Controlled Radical Polymerization Guide - Sigma-Aldrich

Preface
Preface
Chain-growth polymerization has been successfully performed
for many decades through conventional free radical, anionic, or
cationic polymerization. These polymerization techniques generate
many important commodity polymers where their broad range
of molecular weight distribution gives rise to important physical
properties. While these techniques are useful for a number of
applications starting from a wide variety of monomers, several
applications benefit from using more precisely controlled polymers.
“Living” polymerization pioneered by Michael Szwarc enables
control over the polymer architecture, which includes molecular
weight, molecular weight distribution (polydispersity), functionality,
and composition. The occurrence of premature termination is
minimized, and molecular weight proceeds linearly with time
until all monomer is consumed or intentionally terminated. In the
1990s, new methods were developed which enabled an adaptation
of living ionic polymerization to living radical polymerization
(LRP), also referred to as controlled radical polymerization (CRP).
Controlled radical polymerization has branched into three
fundamental techniques which are listed below.
yyAtom Transfer Radical Polymerization (ATRP)
yyReversible Addition/Fragmentation Chain Transfer
Polymerization (RAFT)
yyNitroxide-mediated Polymerization (NMP)
CRP can be utilized with a broad range of vinyl monomers for a
wide variety of applications. Moreover, CRP enables a new level
of materials design and is accessible to all levels of synthetic
expertise due to the robustness of the polymerization conditions.
Figure 1 illustrates the trend in literature citations for the main
CRP techniques.
Citation Count
1200
1000
800
600
400
200
0
ATRP
RAFT
NMP
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
Year
Figure 1. SciFinder search results as of 2011 for ATRP, RAFT, and NMP technologies.
All of these technologies are popular in the research community
and are being explored for industrial adoption. ATRP has
consistently held the most citations. RAFT technology has gained
a substantial increase in publications over the last 5-8 years. NMP
remains relevant in research with approximately 150 annual
citations since 2005. Table 1 is a brief summary of benefits and
limitations of the different CRP techniques.
Aldrich.com
Table 1. Benefits and limitations of ATRP, RAFT, and NMP processes.
Primary
Benefits
Primary
Limitations
ATRP RAFT NMP
yyVersatile yyAbility to tailor catalyst
to meet specific needs
yyUse of transition
metals
yyMany variables affecting
polymer characteristics
yyVersatile yyNo use of transition
metals
yyHigh potential for odor
and discoloration
(especially for low
molecular weights)
yyNo use of transition
metals
yyLow potential for odor
and discoloration
yyLeast versatile
Polymers generated by controlled radical polymerization are used
in many applications. Surface modification, commonly performed
through ATRP, enables advancement in many applications which
rely on tailored hydrophilicity, adhesive properties, or nanoparticle
functionalization. Block copolymers for bio-applications, commonly
performed through RAFT or ATRP, enable advancements in drug
delivery, bio-mineralization, bio-compatibilization, and hydrogel
applications. Block copolymers generated from NMP are used in
pigment dispersion, memory devices, composite manufacturing,
and many others.
This guide provides a fundamental review of ATRP, RAFT, and
NMP techniques, as well as corresponding procedures and
product information to utilize these techniques. The guide has
been arranged in four sections: the ATRP section contains four
articles, two procedures and tables for initiators and catalysts; the
RAFT section contains three articles, two procedures and RAFT
agent tables; the NMP section contains an article and an NMP
agent product table; and the monomer section contains tables
of six monomer classes. We hope that this publication will enable
chemists and engineers to explore different
CRP techniques.
Sebastian Grajales, Ph.D.
Aldrich® Materials Science
Milwaukee, WI 53209
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