Ch1b09Lecture24

Ch1b09Lecture24 - Lecture 24 - March 5, 2009 Summary of...

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Unformatted text preview: Lecture 24 - March 5, 2009 Summary of last lecture •intermolecular forces, part II •hydrophobic effect Preview of coming attractions •polymers •Nylon demonstration •elasticity 1 Polymers polymers are giant molecules made from repeated small molecule units known as monomers linked together by the chemical reaction known as polymerization by varying the monomers and polymerization mechanisms, polymers can be produced with different structures, sizes, and physical properties CH CH 2 CH CH 2--(CH 2 CH 2 ) n-- polystyrene polyethylene backbone substituents or sidechains 2 the polymerization of propylene: possible products head-to-tail head-to-head, tail-to-tail head tail random the head-to-tail polymer is generally produced industrially 3 stereochemical aspects of head-to-tail polymerization head-to-tail polypropylene has asymmetric centers at * * * * BPOC Fig. 29-8 Parsons pg 186 4 2.5 Å 3.5 Å isotactic syndiotactic CH 3 CH 3 CH 3 CH 3 H H H H CH 3 CH 3 CH 3 CH 3 random = atactic alternating - syndiotactic all chiral centers the same - isotactic CH 3 CH 3 CH 3 CH 3 CH 3 CH 3 5 polymer structure and physical properties The physical properties of a polymer can have a strong dependence on tacticity. isotactic and syndiotactic polypropylene have regular structures, which allow favorable polymer-polymer packing atactic polyprop. has an irregular structure and poor packing isotactic and syndiotactic forms have higher melting temperatures (~165˚ and 130˚ C) and are poorly soluble in many solvents. atactic has lower melting temp (< 0˚ C), is soft, rubbery, and can be molded. It is also more soluble in most solvents. 6 mechanisms of polymer synthesis 7 free-radical chain reaction polymerization: (lecture 18) Ring-opening metathesis polymerization (ROMP) Grubb ’ s catalyst catalyst polymer R.H. Grubbs, Nobel Lecture slides polymer synthesis: condensation reaction----A + B---- →----AB---- C R 1 OH O C R 1 N H O R 2 R 2 –NH 2 + + H 2 O carboxylate + amine amide/peptide + water each reactant must be bifunctional: two strategies...
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This note was uploaded on 09/25/2010 for the course CH 104 taught by Professor Bopanna during the Fall '09 term at UMBC.

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Ch1b09Lecture24 - Lecture 24 - March 5, 2009 Summary of...

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