1. Polymers: 1. Introduction 2. The variety of Polymeric Materials Dept. Phys., Tunghai Univ. C. T. Shih

2. Introduction Polymers: a giant molecule, made up of many repeat units covalently joined together Common characteristics: long, string-like molecules Living polymers: long-chain objects whose subunits are joined by physical bonds, e.g., actin filaments

3. Variety of Polymeric Materials Polymer chemistry Stereochemistry Architecture Homopolymers and Copolymers Physical state

4. Polymer chemistry Most polymers contains carbon atoms. Simplest polymer: polyethylene （聚乙烯）

5. Polymer chemistry (conti.) The main chain can have different side groups: polymethyl methacrylate （聚甲基丙烯酸甲酯）

6. Polymer chemistry (conti.) The main chain can incorporate non- carbon atoms, e.g., Nylon

7. Polymer chemistry (conti.) The main chain can involve loops, e.g., amylose （澱粉）

8. Polymer chemistry (conti.) The polymer can be multiply connected, forming a ladder structure, e.g., poly(dioctyl fluorene)

9. Polymer chemistry (conti.) The main chain can contain no carbon atoms at all, e.g., PDMS (silicone oil)

10. Stereochemistry If a polymer has more than one type of chemical group attached to each main chain (carbon) atom, then different arrangement of the groups in 3D are possible: isotactic, syndiotactic, and atactic.

11. Quenched disorder → Glasses

12. Architecture Linear vs. Branched polymers Linear polymers can be characterized by N, the number of repeated units: degree of polymerization N is proportional to the relative molecular mass M Degree of polymerization is not a constant for a group of polymers – a distribution PDI: polydispersity index ≡ (weight average)/(number average)

13. PDI=M w /M n Number average: Weight average: Standard error:

14. Branched Polymer The polymers may be branched The branched points introduce quenched disorder, and hinder the formation of crystals A lot of branch points – a network

15. Copolymers The building units are all the same – homopolymers Different building units – copolymers Phase separation and microphase separation DNA and proteins are copolymers

16. Physical States Liquid – melts and solutions, usually very viscous/viscoelastic Glass – is common because of the difficulty of crystallization Crystalline – usually incomplete/small due to quenched disorder Liquid crystal