Chap._800007 - 7 Preparation R Li styrene —— R——...

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Unformatted text preview: 7 * Preparation R Li + styrene ——- R—— bunk“ pulpljlznr 'Li' R—mew ' Li ' ——~—.. polystyrene pom-milieu: ElDl-I MMNVVU— polyhuudérn: plylzyrenc 'Li' R—_IVWVWW'————_DH polymer I I molecular l 1 weight : : s'equenci 1 additicin ‘i’f monomers : l I I l I I l butadiene % monomer conversion 0 —-—+ 100 0 —"'—" 100 0 -——-->100 ll: It!3 2311 1I311 mono —-——»“ to C if U butadiene styrene —""'—'—" -—-—-—> $133 RLi+styrene ‘—"“—“' R ”(mum R , ‘ Li ' polyfiyrene polyhulidlem + SW1: dun—um 'Li‘ E|3u it) ' + The ttiblock copolymers are prepared by anionic living polymerization (using, for example, ethyllitln'um as initiator), utilizing I the indefinite activity of the growing chains. Essentially, the initiator is added to a solution of styrene in an inert solvent (e. g. benzene); butadiene is then added, followed by more styrene. The copolymer is then precipitated with ethanol. number of polymer chain I | number of initiator M. [I] Xn: Difunctional anionic initiator has been developed,which reduced the process to tWo sequential steps. The current - commercial process is based on difunctional initiators The radial block copolymers are also prepared by anionic polymerization. Firstly, _ a styrene-hutadiene diblock which is active at : the butadiene end is formed. A polyfunctional coupling agent such as silicon tetrachloride is then added to produce the radial structure. ...
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