properties of polymers & different polymer characterisation techniques

1. POLYMER PROPERTIES AND
CHARACTERISATION
PRESENTED BY
ARCHANA S NAIR
MPHARM PART I
PHARMACEUTICS
1

2. CONTENTS
• Introduction
• Properties
• Molecular weight determination
• Vibrational spectroscopy
• Nuclear magnetic resonance spectroscopy
• Microscopy
• Thermal analysis
• X-ray diffraction methods
• Mechanical and rheological analyses
• Conclusion
• References
2

3. INTRODUCTION
• “Polymer” means “many parts.”
• Use of polymer in drug delivery is guided by various properties like;
 molecular properties
 bulk properties
• Polymer characterization is the process of determining the size,
structure and physical properties (such as thermal and mechanical
properties) of polymeric materials.
3

4. CRYSTALLINE AND AMORPHOUS
POLYMERS
• If the structure is linear, polymer chains can pack together in
regular arrays.
• For e.g.; polypropylene chains
• With increased temperature, the crystal cells (crystallites) start to
melt and the whole polymer mass suddenly melts at a certain
temperature.
• Amorphous structure is formed due to either rapid cooling of a
polymer melt in which crystallization is prevented.
4

5. CRYSTALLINE AND AMORPHOUS
POLYMERS
• Crystalline
▫ Ordered
• Amorphous
▫ Random
• Semi-crystalline
▫ Consists of both
5

6. CRYSTALLINE AND AMORPHOUS
POLYMERS
• Polymer strength and stiffness increases with crystallinity.
• With increase in crystallinity, the optical properties of a polymer are
changed.
• Crystallinity increases the barrier properties of a polymer
packaging.
• Crystallinity topology and isomerism, molecular weight,
intermolecular forces, rate of cooling etc.
• Anisotropy.
6

7. THERMAL TRANSITIONS
• Volume of a polymer can change with temperature as first or second
order transition.
• Tm – first order thermal transition.
• Tg – second order thermal transition.
7

8. GLASS TRANSITION TEMPERATURE
8

9. GLASS TRANSITION TEMPERATURE
• Rigid glass state – soft rubber state.
• 100◦C to above 300◦C.
• Important in solid dosage form.
• Tg of a polymer depend on many factors,
 length of polymer chain, side chain group.
 polymer chain flexibility.
 polymer chain branching, polymer chain cross linking.
 processing rate, plasticizers.
9

10. GLASS TRANSITION TEMPERATURE
10

11. 11

12. GLASS TRANSITION Vs MELTING
Glass Transition Melting
 Property of the amorphous region
 Below Tg: Disordered amorphous
solid with immobile molecules
 Above Tg: Disordered amorphous
solid in which portions of
molecules can wiggle around
 A second order transition
 Property of the crystalline region
 Below Tm: Ordered crystalline
solid
 Above Tm: Disordered melt
 A first-order transition
12

13. Techniques of Tg measurement
Differential scanning calorimetry
Refractive index
Dynamic mechanical measurements
Specific heat measurements
Thermo mechanical analysis
Thermal expansion measurement
Micro-heat-transfer measurement
Isothermal compressibility
Heat capacity
Elastic modulus or hardness
Broad-line NMR
13

14. IMPROVED PROCESSING AND HANDLING
QUALITIES – SPRAY DRYING
• Non-sticky and sticky products.
• Sticky products - difficult to spray dry.
• Remain as syrup or stick on the dryer wall, or form unwanted
agglomerates in the dryer chamber and conveying system .
• Mainly due to the low glass transition temperature (Tg) of the low
molecular weight sugars present in such products, essentially
sucrose, glucose, and fructose.
• For bulky side groups-T g is higher
14

15. GLASS TRANSITION IN SPRAY DRYING
15

16. IMPROVED DISSOLUTION AND BIOAVAILABILITY
• Indomethacin & nifedipine are poorly water soluble drugs exhibiting
dissolution rate limited oral bioavailability.
• Both are prepared as glass solutions.
• Glass solutions showed increased drug dissolution rate than
crystalline forms of drugs.
16

17. VISCOELASTIC PROPERTIES
• Neither a pure elastic nor a pure fluid material.
• Have ability to store energy and to dissipate it.
• Viscoelastic materials
• Eg: PVC
• Creep test , polymer is first loaded with a certain weight and its
deformation is then monitored over the time.
• Stress relaxation test, polymer is first deformed to a certain extent,
and then its stress relaxation is monitored with the time.
17

18. CREEP TEST
• Using a tensile specimen to which a constant stress is applied, often by the
simple method of suspending weights from it.
• Surrounding the specimen is a thermostatically controlled furnace, the
temperature being controlled by a thermocouple attached to the gauge
length of the specimen.
• The extension of the specimen is measured by very sensitive extensometer,
results of the test are then plotted on a graph
of strain versus time to give a curve .
18

