Sacrificial initiator

Matyjaszewski K, Miller PJ, ShuklaN, Immarapom B, Gelman A, LuokalaBB, Siclovan TM, Kickelbick G, Valiant T, Hoffmann H, Pakula T (1999) Polymers at interfaces using atom transfer radical polymerization in the controlled growth of homopolymers and block copolymers from silicon surfaces in the absence of untethered sacrificial initiator Macromolecules 32 8716-8724... 

Polymer brushes can be grown from CNTs in the presence of CNT-based macroinitiators by an in situ ATRP technique with or without a sacrificial initiator. The monomers used in such a protocol are shown in Scheme 5.2, and the corresponding polymerization conditions and results are listed in... 

C) streptavidin-polyNIPAAm (obtained in the presence of sacrificial initiator), (D) streptavidin-biotin control, (E) streptavidin-polyPEGMA (obtained in the presence of sacrificial initiator). Reprinted with permission from Bontempo, D. Maynard, H. D. J. Am. Chem. Soc. 2005, 127,6508-6509. Copyright 2005 American Chemical Society. 

Recently, we report an approach for the preparation of polymer brushes on different kinds of PET surfaces (films, fibers and fabrics). The PET surfaces were first reacted with 1,2-diaminoethane by aminolysis reaction to incorporate functional groups on the surface. Then, in a second step, atom transfer radical polymerization (ATRP) initiators were grafted by reaction with bromoisobutyryl bromide. Surface-initiated ATRP was performed in bulk using styrene monomer and the adequate catalytic system in the presence of sacrificial initiator. Polymer brushes were obtained with a good controlled of polymerization (46). 

Using atom transfer radical polymerization in the controlled growth of homopolymers and block copolymers from silicon surfaces in the absence of unteth-ered sacrificial initiator, 32 8716-8724. 

Matyjaszewski, K., MiUer, P. J., Shukla, N., Immarapom, B., Gehnan, A., Luokala, B. B., Siclovan, T. M., Kickelbick, G., Valiant, T., Hoffmann, H., Pakula, T., Polymers at Interfaces Using Atom Transfer Radical Polymerization in the Controlled Growth of Homojxrlymers and Block Copolymers from Silicon Surfaces in the Absence of Untethered Sacrificial Initiator, Mamnwlegd 1999, 32,8716-8724. 

Since the concentration of attached surface initiators is low it is almost impossible to generate the PRE based on initiator-initiator termination reactions and either a sacrificial initiator has to be added or a fraction of Cu(II)-based catalyst complex should be added to provide control over the polymerization process. A kinetic model showed, through modeling, that adding deactivator provides better control over polymer MW and a thicker graft layer than added free initiator under similar conditions. ... 

The main drawback of the previous approach is the use of TBHP or other radical initiator that is consumed or decomposed in the initiation steps of the chain mechanism. It would be even more convenient if no organic sacrificial initiator is added. In this regard, the pioneer work of Ishii et al. using aromatic A-hydroxylamines in combination with first-row transition metal ions such as Co ", Fe ", or Mn + has shown that by coordination of the A-hydroxylamine with these transition metals oxyl radicals are formed and these oxyl radicals can act as suitable radical initiators [40,41] (Scheme 2.12). Due to the stability of the molecule and the corresponding oxyl radical, A-hydroxylphthalimide (NHPI) has been one of the preferred organic initiators in combination with Co " or Fe " ions. 

Fig. 9 Growth profiles of grafted polystyrene on a silicon wafer with addition of sacrificial initiator (circles) or deactivator (squares). Reprinted with permission from Jeyaprakash et al. [118]...

Hence, the growth profile of the polymer layer with conversion is expected to be linear in an ideal case, where the polymerization rates of solution and surface chains are the same. Deviation fi om linearity in the growth profile with time or with conversion (added deactivator or sacrificial initiator, respectively) could be explained by applying the philosophy of either the school of propagation or school of termination, as previously discussed. 

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