Lab7 Anionc - CHEM 5384 Polymer Characterization II Lab 7...

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CHEM 5384 Polymer Characterization II Lab 7: Anionic Polymerization of Styrene Mengfang Li 03/15/2013
Abstract: Polystyrene (PS) is synthesized via anionic polymerization. During the polymerization, Nuclear Magnetic Resonance Spectroscopy (NMR) and Gel Permeation Chromatography (GPC) were used to discover functional groups and molecular weight of polymer. The result indicates some of the features of anionic polymerization. Introduction: The main purpose of this laboratory experiment is to perform the anionic polymerization of styrene. The tert-butyl lithium induced anionic polymerization is used to produce a living polymer. The living nature of the polymerization is demonstrated in this lab. The influence of initiator concentration on the degree of polymerization is investigated. Anionic polymerization occurs by chain growth mechanism similar to free radical polymerization, except the active center for the initiation and propagation processes is anionic. It is one of a few polymerization techniques that can be termed “living”. Living polymerization requires that the active site does not experience chain transfer or termination, and the rate of initiation is faster than propagation. Anionic process takes place with monomers possessing electron withdrawing group such as nitrile, carboxyl, phenyl and vinyl. The reaction is initiated by nucleophilic addition to the double bond of monomer [1,2] . The nucleophile is usually a hydroxide, cyanide or carbanion. The carbanion can be created from an organo-matallic species such as alkyl lithium. The mechanism of anionic polymerization is shown below: Figure1: the mechanism of anionic polymerization 1 In this experiment styrene was polymerized using sec-Bu Li:
Figure 2. the reaction of anionic polymerization of styrene

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