Transcript Introduction to polymers

Introduction to polymers
Definition, classifications, chemical/physical properties,
some structures, applications
Rheology
Viscosity, newtonian and non-newtonian flow,
rheograms, application in pharmaceutics
Colloids
Lyophilic, lyophobic, association
Introduction to polymers
Poly = many, mer = unit, many units
Classification:
Homochain polymers
Heterchain polymers
Polymerization
• Addition
• Condensation
Initiation:
R-CO-O-O-CO-R  2 R-CO-O*
R-CO-O* + H2C=CH-C6H5  R-CO-O-CH2-C*H-C6H5
Propagation: Mn-CH2-CHR* + H2C=CHR  Mn-CH2-CHR-CH2-CHR*
Termination: Mn-1-CH2-CHR* + Mm-1-CH2-CHR*
 Mn-1-CH2-CHR-CHR-CH2-Mm-1
Polymers
• Homopolymers
(A-A-A-A-A-A)
• Copolymers
-- Random copolymer
A-A-B-A-B-B-B-A-A-B-A-B-
-- Alternating copolymer
A-B-A-B-A-B-A-B
-- Block copolymer
A-A-A-A-B-B-B-B-B-A-A-A
Types of polymers
• Thermoplastics (material that is plastic or deformable,
melts to a liquid when heated and freezes to a brittle, glassy state
when cooled sufficiently), polystyrene, polyethylene
• Thermosets (cannot be melted and remolded)
phenolic resins, urea-formaldehyde resin
• Elastomers
Rubbers
Chemical, physical properties
• Molecular weight:
Number average Mw = ∑ Xi Mwi
Weight average Mw = ∑ wi Mwi
• Conformation of
polymers dissolved in
solutions (molecular
interactions)
-- Randomly coiled linear polymer
-- Very dilute polymer solution
-- Gel state of polymers
(elastmers)
Intramolecular interactions
Diluted polymer solution and gel
Polymer blend
Poly (Vinyl alcohol)-(vinyl pyrrolidone), PVA-PVP
Structures of selected polymers
Sodium alginate
Sodium carboxylmethycellulose
methylcellulose
Carbopol
hydroxypropylmethylcellulose
Pharmaceutical applications
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Pharmaceutical excipients
Drug delivery (PLGA microparticles)
Hydrogels
Adhesive biomaterials
Pharmaceutical excipients
• Coat tablets: Microcrystalline cellulose (MCC), sodium
carboxylmethylcellulose (NaCMC), hydroxypropylmethycellulose (HPMC),
hydroxyethylcellulose (HEC), Hydroxypropylcellulose (HPC), PEG,
povidone
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Binder: acacia, gelatin, sodium alginate
Disintegrants: Starch, carboxymethylstarch, povidone
Plasticizer, PEG
Thickening agents: xanthan gum (a natural gum polysaccharide
used as a food additive and rheology modifier )
PLGA microparticles
Prolonged release
Leuprolide release from
PLGA microparticles
Treat endometeriosis
Prostate cancer
Treat growth deficiency
Rheology
• Rheo = flow
• Viscosity (h, poise) is an
expression of the resistance of a
fluid to flow (1 p = 0.1 Pa.s)
• Fluidity (f) = 1/h
• Newton’s theory
Newton’s theory
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F’/A = h dn/dr; h = F/G;
G = dn/dr = velocity gradient/rate of shear
F = F’/A = shear stress
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Rate of shear is directly proportional to
shearing stress.
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Kinematic viscosity = h/ ( is density)
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Effect if temperature on viscosity
h = A e EvRT (A is a constant, Ev is the
activation energy required to initiate flow
between molecules
Newtonian and non-newtonian systems
Rheograms of different fluids
Viscosity vs. Shear rate
Non-newtonian systems
1. Bingham plastic flow
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does not begin to flow until a shear stress
corresponding to the yield value is exceeded.
Flocculated colloid particles
2. Pseudoplastic flow
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Typically exhibited by polymers in solution (tragacanth, sodium
alginate, methylcellulose, NaCMC)
Viscosity decreases with the increase of shear rate/shear thinning
Caused by the re-alignment of polymer and/or the release of
solvents associated with the polymers.
3. Dilatant flow
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Volume increases when sheared
Shear-thickening
Suspension containing a high concentration of small, deflocculated particles
Thixothropy and anti-thixotropy
Thixotropy in formulation
• Procaine benzylpenicillin
• Procaine benzylpenicillin, also known as procaine
penicillin, is a combination of benzylpenicillin with the
local anaesthetic agent procaine. Following deep
intramuscular injection, it is slowly absorbed into the
circulation and hydrolysed to benzylpenicillin – thus it
used used where prolonged low concentrations of
benzylpenicillin are required.
• This combination is aimed at reducing the pain and
discomfort associated with a large intramuscular
injection of penicillin. It is widely used in veterinary
settings.
Colloids
• a mixture in which one substance is divided into
minute particles (called colloidal particles) and
dispersed throughout a second substance.
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Size: 1 nm to 0.5 mm
Visible under electron microscope
Not resolved by ordinary microscope
Do not pass through semipermeable
membrane
Type of colloid systems
1. Lyophilic colloids (solvent-loving)
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Systems containing colloidal particles that interact to an appreciable
extend with the dispersion medium.
Acacia in water or celluloid in amyl acetate lead o the formation of a sol.
Solvation, hydration, hydrophilic sols (gelatin, acacia, insulin, albumin in
water), lipophilic sols (rubber, polystyrene in non-aqueous solvents)
2. Lyophobic colloids (solvent-hating)
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Colloids are composed of materials that have little attraction, if any, for
the dispersion medium.
No solvent sheath around the particles
Gold, silver, arsenous sulfide, silver oxide in water
3. Association colloids
Classification of colloids