1. Macromolecular Synthesis
CHEM 7010
Macromolecular Synthesis
2nd Introduction to Polymer Synthesis: General Aspects of Polymer Structures on
Polymer Properties
2011

2. Multidimensional Order of Structure-Property Relationships in Polymers
Microscopic
*Crystallinity
*Phases *Orientation
Molecular
Microscopic
Synthesis and
Processing
Molecular
*Chemical Composition
*MW/MWD
*Branching and/or
Cross-linking
Macroscopic
*Strength
*Modulus
*Impact Resistance
Permeability
Clarity
Macroscopic

3. IMPACT OF MOLECULAR WEIGHT ON MATERIAL PROPERTIES
Increasing Degree of Polymerization, DP

4. Vinyl Monomers, CH2=CH-X
X Polymer Abbreviation
H Polyethylene PE
CH3 Polypropylene PP
Cl Poly(vinyl chloride) PVC
Phenyl Polystyrene PSt
CN Polyacrylonitrile PAN
COOCH3 Poly(methyl acrylate) PMA
O-COCH3 Poly(vinyl acetate) PVAc

5. Vinylidene Monomers, CH2=C(X)Y
X Y Polymer Abbreviation
CH3 CH3 Polyisobutylene PIB
Cl Cl Poly(vinylidene chloride) PVDC
F F Poly(vinylidene fluoride) PVDF
Phenyl CH3 Poly(-methyl styrene)
CH3 COOCH3 Poly(methyl methacrylate) PMMA
CN COOR Poly(alkyl -cyanoacrylate

6. Structural Complexity of Polymers
Homopolymers
Head to Tail vs. Head to Head Adducts
e.g. a-olefins
1,2- vs 1,4 Adducts; e.g. butadiene
Tacticity of Enchainments
Branching

7. Tacticity Isotactic All asymmetric carbons have same configuration
Methylene hydrogens are meso
Polymer forms helix to minimize substituent interaction
Syndiotactic
Asymmetric carbons have alternate configuration
Methylene hydrogens are racemic
Polymer stays in planar zig-zag conformation
Heterotactic (Atactic)
Asymmetric carbons have statistical variation of configuration

8. Structural Complexity of Polymers
Copolymers
Identity and Number of Comonomers
Ratio and Distribution of Comonomers
Statistical Alternating
Gradient
Blocks Grafts

9. Structural Complexity of Polymers
Molecular Weight
Molecular Weight Distribution, MWD
Polydispersity Index, PDI
Mn, Mw, Mz, Mv Averages
Crosslinking Density
Length of Crosslinks

10. Structural Complexity of Polymers
Time Dependent Changes
Chemical Reactions
Hydrolysis
Dehydrohalogenation
Photodegradation
Oxidation

11. Structural Complexity of Polymers
Thermal Degradation
Processing
Aging
Crystallization
Changes in Polymorphism
Weathering-- Combination of Above
Plasticizer Loss -- Imbrittlement

12. Microscopic Properties (Intermolecular Interactions)
Morphology
Chain entanglement –amorphous
Chain ordering--liquid crystalline
Crystallinity
Phase separations (microdomains)

13. Types of Intermolecular Forces
Type of Force Relative Strength Low Molecular Analog Polymer
Dispersion or Weak Methane Polyethylene
Van der Waals Hexane Polypropylene
Dipole-Dipole Medium CH3Cl PVC
CH3CO2CH3 PMMA
Hydrogen bonding Strong H2O Cellulose
CH3CONH2 Proteins
Electrostatic Very Strong CH3CO2-Na+ Ionomers

14. GLASS TRANSITION, Tg
Definition: The onset of seqmental motion of seqments with carbons atoms
Physical Change Expansion of volume
Free volume required to allow segmental motion
Tg is an approximation
Depends upon measurement technique
Depends upon molecular weight
Polystyrene MW = 4000 Tg = 40C
= 300, = 100

15. GLASS TRANSITION, Tg Properties Affected Specific Volume / Density
Specific Heat, Cp
Refractive Index
Modulus
Dielectric Constant
Permeability

16. FACTORS INFLUENCING Tg
Tg is proportional to Rotational Freedom
For symmetrical polymers Tg, / Tm in K  1/2
unsymmetical polymers  2/3
1. Chain flexibility
Silicone  Ether  Hydrocarbon  Cyclic HC  Aromatics

17. FACTORS INFLUENCING Tg
2. Steric Bulk of Substituents
Tg = -120C 5C C -50C
Long side chains may act as plasticizers (C  6)
Tg = C C

18. FACTORS INFLUENCING Tg
3. Molecular Symmetry
Asymmetry increases chain stiffness.
4. Polar Interactions increase Tg
Hydrogen bonding
5. Molecular Weight up to Critical Limit
6. Crosslinking
Reduces Segment Mobility

19. FACTORS INFLUENCING Tm
1. Chain flexibility
Silicone  Ether  Hydrocarbon  Cyclic HC  Aromatics
2. Substituents Producing Lateral Dipoles
Hydrogen bonding
3. Molecular Symmetry
Symmetry allows close packing

20. FACTORS INFLUENCING Tm
4. No Bulky Substituents to Disrupt Lattice if placement is Random
5. Structural Regularity
monomer placement
head to tail
1,2- vs 1,4-
1,2- vs 1,3- vs 1,4- aromatic substitution
geometric isomers of enchainments
cis or trans -C=C-; cyclic ring
tacticity

21. FACTORS REQUIRED TO PROMOTE CRYSTALLIZATION
Thermodynamic
1. Symmetrical chains which allow regular close packing in crystallite
2. Functional groups which encourage strong intermolecular attraction to stabilize ordered alignment.

