13 Polymer Physicals Properties Flashcards
Structure: Polymer architecture
Properties: Crystallinity, viscosity,
mechanical properties
Structure: Molecular weight and
distributions
Properties: Melting point, viscosity,
solubility
Structure: Additives (Plasticizers)
Properties: Mechanical properties
Structure: Stereoregularity
properties: Crystallinity, solubility
Polymer architecture
- linear
- Comp
- Branched
- Star
- Dendritic
- Crosslinked
High vs low density
Linear=high
branched = low
Molecular weight affects
affect solubility, strength, viscosity, among other
properties.
Number average molecular weight (𝑴𝒏)
sum( number of polymer chains of a given mass (Ni) *molecular weigh (Mi)/sum
use colligative properties (i.e. osmotic
pressure) to determine MW we obtain a
number-average molar mass.
Weight average molecular weight (𝑴𝒘)
=sum(NiMi^2)/sum(NiMi)
If light scattering measurements are used to
determine MW, a weight average (Mw
) is
obtained. Mw
is biased towards higher
molecular weight polymers.
Mv
viscosity average molecular weight. Useful
to compare viscosity of polymer chains.
Mz
centrifugation average molecular weight.
Useful for describing mechanical properties.
Rank all the M
Mz > Mw > Mv > Mn.
number of molecules is opposite
What is PDI
Polydispersity = Mw/Mn
Provides a measure of the heterogeneity of
polymer lengths.
Degree of poymerization
DPn = Xn = Mn/M0
Number average number of repeat units in chain
what is M0
MW monomer
MW and mechanical strength
MW below certain point poly no mechanical strength
MW increases
beyond that point, mechanical strength
increases rapidly
At a given chain length,
the increase in MW does not significantly
change the mechanical strength of the material
Mw and processing
- Large MW increases mechanical
strength/viscosity. (Increased viscosity undesirable for melt extrusion/injection molding
.
– Broad MW favor low
softening point.
– Narrow MW distribution favors crystallization.
Crystalline vs. amorphous domains polymers
- Polymers have
crystalline and amorphous
domains. - # domains impactsmechanical strength
Glass transition temperature (Tg)
- Temperature below which a material has
properties similar to that of a glass (rigid,
brittle). - Above Tg
the material is elastic.
Tuning Tg
Plasticizers interfere with intermolecular
interactions between the chains,
- plasticizers reduce theTg
Tg vs Tm
Tm involves change in latent
heat where Tg does not.
Thermoplastics
amorphous polymer with a
Tg
above room temperature. Polymer can be
reversibly shaped by heating while applying a
stress before cooling.
Elastomer
An amorphous polymer with a Tg
below room temperature
Thermosets
Soft solid or liquid that crosslinks
upon heating (a process known as curing). After
curing the shape of the polymer is irreversibly
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