1. CHAPTER 4 Classification based on mode of formation- chain growth and step growth polymerization week 12

2. Polymers are large molecules made up of repeating units called Monomers
The synthetic process is Polymerization.
E.g.

3. A polymer prepared from a single monomer is a homopolymer
If two or more monomers are employed, the product is a copolymer
Linear polymer has no branching
Graft copolymer is an example of a branched network

4. Two main classifications of Polymerization
Addition reaction or Chain growth
Molecular weight increases by successively adding monomers to a reactive polymer chain end resulting in high molecular weights at low conversions.
STEP reaction or growth
Polymers are formed by linking monomer molecules to form dimers, trimers and higher species in a step-wise fashion. The most abundant species react, and thus high molecular weight formed only beyond 99% conversion.

5. Polymerizations carried out at very low temperatures
Addition reaction or Chain growth
Ionic Chain (addition)-Growth Polymerization
The choice of ionic procedure depends greatly on the electronic nature of the monomers to be polymerized
Vinyl monomers with electron-accepting groups
Anionic Polymerization
Vinyl monomers with electron-donating groups
Cationic Polymerization
Monomers and reagents should be purified; water and oxygen should be removed.
Polymerizations carried out at very low temperatures

6. Anionic Polymerizations
Initiators include alkyl lithiums and sodium amide

7. Cationic Polymerization -- the formed carbocation must be quite stable
Stable tertiary carbocation
stable oxonium ion
E.g. proton initiates polymerization of isobutane (2-methylpropene)
Adhesive, sealant, insulating oil, lubricating oil

8. Chain Reaction: Free Radical Polymerization
Initiation
Propagation
Random Termination
Dead chains

9. Examples of Polymers Prepared by Radical Polymerization
Monomer
Polymer n
Poly(styrene) n
Poly(acrylonitrile) n
Poly(methylacrylate) n
Poly(vinylacetate)

10. Recent Example of a Graft Copolymer Synthesis+
Copolymerization
macromonomer
monomer
Graft copolymer
Poly(AA)
NIPAM +
N-Isopropylacrylamide
NIPAM monomer (excess)
Poly(acrylic acid) macromonomer
Insoluble in water above the lower critical solution temperature (LCST)
McHale, Aldabbagh, Carroll, Yamada, J. Polym. Sci. Part A: Polym. Chem. 2007, 45,

11. Step-growth Polymerization
Step-polymers are made by allowing difunctional monomers with complementary functional groups to react with one another
Condensation between two molecules
Poly(ethylene terephthalate)
terephthalic acid
ethylene glycol
PET
This is an example of a poly(ester)
The reaction is a transesterification
Recyclable plastic bottles and textile fabrics
Using a condensation reaction

12. Time for litter to biodegrade
Product
Time to biodegrade
Paper
2-5 months
Wool socks
1 to 5 years
Plastic coated paper milk cartons
5 years
Plastic bags
10 to 20 years
Nylon fabric
30 to 40 years
Aluminum cans
80 to 100 years
Plastic 6-pack holder rings
450 years
Glass bottles
1 million years
Plastic bottles
Forever