1. KE-100.3410 Polymer Properties
Steve Spoljaric, PhD

2. Polymer Properties (5 credits)
Learning outcomes:
After completing the course, the student understands:
1) The basics of polymer physics and structure hierarchy of polymers
2) The basics of the most important methods of polymer analysis
3) Theories of polymer rheology
4) Stability and degradation of polymers
5) The ability to calculate the above mentioned phenomena

3. Polymer Properties Content: Structure hierarchy in polymers
Theoretical aspects:
Polymer analysis
Physics
Rheology
Stability and degradation of polymers
Calculation of polymer properties

4. Lectures and corresponding book chapters (Fried)
Lecture I (Structure and Molecular Weight) – Chapters 1 and 3.3
Lecture II (Crystallinity) – Chapter 4
Lecture III (Spectroscopic analysis techniques) – Chapters 2.6 and 4
Lecture IV (Rheology) – Chapters 5 and 11
Lecture V (Solution fractionation and permeation) – Chapters 3.2 and 12.1
Lecture VI (Stability, degradation and microscopy) – Chapter 6

5. Schedule for the course
6 Lectures on Mondays from
Lecture notes available on MyCourses
5 Problem solving exercises on Thursdays from
Chemistry building, Luentosali 4, Room C301
Textbook for the course: Polymer Science and Technology, Fried JR.
Exam: at Luentosali1, Luentosali2
(Chemical Technology, Kemistintie 1)

6. Other recommended references
Spectroscopy of Polymers, Jack L. Koenig
Good for further information about spectrsocopy and charactersiaton (Lecture III)
Polymer Physics, Ulf Gedde
A good all-round textbook, includes some information about microscopy (Lecture VI)

7. Classification of polymers
Monomer and thus polymer
Oil (or coal, gas) based
Bio-based
Polymers
Synthetic
Natural
Polymerization mechanism
Step polymerization
Chain polymerization
Structure
Thermoplastic
Thermoset
Product
Biodegradable or stable

8. Structure-property correlations
Structure considerations:
Linear / branched / cross-linked
Thermoplastic / thermoset
Molecular weight / molecular weight distribution
Homopolymer – copolymer
Block, alternating, random, graft
Copolymer / blend
Properties:
Thermal properties
Glass transition temperature, melting temperature
Amorphous or partly crystalline polymer
Operating temperature range for continuous use
Mechanical properties
Tensile stress and strain, modulus, hardness, impact strength

10. Questions?
How much new material was in the first few slides? Was it mostly reviewing what you have learned before?
Have you completed the course ‘Polymeerien valmistus’ (Polymer synthesis)?
What would you like to know more about regarding polymers? What do you think will be the topics in this course?
Any comments or wishes at this moment?

11. Polymerisation overview
Step polymerisation
Chain polymerisation
Radical polymerisation
Emulsion polymerisation
Ionic polymerisation (anionic and cationic)
Co-ordination polymerisation
Living radical polymerisation
Atom Transfer Radical Polymerization (ATRP)
Stable Free Radical Polymerization (SFRP)
Reversible Addition-Fragmentation chain Transfer (RAFT)
Ring-opening polymerisation
Co-polymerisation

12. To begin with:
What affects the molecular weight in different polymerization mechanisms?
Step polymerization
(stoichiometric equivalence of functional groups)
Radical polymerization
(initiator concentration, chain transfer)
Living polymerization
(monomer and initiator concentration)
How is crosslinking achieved in thermoset materials?
What are the crosslinks?

13. Course content / overview
Structure and average molecular weights
Solid-state properties:
Crystallinity
Thermal transitions
Characterization methods:
Thermoanalytical methods (DSC, DMTA)
Structure analysis (FTIR and Raman, solution and solid NMR, fractionation SEC)
Rheological properties and their measurement
Solubility and gas permeability
Microscopy methods, X-ray analysis
Stability and degradation

14. Polymer Structure

15. Stereochemistry of polymerization
Conformation:
Different orientations of atoms and substituents in a molecule
Result from rotations around single bonds
Can be changed by bond rotations
Extended chain / Helix
Configuration:
Isomers differ in the spatial arrangement of their atoms and substituents; that can only be changed by breaking and reforming primary chemical bonds

16. Tacticity
Regularity in the configurations of successive stereocenters determines the overall order of the polymer chain:
If the R groups are randomly distributed on the two sides of the planar zigzag polymer, the polymer does not have order and is atactic
Ordered structures are isotactic and syndiotactic
When the sterocenter of each repeating unit has the same configuration the structure is termed isotactic
When the stereocenter alternate from one repeating unit to the next the structure is syndiotactic
Even more complicated structures can be seen in some 1,2-disubstituted polymers

