Lecture 17 Flashcards
Pharmaceutical Polymers - Yeo
nitrocellulose
gun cotton, 1845
the first semisynthetic polymer
discovered by Christina Schonbein in Basel, Switzerland in his kitchen
Bakelite
1907
first synthetic polymer based on phenol and formaldehyde
discovered by Leo Baekeland
strong and durable
substitute for parts in auto and electric industries
history of polymers
polyethylene (1933) –> Polyvinyl chloride (1933) –> Polystyrene (1933) –> Polyamide (1935) –> Teflon (1938) –> Synthetic Rubbers (1942)
polyethylene
discovered in 1933
used to insulate radar equipment for airplanes
polyamide
discovered in 1935
nylon (wallace carothers at DuPont) to replace silk
used in parachutes
teflon
discovered in 1938
used in atomic bombs to isolate hot isotopes of uranium
synthetic rubbers
discovered in 1942
1h to synthesize (7 years of natural rubbers)
used for tires and military supplies
polymers in pharmaceutical and biomedical products
controlled drug delivery
scaffolds for tissue engineering
oral drug delivery
transdermal patches
oral drug delivery types
coating
binders
taste maskers
protective agents
polymer
a large molecule made up of many small repeating units (parts)
macromolecules
any large molecule
not necessarily those made of repeating units
polymers are subsets
plastics
plastic materials that can be molded, cast, extruded, drawn, thermoformed, or laminated into a product
natural polymer examples
nucleic acids (DNA,RNA)
proteins (gelatin)
polysaccharides (cellulose, chitosan, alginic acid)
synthetic polymer examples
polyethylene
poly(vinyl chloride)
poly(tetrafluoro ethylene) aka teflon
polyurethane
polyacrylate
poly(p-phenylene terephthalamide) aka Kevlar
nylon
silicon rubber
rayon
polymer naming
in repeating units
poly(repeating unit)
types of structures
homopolymer (all the same)
random copolymer (random insert of different type)
alterante copolymer (every other type)
block copolymer (type 1 then type 2)
graft copolymer (side chain of different type)
linear structure
increased
- viscosity
- processability
- solubility
cross-linked structure
connected at different points in the polymer
increased
- glass transition temperature
- swellability
- rigidity
- thermal stability
condensation polymerization
also known as step polymerization
two or more (bifunctional) monomers carrying different reactive functional groups interact with each other
example - nylon
addition polymerization
also known as free-radical polymerization or chain polymerization
stages: initiation (by radical), propagation, and termination (by an inert molecule)
example - polyacrylate, polystyrene
types of polymer synthesis
condensation polymerization (small grouping)
addition polymerization (chains)
monodispersed
number average (Mn) = weight average (Mw)
polydispersity (Mv/Mn): 1
polydispersed
weight average (Mw)»_space; number average (Mn)
polydispersity»_space; 1
crystalline
linear polymer
polymer can pack together in regular arrays at T < Tm
manifests a sharp Tm
good barrier to drug diffusion
durable
first order (Tm)
specific volume (diagonal, up, diagonal)
enthalpy (straight, V, straight)
amorphous
more common
polymers with irregular structure
polymers forms “glass” at T < Tg
softens over a wide temperature range (Tg)
Glass transition temperature (Tg)
temperature range where a polymer changes from a hard, rigid, or glassy state to a more pliable, compliant, or rubbery state
at T «_space;Tg
polymers are hard, stiff, and glassy
at T»_space; Tg
polymers are rubbery and may flow
chewable dosage forms
example - nicotine gum
contain a polymer with Tg close to 37 degrees C so that the gum is softened at mouth temperature
chew would then release nicotine quickly
parking it between cheek and gums slow down nicotine release
factors affecting Tg
polymer length
side chains
crosslinking
plasticizers
polymer length
the longer, the higher Tg
side chains
the bulkier, the higher Tg
crosslinking
the more crosslinked, the higher Tg
plasticizers
molecules that increase the entropy and mobility of the polymer chains
lower Tg when included in polymer products
example - water
high Tg components
longer polymer length
bulkier side chains
more crosslinked
less plasticizers
mechanical properties
stress vs strain
slope
area under the curve
elastic polymers
rubbers or elastomers
stress vs strain
force/are VS deformation
slope
stress/strain
: modulus (or stiffness)
area under the curve
: toughness
elastic polymers
test linear stress vs strain curve up to breaking point
deform limitation
example - fibers; highly crosslinked polymers
rubbers or elastomers
may deform 10 to 15 times their original lengths
hydrogels
crosslinked networks of hydrophilic polymers
swell rapidly when placed in water
retain large volume of water in their structures
chemical hydrogels
covalently crosslinked
physical hydrogels
crosslinked via hydrogen bonding, hydrophobic interaction, or complexation
reason for hydrogels swelling rapidly
chain-water interaction
electrostatic repulsion
osmotic forces
polymers in dosage forms
cellulose-based polymers
hydrocolloids
water-soluble synthetic polymers
water-insoluble synthetic polymers
cellulose-based polymer examples
ethylcellulose (tablet coating)
carboxymethyl cellulose (superdisintegrant; emulsifier)
hydroxpropyl methyl cellulose (tablet binder, coating)
hydrocolloids examples
alginic acid (thinking agent in suspension)
chitosan (mucoadhesive dosage forms)
water-soluble synthetic polymers examples
poly(ethylene glycol) (plasticizer, suppository base, stealth coating)
poly(vinyl alcohol) (tablet binder, coating)
water-insoluble synthetic polymers examples
poly(lactic-co-glycolic acid) (controlled drug release)
polylactic acid (controlled drug release)
