Initiators, anionic functionalized

Surprisingly, after this very first example, there was a 20 year delay in the literature in the appearance of the second report on siloxane macromonomers. However, during this period there have been numerous studies and developments in the vinyl and diene based macromonomers91 -94). The recent approach to the synthesis of siloxane macromonomers involves the lithiumtrimethylsilanolate initiated anionic polymerization of hexamethyltrisiloxane in THF 95,123). The living chain ends were then terminated by using styrene or methacrylate functional chlorosilanes as shown in Reaction Scheme X. 

The reaction is complicated in aprotic media by polymerization of the olefin at the electrode 132> apparently because anions such as 134 or 136 can initiate anionic polymerization of the activated olefin. Steric hindrance about the double bond can retard polymerization yields of hydrodimer from 132 in di-methylformamide as a function of the size of R are R = hydrogen or methyl, 0%, R % n-propyl, 25% R % i-propyl, 65% R % /-butyl, 95%, 32). Saturation of the double bond to produce, e.g., 136 from 132, is a side reaction in neutral... 

The alkyllithium-initiated, anionic polymerization of vinyl and diene monomers can often be performed without the incursion of spontaneous termination or chain transfer reactions (1). The non-terminating nature of these reactions has provided methods for the synthesis of polymers with predictable molecular weights and narrow molecular weight distributions (2). In addition, these polymerizations generate polymer chains with stable, carbanionic chain ends which, in principle, can be converted into a diverse array of functional end groups using the rich and varied chemistry of organolithium compounds (3). 

A dual-function alkoxyamine with an appropriate functional group, such as the hydroxyl-containing alkoxyamine LX, can initiate anionic polymerization (in the presence of... 

The halo-surface groups were readily converted to lithiated derivatives which allowed their use as macromolecular templates from which to initiate anionic polymerizations. A wide variety of surface functionalities were introduced by combining the lithiated monodendron with various electrophiles. 

Surface-initiated anionic polymerization provides an alternative approach to polyolefin-functionalized CNTs that would have potential applications in the reinforcement of widely used polyolefins such as PE and PP. 

Anionic polymerization initiators can function in two different ways. In the simplest case, the added initiator contains the actual polymerization-initiating species. For example, in the polymerization of styrene induced by potassium amyl, styrene adds directly onto the amyl anion the amyl group becomes one of the end groups of the polymer ... 

It is desirable to develop anionic functionalization reactions using alkyllithium initiators that proceed in hydrocarbon solution at room temperature and above. These conditions maintain the uniqueness of alkyllithium-initiated anionic polymerization, in particular the ability to prepare polydienes with high 1,4-microstructure, and these conditions are also analogous and relevant to commercial anionic polymerization processes. In contrast, functionalizations that proceed efficiently only at -78 °C in tetrahydroftiran (THF) are of more limited utility. 

In this reaction scheme, the initiating species might be a free radical, anion, cation, or some more complex species. Broadly speaking, free radical initiators are produced by homolysis, i.e. the breaking of a covalent bond in such a way that its electrons are shared equally between the two fragments of the original molecule. Ionic initiators may function by the heterolytic scission of a covalent... 

Anionic polymerization is initiated in the presence of a highly reactive anion, such as butyl lithium. The anion functions as a nucleophile and attacks the Tt bond of a monomer, thereby generating a new carbanion. The carbanion generated during the initiation stage then functions as a Michael donor and attacks another monomer, which functions as a Michael acceptor ... 

A comprehensive list of the grafting reactions of (a) and (b) onto different polymer backbones is given in Ref 543. The methods summarized there include radiation techniques [623], grafting by radical transfer [624], and grafting initiated by functional groups in backbone polymers [625,626]. Macromonomers of (a) have been synthesized by means of anionic polymerization techniques and have been copolymerized with styrene [627,628]. Only a few examples are known in which polymers from (a) and (b) were used as backbone [629]. Star shaped block copolymers with four arms were prepared by coupling living styrene/(a) block copolymers with 1,2,4,5-tetrakis-bromomethyl-benzene [626]. 

Alkyllithitim-initiated, anionic polymerization of vinyl monomers is a very useful synthetic method since the major variables affecting polymer properties can generally be controlled, e.g., molecular weight, molecular weight distribution, copolymer structure and composition, configurational microstructure, molecular architecture, and chain-end functionality. This control is a direct consequence of the fact that in the absence of reactive impurities many of these polymerizations are termination and chain transfer free therefore, the products of these polymerizations are living polymers" with carbanionic chain ends. 

Block copolymers with polyisobutylene midsegments (e.g., S-iB-S) are m e by carbocationic polymerization [8,41]. This is a more complex system than the anionic system described earlier. The initiators have functionalities of two or more. They have the general formula (X-R)nx (where X-R represents a hydrocarbon moiety with a functional group X and X represents an n-ftmctional junction point). X can be a chlorine, hydroxyl, or methoxy group. Polymerization is carried out at low temperatures (about — 80°C) in a moderately polar solvent and in the presence of a coinitiator (TiCl or BQ3). As in anionic polymerization, the polymer segments are produced sequentially from the monomers. Thus, an S-iB-S block copolymer would be produced in two stages ... 

Equation (273) is the adsorption equation for divalent anion adsorption, at the aqueous S-MO interface as a function of anion solution molar concentration, xa-The adsorption equation for divalent anion adsorption, can be expressed as a function of total or initial anion solution molar concentration, cj, by first solving the... 

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