Exam 3 Flashcards
What is Mn a measure of in terms of polymers?
A number average
What is Mw a measure of in terms of polymers?
A weight average
What does polydispersity mean?
The molecular weight or weight average is greater than the Mn or number average. polydispersity >1
polydispersity = Mw/Mn
What is the glass transition temperature of polymers?
the temp range where a polymer changes from a hard, rigid, or glassy state to a more pliable, compliant, or rubbery state
What does polydispersity mean in terms of polymers?
a more broad distribution of molecular weight.
What does Tm mean for polymers?
crystalline melting temperature (Tm) - temperature at which a crystalline polymer converts to a liquid
what does it mean when T<Tm?
the (crystalline) polymer can pack together in regular arrays at T<Tm
What is a crystalline polymer?
A linear or uniform polymer; good durable barrier to drug diffusion
packs together in regular arrays at T<Tm
What is an amorphous polymer?
The most common; has an irregular structure
Forms glass at T<Tg
softens over a wide temperature range.
What is the Tg?
The glass transition temperature; the temp where a polymer changes from rigid and glassy to a more rubbery or pliable state.
What happens when the T<Tg
the polymer is hard, stiff, and glassy
What happens when the T»Tg?
Polymers are rubbery and may flow
What factors affect the Tg of a specific polymer?
polymer length, side chains, cross linking, and plasticizers.
Basically the longer, bulkier, and more cross-linked a polymer is, a higher temp is required to bring it to a rubbery/ pliable state.
What are plasticizers and what effect do they have on Tg?
Plasticizers increase the entropy and mobility of polymer chains and have a lower Tg when included in polymer products
