in which case there is a linear relationship between the composition of the feed and that of the polymer.
• r 1 > 1 and r 2 > 1: each monomer reacts preferentially with itself, and the copolymerization results in a mixture
of two homopolymers.
Since the first paper of Mayo and Lewis (1944) till today (Kanellou et al. 2015), many works concerning the
co- and ter-polymerization and the determination of the reactivity ratio of the monomers have been published, resulting in
a helpful and wide range of data available to the scientific community.
Blocky, statistical, and alternating sequences are the three types of structures most commonly encountered.
However, it is noticeable that, despite the numerous possibilities of structures that can be designed by varying the nature
of comonomers, RP performed in conventional conditions generally leads to alternating or random copolymers, and
optionally to a gradient composition, but most rarely to a blocky structure. Indeed, diblock or multiblock structures
cannot be directly achieved via RP in homogeneous solutions: they require proper chain-end functionalization of two
homopolymers to allow a specific coupling reaction between the two macromolecules (see Fig. 4.44A, § 4.6.6.2, and
references in Bertin and Boutevin 1996).
When the comonomers are not miscible in the same medium and/or can be segregated in two different phases,
blocky structures are preferentially obtained via RP or CRP performed in dispersed media, either as classical or inverse
emulsions (Candau et al. 1996; Volpert et al. 1996), as micro-emulsions (Matyjaszewski and Tsarevsky 2014), or as
solvent-free polymer mixtures (blends) (Ruzette and Leibler 2005) (Fig. 4.44B).
In principle, diblock structures could be obtained via living polymerization performed in bulk (Bertin and
Boutevin 1996), because it is conceivable, under proper conditions, to react the dormant form of a homopolymer of a
monomer M 1 , obtained by CRP, with a second monomer M 2 , so as to yield a M 1 -co-M 2 diblock copolymer. Up till
recently (and for reasons that will not be explained here), blocky structures of higher order (triblock or multiblock)
remained achievable only by block conjugation following polymerization (see Fig. 4.44A and Golas and Matyjaszewski
2010). Thanks to the latest improvements of CRP, they are now accessible via iterative polymerization reactions
(Soeriyadi et al. 2011; Alsubaie et al. 2014) (Fig. 4.44C), but multiblock copolymers of higher molecular weight than
~25 kDa remain inaccessible by this method (Alsubaie et al. 2014).
Alternatively, multiblock copolymers can be obtained by chemical modification of a homopolymer precursor
performed in dispersed media (Liu et al. 2007; Gohon et al. 2011) (Fig. 4.44D). Although the effectiveness of this method
has been demonstrated, its use is not widespread.
For further information regarding the development of original polymeric microstructures obtained by CRP, the
reader is referred to reviews by Braunecker and Matyjasziewski (2007), Rizzardo and Solomon (2012), Matyjaszewski
and Tsarevsky (2014), and Boyer et al. (2016).
4.6.6
Annex 4.6. Functionalizing Polymers
4.6.6.1 General Considerations
As the case of APols demonstrates, polymers and copolymers present interesting intrinsic properties, but further
functionalities can be conferred onto them by endowing them with one or more appropriate moieties. This can be
achieved according to several methods, which can be classified into the following four categories:
• Polymerization starting from functional initiators or transfer agents. The method consists in performing RP or
CRP in the presence of a functionalized initiator or transfer agent, which will endow the polymers with the
desired functional moiety (Fig. 4.45A).
• Post-polymerization modification of end-group functionality. This two-step procedure involves the polymerization by RP or CRP of a monomer in the presence of a functionalizable initiator or transfer agent and
subsequent modification of the reactive extremities (Fig. 4.45B).
• Introduction, during polymerization, of functional monomers (Fig. 4.46A).
• Post-polymerization modification of functionalizable monomers introduced into the polymer. Following a
similar approach, a functionalizable monomer is homo- or copolymerized via RP or CRP, and the functional
polymer is obtained by modifying it (Fig. 4.46B).
Each method presents its advantages and drawbacks. Those must be carefully considered before opting for one or
the other strategy, which must be adapted to the functionality to be introduced. For instance, introduction of a functional
moiety that inhibits radical reactions can only be achieved after polymerization. Post-polymerization modifications can
4.6 Annexes
225
• r 1 > 1 and r 2 > 1: each monomer reacts preferentially with itself, and the copolymerization results in a mixture
of two homopolymers.