19. STRESS RELAXATION TEST
• Determine a sample's creep properties when subjected to a prolonged
tensile or compressive load at a constant temperature. The rate of
deformation of a sample to stress at a constant temperature is known as the
creep rate. It is the slope created by the creep vs. time.
• If creep recovery is measured, the test will determine the stress-relaxation -
the rate of decrease in deformation that takes place when the load is
removed.
19

20. MECHANICAL PROPERTIES
• Polymers resist differently when they are stressed.
• Can resist against stretching, compression, bending, sudden stress,
and dynamic loading.
• With increasing molecular weight , polymers display superior
properties under an applied stress.
• Flexible polymer can perform better under stretching whereas a
rigid polymer is better under compression.
20

21. MECHANICAL PROPERTIES
21

22. MOLECULAR WEIGHT
• Average molecular weight-Fundamental characteristic of a polymer
sample.
• Controls the function of biomedical polymers.
• Pure sample contain molecules differing only in degree of
polymerization.
• Molecular weight may be
a) Number averaged molecular weight
b) Weight averaged molecular weight
c) Viscosity averaged molecular weight
d) z-averaged molecular weight
22

23. MOLECULAR WEIGHT
d) Viscosity average molecular weight
23

24. NUMBER AVERAGE MOLECULAR WEIGHT
• The number average molecular weight(Mn) is the statistical average
molecular weight of all the polymer chains in the sample.
• Mn can be predicted by polymerization mechanisms.
• Measured by methods that determine the number of molecules in a
sample of a given weight; for example, colligative methods such as
end-group assay.
24

25. WEIGHT AVERAGE MOLECULAR WEIGHT
• Molecular weight of a chain in determining contributions to the
molecular weight average.
• The more massive the chain, the more the chain contributes to Mw.
• Mw is determined by methods that are sensitive to the molecular
size rather than just their number, such as light scattering
techniques.
25

26. VISCOSITY AVERAGE MOLECULAR
WEIGHT
• The molecular weight of the polymer is measured by using
viscometer and the molecular weight obtained by this technique is
called viscosity average molecular weight.
• From the Mark-Houwink equation the relationship among the
molecular weight and viscosity are given below
26

27. Z- AVERAGED MOLECULAR WEIGHT
• Mz is especially sensitive to the presence of high molecular weight chains.
• Mz may be determined directly by sedimentation
equilibrium(ultracentrifugation) & light scattering.
27

28. TECHNIQUES TO DETERMINE MOLECULAR
WEIGHT
Methods Measured
Parameter
M.Weight
Measured
Upper Limit
(g per mole)
Membrane
osmometry
Osmotic pressure of
polymer solvent
Mn 5x10⁴
Light scattering
(LS)
Intensity of light
scattered by dilute
polymer solutions
Mw, Mz 1x10⁸
Gel permeation
chromatography
(GPC)
Elution volume of the
polymer
solution through a
GPC column
packed with porous
microparticles
Mn , Mw 1 x 108
Viscometry
Flow time of polymer
solution
through a capillary
M v 1 x 108
28

29. MOLECULAR WEIGHT
• The molecular weight of polymers can be determined by a number
of physical and chemical methods
• Light scattering
• Gel permeation chromatography (GPC)
• Viscometry
29

30. LIGHT SCATTERING
 Rayleigh scattering.
 Additional scattering shows presence of solute molecules, this may
be a function of the concentration, as well as their size and shape.
 By measuring differences in intensity of scattered light, averaged
size of polymer solutes and their molecular weights can be
determined.
30

31. LIGHT SCATTERING
31

32. GEL PERMEATION CHROMATOGRAPHY
32

33. VISCOMETRY
33

34. VISCOMETRY
34

35. VIBRATIONAL SPECTROSCOPY —
INFRARED AND RAMAN SPECTROSCOPY
• At low temperatures, a molecule will exist in its ground vibrational
state and will be excited to a higher vibrational state if radiant
energy is absorbed.
• ∆E is related to the frequency of radiation (µ) absorbed, and the
relationship is given by,
∆E = hµ
• The spectral transitions are detected by scanning through the entire
IR frequency.
35

36. VIBRATIONAL SPECTROSCOPY —
INFRARED AND RAMAN SPECTROSCOPY
• The energies of molecular vibrations of interest for analytical work
mostly correspond to wavelengths in the range 2.5 to 25 µm.
• Results in identification of the functional groups and the modes of
their attachment to the polymer backbone.
• Characterize the polymer’s molecular and material structure.
• Eg: Determination of level of amine groups in chitosan.
36

