Controlled/living polymerizations architectural possibilities with

ARCHITECTURAL POSSIBILITIES WITH CONTROLLED/LIVING POLYMERIZATION METHODS... 

In 1998, Chiefari et al. [10] attempted to combine the convenience of radical polymerization with the many benefits of living polymerization, e.g. control of the molecular weight and polydispersity and the possibility of synthesizing block copolymers of complex architecture. They used free-radical polymerization reagents of formula (I) to produce a sequence of reversible addition-fragmentation in which the transfer of the S=C (Z) S moiety between active and dormant chains serves to maintain the living character of the polymerization ... 

Living polymerizations in which initiation is fast and quantitative and which have irreversible growth offer several advantages over conventional polymerizations. In addition to the ability to obtain polymers with controlled molecular weights and narrow molecular weight distributions, it is also possible to control the polymer architecture and chain end functionality. For example, diblock and triblock copolymers containing liquid crystalline blocks have been prepared by living polymerizations. 

Further progress in the field of IPECs has been associated with involvement of more complex polyionic architectures, such as branched ionic (co)polymers (polyelectrolyte stars and cylindrical polyelectrolyte brushes) as well as self-assemblies of linear ionic diblock copolymers (polymeric micelles) (Fig. 6a-c), into interpolyelectrolyte complexation. Synthesis of well-defined polymeric architectures with nonlinear topology has become possible only recently due to considerable developments in living and controlled polymerizations. In this section, we briefly... 

For systems that are not (strictly speaking) living and may be subject to chain-breaking reactions with possible interruption of chain growth, most of the advantages of truly living polymerizations may, however, be preserved, provided that transfer and termination are minimized. Indeed, if the latter reactions occur only to a limited extent and the initiation step is short compared to that of propagation, polymer chains of controlled size and relatively well-defined complex architectures can nonetheless be obtained. Such polymerizations are called controlled. ... 

In an attempt to combine the advantages of living polymerization with the flexibility of free radical polymerization, there has been a significant amount of research into the possibility of controlled/living radical polymerization (C/LRP). These polymerization methods allow nearly unlimited control of the polymer s composition, architecture and functionality. It seems possible nowadays to prepare various novel architectures from virtually all kinds of vinyl monomers by C/LRP methods in common mass, suspension or even emulsion processes. 

During the last decade, more and more advanced techniques of living or controlled polymerization to prepare block copolymers have become available. It has become possible to prepare block copolymers of various architectures, solubility, and functionality [6]. Architectures comprise diblock, triblock, and multiblock copolymers arranged linearly, as stars or grafts. The solubilities vary from polar solvents such as water to media with very low cohesion energies such as silicon oil or fluorinated solvents. Control of functionality has become impor-... 

The development of PPE synthetic chemistry makes the synthesis of PPEs with various structures possible. Recently, PPE-based polymers with different topological structures including linear random copolymers, block copolymers, star polymers, miktoarm polymers, and brush and hyperbranched polymers have been synthesized. Among them, linear homopolymers or random copolymers of PPEs are perhaps the most studied. Different block copolymers with AB, ABA, and ABC architectures have been synthesized by controlled ROP. By the combination of ROP of PPE with other controlled polymerization methods, such as living radical polymerization, or click chemistry, more complex architectures including miktoarm, comb, or graft copolymers can be synthesized. The richness of structures has allowed the convenient adjustment of material properties of PPE for biomedical applications. 

---