CHARACTERIZATION, ANALYSIS, AND TESTING Flashcards
(106 cards)
analytical branch of polymer science
Polymer characterization
technique used to determine the
molecular properties, structure, and behavior of polymers
Polymer characterization
The information obtained from polymer characterization can also be
used for
process control and product quality assessment.
Characterization techniques are typically used to determine
molecular mass, molecular structure, morphology,
thermal properties, and mechanical properties
____________ molecular weights are observed in polymers with
very long chain
extremely large
The distribution of molecular masses can be summarized by the
number average molecular weight, weight average molecular weight,
and polydispersity
Some of the most common methods for determining these
parameters are
colligative property measurements, static light
scattering techniques, viscometry, and size exclusion
chromatography
There are four molecular weight
averages in common use
number-average molecular
weight, Mn
; the weight-average
molecular weight, Mw
; the zaverage molecular weight, Mz
;
and the viscosity-average
molecular weight, Mv
involves a count of the number
of molecules of each species, NiMi
, summed over i, divided by the total
number of molecules
The number-average molecular weight, Mn
If all species in a polymer sample have the same molecular weight (that
is, the polymer is
monodisperse
commonly used
as a simple measure of the polydispersity of the polymer sample
Mw/Mn polydispersity index (PDI)
Determination of
Molecular Weight
- end group analysis
- measurement of colligative properties
- light scattering
- Ultracentrifugation
- dilute solution viscosity
- gel permeation chromatography (GPC)
chemical method use for calculating the numberaverage molecular weight of polymer samples whose molecules contain
reactive functional groups at one end or both ends of the molecule.
end-group analysis
end-group analysis is limited to the determination of polymers with a molecular
weight of
less than about 20,000
methods of analysis under end-group analysis
✓Titrimetric method
✓Nuclear magnetic resonance (NMR)
✓mass spectrometry
✓vibrational spectrometry, like infrared and raman spectroscopy
Properties of solutions that depend on the number of molecules present
and not on the kind of molecules are called
colligative properties.
colligative properties include
boiling point elevation, freezing point depression,
and osmotic pressure.
Boiling point of the solution is __________ than
the pure solvent.
higher
the boiling point of a
solution of known concentration is compared
to that of the solvent at the same pressure
Ebulliometry (Boiling Point Elevation
It works by analyzing the melting behavior of a
substance as it is frozen. By measuring the time it
takes for a specific substance to melt at a certain
temperature, its molecular weight can be calculated.
Cryoscopy (Freezing Point Depression)
most important among
all colligative properties for the determination of
molecular weights of synthetic polymers
osmotic pressure
technique for the
determination of molecular masses of polymers
by means of osmosis.
Membrane osmometry
Membrane osmometry is useful to determine
Mn about
20,000-30,000 g/mol and less than
500,000 g/mol
important
technique for the determination of weight-average molecular weight, M
Light-Scattering
Method
