limitation in the nature of solvents and conventional specific conditions required by RP (Braunecker and Matyjasziewski
2007; Matyjaszewski and Tsarevsky 2014; Boyer et al. 2016). ATRP is nowadays one of the most widely used
approaches to CRP.
Globally, CRP approaches represent efficient and reliable ways for synthesizing polymers by RP while limiting
the recurrent problem of size heterogeneity, but they are also useful tools for achieving particular designs and the
incorporation of functional moieties that had remained hitherto inaccessible. The main advances made in polymer design
and chemistry since CRP became a standard polymerization method are shortly reviewed in the next Annex.
4.6.5
Annex 4.5. Polymer Topology and How to Control It
Prior to the development of CRP, the design and functionalization of polymers were severely restricted due to the
limitations of RP and of the various techniques of polymer chemical modification. A brief description and comparison of
the various strategies developed during the pre- and the post-CRP period is given in the following paragraphs.
Three main parameters, namely the topology, the composition, and the functionality, are to be considered when
designing polymers. Whereas the synthesis of a linear homopolymer can be (in theory) easily achieved, difficulties tend
to accumulate when aiming at building more complex structures comprising two or more types of comonomers. CRP has
become the prevalent approach to try to circumvent them (Braunecker and Matyjasziewski 2007; Matyjaszewski and
Tsarevsky 2014).
4.6.5.1 Polymer Topology
The topology (or architecture) of a polymer characterizes its three-dimensional architecture. This structure may be very
simple (linear) or highly elaborate (branched, multiarm, etc.), particularly when the polymer is comprised of different
macromolecular parts (“macromeres”) (Fig. 4.43). CRP, thanks to its versatility, has become a favorite strategy for the
synthesis of well-defined complex macrostructures, a task that would be very laborious if not downright out of reach if
attempted by conventional RP. Indeed, the versatility of CRP lies here in the fact that macromolecules obtained by living
polymerization are dormant species that can be easily activated to react with another target center. Because of the
termination reactions, this is not possible with conventional RP, where the macromeres composing the polymer must be
assembled with each other by chemical conjugation mediated by appropriate functional groups bound to each of them
(see below).
The advantages and advances brought by CRP to the development of polymers with original topologies will not
be further discussed in this section. For more information, see e.g. Matyjaszewski and Spanswick (2005), Boyer et al.
(2009), and Matyjaszewski and Tsarevsky (2014).
Fig. 4.42 Examples of chemical structures of reactants used in controlled radical polymerization. (A) In
nitroxide-mediated polymerization (NMP), the control of polymerization is mediated by the establishment
of an equilibrium between a nitroxide, (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO) (left) and its
alkoxyamine derivative (right). P n
• is a growing chain. (B) In atom transfer radical polymerization
(ATRP), control is ensured by a reversible reaction between an alkyl halide and a liganded (L being an
organic ligand) copper salt. (C) In reversible addition-fragmentation chain transfer polymerization
(RAFT), the size of the chains is controlled by exchange with a dithioester or a trithiocarbonate
(R 1 ¼ R-S-) (See references in Table 4.6 for detailed structures and mechanisms).
222
4 Chemical Structure, Synthesis, and Physical-Chemical Properties of Amphipols
2007; Matyjaszewski and Tsarevsky 2014; Boyer et al. 2016). ATRP is nowadays one of the most widely used
approaches to CRP.
Globally, CRP approaches represent efficient and reliable ways for synthesizing polymers by RP while limiting
the recurrent problem of size heterogeneity, but they are also useful tools for achieving particular designs and the
incorporation of functional moieties that had remained hitherto inaccessible. The main advances made in polymer design
and chemistry since CRP became a standard polymerization method are shortly reviewed in the next Annex.
4.6.5
Annex 4.5. Polymer Topology and How to Control It
Prior to the development of CRP, the design and functionalization of polymers were severely restricted due to the
limitations of RP and of the various techniques of polymer chemical modification. A brief description and comparison of
the various strategies developed during the pre- and the post-CRP period is given in the following paragraphs.
Three main parameters, namely the topology, the composition, and the functionality, are to be considered when
designing polymers. Whereas the synthesis of a linear homopolymer can be (in theory) easily achieved, difficulties tend
to accumulate when aiming at building more complex structures comprising two or more types of comonomers. CRP has
become the prevalent approach to try to circumvent them (Braunecker and Matyjasziewski 2007; Matyjaszewski and
Tsarevsky 2014).
4.6.5.1 Polymer Topology
The topology (or architecture) of a polymer characterizes its three-dimensional architecture. This structure may be very
simple (linear) or highly elaborate (branched, multiarm, etc.), particularly when the polymer is comprised of different
macromolecular parts (“macromeres”) (Fig. 4.43). CRP, thanks to its versatility, has become a favorite strategy for the
synthesis of well-defined complex macrostructures, a task that would be very laborious if not downright out of reach if
attempted by conventional RP. Indeed, the versatility of CRP lies here in the fact that macromolecules obtained by living
polymerization are dormant species that can be easily activated to react with another target center. Because of the
termination reactions, this is not possible with conventional RP, where the macromeres composing the polymer must be
assembled with each other by chemical conjugation mediated by appropriate functional groups bound to each of them
(see below).
The advantages and advances brought by CRP to the development of polymers with original topologies will not
be further discussed in this section. For more information, see e.g. Matyjaszewski and Spanswick (2005), Boyer et al.
(2009), and Matyjaszewski and Tsarevsky (2014).
Fig. 4.42 Examples of chemical structures of reactants used in controlled radical polymerization. (A) In
nitroxide-mediated polymerization (NMP), the control of polymerization is mediated by the establishment
of an equilibrium between a nitroxide, (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO) (left) and its
alkoxyamine derivative (right). P n
• is a growing chain. (B) In atom transfer radical polymerization
(ATRP), control is ensured by a reversible reaction between an alkyl halide and a liganded (L being an
organic ligand) copper salt. (C) In reversible addition-fragmentation chain transfer polymerization
(RAFT), the size of the chains is controlled by exchange with a dithioester or a trithiocarbonate
(R 1 ¼ R-S-) (See references in Table 4.6 for detailed structures and mechanisms).
222
4 Chemical Structure, Synthesis, and Physical-Chemical Properties of Amphipols