Exam 2 Polymers Flashcards
What are the two ways to make a polymer?
- condensation polymerization
2. addition polymerization
What is condensation polymerization?
- also called step polymerization
- consists of two or more (bifunctional) monomers carrying different reactive functional groups that interact with each other
- 1 part + 1 part = 2 parts → which can interact with another part or 2 parts or even 4 parts
- examples: nylon, polyamide, polyurethane, polyester
What is addition polymerization?
- also called free radical polymerization or chain polymerization
- consists of 3 main steps → 1) initiation (initiated by a radical) 2) propagation
3) termination (terminated by an inert molecule) → radical breaks the double bond and propagates until it gets terminated - examples: polyacrylate, polystyrene
What is the main difference between condensation polymerization and addition polymerization?
condensation polymerization → needs 2 or more monomers to form the polymer, creates polymer that are short little chains (like lil poop droppings)
addition polymerization → need a radical that initiates and propagates until something terminates the polymer, creates polymer that is long and more snake like
What are the 2 things that characterize polymers?
molecular weight and molecular weight distribution
What are the 2 things that characterize polymers?
molecular weight and molecular weight distribution
What does molecular weight consist of?
- number average (Mn)
2. weight average (Mw)
What are the two types of molecular weight distributions?
- monodispersed → Mn = Mw so polydispersity (Mw/Mn) is 1
2. polydispersed → Mw»_space; Mn so polydispersity»_space; 1 (has a greater range/distribution than monodispersed)
What is polydispersity and what is its equation?
polydispersity is a range/distribution of the weight of the polymer and is given by the equation Mw/Mn
What is the difference between monodispersed and polydispersed?
monodispersed is very homogenous in which all polymers have about the same weight
polydispersed is not homogenous in which the polymers have a range of weights
When given two batches of polymers with their Mn, Mw, and polydispersity, how do you know which batch is more homogenous?
the batch with the smaller polydispersity will be the more homogenous batch (have closer Mn and Mw values)
What happens when you have identical polymers?
the number average (Mn) and weight average (Mw) should be the same
What happens when you don’t have identical polymers and they have a range of weights?
the weight average (Mw) should be higher than the number average (Mn)
What is another characteristic that defines polymers?
crystalline versus amorphous
What are properties of crystalline polymers?
- linear polymer
- polymer can pack together in regular arrays at T < Tm
- manifests a sharp Tm → has a distinct melting temperature
- good barrier to drug diffusion → durable
- rigid at low temps and liquid at high temps
- first order
What are properties of amorphous polymers?
- is more common
- polymers with irregular structure
- polymer forms “glass” at T < Tg
- softens over a wide temperature range (Tg) → does not have a distinct melting temperature
- at low temp is rigid but and higher temps is rubbery → not defined as a single melting temp as it turns rubbery over time (more soft and pliable)
- second order
What is an analogy that describes crystalline and amorphous polymers?
spaghetti noodles are long and hard before cooking → crystalline
spaghetti noodles are all tangled after cooking → amorphous
What is glass transition temperature (Tg)?
the temperature range where a polymer changes from a hard, rigid or “glassy” state to a more pliable, compliant or “rubbery” state
What happens when T «_space;Tg?
polymers are hard, stiff, and glassy
What happens when T»_space; Tg?
polymers are rubbery and may flow
What type of dosage form shows a glass transition temperature?
chewable dosage forms (aka like nicotine gum) →
- contain a polymer with a Tg close to 37 degrees Celsius so that the gum is softened at mouth temperature
- chewing releases the nicotine quickly
- “parking” between the cheek and the gums slow down nicotine release → since the temperature is not as warm and is under the Tg
What is the advantage of using Tg?
can control the drug release
What are the different factors that can affect Tg?
