A Renaissance in Living Cationic Polymerization

The development of reversible-deactivation radical polymerization (RDRP) has made a great contribution not only in controlling the molecular weight and terminal structures but also in the precise synthesis of copolymers. An additional design for controlled propagation via RDRP could lead to control of the order of repeating units, that is, the 'sequence control', which has been recognized as the ultimate control of precision polymerizations. In this review article, some concepts and methodologies are summarized for synthesizing sequence-controlled polymers based on RDRP.

Section: Sequence-controlled Polymers M Ouchi and M Sawamotomentioning

confidence: 99%

Sequence-controlled polymers via reversible-deactivation radical polymerization

Ouchi

Sawamoto

2017

“…2-PVL_F and 2-PVL_M showed very similar GPC profiles and molecular weights (Figure 17), which is in good agreement with the results discussed above and as seen in the case of RLBC, indicating that these polymers have a similar hydrodynamic volume. Considering the strong intercomponent interaction, 2-PVL_F will act as a linear-shaped polymer in a less polar solvent, such as CHCl 3 .…”

Section: Topology-transformable Polymers T Takata and D Aokimentioning

confidence: 99%

Topology-transformable polymers: linear–branched polymer structural transformation via the mechanical linking of polymer chains

Takata

Aoki

2017

In this review article, we discuss the synthesis and dynamic nature of macromolecular systems that have mechanically linked polymer chains capable of undergoing a topology transformation driven by a rotaxane molecular switch. The rotaxane linking of polymer chains plays a crucial role in these systems. A linear polymer possessing a crown ether/sec-ammonium salt-type [1] rotaxane moiety at the axle chain terminal was prepared via the rotaxane linking of a single polymer chain. A linear-cyclic polymer topology transformation was achieved via the movement of the wheel component from one end to the other end of the axle component using the rotaxane macromolecular switch function. The successful synthesis of a macromolecular [2]rotaxane (M2R) possessing a single polymer axle and one crown ether wheel led to a variety of unique applications, such as the development of topology-transformable polymers and the synthesis of rotaxane crosslinked polymers (RCPs). The introduction of a polymer chain to the wheel component of M2R (rotaxane linking of two polymer chains) produced a rotaxane-linked AB block copolymer that transformed its topology from linear to branched. Furthermore, a rotaxane-linked three-component polymer and an ABC triblock copolymer were synthesized and transformed to the corresponding 3-arm star (co)polymers, and the transformation was confirmed by measuring the hydrodynamic volume change. The structural transformation of 4-arm and 6-arm star polymers was also accomplished using the dynamic mobility of a similar rotaxane. As a useful application, M2R-based vinylic crosslinkers (RCs) were prepared and applied to the synthesis of RCPs, whereby the addition of RCs into radical polymerization systems of vinyl monomers afforded polymers with excellent toughness by enhancing both of tradeoff properties that cannot be achieved using typical covalent crosslinkers.

“…Herein, the covalent species with the carbon-halogen terminal is called the 'dormant' species as in the other living anionic and cationic polymerizations via similarly reversible, but heterolytic activation of the covalent terminal group into the active species. 36,37 Such a metal-catalyzed reversible activation of the carbon-halogen terminal gives an almost equal opportunity of propagation to each polymer chain to enable control of the chain length of the resulting polymer chains. In addition, the equilibrium between the radical and dormant species can diminish the radical concentration, which contributes to the suppression of the bimolecular termination between the growing radical species.…”

Section: Introductionmentioning

confidence: 99%

Recent developments in metal-catalyzed living radical polymerization

Kamigaito

2010

This review presents a short overview of recent developments in metal-catalyzed living radical polymerization, mainly focusing on our recent research studies related to the subject. Metal-catalyzed living radical polymerization or atom transfer radical polymerization, which was originally developed via evolution of the metal-catalyzed Kharasch or atom transfer radical addition to chain-growth polymerization via reversible activation, has now been widely developed in many aspects. The effective metal catalysts include various transition metals, such as ruthenium, copper, iron and nickel, and highly active and versatile catalytic systems have been developed by designing ligands, applying lower oxidation metal species and using additives to widen the scope of controllable monomers and to minimize the amount of metal catalysts and the residual metals in the products. The development of the initiating systems has enabled the synthesis of a wide variety of novel, well-defined polymers, including end-functionalized, block, graft and star polymers, but also more complicated polymers possessing multiple controlled structures. Furthermore, metal-catalyzed living radical polymerization has been judiciously combined with stereospecific radical polymerization based on the use of polar solvents or Lewis acid additives, resulting in the dual control of the molecular weight and the tacticity of the resulting polymers and enabling the preparation of stereoblock and stereogradient polymers. Keywords: block polymer; living radical polymerization; precision polymer synthesis; transition metal catalyst; star polymer; stereospecific polymerization INTRODUCTIONSince the discovery of metal-catalyzed living radical polymerization or atom transfer radical polymerization (ATRP), there have been many developments in this research area, including active and versatile metal catalytic systems; the scope of controllable monomers; well-defined polymers with various controlled architectures; hybridization of the controlled polymers with inorganic, metal and biomolecular compounds; and attempts or real applications to a variety of industrial materials. 1-17 Besides these metal catalytic systems, there have also been substantial developments in various living radical polymerizations, such as nitroxide-mediated polymerizations, reversible addition fragmentation chain-transfer polymerizations and others, and in all of these, there are characteristic features of the mechanisms and components. [18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34] The metal-catalyzed living radical polymerization was originally discovered via evolution of the metal-catalyzed Kharasch or atom transfer radical addition reaction 35 to the chain-growth polymerization of vinyl monomers (Figure 1). 1 The initiating system generally consists of a transition metal complex in a lower oxidation state and an organic halide, in which the carbon-halogen bond of the halogen compound is activated by the metal catalyst to generate the carbon radical species upon a one-e...