Since the first paper of Mayo and Lewis (1944) till today (Kanellou et al. 2015), many works concerning the
co- and ter-polymerization and the determination of the reactivity ratio of the monomers have been published, resulting in
a helpful and wide range of data available to the scientific community.
Blocky, statistical, and alternating sequences are the three types of structures most commonly encountered.
However, it is noticeable that, despite the numerous possibilities of structures that can be designed by varying the nature
of comonomers, RP performed in conventional conditions generally leads to alternating or random copolymers, and
optionally to a gradient composition, but most rarely to a blocky structure. Indeed, diblock or multiblock structures
cannot be directly achieved via RP in homogeneous solutions: they require proper chain-end functionalization of two
homopolymers to allow a specific coupling reaction between the two macromolecules (see Fig. 4.44A, § 4.6.6.2, and
references in Bertin and Boutevin 1996).
When the comonomers are not miscible in the same medium and/or can be segregated in two different phases,
blocky structures are preferentially obtained via RP or CRP performed in dispersed media, either as classical or inverse
emulsions (Candau et al. 1996; Volpert et al. 1996), as micro-emulsions (Matyjaszewski and Tsarevsky 2014), or as
solvent-free polymer mixtures (blends) (Ruzette and Leibler 2005) (Fig. 4.44B).
In principle, diblock structures could be obtained via living polymerization performed in bulk (Bertin and
Boutevin 1996), because it is conceivable, under proper conditions, to react the dormant form of a homopolymer of a
monomer M 1 , obtained by CRP, with a second monomer M 2 , so as to yield a M 1 -co-M 2 diblock copolymer. Up till
recently (and for reasons that will not be explained here), blocky structures of higher order (triblock or multiblock)
remained achievable only by block conjugation following polymerization (see Fig. 4.44A and Golas and Matyjaszewski
2010). Thanks to the latest improvements of CRP, they are now accessible via iterative polymerization reactions
(Soeriyadi et al. 2011; Alsubaie et al. 2014) (Fig. 4.44C), but multiblock copolymers of higher molecular weight than
~25 kDa remain inaccessible by this method (Alsubaie et al. 2014).
Alternatively, multiblock copolymers can be obtained by chemical modification of a homopolymer precursor
performed in dispersed media (Liu et al. 2007; Gohon et al. 2011) (Fig. 4.44D). Although the effectiveness of this method
has been demonstrated, its use is not widespread.
For further information regarding the development of original polymeric microstructures obtained by CRP, the
reader is referred to reviews by Braunecker and Matyjasziewski (2007), Rizzardo and Solomon (2012), Matyjaszewski
and Tsarevsky (2014), and Boyer et al. (2016).
4.6.6
Annex 4.6. Functionalizing Polymers
4.6.6.1 General Considerations
As the case of APols demonstrates, polymers and copolymers present interesting intrinsic properties, but further
functionalities can be conferred onto them by endowing them with one or more appropriate moieties. This can be
achieved according to several methods, which can be classified into the following four categories:
• Polymerization starting from functional initiators or transfer agents. The method consists in performing RP or
CRP in the presence of a functionalized initiator or transfer agent, which will endow the polymers with the
desired functional moiety (Fig. 4.45A).
• Post-polymerization modification of end-group functionality. This two-step procedure involves the polymerization by RP or CRP of a monomer in the presence of a functionalizable initiator or transfer agent and
subsequent modification of the reactive extremities (Fig. 4.45B).
• Introduction, during polymerization, of functional monomers (Fig. 4.46A).
• Post-polymerization modification of functionalizable monomers introduced into the polymer. Following a
similar approach, a functionalizable monomer is homo- or copolymerized via RP or CRP, and the functional
polymer is obtained by modifying it (Fig. 4.46B).
Each method presents its advantages and drawbacks. Those must be carefully considered before opting for one or
the other strategy, which must be adapted to the functionality to be introduced. For instance, introduction of a functional
moiety that inhibits radical reactions can only be achieved after polymerization. Post-polymerization modifications can
4.6 Annexes
225