17. Tacticity: structures
Atactic
Syndiotactic
Isotactic

18. Tacticity: influences
In general, isotactic and syndiotactic polymers are partly crystalline and atactic are amorphous
In addition to crystallinity, tacticity affects also other properties such as thermal and mechanical properties
The tacticity of a polymer is determined by several factors:
Polymerization temperature
Pressure
Catalyst
Solvent

19. Tacticity in commercial polymers
Isotactic
Atactic
Syndiotactic
Polypropylene (PP) used and sold is mostly isotactic but it is also possible to produce syndiotactic or atactic polymer
Polyvinylchloride (PVC) is usually atactic but contains some syndiotactic structures which results in some crystallinity in the material. It is also possible to produce highly syndiotactic and isotactic PVC

20. Isomerism
In chemistry, isomers are molecules with the same molecular formula but different chemical structures.
In other words, isomers contain the same number of atoms of each element, but have different arrangements of their atoms in space
Unsaturated carbons (double or triple bonds) result in different isomers:
1,3-butadiene (dienes in general)
Cis and trans isomers possible
Results in geometric isomerism (isotactic, syndiotactic or atactic)

21. Geometric isomerism
Geometric isomers have the same structural formulas but differ in the arrangement of groups at a single atom, at double bonds, or in rings
Polybutadiene isomers:
Isotactic
Isotactic
Syndiotactic

22. Optical isomerism (enantiomerism)
Optical isomers (also called enantiomers) are mirror images that are not superimposable (that is, they can’t be put on top of one another)
They differ in only one characteristic; their interaction with plane polarized light
More general in bio-based polymers
An example is synthetic polymer is poly(propylene oxide)

23. Lactic acid-based materials
Commercial optically-active polymers are lactic acid based
Lactic acid is available both in optically-active enantiomers as well as an optically-inactive racemic mixture
Synthetic lactic acid is always a mixture of the two isomers, whereas in bio-technically produced lactic acid the L/D ratio can be tailored with the fermentation process
Lactic acid based polymers are either optically-active or not depending on the monomer used

24. Lactic acid monomers D,L-lactic acid is a mixture of the two
D-lactic acid

25. Lactide monomers
Polylactide is polymerized with Ring Opening Polymerization (ROP)

26. Polylactides
Partly crystalline
PLA
Amorphous
PLA

27. Average molecular weights

28. Average molecular weights

29. Average molecular weights

30. Average molecular weights
Number average molecular weight:
Weight average molecular weight
Viscocity average molecular weight

31. Average molecular weights
Z-average molecular weight
Polydispersity
ni = Number of molecules with molecular weight Mi
wi = weight fraction with molecular weight Mi
a = constant, depends on polymer/solvent combination

32. Molar mass distribution for a narrow and broad polystyrene (molar mass averages are also given)

33. Molar mass vs. molecular weight
Molar mass is the mass of one mole of a substance
Molecular weight is the mass of one molecule of a substance

34. Determination of average molecular weights
Primary (absolute values) methods:
Osmometry (Mn)
Scattering (Mw)
Sedimentation (Mz) Z-average molecular weight is obtained from centrifugation data
Secondary (relevant to reference or calibration) methods:
Gel permeation chromatography (GPC), also called size exclusion chromatography (SEC) to obtain molecular weight distribution
Intrinsic viscosity for determining viscosity average molecular weight

35. Average molecular weight Range of molecular weight
Determination of average molecular weights
Method
Relative/ absolute
Average molecular weight
Range of molecular weight
Comments
Ebulliometry A
< 104
Insensitive
Cryoscopy
Small sample size
Membrane osmometry 5x
Difficulties with the membrane, slow measurement
Vapor pressure osmometry
< 3x104
Only few suitable solvents
End-group analysis
x104
Restricted to low molecular weights, assumption of 2 end-group/molecule
Light scattering
Insensitive for small molecules, slow measurement
MALLS, LALLS
Ultracentrifugation 2x
Slow measurement, expensive instrument
Viscometry S%
Simple measurement, inexpensive instrument
SEC (GPC)
all
Gives molecular weight distribution. Requires calibration.

