Functional initiators disulfides

First several authors planned their use as initiators for thermal or photochemical polymerization for different monomers. Thus, Otsu [55] compared the activity of these xanthogens, sulfides, disulfides and thiuram with several monomers — MMA, S., A.N., VAc, VDC. The results allowed him to classify products as telogens and not as functional initiators. In the same way, these surveys showed that they are photoinitiators without having retarding or inhibiting effects as are observed for several disulfides. 

Similar to functionalized initiators, RAFT CTAs can be designed to contain protein-reactive moieties to yield polymers with a-functionality and/or co-functionality. Many of the same groups used in protein-reactive ATRP initiators are also installed in RAFT agents. RAFT agents functionalized with malemide, pyridyl disulfide,and biotin have been synthesized and the polymers used to conjugate to proteins. Other CTAs have targeted amines and conjugation via click chemistry. ... 

As shown in Fig. 3.16, disulfide-functional initiator was prepared through a five-step synthesis. Figures 3.17 and 3.18 confirm the high purity of the initiator and the intermediate compounds. As calculated in Fig. 3.17, the integral area ratio of peak (a), peak (i) and peak (d+e) is 1.00/3.10/4.09, in consistency with its theoretical ratio of 1.00/3.00/4.00. Using this functional initiator. Seesaw-type polystyrene macromonomer =-S-S-(PS-Br)2 was successfully prepared by ATRP, and its typical NMR spectrum is shown in Fig. 3.19. 

Figure 5. Preparation of degradable polyMMA-based gels by ATRP and their use as supermacroinitiators The disulfide and thiol groups originating from the functional initiator are shown in italics and the ones from the functional monomer in regular font. PolyMMA and polySty chains are represented with solid and dotted lines, respectively. (Reproduced from reference 17. Copyright 2005 American Chemical Society.)...

Many reports related to SI-CRP on metal describe the use of gold nanoparticles and mainly from SI-ATRP. We note only one report describing the modification of gold nanoparticles with SI-NMP. In this report, the NMP initiator was a TEMPO-derivative functionalized with disulfide as ligand for the synthesis of gold nanoparticles [61]. Two populations of gold nanoparticles, of 1.5 and 5.5 nm diameter, covered with PS of 10,000 g moP were prepared. 

Disulfide derivatives and hexasubstituted ethanes2,15 may also be used in this context to make cnd-functional polymers and block copolymers. The use of dilhiuram disulfides as thermal initiators was explored by Clouet, Nair and coworkers.206 Chain ends are formed by primary radical termination and by transfer to the dilhiuram disulfide. The chain ends formed are thermally stable under normal polymerization conditions. The use of similar compounds as photoin iferters, when some living characteristics may be achieved, is described in Section 9.3.2.1.1. 

Since the dithiocarbatnyl end groups 8 are thermally stable but pholochemically labile at usual polymerization temperatures, only photo-initiated polymerizations have the potential to show living characteristics. However, various disulfides, for example, 9 and 10, have been used to prepare end-functional polymers37 and block copolymers38 by irreversible chain transfer in non-living thermally-initiated polymerization (Section 7.5.1). 

N-Allenylazetidinone 181 rearranges to cephalosporin 182 in the presence of lithium chloride (Eq. 13.62) [70], This is a very unusual reaction that is presumed to be initiated by chloride ion-induced cleavage of the disulfide to give sulfenyl chloride 183. Thiolate attack at the allene sp carbon atom of 183 generates ester enolate 184, which cyclizes to 182. The reactivity of the allene function in 181 ensures the success of the reaction. 

New functional groups can arise as a result of oxidation of the compounds mentioned above. For example, the oxidation of a thiol yields a disulfide (R-S-S-R). Double oxidation of a primary alcohol (R-CH2-OH) gives rise initially to an aldehyde (R-C(O)-H), and then to a carboxylic acid (R-C(O)-OH). In contrast, the oxidation of a secondary alcohol yields a ketone (R-C(O)-R). The carbonyl group (C=0) is characteristic of aldehydes and ketones. 

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