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CHAPTER 14 Polymer Structures.

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Presentation on theme: "CHAPTER 14 Polymer Structures."— Presentation transcript:

1 CHAPTER 14 Polymer Structures

2 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 Covalent Bonding H-C-H H Methane Ethylene Similarly

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

4 RESULT Angle =109o

5 Similarly Unpaired electron Methyl group


7 MOLECULAR WEIGHT Number average Weight-average
Not all chains same length Weight-average

8 For copolymers Degree of polymerization Molecular weight of mer j

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

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

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

= 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%.

13 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

14 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 Irregular and random mer  less crystallinity Alternating and block copolymers  likelihood of crystallization. Random and Graft copolymers Normally Amorphous

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