36. Number average molecular weight

37. Number average molecular weight
Determination methods based on various phenomena or factors:
End groups
Property changes
Osmotic pressure
Increase in boiling point
Decrease in freezing point or vapour pressure

38. Osmometric measurement
Pure solvent and a dilute solution of polymer in the same solvent are placed on opposite sides of a semi-permeable membrane
Membrane will allow the solvent to pass through but will retain the polymer molecules in solution
In equilibrium the difference in the heights of the solvent and solution in capillaries can be used to calculate the osmotic pressure

39. Osmometric measurement
Van’t Hoff equation for the osmotic pressure of an ideal, dilute solution:
p = osmotic pressure
c = concentration
R = gas constant
T = temperature (K)
= number average molecular weight (g/mol)
g = gravitational constant m/s2
ρ = solvent density

40. Osmometric measurement
Van’t Hoff equation is for ideal, dilute solutions. In real solutions the equation will be following:
For the determination of molecular weight, 4-6 pressure measurements with different concentrations are required. When solutions are dilute enough, p/c can be obtained by extrapolation of c to 0. Average molecular weight can be calculated from:
Polymer concentration is g/dm3 and p/c in J/kg
B, C are virial coefficients

41. Osmometric measurement: determining π/c
PS in toluene
PS in acetone
c (g/dm3)

42. Osmometric measurement: challenges
Simple experimental procedure, but can be very time consuming
Performance of the membrane can be a problem
Membrane can let some smaller polymer molecules through and this will result in an artificially-higher Mn value
Thus, the method is considered accurate for molecular weights above 20,000 g/mol
The upper limit for molecular weight is 500,000 g/mol due to inaccuracy in measuring small osmotic pressures

43. Vapor-pressure osmometry
When a polymer is added to a solvent, the vapor pressure of the solvent is lowered due to the decrease in solvent activity
Osmometry uses two matched thermistors that are in a closed chamber containing saturated solvent vapor
A drop of solvent and a drop of dilute polymer solution is placed on thermistors
Condensation of solvent vapor onto the solution causes the temperature of the solution thermistor increase until vapor pressure of solution equals to that of a solvent

44. Vapor-pressure osmometry cont.
The difference in temperatures is recorded in terms of difference in resistance DR, which is calibrated by use of a standard low molecular weight sample
Several polymer concentrations are measured and extrapolation of DR/c to zero concentration yield Mn (requires calibration constant obtained with the standard sample hence VPO is secondary method)

45. Vapor-pressure osmometry: measurement principles
Closed chamber
Pure solvent
For the characterization of low molecular weight oligomers and polymers, vapor-pressure osmometry is recommended

46. Ebullioscopic method Tb = increase in Tb Kb = ebullioscopy constant
The determination of molecular weight, in which the differential thermometer is used to measure the rise in boiling point
Boiling point of the polymer solution is compared to the boiling point of the solvent. An increase in boiling point is comparable to polymer properties:
Top limit of the measurement is g/mol
Tb = increase in Tb
Kb = ebullioscopy constant
WA = mass of the polymer
WS = mass of the solvent

47. Cryoscopic method Kf = cryoscopic constant
Resembles ebullioscopy method
Compares the freezing point of a polymer solution and pure solvent
For dilute solutions:
Top limit of the measurement is g/mol
Kf = cryoscopic constant

48. End group method The structure of the polymer chain must be known!!!
End groups to be either quantitatively determined with appropriate reagents (titration) or determined by IR or NMR
IR: Number average molecular weight can be calculated assuming the chain is linear with no branch points
Number of end groups of the polymer is thus one or two per molecule
End groups are not spectroscopically coupled to the remainder of the chain, low molecular weight analogs can be used for calibration
Particularly useful for insoluble systems (eg. fluorocarbons)

49. Viscosity average molecular weight

50. Viscosity average molecular weight
Based on the determination of intrinsic viscosity of a polymer solution through measurements of solution viscosity
Widely used for routine molecular weight determination
Cheap equipment and simple measurement procedure
In this method, the viscosities of pure solvent and dilute polymer solutions are compared
To determine the molecular weight, the empirical constants K and a, that are specific for a given polymer, solvent and temperature, need to be known. Extensive libraries of the values for constants exist for different polymer solvent combinations

51. Staudinger equation hsp = specific viscosity
Staudinger equation is valid only for a relatively narrow molecular weight distribution
hsp = specific viscosity
c = solution concentration
Km = constant for specific polymer-solvent combination

52. Mark-Houwink equation
Mark-Houwink equation is valid for broad molecular weight distribution:
[h] = intrinsic viscosity
= viscosity average molecular weight
K and a = constants for particular polymer-solvent combination
For flexible polymer chains a is , for stiff and rod like chains a is 2.0.

