Carey6e_Ch29_Summary

Carey6e_Ch29_Summary - car28374_ch29_1242-1271 08/23/04...

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1266 CHAPTER TWENTY-NINE Synthetic Polymers polymerization of styrene in the presence of poly(1,3-butadiene). Instead of reacting with styrene, the free-radical initiator abstracts an allylic hydrogen from poly(1,3-butadiene). Polystyrene chain growth begins at the allylic radical site and proceeds in the usual way at this and random other allylic carbons of poly(1,3-butadiene). Polystyrene grafts on a poly(1,3-butadiene) chain are the result. Polystyrene alone is brittle; poly(1,3-butadiene) alone is rubbery. The graft copoly- mer is strong, but absorbs shock without cracking because of the elasticity provided by its poly(1,3-butadiene) structural units. 29.16 SUMMARY Section 29.1 Polymer chemistry dates to the nineteenth century with the chemical modiF- cation of polymeric natural products. Once the structural features of polymers were determined, polymer synthesis was placed on a rational basis. Section 29.2 Polymers are usually named according to the monomers from which they are prepared ( source-based nomenclature ). When the name of the monomer is Poly(1,3-butadiene) Polystyrene Poly(1,3-butadiene) CH CH CH 2 CH Poly(1,3-butadiene) Poly(1,3-butadiene) CH CH CH 2 CH ±urther reaction with styrene CH CH 2 CH CH 2 Poly(1,3-butadiene) Poly(1,3-butadiene) CH CH CH 2 CH Poly(1,3-butadiene) Poly(1,3-butadiene) CH CH CH 2 CH CH CH 2 CH CH 2 Poly(1,3-butadiene) Poly(1,3-butadiene) CH CH CH 2 CH Poly(1,3-butadiene) Initiator Poly(1,3-butadiene) CH CH CH 2 CH H car28374_ch29_1242-1271 08/23/04 07:53 Page 1266 EQA
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1268 CHAPTER TWENTY-NINE Synthetic Polymers Section 29.9 Anionic polymerization of alkenes that bear a carbanion-stabilizing sub- stituent (X) can be initiated by strong bases such as alkyllithium reagents. The product of this step is a new organolithium reagent that can react with a second monomer molecule, then a third, and so on. The growing organo- lithium chain is stable and is called a living polymer. Section 29.10 Cationic polymerization of alkenes that can form relatively stable carbocat- ions can be initiated by protonation of the double bond or coordination to Lewis acids such as boron triFuoride. Section 29.11 The key bond-forming process in many polymerizations is a condensation reaction. The most common condensations are those that produce polyamides and polyesters. Polyamide synthesis is illustrated by the preparation of nylon 66, the most commercially successful synthetic ±ber.
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This note was uploaded on 11/04/2009 for the course CHE 12184 taught by Professor Bobkane during the Spring '09 term at Baylor.

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Carey6e_Ch29_Summary - car28374_ch29_1242-1271 08/23/04...

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