Cationic alkoxyamine

Scheme 15 Structure of cationic alkoxyamines used for SI-NMP from clay surfaces...

An alkoxyamine with an appropriate functional group can be used to terminate a non-NMP polymerization to yield a polymer with an alkoxyamine end group, which subsequently initiates NMP of the second monomer, such as termination of a cationic polymerization by LX... 

In another example, Yildirim et al. photochemically generated anthracene radical cations in the presence of TEMPO [29]. TEMPO immediately trapped the radical to form the TEMPO-anthracene cation, which was subsequently used to initiate cationic polymerization of cyclohexene oxide (CHOX). The resulting alkoxyamine-functional polycyclohexene oxide was used to macroinitiate styrene polymerization, resulting in the formation of S-6/-CHOX (Scheme 8.9). 

Similar to hydroxylamines, alkoxyamines may be oxidized to the nitroso compounds under loss of the alkyl group [165]. Radical cations or radicals obtained from 7V-alk-oxyamines may undergo intramolecular cyclization to double bonds like in pentenyl-alkoxyamines [26] or in 5-methoxyamino-5-methyl dibenzocycloheptene [166] [Eq. (33)]. 

These tenns were coined by Otsu and Yoshida " based on the similar terminology introduced by Kennedy to cover analogous cationic systems. Except for the case of the dithiuram disulfides and related species (Section 9.3.2.1), these expressions have now fallen from favor and are no longer used as a generic terminology. In this chapter, we use the term initiator to denote alkoxyamines in NIMP and halo-compounds in ATRP despite the confusion this can create, especially when the process also involves added conventional initiators. 

NMP of S with 346 as initiator gave PS with pendant oxazoline groups. Cationic polymerization of this macromonomcr gave a polyoxazolinc with PS grafts that retained the alkoxyamine functionality. ATRP with 156 as catalyst and ethyl 2-bromoisobutyrate (125a) as initiator has been used to prepare... 

NMRP was also extended to azo-containing polymeric initiators obtained by cationic polymerization [74]. In this case, nitroxyl radicals were formed. In the presence of styrene, the block copolymers produced had a controlled molecular weight, as the termination reactions were minimized and the equihbrium between dormant and active species allowed a controlled growth (Scheme 11.17). 

LRP is a powerful tool for the synthesis of complex polymer architectures as was shown above. However, in some cases it is desirable to combine structures that are hardly or not at all accessible via radical polymerization techniques. In such cases it may be beneficial to combine LRP with another polymerization mechanism. Many examples have been reported so far. A few examples will be listed here. Polystyrene-6-pol3risobutylene-6-polystyrene was synthesized via a combination of living cationic polymerization and ATRP (98). Polyolefin Graft Copolymers (qv) were synthesized by first polymerizing alkoxyamine-substituted olefins via metallocene catalysis, and subsequent polymerization of vinyl monomers via... 

The scheme PI 1.4.1, outlined below for the simultaneous cationic ROP and controlled free radical polymerizations, is based on the methods that were rst used and experimentally veri ed by Weimer et al. (1998). A multifunctional initiator, such as (P4-I), containing orthogonal reactive sites for CRP and ROP is used This alkoxyamine adduct, namely, benzoic acid 2-(4-chloromethyl)phenyl)-2-(2,2,6,6-tetramethyl piperidin-1-yloxy) ethyl ester, can be prepared (Puts and Sogah, 1997) by heating a solution of benzoyl peroxide and TEMPO in 4-vinylbenzyl chloride at 80°C for 24 h, followed by puri cation by chromatography. 

A similar strategy has been used to allow SI-NMP from other clay minerals such as laponite [50] and saponite [51]. In the case of laponite, a SGI-based alkoxyamine bearing an ammonium group 16 (Scheme 15) was first inunobilized by cation exchange (Scheme 16) [50]. Then, PS chains were obtained from its surface in the presence of a sacrificial alkoxyamine initiator to afford composites exhibiting improved colloidal stability in inorganic solvent. Transmission electron... 

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