37. VIBRATIONAL SPECTROSCOPY —
INFRARED AND RAMAN SPECTROSCOPY
37

38. RAMAN SPECTROSCOPY
• Detects the inelastic scattering of photons by molecules.
• Provide a fingerprint by which molecules can be identified.
• Used to observe vibrational, rotational, and other low-frequency
modes in a system.
• The laser light interacts with molecular vibrations, photons or other
excitations in the system, resulting in the energy of the laser
photons being shifted up or down.
• The shift in energy gives information about the vibrational modes in
the system.
38

39. RAMAN SPECTROSCOPY
• Stokes shift.
39

40. RAMAN SPECTROSCOPY
40

41. NUCLEAR MAGNETIC RESONANCE
SPECTROSCOPY
• Microstructure and chain configuration of polymers, both in
solution and in the solid state.
• Identification of certain atoms or groups in a polymer molecule as
well as their positions relative to each other can be obtained by one-,
two- and three-dimensional NMR spectra .
• When a strong external magnetic field is applied to material
containing nuclei possessing property of spin, behave like bar
magnets -orientate themselves in two energy states, a low-energy
state & a high-energy state.
41

42. NUCLEAR MAGNETIC RESONANCE
SPECTROSCOPY
• The transition of a nucleus from one energy state to another occurs
if a discrete amount of energy is absorbed from an electromagnetic
radiation.
E = hV = 2µH0
• If the resonance frequency for all nuclei of the same type in a
molecule were identical, only one line or peak would be observed.
42

43. NUCLEAR MAGNETIC RESONANCE
SPECTROSCOPY
43

44. MICROSCOPY
• Characterization of polymer material ultrastructure.
• Used to examine the detailed shape, size and distribution of
polymeric micro and nanoparticles, and their interactions with
biological environments.
• These include traditional optical microscopy, scanning electron
microscopy (SEM), transmission electron microscopy (TEM) and
scanning probe microscopy (SPM).
44

45. OPTICAL MICROSCOPY
• Microstructural information with a resolution on the order of 1 µm.
• Imaging is carried out using both reflected and transmitted light.
• If the absorption coefficient varies regionally within a sample, when
a beam of light travels through such a sample, contrasting regions of
intensity will be obtained in the final image.
• For a specimen that can be prepared as a thin film, by
casting on the microscope slide, examination using
transmitted light is most useful
45

46. OPTICAL MICROSCOPY
• Two common are polarized-light microscopy and phase-contrast
microscopy.
• Former exploits the ability of crystalline materials to rotate the plane of
polarized light.
• Structure of polymer liquid crystals may also be studied using polarizing
microscopy.
• Reflected-light microscopy - topographical features of solid polymer
materials.
46

47. SCANNING ELECTRON MICROSCOPY
• SEM is very valuable electron microscopy technique with a
resolution of about 5 nm.
• A fine beam of electrons is scanned across the surface of an opaque
specimen, and an appropriate detector collects the electrons emitted
from each point.
• An image having a great depth of field and a remarkable three-
dimensional appearance is built up line by line.
47

48. SCANNING ELECTRON MICROSCOPY
• To produce stable images, the specimen is usually coated with a
conducting film prior to examination.
• The typical film thickness is about 20 nm.
• Coating materials can give a high secondary electron yield and thus
increase image contrast.
48

49. 49

50. TRANSMISSION ELECTRON MICROSCOPY
• Involves transmitting a beam of electrons instead of light through a
sample in a high-vacuum environment.
• Images and associated contrasts arise from regional differences in
electron densities.
• Resolution of about 1 to 100 nm.
• Specimen needs to be very thin in order to transmit electron beams
through the sample.
• Specimens are placed on copper grids or carbon-coated copper grids
and viewed through the holes in the grid.
50

51. TRANSMISSION ELECTRON MICROSCOPY
• Replication, heavy-metal staining, are widely used to increase image
contrast.
• Rapidly adjusted to provide electron diffraction pattern from a
selected area, facilitating the investigation of crystal structure and
orientation and particular morphological features to be identified.
51

52. TRANSMISSION ELECTRON MICROSCOPY
52

53. TRANSMISSION ELECTRON MICROSCOPY
53

54. SCANNING PROBE MICROSCOPY
• When a probe tip is brought very close to a surface, the physical
phenomenon, may be exploited to produce a three-dimensional
topographical image of the surface.
• The resolution is at the nanometre level.
• The most popular scanning probe microscopy (SPM) techniques include
 scanning tunnelling microscopy (STM)
 atomic force microscopy (AFM).
• AFM operates by measuring attractive or repulsive forces between a tip
and the sample surface, and can image samples both in air and in
liquids.
54

55. SCANNING TUNNELLING MICROSCOPY
• Imaging surfaces at the atomic level.
• STM is based on the concept of quantum tunnelling.
• A conducting tip is brought very near to a metallic semi conducting
surface, a bias between two can allow electrons to tunnel through
vacuum between them.
• Variations in the tunnelling current as the probe passes over the
surface are translated in to an image.
55

