1. Polymer Structures and Properties
Polymer Research Center
Institute of Applied Chemistry of NCTU
Polymer Structures and Properties
Dr. Ying-Chieh Yen 嚴英傑
Ref: INTRODUCTION TO POLYMERS 2nd edition, R. J. Young and P. A. Lovell.

2. Polymer Structures Polymer Research Center
Institute of Applied Chemistry of NCTU

3. Basic Definitions and Nomenclature
Polymer Research Center
Institute of Applied Chemistry of NCTU
Basic Definitions and Nomenclature
A polymer is a substance composed of molecules which have long sequences of one or more species of atoms or groups of atoms linked to each other by covalent bonds.
The words, polymers and macromolecules are used interchangeably, the latter strictly defines molecules of which the former is composed.

4. Basic Definitions and Nomenclature
Polymer Research Center
Institute of Applied Chemistry of NCTU
Basic Definitions and Nomenclature
Macromolecules are formed by linking together monomer molecules through chemical reactions, the process by which this is achieved being known as polymerization.

5. Molecular Mass and Polydispersity
Polymer Research Center
Institute of Applied Chemistry of NCTU
Molecular Mass and Polydispersity
Number average molecular mass ( ):
Weight average molecular mass ( ):
The ratio must be greater than unity for a polydisperse polymer and is known as the polydispersity or heterogeneity index.
A perfectly monodisperse polymer would have polydispersity = 1.00.

6. Classification of Polymers
Polymer Research Center
Institute of Applied Chemistry of NCTU
Classification of Polymers

7. Classification of Polymers
Polymer Research Center
Institute of Applied Chemistry of NCTU
Classification of Polymers
Thermoplastics: It often referred to just as plastics (linear or branched polymers) which can be melted upon the application of heat.
Crystalline: Those which do crystallize invariably do not form perfectly crystalline materials but instead are semi-crystalline with both crystalline and amorphous regions. (Tm)
Amorphous: Many thermoplastics are completely amorphous and incapable of crystallization. (Tg) At the temperature, thermoplastics transform abruptly from the glass state (hard) to the rubbery state (soft).

8. Classification of Polymers
Polymer Research Center
Institute of Applied Chemistry of NCTU
Classification of Polymers
Elastomers are rubbery polymers (i.e. rubbery networks) which can be stretched easily to high extensions (e.g. 3x to 10x their original dimensions) and which rapidly recover their original dimensions when the applied stress is released.
Thermosets normally are rigid materials and are network polymers in which chain motion is greatly restricted by a high degree of crosslinking.

9. Skeletal Structures Linear structure: A chain with two ends.
Polymer Research Center
Institute of Applied Chemistry of NCTU
Skeletal Structures
Linear structure: A chain with two ends.
Non-linear structures:
Branched structure: Side chains, or branches, of significant length bonded to the main chain at branch points (junction points).

10. Skeletal Structures Non-linear structures:
Polymer Research Center
Institute of Applied Chemistry of NCTU
Skeletal Structures
Non-linear structures:
Network structure (crosslinked): Polymers have three-dimensional structures in which each chain is connected to all others by a sequence of junction points and other chains.

11. Polymer Research Center
Institute of Applied Chemistry of NCTU
Homopolymers
The formal definition of a homopolymer is a polymer derived from one species of monomer.
However, it often is used more broadly to describe polymers whose structure can be represented by multiple repetition of a single type of repeat unit.

12. Some Common Homopolymers
Polymer Research Center
Institute of Applied Chemistry of NCTU
Some Common Homopolymers

13. Some Common Homopolymers
Polymer Research Center
Institute of Applied Chemistry of NCTU
Some Common Homopolymers

14. Some Common Homopolymers
Polymer Research Center
Institute of Applied Chemistry of NCTU
Some Common Homopolymers

15. Polymer Research Center
Institute of Applied Chemistry of NCTU
Tacticity
For polymers prepared from monomers of the general structure CH2=CXY, where X and Y are two different substituent groups, there are two distinct configurational arrangements of the repeat unit.

16. Tacticity Isotactic: Syndiotactic: Atactic: Polymer Research Center
Institute of Applied Chemistry of NCTU
Tacticity
Isotactic:
Syndiotactic:
Atactic:

17. Polymer Research Center
Institute of Applied Chemistry of NCTU
Copolymers
The formal definition of a copolymer is a polymer derived from more than one species of monomer.
However, it often is used more broadly to describe polymers whose molecules contain two or more different types of repeat unit.

18. Polymer Research Center
Institute of Applied Chemistry of NCTU
Copolymers
Statistical copolymers: The sequential distribution of the repeat unit obeys the statistical laws. (Markovian)
Random copolymers: A special type of statistical copolymer in which the distribution of repeat units is truly random. (Older textbooks and scientific papers often use the term random copolymer to describe both random and non-random statistical copolymers.)

19. Polymer Research Center
Institute of Applied Chemistry of NCTU
Copolymers
Alternating copolymers: Only two different types of repeat units are arranged alternately along the polymer chain.
Block copolymers: Linear copolymers with repeat units existing only in long sequences or blocks.

20. Polymer Research Center
Institute of Applied Chemistry of NCTU
Copolymers
Graft copolymers: Branched polymers with the branches having different chemical structure to that of the main chain.

21. Polymer Properties Polymer Research Center
Institute of Applied Chemistry of NCTU

22. Polymer Research Center
Institute of Applied Chemistry of NCTU
The Glass Transition
If the melt of a non-crystallizable polymer is cooled it becomes more viscous and flows less readily. If the temperature is reduced low enough it becomes rubbery and then as the temperature is reduced further it becomes a relatively hard and elastic polymer glass.
The temperature at which the polymer undergoes the transformation from a rubber to a glass is known as the glass transition temperature, Tg.

