Termination reagent

We have decorated different generations of polyphenylene dendrimers based on a biphenyl core with up to 16 perylenemonoimide chromophores at the periphery [67]. This has been achieved via the Diels-Alder reaction of a perylenemonoimide functionalized cyclopentadienone as a terminating reagent with the ethynyl precursor dendrimers. A strongly emitting nanoparticle is thus obtained. 

The published values of related to olefin polymerization with soluble and heterogeneous catalysts are in the range from several seconds to hours 7). It should be noted that the value of is strongly dependent upon the polymerization conditions since the rates of chain-terminating reactions Rt are functions of the temperature and concentrations of chain-terminating reagents. In a living polymerization the value of is infinite. 

Reactive group 1 (e.g. on surface) Intermediate Reactive group II (e.g. on terminal reagent) Coupling linkage type ... 

Fig. 66 Cobalt-catalyzed radical cyclizations of using other radical acceptors and termination reagents...

Most controlled/living cationic systems provide well-defined polymers of relatively low molecular weight, typically in the range M = 5,000 to 20,000. The degrees of polymerization are equal to the ratio of concentrations of the reacted monomer to that of the introduced initiator (DP = d[M]/[I]0), and the polydispersities remain relatively low, MJMn < 1.2. The addition of new portions of monomer (sometimes called incremental monomer addition, IMA) [5] leads to the expected increase of molecular weights, and the addition of another comonomer results in block copolymers, whereas the addition of terminating reagents provides end-functionalized macromolecules (cf. Chapter 5). 

Therefore, all requirements for living polymerization seem to be satisfied, at least in a practical sense, in the microflow system controlled cationic polymerization. The livingness strongly depends on the reaction time. In a very short period of time highly reactive intermediates, in this case reactive propagating polymer ends, can survive and they can be utilized for subsequent reactions when different monomers or a terminating reagent are added. This concept is quite similar to that discussed in Section 6.3. 

Functional groups can be attached to the living polymer chains by choosing suitable termination reagents, resulting in linear or star-shaped molecules. With bi- or multifunctional organolithium initiators , a greater variety of polymer products can be synthesized,... 

Bf Container fbrthe Ti-solution 02 Container fbrthe Al - solution B3 Container fbrthe termination reagent... 

The first method of transformation of living ROMP into controlled/ living ATRP was reported by Matyjaszewski for the preparation of diblock copolymers. Thus, macroinitiators were prepared by ROMP of norbomene (Scheme 5) or dicyclopentadiene and subsequent Wittig-like reactions with /7-(bromomethyl)benzaldehyde. In these cases, the ROMP of norbomene was terminated with a terminating reagent that could also function as an ATRP initiator. Thus, these compounds were used as efficient macroinitiators for homogeneous controlled/ living ATRP to prepare block copolymers with styrene and methyl acrylate (Scheme 6) [21]. 

After consumption of the monomer under living, anionic conditions, electrophilic terminating agents can be added to functionalize the chain ends. Examples of terminating reagents include CO2 and ethylene oxide, which, after protonation, form carboxylic acid and alcohol-terminated chains, respectively. 

S.6.6.2. Reaction with Termination Reagents. Because of their very high reactivity, carbanionic species react with many compounds—in particular, those exhibiting an acidic character ... 

Several atmospheric components can be utilized as terminating reagents ... 

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