exam 3 lecture 4 Flashcards
molecular weight
number average (Mn)
weight average (Mw)
molecular weight distribution
monodispersed: Mn = Mw –> narrow distribution
polydispersed: Mw»_space; Mn –> broad distribution
crystalline
linear polymer
polymer can pack together in regular arrays at T<Tm
manifests sharp Tm
good barrier to drug diffusion
amorphous
more common
polymers with irregular structure
polymers forms “glass” at T«Tg
softens over a wide temperature range
Tg (glass transition temp)
temperature range where polymer changes from hard, rigid, glassy to pliable, compliant, rubbery state
T«Tg = hard glass
T»Tg = rubbery and flow
chewable dosage forms Tg
have low Tg –> the gum softens at mouth temperature
ex - nicotine gum
factors affecting Tg
polymer length: longer is higher Tg
side chains: bulkier is higher Tg
crosslinking: more crosslinked is higher Tg
plasticizers: increase entropy and mobility of polymer chains –> lower Tg when included in polymer products
plasticizers
increase entropy and mobility of polymer chains –> lower Tg when included in polymer products
mechanical properties graph
stress (force/area) vs strain (deformation)
mechanical properties (EXAM QUESTION)
slope (stress/strain): modulus (stiffness)
area under the curve: toughness
elastic polymers: fibers or highly crosslinked polymers
- linear stress vs strain curve up to a break point
rubbers or elastomers:
- may deform 10-15 times their original lengths
hydrogels
crosslinked hydrophillic polymers
- chemical gels + physical gels
swell rapidly when placed underwater
- chain-water interaction, electrostatic repulsion, osmotic forces
retain large volume of water in their structures
cellulose-based polymers
ethylcellulose (tab coating)
carboxymethyl cellulose ( superdisintigrant ; emulsifier)
hydroxypropyl methyl cellulose (tablet binder, coating)
hydrocolloids
alginic acid (thickening agent in suspension)
chitosan (mucoadhesive dosage forms)
water-soluble synthetic polymers
poly (ethylene glycol) (plasticizer, suppository base, stealth coating)
poly(vinyl alcohol) (tablet binder, coating)
water- insoluble synthetic polymers
poly(lactic-coglycolic acid) (controlled drug release)
polylactic acid (controlled drug release