Telechelic ATRP process

Different reactions may affect the chain-end bromine atom of PS during ATRP transfer process, bimolecular terminations, or elimination reactions induced by the Cu(II) complex. The authors showed that the loss in functionality was predominantly due to /1-hydrogen elimination reactions. This result is very important for the synthesis of telechelic polymers by ATRP, because all processes (described later) are based on the halogen transformation. 

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 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. 

In the area of novel materials CMU protected (co)polymers prepared by ATRP except with CCI4 initiator and telechelic polymers prepared by CRP with MW > 20,000 (49) copolymers with a tme gradient segment (30) polar ABA block copolymers, (30) and well defined graft copolymers and segmented copolymers with one or more CRP blocks where the macroinitiator had been prepared by another polymerization process. (36) In addition, the use of tethered initiators allowed synthesis of hybrid core/shell copolymers. Pending applications disclose other novel polymeric materials. 

Obviously, ATRP leads to the formation of monofunctional telechelics since the other chain always contains halogen as a result of the fast deactivation process. These polymers could be called heterotelechelic since halogen is also a functional group. Therefore, a , y-telechelics can only be prepared by transformation of the... 

A functional initiator may catty a second noninitiating functionality, in addition to a radically transferable atom or group, to yield hetero-telechelic materials. Since ATRP is a radical-based process, many functional groups can be tolerated in the initiator molecule including hydroxy, epoxy, amino, amido, cyano, and azido and many other functional groups can be incorporated in a proterted form. Therefore, the added initiator can also be used to introduce additional functionality into the a-chain end or within the core of a mrrltiarmed star or composite material, see Sections 3.12.8 and 3.12.10 (Scheme 10). 

For nitroxide-mediated radical polymerizations and in the RAFT process, the same synthetic strategy as for ATRP can be used in the synthesis of AB and ABA block copolymers. The first step is coupling a functionalized alkoxyamine with a telechelic or monofunctional nonvinylic polymer to give a macroinitiator. This macroinitiator can be used in standard controlled free-radical polymerization procedures. This approach is best illustrated by the preparation of PEO-based block copolymers [81-84]. One example is the preparation of macroinitiator LMI-7 by the reaction of a monohydroxy-terminated PEO with sodium hydride followed by reaction with the chloromethyl-substituted alkoxy amine as shown in Scheme 3.16. 

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