Living propagation

Sato, T. and Otsu, T. Formation of Living Propagating Radicals in Microspheres and Their Use in the Synthesis of Block Copolymers. Vol. 71, pp. 41 —78. 

It is to be noted that N-vinylcarbazole (NVC) undergoes also living cationic polymerization with hydrogen iodide at —40 °C in toluene or at —78 °C in methylene chloride and that in this case no assistance of iodine as an activator is necessary 10d). NVC forms a more stable carbocation than vinyl ethers, and the living propagation proceeds by insertion between the strongly interacting NVC-cation and the nucleophilic iodide anion. 

The Ti-FI dimethyl complexes 42 and 43 can readily be activated with B(C6F5)3 or [CPh3]+[B(C6F5)4] to form a methyl cationic species. The addition of ethylene to the cationic species derived from 42 allows room temperature observation of the living propagating species, which displays XH NMR peaks centered at 1.45 and 2.88 ppm that are attributed to the diastereotopic a-methylene protons connected... 

In the paper published in 1900, he reported that hexaphenylethane (2) existed in an equilibrium mixture with 1. In 1968, the structure of the dimer of 1 was corrected to be l-diphenylmethylene-4-triphenylmethyl-2,5-cyclohexadiene 3, not 2 [38]. Since Gomberg s discovery, a number of stable radicals have been synthesized and characterized, e.g., triarylmethyls, phenoxyls, diphenylpicryl-hydrazyl and its analogs, and nitroxides [39-43]. The radical 1 is stable, if oxygen, iodine, and other materials which react easily with it are absent. Such stable radicals scarcely initiate vinyl polymerization, but they easily combine with reactive (short-lived) propagating radicals to form non-paramagnetic compounds. Thus, these stable radicals have been used as radical scavengers or polymerization inhibitors in radical polymerization. 

When the initiator (I) is very efficient, e.g. kp/k < 0.3, and an excess of monomer (M) is used, the initiator disappears according to a near-first-order law before much monomer has been consumed. Once it is all used up the monomer disappears exactly according to a first-order law since the concentration of living propagating species (P) is now constant and equal to the original concentration of initiator. Hence, provided that both initiator and monomer concentrations can be followed, say by H NMR, both k and kp may be determined60. 

E.s.r. evidence for a living (propagating) polymer radical in grafting reactions of vinyl monomers with irradiated cellulose has also been reported (26). 

Cationic polymerization of 3,9-dibenzyl-1,5,7, ll-tetraoxaspiro[5.5]undecane (123) with tri-phenylmethylcarbenium tetrafluoroborate or boron trifluoride etherate proceeded at room temperature. After the complete consumption of the monomer, the polymerization took place again when the monomer was added to the reaction system. This fact strongly indicates the presence of a stable and long-lived propagating chain end (124) in the polymerization of 123. 

Interestingly enough, this process is effective in bulk, in water suspension and in aqueous miniemulsion . The long-lived propagating species can be derivatized into a series of functional groups by addition of properly substituted nitroxides or nonpolymerizable olefins". Moreover, PVac-fc/oc -PS diblock copolymers were synthesized successfully, which is an additional step in the macromolecular engineering of PVac. ... 

Two different types of (PS-b-PBDh) diblock can be presently synthesized. The first one by classical anionic initiation (s-buty1-lithium) and "living" propagation of the (PS-b-PBD) copolymer (8), followed by the hydrogenation procedure described here as discussed above, the resulting product will be close to a (PS-b-LLDPE) copolymer. The second one came from the discovery (9) of a "living" polymerization of butadiene into a pure (99 %) 1,4 polymer by a bis n allylnickel-tri-fluoroacetate) coordination catalyst, followed by styrene polymerization unfortunately, the length of the polystyrene block is limited (to a M.W. of ca. 20,000) by transfer reactions. 

Acetylenes copolymerize with each other and with cycloalkenes under the influence of olefin metathesis catalysts, as summarized in Tables 10.6 and 10.7, respectively. Each table is divided into two sections according to whether the catalyst system gives long-lived propagating species or not. 

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