Which plot represents an LCST for a polymer solution
the open up parabola, where the single-phase region is on top
When deciding the maximum operation temperature in semicrystalline polymers, should we consider the glass transition or melting temperature
Glass transition temperature. below Tg the amorphous regions are glassy and stiff. Above Tg, those amorphous regions become rubbery and mobile.
Why does lowering molecular weight reduces glass transition temperature of polymers
Lower molecular weight lowers glass transition temperature because shorter polymer chains are more mobile.
What is the flory-fox equation used for?
It is used to predict how a polymer’s glass transition temperature depends on molecular weight. As molecular weight increases, Tg increases and approaches a limiting value.
What method is used to measure glass transition and melting temperature?
DSC technique: power required to keep reference and sample monitored as sample is heated through transitions
True or False: Volume, enthalpy and entropy changes abruptly at the Tg
False
Name three factors that affect a polymer’s melting point
molecular weight, secondary interactions, side-group size, chain structure
Given that the Gibbs Thompson relation is: — define all the variables Tm, Tm0, sigma e, l, delta h sub f
sigma e: free energy per unit area (surface tension) of the “top” of the crystal
Tm0: equilibrium Tm of very large ideal crystals formed from fully extended chains
delta h sub f: entropy of fusion
Tm: melting temperature
l: crystal thickness, the longest length from side to side
as crystal thickness increases, the melting point approaches Tm0
from the modulus temperature plot, name regions 1-5
Top: Glassy region - hard
Glass transition
Rubbery plateau
Rubbery flow
Viscous flow - lube
For the modulus vs temperature plot, what is the type of polymer that represents the solid, dashed, and dotted line
dashed - semicrystalline
dotted - cross-linked
solid - crystalline
What governs the modulus of a polymer in the rubbery plateau region?
the number of cross links and chain length between entanglements
How do you determine solubility - how do you determine what polymer has the best solubility in a solvent
if their Hildebrand values are the same/similar the polymer will be soluble
What is the rouse model used for
unentangled melts - rouse model explains the dynamics of unentangled polymer melts but not polymer solutions
rouse time is the time taken for the polymer to travel a distance equivalent to its size
what is the zimm model used for
unentangled polymer solutions - the zimm time is the time taken for the polymer to travel a distance equivalent to its size in a solvent
what is the reptation model used for
entangled melts - the rep time is the time for the chain to diffuse out of the tube
