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CHAPTER 14 Polymer Structures

CHAPTER 14 Polymer Structures. H. H-C-H. Similarly. H. Methane. Ethylene. Covalent Bonding. INTRODUCTION. Natural Polymers  Leather, wood, rubber, cellulose, cotton, wool. Synthetic polymers  Synthesized from small organic molecules. CHEMISTRY OF POLYMER MOLECULES.

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CHAPTER 14 Polymer Structures

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  1. CHAPTER 14 Polymer Structures

  2. H H-C-H Similarly H Methane Ethylene Covalent Bonding INTRODUCTION Natural Polymers Leather, wood, rubber, cellulose, cotton, wool. Synthetic polymers Synthesized from small organic molecules. CHEMISTRY OF POLYMER MOLECULES Hydrocarbons (many organic materials)=composed of hydrogen and carbon

  3. Ethylene(C2H4) gas Catalyst bonding unsatisfied for this C atom bonding satisfied for C atom POLYMERISATION Mers= small structural entities making up the ‘poly’mer. CAN BE CONVERTED TO POLYETHYLENE(PE) Solid

  4. Angle =109o RESULT

  5. Similarly Unpaired electron Methyl group

  6. MOLECULAR WEIGHT Number average Not all chains same length Weight-average

  7. For copolymers Degree of polymerization Molecular weight of mer j

  8. Branched Linear e.g. Polyethylene, Nylon Lower density Crosslinked Network e.g. Rubber e.g. Epoxy

  9. HOMOPOLYMERS COPOLYMERS Polymers composed of two or more different ‘mer’ units Bifunctional, trifunctional mers

  10. Styrene-butadiene rubber (SBR) random copolymer Used in automobile tires.

  11. POLYMER CRYSTALLINITY = Packing of molecular chains so as to produce an ordered atomic array. Small molecules (Methane, H2O)  either either totally crystalline (as solids) or amorphous (as liquids) However POLYMERS  only partially crystalline (semi-crystalline) Max. crystallinity  ~ 95%.

  12. Properties greatly affected by degree of crystallinity (crystalline = stronger and more resistant to softening by heat.  important to quantify degree crystallinity Crystalline polymer = higher density

  13. Slower cooling rates from the melt favor higher crytallinity (giving time for ordered configurations) Linear Polymers Crystallization easily accomplished, since no restriction to chain alignment Branched polymers NEVER highly crystalline Side branches interfere with crystallization Network Polymers AMORPHOUS COPOLYMERS More Irregularand random mer  less crystallinity Alternating and block copolymers  likelihood of crystallization. Random and Graft copolymers Normally Amorphous

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