53. Mark-Houwink equation: K and a constants
Values for the constants can be found in:
‘Polymer Handbook’, Bandrup, J., Immergut, EH. (ed.)
Some examples of polymer/solvent combinations

54. Viscosity parameters
Capillary viscometers are used to carry out the measurement:
Ostwald-Fenske or Ubbelodde type capillary
Constant temperature, typically 25 or 30°C
The time required for a dilute solution and pure solvent to pass through the capillary is measured
4-6 polymer solutions are measured
Efflux times need to be more than 100 s, which can then be used to calculate the relative viscosity:
t = efflux time for dilute polymer solution
T0 = efflux time for pure solvent
h = dynamic viscosity of the solution
h0 = dynamic viscosity of the solvent

55. Capillary viscometers (‘U’ tubes)
Ostwald
Uppelohde
Reverse flow
The time for the fluid to fall or rise between marks A and B determines the flow rate (Q)
The pressure drop (DP) is calculated from the head of fluid
The viscosity can be determined from these values and the geometry of the viscometer

56. Viscosity parameters
Specific viscosity can be calculated from viscosities or the efflux times:
The viscosity number or reduced viscosity is obtained by dividing specific viscosity by the solution concentration:
Molecular weight determination, Rheological measurements in Polymers: Polymer Characterization and Analysis, Ed. J.I. Krowchwitz, John Wiley & Sons Inc, 1990

57. Viscosity parameters Logarithmic viscosity number, inherent viscosity:
Limiting viscosity number, intrinsic viscosity is obtained from the parameters of logarithmic viscosities

58. Viscosity measurement
Unit used in concentration is g/cm3

59. Viscosity measurement
Measuring viscosity for several polymer solutions with different concentrations, the intrinsic viscosity can be determined graphically:
sp /C
 inh
 red C
Huggins/Kraemer Plot

60. Weight average molecular weight

61. Light scattering in nature
Why is the sky blue?
How can we see clouds?
Lord Rayleigh 1871
When light passes through matter, most of the light continues in its original direction but a small fraction is scattered in other directions
incident beam
scattered light
Notes: Simple questions about our everyday world, such as “Why is the sky blue?”, “How can we see clouds?”, or “Why are sunsets red?” have interesting answers that depend upon light scattering. In fact, it was the question of the blue sky and the polarization of skylight that lead Lord Rayleigh to develop a theoretical description of light scattering in 1871.
When light passes through matter, most of the light continues in its original direction. However, some of the light is scattered into new directions. A careful analysis of the scattered light can yield detailed information about the scattering system.

62. Light scattering in the lab
In the lab we can control polarization, wavelength (l) and intensity (Ii) of the coming light
We can detect the scattered light (Is) as a function of angle (q)
Scattered light is proportional to the concentration and molecular weight of the polymer
Notes: In the laboratory we can control the conditions to retrieve detailed information about the light scattering. We can choose the wavelength (l), polarization, and intensity (Ii) of the incident light. The size of the laser beam and the field of view of the detector define a scattering volume. We can detect the scattered light (Is) from this volume as a function of angle (q) and polarization.
With such exquisite control of the experimental parameters, we can use light scattering to retrieve fundamental physical properties of the scattering medium.

63. Light scattering
The weight average molecular weight can be obtained directly only by scattering experiments
Most commonly used is light scattering from dilute polymer solution
Polymer molecules in solution cause stronger scattering than solvent molecules
The intensity of the light is proportionate to the absolute molecular weight of the particle causing the scattering

64. Light scattering procedure
Polymer is dissolved in appropriate solvent
The particles have interactions in solution and self organize
Local changes in concentration and density in solution
Light scattering is observed in different angles
Measurements with several concentrations and angles

65. Light scattering
Intensity distribution of LS at various angles for a small particle (dashed line) and a large polymer molecule (solid line)

66. Light scattering instrumentation
Conventional LS instrumentation showing incident and scattered light, sample cell, and photomul’plier (Fried et al.)

67. Light scattering
In order to determine molecular weight, the following information must be known/determined:
Refractive index for the solvent
Difference between refractive indices for the solution and solvent
Polymer concentration
Absolute light intensity for certain scattering angles

68. Light scattering Rayleigh formula:
Problem is determining R(q) value, which should be known for all  values
n0 = refractive index for solvent
l = wavelength of the light
N0= Avogadro number
Rb= Rayleigh constant
I0= light intensity at 90o angle that scattered from solvent
c = polymer concentration in solution
 = measuring angle
R = measured intensity, contains the angle and correction for concentration

69. Low-Angle Laser Light scattering (LALLS)
Helium-Neon lasers have replaced conventional light sources in scattering instruments
The high intensity of the light sources permits measurements at much smaller angles (2–10 o). Then, the scattering by small spherical particles can be expressed:
Only at one single angle chain dimensions cannot be obtained

