Functional Polymers - American Chemical Society

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Chapter 4

Use of Protecting Groups in Polymerization 1

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D. N. Schulz , S. Datta , and R. M . Waymouth

Downloaded by CORNELL UNIV on May 28, 2012 | http://pubs.acs.org Publication Date: May 8, 1998 | doi: 10.1021/bk-1998-0704.ch004

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Corporate Research Laboratory, Exxon Research and Engineering Company, Route 22 East, Clinton Township, Annandale, NJ 08801 Exxon Chemical Company, 5200 Bayway Drive, Baytown, TX 77520 Department of Chemistry, Stanford University, Stanford, CA 94305 2

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Functional polymers are often difficult to synthesize because of the antagonism or competition of functional groups with the active sites of catalysts or initiators. In addition functional groups can sometimes act as sites for chain transfer or termination. This paper reviews recent advances in the application of protecting groups in anionic, cationic, Ziegler-Natta, metallocene and metathesis polymerization. Such groups have been built into initiators, terminating agents, and monomers. The most versatile and robust protecting groups are the silyl ethers, which have remarkably been applied to all of the above polymerization types. Borane mediated synthesis of functional polymers has also been proven effective for several polymerization methods.

Functional polymers are macromolecules containing functional groups that have polarity or reactivity different from backbone chains. Such polymers often show improved properties by virtue of enhancements in phase separation, reactivity, or interpolymer associations. Aternatively, functional polymers may be viewed as polymers that have a function or use. Unfortunately, functional polymers are often difficult to synthesize because of the antagonism or competition of functional groups with the active sites of catalysts or initiators. In addition, functional groups can sometimes act as sites for chain transfer or termination. Following the lead of peptide chemists, polymer chemists have increasingly used protecting groups during polymerization to mask reactive functionality. This paper reviews recent advances in the application of protecting groups in anionic, cationic, Ziegler-Natta, metallocene and metathesis polymerization.

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©1998 American Chemical Society In Functional Polymers; Patil, A., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1998.

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Protecting Groups In Anionic Polymerization Protecting groups have been used in several ways for the preparation of functional anionic polymers; e.g. as protected functional initiators, terminating agents, and monomers. Scheme 1 illustrates these methods. Scheme 1 •

Protected Inititiators

Downloaded by CORNELL UNIV on May 28, 2012 | http://pubs.acs.org Publication Date: May 8, 1998 | doi: 10.1021/bk-1998-0704.ch004

B - R - X - ^ t g c L *

@ — R - X

(I)

(I) + Li or BuLi (II)+ M

R-Li (II) ® PZfl » (2) © R ROH OH

(PG)—RfM)-H W n J

:Protic Functional Group x = Reactive Groip (e.g Halogen) M = Monomer

(III)

Deprotect

© — R f M > - H

Protecting ©•: Group

(IV)

•

Protected Terminating Agents R'-^-M}—Li +

X-R-4N F®

acid catalyst

acid catalyst out at

78lo25°C.

Terminal inn icaetiuns

wcie < anied

• Termination quantitative in THF and THF/heptane; deprotection requires care because of possible oxidation of -SH.

• Termination in heptane had coupling side reaction; termination near quantitative in THF and THF/heptane; deprotection quantitative.

• Termination in heptane had coupling side reaction; termination near quantitative in THF and THF/heptane; deprotcction quantitative.

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Table II. Protected Functional Terminating Agents for Anionic Polymerization

Downloaded by CORNELL UNIV on May 28, 2012 | http://pubs.acs.org Publication Date: May 8, 1998 | doi: 10.1021/bk-1998-0704.ch004

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27,32

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