thermoset polymer
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CROSSLINK DENSITY
The extent of crosslinking in a polymer is expressed as the crosslink density
As number of crosslinks increases, the glass transition temperature increases.
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From: Florence & Attwood
MOLECULAR WEIGHT/TEMPERATURE & POLYMER PROPERTIES
MOLECULAR WEIGHT
Both natural and synthetic polymers do not have specific molecular weight
Molecular weight is normally expressed as an average
The range of molecular weight is described by the POLYDISPERSITY
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MOLECULAR WEIGHT DETERMINATION
Methods that can be used are:-
1. Chemical analysis
2. Osmotic pressure
3. Light scattering measurement
4. Gel permeation chromatography
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AVERAGE MW
• The averages can be in terms of:-• Number• Weight• Viscosity• Z (sedimentation)
• The above depends on the type of analytical method employed
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NUMBER AVERAGE MW
i
iin
n
MnM
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Determined by:1. Osmometry2. End-group titration 3. Colligative properties
WEIGHT AVERAGE MW
ii
iiw
Mn
MnM
2
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• Determined from1. Light scattering 2. Small Angle Neutron Scattering
(SANS) 3. Sedimentation velocity [Hiementz]
• Bias towards larger molecules
VISCOSITY AVERAGE MW
Determined by intrinsic viscosity
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a
ii
aii
vMn
MnM
/11
MARK-HOUWINK EQUATION
h = KMva
• ‘K’ and ‘a’ are the Mark-Houwink parameters and depend on polymer-solvent characteristics.
• rigid rods, a=2. • hard sphere, a=0. • good solvent, a=0.8
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Z-AVERAGE MW
Determined by sedimentation equilibrium
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2
3
ii
iiz
Mn
MnM
POLYDISPERSITY
• The ratio of Mw/Mn is the degree of
polydispersity
Mw/Mn > 1
• The smaller the ratio, the narrower is the
distribution in molecular weight of the
polymer
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MOLECULAR WEIGHT DISTRIBUTION
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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