1. Chapter 24 Synthetic Polymer
Contents
Identifying the Repeating Units for Polymer
Understanding the Mechanisms, Structures of
Polymers and their Chemical, Physical Properties

2. Introdution : What is the Polymer ?
Macromolecules
Can be Classified according to Mechanisms
Addition Polymers : Chain-growth Polymers (eg: Free radical mechanism)
Condensation Polymers :
Others:
p. 1054

3. 24.1 Radical Chain Polymerization
Comment :
p. 1054

4. Initiation
Propagation
Comment
p. 1055

5. Termination
h-t polymers
More stable radical
p. 1055

6. 24.2 Structures of Polymers
Linear Structure vs Branched Structure Chain transfer Mechanism
Mechanism for the Formation of Long Branch
Fig. 24-1, p. 1058

7. Mechanism for the Formation of Shorter Branch
Irregularity  Polymer property change Irregularity: - from Branched Polymer - from Tacticity
Thru 6-Member TS  Butyl Branch
Fig. 24-2, p. 1059

8. Irregularity from Tacticity
FR polymerization?
ACTIVE FIGURE 24.2: MECHANISM OF THE FORMATION OF A BUTYL BRANCH DURING THE POLYMERIZATION OF ETHYLENE.
p. 1059

9. 24.3 Ionic Polymerization Cationic polymerization Vinyl monomers:
- Anionic polymerization
Oxirane:
h-t polymers
Needs stabilizing groups for carbocation
p. 1060

10. Anionic polymerization
Phenyl group
stabilize carbanion
Driving force: ring strain energy
p. 1061

11. Focus On – Super Glue Two EWGs stabilize carbaion Any Nu can initiate
Polymerizarion
(Si-OH, Fe-OH,
Skin-NH2,.. )
Anionic polymerization : acrylonitrile vs isobutylene
(stabilization of cabanion vs carbocation)
p. 1062

12. 24.4 Coordination Polymerization
Catalyst (TiCl4+AlEt3) Mechanism: Metal Coordination PP: Why not FR polymerization? Most important method - Linear, no branch - Gives Tacticity  better physical property
Fig. 24-3, p. 1063

13. Syndiotactic polymer :
Example.
FIGURE 24.3: MECHANISM OF POLYMERIZATION INVOLVING A METAL COORDINATION CATALYST (SIMPLIFIED VERSION).
Isotactic polymer :
Syndiotactic polymer :
p. 1064

14. 24.5 Physical Properties of Polymers
Two-Dimensional picture of a Crystallite
Crystalline region: anti conformers, ~100nm in size, more polar structure,
no branching  increase physical property; Tg, Tm
Amorphous region: branching, irregularity, …
p. 1064

15. 24.6 Major Thermoplastic Addition Polymers
Output of Thermoplastic Polymers (2002)
PE> PVC> PP> PS
PVC: polar C-Cl higher Tg
PP: after 1957, stiff & hard
PMMA: higher Tg, 110oC
PVC is ridged, but can be flexible
by adding Plasticizer (DOP)
HDPE: by coordination catalyst, regular structure, high density, higher Tm
LDPE: by radical polymerization, branching, used for films, low cost
Table 24-1 p. 1066

16. 24.7 Elastomers
Amorphous, Tg below RT, random, coiled conformers, nonpolar structure
Need cross-linkers to prevent from slipping: by vulcanization
p. 1068

17. 1, 4 addition makes trans conformer (higher Tg) vs
1, 2 addition vs 1,4 addition
1, 4 addition makes trans conformer (higher Tg) vs
Natural rubber (cis conformer)
SBR (25% St + 75% butadiene): Synthetic rubber, 2/3 of rubber w/w
Random incorporation of St  rubber like structure
p. 1069

18. 24.8 Condensation Polymers
Condensation polymerization : step growth polymerization
Natural polymer : Proteins from AA, DNA form NA
Synthetic polymers : Polyesters, Polyurethanes
p. 1070

19. Poly(ethylene terephthalate); PET
Water should be removed
Highly crystalline due to linear & polar structure
High MP(270oC)
High tensile strength  good for fiber
SMs should be very pure to get high MW
via Trans esterification : MeOH can be easily distilled off
p. 1071

20. Polycarbonate , Polyamide
Interfacial polymerization (계면 중합) : MC/water with vigorous mixing
High impact strength : helmets, CD, ..
Acid chloride method  cheaper?
Molten method : for industry
Strong intermolecular force : HB  high mp (250oC)
Fibers with food tensile strength
eg) Nylon 6,10 : tooth brush
p. 1072

21. Polyamide Highly crystalline, strong, stiff, high-strength fibers
Nylon 6,6 : original from Dupont, USA
Nylon 6 : EU, Jpn, Korea
Highly crystalline, strong, stiff, high-strength fibers
bulletproof cloth
Need special condition for spinning  needs scale up research
p. 1073

22. Polyurethane
MW 1000~2000
Soft Segment –Hard Segment
p. 1074

23. Polyurethane
A lot of dialcohols can be used  different physical properties
PU foams : via addition of water during molding process
p. 1075

24. 24.9 Thermoset Polymers
Thermoplastic Polymers: linear, not crosslinked polymer
Thermoset Polymer : crosslinked when heated
not reversible, makes environmental problem
Plastic : Mixture of polymer and others,
solid after processing
Polymer(major) + Plasticizer + Filller + Dye,
Pigment + Lubricant + flame retardant +
antioxidant + binder
Phenolic resin : phenols + formaldehyde eg) Bakelite
highly crosslinked  no melting : electrical insulator, PC board, Billard ball,..
Amino resin : urea (melamine) + formaldehyde
Epoxy resin : bisphenol A + epichlorohydrin
p. 1075

25. Partial mechanism of the polymerization of phenol and formaldehyde
Fig 24-4 p. 1076

26. Epoxy Resin : mechanism of glue (by Mixing A and B)
slightly in exess
p. 1077

27. 24.10 Chemical Properties of Polymers
Same chemistry can be applied on the polymer
Ion exchange resins : PS resin by suspension polymerization process
p. 1078

28. Surface of the Beads Cation exchange resin Anion exchange resin
Process for pure water
p. 1078

29. Focus On – Recycling Plastics
Collecting & Sorting : labor cost for collecting,
automatic sorting machine (with IR sensor)
Mixing to virgin polymer :
Pyrolyze to Chemical Feedstock :
Fuel : burning as a fuel, part of energy is recovered
not safe in case of halogen containing plastics  Dioxin, HCl waste
Reverse polymerization : In the case of condensation polymer
Not applicable to Thermosetting Resin :
- Have to change to Thermoplastic Resin
- New process to reverse polymerization  New National Project
p. 1080