L17PolymerII145s10r

L17PolymerII145s10r - Lecture 17, spring 2010 ENGR 145,...

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Unformatted text preview: Lecture 17, spring 2010 ENGR 145, Chemistry of Materials Case Western Reserve University Reading assignment : C&R 14.11; OGC 23.1-23.2 Learning objectives: Understand the two basic types of polymerization reactions Addition Condensation Describe three types of addition polymerization reactions: Free radical polymerization Ionic polymerization Coordination polymerization Be able to explain how these reaction mechanisms affect the structure and properties of the resulting polymer Lecture 17: Polymer Structure & Synthesis II 1 Lecture 17, spring 2010 ENGR 145, Chemistry of Materials Case Western Reserve University low density poly(ethylene) LDPE (CH 2-CH 2 ) n poly(vinyl chloride) PVC (CH 2-CHCl) n poly(methyl methacrylate) CH 3 PMMA | (-CH 2 C-) n | COOCH 3 Common Polymers Formed via Free Radical Polymerization [OGC 23.1; C&R 14.11] 2 Lecture 17, spring 2010 ENGR 145, Chemistry of Materials Case Western Reserve University What are free radicals? Two ways to break an A-B single bond into two fragments: ionization: A-B A + + B (we ll use this later) free radicals: A-B A + B the dots denote unpaired electrons very reactive Typical initiator: benzoyl peroxide C 6 H 5 COO-OOCC 6 H 5 2 C 6 H 5 COO benzoyl free radicals General behavior for peroxide initiators: Free Radical Polymerization 3 Lecture 17, spring 2010 ENGR 145, Chemistry of Materials Case Western Reserve University Ethylene (C 2 H 4 ) forms polyethylene (PE) in the presence of free radical R (catalyst or initiator) Free Radical Polymerization monomer initiation propagation electrons in bond electrons in bond 4 Lecture 17, spring 2010 ENGR 145, Chemistry of Materials Case Western Reserve University Note: Propagation is a chain reaction Unpaired electrons are not consumed in propagation reaction Number of radicals is unchanged during propagation But the reaction can stop via termination reactions: Combination reactions between radicals Transfer of hydrogen between radicals Free Radical Polymerization 5 Lecture 17, spring 2010 ENGR 145, Chemistry of Materials Case Western Reserve University Possible termination reactions between two free radicals Two radicals combine to form one new (~unreactive) molecule: or a hydrogen atom transfers from one free radical to another: and there is yet another possibility Free Radical Polymerization double bond on the other saturated C on one chain 6 Lecture 17, spring 2010 ENGR 145, Chemistry of Materials Case Western Reserve University Some termination reactions transfer the radical to a new chain R-(CH 2-CH 2 ) n can react with molecules besides the monomer: R-(CH 2-CH 2 ) n + A-B R-(CH 2-CH 2 ) n-A + B Typically: A-B is another polymer molecule often A is a hydrogen Free Radical Polymerization 7 Lecture 17, spring 2010 ENGR 145, Chemistry of Materials...
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This note was uploaded on 01/30/2011 for the course EMSE 103 taught by Professor Ggh during the Spring '10 term at Case Western.

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L17PolymerII145s10r - Lecture 17, spring 2010 ENGR 145,...

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