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Polymers: 1. Introduction 2. The variety of Polymeric Materials

Polymers: 1. Introduction 2. The variety of Polymeric Materials. Dept. Phys., Tunghai Univ. C. T. Shih. Introduction. Polymers: a giant molecule, made up of many repeat units covalently joined together Common characteristics: long, string-like molecules

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Polymers: 1. Introduction 2. The variety of Polymeric Materials

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  1. Polymers:1. Introduction2. 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=Mw/Mn • 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

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