ch04-Polymers

ch04-Polymers - CHAPTER 4: POLYMER STRUCTURES Spherulite,...

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Chapter 4 - CHAPTER 4: POLYMER STRUCTURES Spherulite, rubber specimen. Chain-folded lamellar crystallites, ~10 nm thick, 30,000×
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c04cof01 2 ISSUES TO ADDRESS. .. What are the general structural and chemical characteristics of polymer molecules? What are some of the common polymeric materials, and how do they differ chemically? How is the crystalline state in polymers different from that in metals and ceramics ?
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4.1 Structures of Polymers Introduction and Motivation Polymers are extremely important materials (i.e. plastics) Have been known since ancient times – cellulose, wood, rubber, etc. . Biopolymers – proteins, enzymes, DNA … Last ~50 years – tremendous advances in synthetic polymers Just like for metals and ceramics, the properties of polymers • Thermal stability Mechanical properties Are intimately related to their molecular structure …
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Chapter 4 - 4 4.1 Ancient Polymers Originally natural polymers were used: Wood Rubber Cotton Wool Leather Silk Oldest known use: Rubber balls used by Incas Noah used pitch (a natural polymer) for the ark Noah's pitch Genesis 6:14 ". ..and cover it inside and outside with pitch." gum based resins extracted from pine trees
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Chapter 4 - 5 4.2 Polymer Composition Most polymers are hydrocarbons – i.e., made up of H and C Saturated hydrocarbons Each carbon singly bonded to four other atoms Example: • Ethane, C 2 H 6 C C H H H H H H
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Chapter 4 - 6 4.2 Unsaturated Hydrocarbons Double & triple bonds somewhat unstable – can form new bonds – Double bond found in ethylene or ethene - C 2 H 4 – Triple bond found in acetylene or ethyne - C 2 H 2 C C H H H H C C H H
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Chapter 4 - 4.2 Structures of Polymers about hydrocarbons Why? Most polymers are hydrocarbon (e.g. C, H) based Bonding is highly covalent in hydrocarbons Carbon has four electrons that can participate in bonding, hydrogen has only one Saturated versus unsaturated C C C C H H H H H H Ethylene Acetylene C C H H H H H H Ethane Unsaturated Saturated Unsaturated – species contain carbon-carbon double/triple bonds Possible to substitute another atom on the carbon Saturated – carbons have four atoms attached Cannot substitute another atom on the carbon
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4.2 Isomerism Isomerism two compounds with same chemical formula can have quite different structures for example: C 8 H 18 normal-octane C C C C C C C C H H H H H H H H H H H H H H H H H H H 3 C CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 3 = H 3 C CH CH 3 CH 2 CH CH 2 CH 3 CH 3 H 3 C CH 2 CH 3 ( ) 6 Isomerism – compounds of the same chemical composition but different atomic arrangements (i.e. 2,4-dimethylhexane
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This note was uploaded on 03/08/2010 for the course CHEN 313 taught by Professor Seminario during the Fall '07 term at Texas A&M.

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ch04-Polymers - CHAPTER 4: POLYMER STRUCTURES Spherulite,...

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