22. FACTORS REQUIRED TO PROMOTE CRYSTALLIZATION
Kinetic
1. Sufficient mobility to allow chain disentanglement and ultimate alignment
Optimum range for mobility
Tm -10  Tg + 30
at Tm segmental motion too high
at Tg viscosity too high
2. Concentration of nuclei
concentration of nucleating agents
thermal history of sample

23. Macroscopic Properties (Physical Behavior)
Tensile and/or Compressive Strength
Elasticity
Toughness
Thermal Stability
Flammability and Flame Resistance
Degradability
Solvent Resistance
Permeability
Ductility (Melt Flow)

24. Step Polymerization (Polycondensation)
After many repetitions:
                                                                                        
Polyethyleneterephthalate (PET)

25. Step Polymerization Two Routes: A-A + B-B; or A-B 1 on 39 1 on 40
Either way, need:
high conversion
stoichiometric amount

26. Step vs. Chain Polymerization
Step Polymerization
Any two molecular species can react.
Monomer disappears early.
Polymer MW rises throughout.
Growth of chains is usually slow (minutes to days).
Long reaction times increase MW, but yield hardly changes.
All molecular species are present throughout.
Usually (but not always) polymer repeat unit has fewer atoms than had the monomer.

27. Step vs. Chain, cont. Chain Polymerization
Growth occurs only by addition of monomer to active chain end.
Monomer is present throughout, but its concentration decreases.
High polymer forms immediately.
MW and yield depend on mechanism details.
Chain growth is usually very rapid (seconds to microseconds).
Only monomer and polymer are present during reaction.
Usually (but not always) polymer repeat unit has the same atoms as had the monomer.

28. Step Polymerization Concepts
Comparison of Step and Chain Polymerization
1. Step: any 2 molecules in the system can react with each other
Chain: chain growth occurs on end of growing polymer
2. Step: loss of monomer at early stage (dimers, tetramers, etc.)
Chain: monomer concentration decreases steadily
3. Step: broad molecular weight distribution in late stages
Chain: narrower distribution; just polymer and monomer

29. Step Polymerization Basis for Kinetics (2-1a): 3 on 40 4 on 40 5 on 40

30. Step Polymerization
Basis for Kinetics:
1on 41
2 on 41

31. Step Polymerization Basis for Kinetics (2-1b):
NOTE: Assume equal reactivity of functional groups
table 2.1on 42
Thus, assumption looks ok

32. Step Polymerization Kinetics (2.2) Example: diacid + diol
Mechanism (acid catalyzed):
2 on 44
1 on 45
2 on 45

33. Chain Polymerization
Concepts
General Mechanism
Initiation
Propagation

34. Chain Polymerization Concepts: Nature of Chain Polymerization; 3-1
3-1a. Comparison of Chain and Step Polymerizations
Step:
a. Monomer gone fast, get
dimer, trimer, etc.
b. MW increases with time
c. No high mw until end
Chain:
a. Rapid high mw
b. Snapshot: monomer,
high poly, growing chains
c. MW does not change
with time

35. Chain Polymerization Concepts: Nature of Chain Polymerization; 3-1
3-1b-1. General Considerations of Polymerizability
Thermodynamics
(Chain t-fer)

36. Chain Polymerization Concepts: Nature of Chain Polymerization; 3-1
3-1b-2. Effects of Substituents on C=C monomers for Ionic Polymerization
A. Initiation opportunities: 2 types of bond cleavage/resonance
B. Radical, Anionic, Cationic: Depends on:
i. Inductance
ii. Resonance

37. Chain Polymerization Concepts: Nature of Chain Polymerization; 3-1
3-1b-2. Effects of Substituents on C=C monomers for Ionic Polymerization
C. Donating Groups
Good for cationic
Inductance
Resonance
e.g. Polym of vinyl ether
Example of resonance stabilization of cation by
Delocalization of of positive charge.
If oxygen not there, no stabilization

38. Chain Polymerization Concepts: Nature of Chain Polymerization; 3-1
3-1b-2. Effects of Substituents on C=C monomers for Ionic Polymerization
C. Donating Groups
ii. Resonance
e.g. Polym of Styrene

39. Chain Polymerization Concepts: Nature of Chain Polymerization; 3-1
3-1b-2. Effects of Substituents on C=C monomers for Ionic Polymerization
D. Withdrawing Groups
i. inductance
Good for anionic
ii. resonance

40. Chain Polymerization Concepts: Nature of Chain Polymerization; 3-1
3-1b-2. Effects of Substituents on C=C monomers for radical polymerization
A. Radicals not affected by charge, but can have resonance stabilization
B. Also stabilized by primary<secondary<tertiary
Draw your own pic

41. Chain Polymerization
Concepts: Structural Arrangement of Monomer Units; 3-2
3-1a. Possible Modes of Propagation
A. Two possible points of attachment
i. On carbon 1:
ii. On carbon 2:

42. Chain Polymerization
Concepts: Structural Arrangement of Monomer Units; 3-2
3-1a. Possible Modes of Propagation
B. If attachment is regular, get head-to-tail (H-T)
C. If attachment is irregular, get head-to-head (H-H) [and T-T]

43. Chain Polymerization
Concepts: Structural Arrangement of Monomer Units; 3-2
3-1a. Possible Modes of Propagation
Usually only 1-2% H-H. How do we know?
A. Chemical Methods
B. NMR Methods (we’ll check this out in the Spectroscopy section)