23. Polymer Research Center
Institute of Applied Chemistry of NCTU
The Glass Transition
There is a dramatic change in the properties of a polymer at glass transition temperature. For example, there is a sharp increase in the stiffness of an amorphous polymer when its temperature is reduced below Tg.
There are also abrupt changes in other physical properties such as heat capacity and thermal expansion coefficient.
There have been attempts to analyse the glass transition from a thermodynamic viewpoint.

24. Polymer Research Center
Institute of Applied Chemistry of NCTU
The Glass Transition
In the first-order transition there is an abrupt change in a fundamental thermodynamic property such as enthalpy, H or volume, V, whereas in a second-order transition only the first derivative of such properties changes.
This means that during a first-order transition, such as melting, H and V will change abruptly whereas for a second-order transition changes will only be detected in properties such as heat capacity, Cp or volume thermal expansion coefficient, α which are definded as:

25. Polymer Research Center
Institute of Applied Chemistry of NCTU
The Glass Transition
As both of these parameters are found to change abruptly at the glass transition temperature it would appear that it may be possible to consider the glass transition as a second-order thermodynamic transition.
At the glass transition, the molecules which are effectively frozen in position in the polymer glass become free to rotate and translate and so it is not surprising that the value of the Tg will depend upon the physical and chemical structure of the polymer molecules.

26. Polymer Research Center
Institute of Applied Chemistry of NCTU
The Glass Transition
The most important factor is chain flexibility which is governed by the nature of the chemical groups which constitute the main chain.

27. Polymer Research Center
Institute of Applied Chemistry of NCTU
The Glass Transition
In vinyl polymers of the type (-CH2-CHX-)n the nature of the side group (bulky and polar groups) has a profound effect upon Tg as can be seen in the table.

28. Polymer Research Center
Institute of Applied Chemistry of NCTU
Crystallization
Crystallization is the process whereby an ordered structure is produced from a disordered phase, usually a melt or dilute solution, and melting can be thought of as being essentially the opposite of this process.
Features:
(a) Polymer crystals are usually thin and lamellar when crystallized from both dilute solution and the melt.

29. Polymer Research Center
Institute of Applied Chemistry of NCTU
Crystallization
(b) The lamellar thickness is related to the crystallization temperature.
(c) Chain folding is known to occur during crystallization.
(d) The growth rates of polymer crystals are found to be highly dependent upon the crystallization temperature and molar mass of the polymer.

30. Thermal Degradation Temperature
Polymer Research Center
Institute of Applied Chemistry of NCTU
Thermal Degradation Temperature
The thermal degradation temperature was determined from the changes in weight in relation to change in temperature using thermogravimetric analysis (TGA).

31. Surface Free Energy high surface free energy ↔ strong cohesion
Polymer Research Center
Institute of Applied Chemistry of NCTU
Surface Free Energy
Surface free energy from work :
The reversible work required to create a unit surface area is related to the surface free energy of the material.
Units: mJ/m2 = mN/m
high surface free energy ↔ strong cohesion
surface tension of liquids corresponds to surface
energy of solids

32. The Theory of Surface Free Energy
Polymer Research Center
Institute of Applied Chemistry of NCTU
The Theory of Surface Free Energy
Three-Liquid Acid-Base Method
γS : apolar component, accounting for Liftshitz-van
der Waals type interactions
γS : polar component, accounting for acid-base or
donor- acceptor type interactions
γS + : Lewis-acid component, electron acceptor
γS- : Lewis-base component, electron donor LW AB

33. Fluoropolymers and Silicones
Polymer Research Center
Institute of Applied Chemistry of NCTU
Fluoropolymers and Silicones
poly(tetrafluoroethylene)
PTFE
The low intermolecular forces present in fluorinated polymers have been recognized to account for the relatively low surface free energy.
poly(dimethylsiloxane) PDMS
polyethylene PE

34. Mechanical Properties
Polymer Research Center
Institute of Applied Chemistry of NCTU
Mechanical Properties
Stress: In consideration of the mechanical properties of polymers we are mainly to interested in effect of applying surface forces such as stress or pressure to the material.

35. Mechanical Properties
Polymer Research Center
Institute of Applied Chemistry of NCTU
Mechanical Properties
Strain: When forces are applied to a material the atoms change position in response to the force and this change is known as strain.
Young’s modulus: E of a material which for simple uniaxial extension or compression is given by E = stress/strain.

36. Mechanical Properties
Polymer Research Center
Institute of Applied Chemistry of NCTU
Mechanical Properties
Viscoelasticity: A distinctive feature of the mechanical behavior of polymers is the way in which their response to an applied stress or strain depends upon the rate or time period of loading.
The behavior of most polymers can be though of as being somewhere between that of elastic solids and liquids.

37. Mechanical Properties
Polymer Research Center
Institute of Applied Chemistry of NCTU
Mechanical Properties
At low temperatures and high rates of strain they display elastic behavior whereas at high temperatures and low rates of strain they behave in a viscous manner, flowing like a liquid.
Polymers are therefore termed viscoelastic as they display aspects of both viscous and elastic types of behavior.

38. Mechanical Properties
Polymer Research Center
Institute of Applied Chemistry of NCTU
Mechanical Properties
General time-dependent behavior:
Creep experiment
Relaxation experiment

39. Mechanical Properties
Polymer Research Center
Institute of Applied Chemistry of NCTU
Mechanical Properties

40. Stress-Strain Curve Brittle!! Ductile!! Neck occurs!!
Polymer Research Center
Institute of Applied Chemistry of NCTU
Stress-Strain Curve
Brittle!!
Ductile!!
Neck occurs!!

41. The End Thanks for Your Attention