56. SCANNING TUNNELLING MICROSCOPY
56

57. ATOMIC FORCE MICROSCOPY
57

58. THERMAL ANALYSIS
• Structure dependent physical properties of the polymer are
measured as a function of temperature or time, while a polymer is
subjected to a controlled temperature program.
• The most common techniques are
 Differential scanning calorimetry (DSC),
 Thermal gravimetry (TG),
 Dynamic mechanical analysis (DMA).
• Used to identify and characterize both polymers and drug-loaded
polymeric delivery systems.
58

59. DIFFERENTIAL SCANNING CALORIMETRY
• Whenever a polymer undergoes a phase transition, temperature
tends to remain constant while energy is taken into the system.
• Differences between the energy acquired or released as a function of
temperature or time while subject to a controlled temperature rise.
• Useful for recording thermal transitions such as the glass transition
temperature Tg, melt temperature Tm, and degradation or
decomposition temperature TD.
• Used to characterize the liquid crystal state of organization and
other forms of self-assembly.
59

60. THERMAL GRAVIMETRY
 Used to measure the change in weight of a polymer sample while it
is heated, using a sensitive balance.
60

61. DYNAMIC MECHANICAL ANALYSIS
• Properties of a polymer are studied as it goes through a time-dependent
mechanical change.
• Analytical technique is able to give important information on polymer
relaxation processes and phase morphologies.
• Useful method for identifying segmental and side-chain motion within a
chain and can also be used to study copolymers and polymer blends.
• It is most useful for studying the
viscoelastic behaviour of polymers.
61

62. X-RAY DIFFRACTION METHODS
• Useful method for investigating arrangements of atoms or molecules
within a material.
• If there is an orderly arrangement of substructures within a material
with repeat distances of a similar magnitude to the wavelength of light
used (0.05–0.25 nm), interference patterns are produced.
• Such patterns provide information on the geometry of polymer
structures.
• Two methods used are
• Wide-angle x-ray scattering (WAXS)
• Small-angle x-ray scattering (SAXS).
62

63. WAXS
 Distance from sample to the detector is shorter and diffraction
maxima at larger angles are observed.
 Degree of crystallinity of polymer samples.
 Sample is scanned in a wide-angle X-ray goniometer, and the
scattering intensity is plotted as a function of 2θ angle.
 Crystalline solid consists of regularly spaced atoms (electrons) that
can be described by imaginary planes.
 Distance between these planes is called the d-spacing.
63

64. SAXS
• Value of angles used is from 1o to 5o.
• Useful in detecting large periodicities from 5 to 70 nm in a structure
such as lamellae or distribution of particles or voids in materials.
64

65. 65

66. MECHANICAL AND RHEOLOGICAL
ANALYSES
• It is a reflection of the polymers molecular properties.
• Carried out in order to establish if the polymer is fit for the purpose.
• Tensile properties of solid polymers can be characterized by their
deformation behaviour.
• Rubbery polymers - lower modulus or stiffness.
• Glass and semi crystalline polymers - higher moduli and lower
extensibility.
66

67. MECHANICAL AND RHEOLOGICAL
ANALYSES
 Used to obtain information related to the flow behaviour of polymer melts and
polymer solutions.
 Capillary and rotational rheometers.
 Polymer fluids are non-Newtonian in behaviour, mostly being shear- thinning or
pseudoplastic.
 Viscoelasticity is a unique property of certain polymers, which display both
viscous- and elastic-type behaviour at ordinary temperatures and loading rates.
 Useful way of assessing hydrogels
67

68. CONCLUSION
• Polymer materials have been used for the administration of
pharmaceuticals & play an important role in fabrication of various
controlled release and drug targeting systems.
• The use of a polymer for drug delivery is controlled by its molecular
properties.
• Considering the polymer’s functional properties, it is important that
adequate polymer characterization is available.
• Many methods available for the characterization of polymers.
68

69. REFERENCES
• Alfred martin. Physical pharmacy; (4): 556-92
• Alan.R.Katritzky, Sulev Sild. Quantitative structure – property
relationship correlation of glass transition temperature of high
molecular weight polymers: Journal of Chemical Information and
Modeling;Feb 1998(2):300-304
• P. Debye. Molecular weight determination by light scattering.The
Journal of Physical Chemistry;Jan 1947,51(1):18-32
69

70. REFERENCES
• A.W Craig, D.A Henderson. A viscometer for dilute polymer
solutions. Journal of polymer science; Jan 1956,Vol 10:124-32
• Heinz.W.Siesler. Vibrational spectroscopy of polymers.
International Journal for Polymer Analysis and Characterization;
Nov 2011,8(16)
• Swee Chye Yeo, A. Eisenberg. Advancement in Modern polymer
Technology Journal of Applied Polymer Science; April 1977,21(4):
875-898
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