1. Chapter 31. Synthetic Polymers
Based on McMurry’s Organic Chemistry, 6th edition

2. Polymers
Large molecules built up by repetitive bonding together of monomers

3. Drawing Polymers
Indicate repeating unit in parentheses

4. 31.1 Chain-Growth Polymers
Produced by chain-reaction polymerization
Initiator (radical, acid or anion) adds to a carbon–carbon double bond of an unsaturated substrate (a vinyl monomer) to yield a reactive intermediate that reacts with a second molecule of monomer and so on

5. Anionic Polymerization
Vinyl monomers with electron-withdrawing substituents (EWG) can be polymerized by anionic catalysts
Chain-carrying step is nucleophilic addition of an anion to the unsaturated monomer by a Michael reaction

6. Examples of Anionic Polymerization Products
Acrylonitrile (H2C=CHCN), methyl methacrylate [H2C=C(CH3)CO2CH3], and styrene (H2C=CHC6H5) react

7. 31.2 Stereochemistry of Polymerization: Ziegler–Natta Catalysts
Polymerization of a substituted vinyl monomer can lead to numerous chirality centers on the chain
A polymer having all methyl groups on the same side of the zigzag backbone is called isotactic
If the methyl groups alternate on opposite sides of the backbone, it is called syndiotactic
Randomly oriented methyl groups are on atactic polymers

8. Ziegler–Natta Catalysts
Allow preparation of isotactic, syndiotactic, and atactic polypropylene
Prepared by treatment of an alkylaluminum with a titanium compound
(CH3CH2)3Al + TiCl4  A Ziegler–Natta catalyst

9. 31.3 Copolymers
Obtained when two or more different monomers polymerize together
They can be random or alternating

10. Types of Copolymers
The exact distribution of monomer units depends on the initial proportions of the two reactant monomers and their relative reactivities

11. Block copolymers
Different blocks of identical monomer units alternate with each other
Prepared by initiating the polymerization of one monomer as if growing a homopolymer chain and then adding an excess of the second monomer to the still-active reaction mix

12. Graft copolymers
Homopolymer branches of one monomer unit are grafted onto a homopolymer chain of another monomer unit
Made by gamma irradiation of a completed homopolymer chain in the presence of the second monomer generating radical sites that can initiate polymerization of the added monomer

13. 31.4 Step-Growth Polymers
Produced by reactions in which each bond in the polymer is formed independently, typically by reaction between two difunctional reactants

14. Step-Growth Polymer from a Lactam
Addition generates new nucleophile
Polyamide from caprolactam is Nylon 6

15. Polycarbonates
Carbonyl group is linked to two OR groups, [O=C(OR)2]

16. Polyurethanes
Urethane - carbonyl carbon is bonded to both an OR group and an NR2 group

17. Preparation of Polyurethanes
Nucleophilic addition of an alcohol to an isocyanate (RN=C=O) gives a urethane
Reaction between a diol and a diisocyanate gives a polyurethane

18. 31.5 Polymer Structure and Physical Properties
Polymers experience substantially larger van der Waals forces than do small molecules, producing regions that are crystallites

19. Heat Transitions
Heating at the melt transition temperature, Tm, gives an amorphous material
Heating noncrystalline, amorphous polymers makes the hard amorphous material soft and flexible at the glass transition temperature, Tg

20. Thermoplastics Have a high Tg and are hard at room temperature
Become soft and viscous when heated
Can be molded

21. Plasticizers
Small organic molecules that act as lubricants between chains
Added to thermoplastics to keep them from becoming brittle at room temperature
Dialkyl phthalates are commonly used for this purpose

22. Fibers
Thin threads produced by extruding a molten polymer through small holes in a die, or spinneret
Fibers are then cooled and drawn out

23. Elastomers
Amorphous polymers that have the ability to stretch out and spring back to their original shapes
When stretched, the randomly coiled chains straighten out and orient along the direction of the pull

24. Natural Rubber and Gutta-Percha
The upper structure is rubber, a natural elastomer
The lower structure is the nonelastic gutta-percha

25. Thermosetting resins
Polymers that become highly cross-linked and solidify into a hard, insoluble mass when heated
Bakelite is from reaction of phenol and formaldehyde, widely used for molded parts, adhesives, coatings