Telechelic polymers ATRC

The use and limitations of Atom Transfer Radical Coupling (ATRC) reactions including polyrecombination reactions for the preparation of telechelic polymers, segmented block copolymers, and polycondensates are presented. Specifically, the preparation of telechelic polymers with hydroxyl, aldehyde, amino and carboxylic functionalities, poly(/i-xylylene) and its block copolymers, and polyesters via ATRC process is described. The method pertains to the generation of biradicals at high concentration from polymers prepared by ATRP or specially designed brfunctional ATRP initiators. The possibility of using silane radical atom abstraction (SRAA) reactions, that can be performed photochemically in the absence of metal catalysts, as an alternative process to ATRC is also discussed. 

In this chapter, the use and hmitations of ATRC reactions including polyrecombination reactions for the preparation of telechelic polymers, segmented block copolymers and polycondensates are discussed. 

ATRC, is based on the application of Cu(0) to an ATRP system, leading to the reduction of any Cu(ll) in the reaction medium to form Cu(I). The increase of Cu(l) in the reaction medium dramatically shifts the equilibrium between active and dormant species to the side of the active radical species. So the high concentration of radicals presents in the system favor the recombination reactions between two macroradicals. This method was performed to obtain telechelic polymer from monotelechelic polystyrene and results showed that it is very effective way with high efficiency in a short reaction time. Figure 1 shows a,co-telechelic polymer with double molecular weights as compared with the mono functional polystyrene obtained by ATRP using aldehyde functional initiator. 

Figure 1. Gel Permeation Chromatography (GPC) traces of mono-aldehyde functional starting polymer and a,co-telechelic polymer obtained by ATRC.

In conclusion, it has been demonstrated that ATRC reactions are useful for preparing various macromolecular stmctures such as telechelics and certain polycondensates. The method preserves to the generation of biradicals at high concentration from polymers prepared by ATRP or specially designed bifimctional ATRP initiators. The radical generation process is not limited to the metal catalyzed atom transfer reactions. Silane radical atom abstraction reactions can also be used for the formation of reactive radicals. Aromatic carbonyl assisted photoinduced reactions seemed to a promising alternative route for silane radical generation since it can be performed at room temperature and does not require metal catalysts. 

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