- polymer length
- side chains
- crosslinking
- plasticizers
What is the importance of the factors that can affect Tg?
the factors change how difficult it is to make the polymer soft → the softer the polymer becomes, the drug will be released faster
How does polymer length affect Tg?
the longer the polymer, the higher the Tg
How do side chains affect Tg?
the bulkier the side chain, the higher the Tg → since it takes more energy the bulkier the group
How does crosslinking affect Tg?
the more the polymer is crosslinked, the higher the Tg → since it takes more energy to make a crosslinked polymer more mobile
How do plasticizers affect Tg?
- plasticizers are molecules that increase the entropy and mobility of the polymer chains
- lower the Tg when included in polymer products
- example is water → if water can get into the polymer, there is more moisture so Tg is lowered
Why is it not a good idea to keep medications in the bathroom?
moisture can get into the medications so Tg is lowered which can change the drug release
What are mechanical properties of polymers?
stress (force/area) and strain (deformation)
What is the slope of the stress v strain graph?
the slope is stress/strain which is the modulus (aka stiffness)
What is the AUC under the curve for a stress v strain graph?
toughness
What are important properties of elastic polymers (like fibers or highly crosslinked polymers)?
the linear stress v strain curve up to a breaking point (deform limitation)
What are important properties of rubbers or elastomers?
are able to deform 10-15 times their original lengths
With a stress v strain graph, what does a higher/steeper slope mean?
the steeper the slope, the more stiff (high modulus) the polymer is
With a stress v strain graph, a larger AUC means what?
larger AUC means more toughness
What is the difference between high modulus polymer and a low modulus polymer?
high modulus polymer is more stiff and is also more tougher than the low modulus polymer
What is the difference between a low modulus polymer and a rubber/elastomer?
the low modulus polymer will be stiffer (higher modulus) than the rubber but the rubber/elastomer will be tougher because it never breaks (has a higher AUC since it does not have a breaking point like the low modulus polymer does)
What are viscoelastic polymers?
- polymers that are neither purely elastic not purely fluid
2. show both elastic and viscous behaviors
What are the mechanical properties of molten polymers or concentrated solutions?
have Non-Newtonian flow (plastic, pseudoplastic, dilatant)
What is a hydrogel?
- crosslinked networks of hydrophilic polymers → chemical gels (covalently crosslinked) and physical gels (crosslinked via hydrogen bonding, hydrophobic interaction, or complexation)
- swell rapidly when placed in water → chain-water interaction, electrostatic repulsion, osmotic forces
- retain large volume of water in their structures
A hydrogel is an example of what?
a specific example of a polymer that is water soluble → like jello (considered a gelatin hydrogel)
Why do hydrogels swell rapidly when placed in water?
when water gets into the polymer, the polymer becomes charged and since charges repel, the polymer swells
What is an example of a chemical gel that is covalently crosslinked?
polyacrylamide gel
What are examples of cellulose based polymers?
- ethylcellulose (used for tablet coating)
- carboxymethyl cellulose (used as superdisintegrant and emulsifier)
- hydroxypropyl methyl cellulose (used as a tablet binder and coating)
What are examples of hydrocolloids (coats droplets so it is a hydrophilic polymer)?
- alginic acid (used as a thickening agent in suspensions)
2. chitosan (for mucoadhesive dosage forms)
What are examples of water soluble synthetic polymers (hydrophilic)?
- poly(ethylene glycol) aka PEG (used as a plasticizer, suppository base, stealth coating)
- poly(vinyl alcohol) (used as a tablet binder and coating)
What are examples of water insoluble synthetic polymers?
- poly(lactic-co-glycolic acid) (used for controlled drug release)
- polylactic acid (used for controlled drug release)
What is poly(lactic-co-glycolic acid)?
is a co-polymer of lactic acid and glycolic acid in which some sutures are made from this polymer
What are properties of water insoluble synthetic polymers?
they are hydrophobic which means they can stay in the body for a long time (degrades in months to a year) and can be degraded and reused in the TCA cycle and can be dissolved → biodegradable!