70. Multi-Angle Laser Light-Scattering (MALLS)
Several detectors (18 angles, 20–150 o )
Absolute molar mass (Mn, Mw, - Mz) and size (Rz , rh)
No standard references, more reliable than calibration techniques
Information about molecules and particles (conformation, branching, partly cross-linked fractions)
Co-polymer, protein, aggregate detection
Easy and fast to use

71. DAWN 8+ 8 angles (23-155 °) Molar mass range <10³-107 g/mol
Molecular size range nm
Laser wavelength 658 nm
(50mW GaAs linear polarized laser)
All solvents compatible (aqueous and organic)
photodiode detectors
incident beam

72. Gel permeation chromatography (GPC )
aka: Size-exclusion chromatography (SEC)

73. Gel permeation chromatography (GPC)
Most widely used method for routine determination of molecular weight and molecular weight distribution is GPC
Separates samples of polydisperse polymers into fractions of narrower molecular weight distributions

74. Principle of GPC:
Polystyrene gel
Polymer molecules

75. GPC measurement
Columns are packed with small, highly porous beads or gel
Pore diameters of the beads range from 10 to 107 Å
Approximately the dimensions of polymer molecules in solution
During GPC operation, pure pre-filtered solvent is continuously pumped through the columns at a constant flow rate. Then a small amount of dilute polymer solution is injected into the solvent stream and carried to through the columns
Polymer molecules diffuse from this mobile phase into the stationary phase in the pores. The smallest polymer molecules penetrate deeply into the pores whereas the largest molecules pass through the columns first

76. GPC measurement
Comprehensive Analytical Chemistry vol 53: Molecular Characterization and Analysis of Polymers, editors John M.Chalmers, Robert J. Meier, 2008

77. GPC measurement
The concentration of polymer molecules in each eluting fraction is monitored by a detector, such as IR
The elution volumes are calibrated with know Mn standards (PS and PMMA standards are most common)
Only apparent molecular weights are determined unless:
Molecular weight standards exist of the same composition and topology as the samples
LALLS or viscometry is used
Mark–Houwink parameters of the standards and sample are known

78. Solvent peak CHCl3
Typical GPC
3 sample curves overlaid

79. GPC distribution plot (data on following slide)

80. GPC results example, cont.
Room temperature, chloroform eluent, PS standards
Sample 1:
Weight average molecular weight 6040 g/mol
Number average molecular weight 2980 g/mol
Polydispersity (Mw/Mn) 2.0 (Think about the accuracy when reporting results)
Mp is the molecular weight of the standard at the peak maximum 6550 g/mol

81. GPC GPC is the most widely used technique for the analysis of polymers
Can be used for samples soluble in organic and aqueous eluents and molecular weights from approximately 100 to several million
Yields all molecular weight averages and the molecular weight distribution
The analysis of the molar mass distribution of polyethylene and polypropylene samples by GPC requires elevated temperature operation for dissolution
Room temperature GPC and GPC operating at higher temperature (for polyolefins 120ᵒC)

82. Effect of molecular weight on polymer properties

83. Properties dependent on Molecular Weights and Molecular Weight Distributions (MWD)
Polymer
Monodisperse (uniform)
Proteins, nucleic acids
Polydisperse (non-uniform)
All synthetic polymers
Melt Viscosity
Tensile Strength
Toughness or Impact Strength
Resistance to heat
Corrosive properties

84. Effect of the molecular weight on polymer properties
Great effect on properties
Some properties have a limit, like Tg and strength at break, whereas some can change without any limit as the molecular weight increases. Dependence of Tg on average molecular weight:
A and B are experimental constants
Tg, is glass transition temperature of a extremely high molecular weight polymer

85. Effect of the molecular weight on polymer properties
Many mechanical properties exhibit similar dependence on molecular weight:
P = property value
K’ = constant

86. Effect of the molecular weight on polymer properties
Tensile strength (Mpa)
Inverse of molecular weight (106/M)
Tensile strength of PS in proportion to molecular weight
Tensile strength (Mpa)

87. Effect of molecular weight and PDI on properties
Examples of how average molecular weight and molecular weight distribution affect different properties:
Property
Molecular weight increases
Molecular weight distribution narrows
Tensile strength +
Tensile strain -
Strength at yield
Ductility
Brittleness
Hardness
Softening point
Melt viscosity
Adhesion
Chemical endurance
Solubility o
Property:
+ = improves
- = worse
o = little effect

88. Crystallinity Thermal transitions
Next week:
Crystallinity
Thermal transitions