New initiating systems

Protonic initiation is also the end result of a large number of other initiating systems. Strong acids are generated in situ by a variety of different chemistries (6). These include initiation by carbenium ions, eg, trityl or diazonium salts (151) by an electric current in the presence of a quartenary ammonium salt (152) by halonium, triaryl sulfonium, and triaryl selenonium salts with uv irradiation (153—155) by mercuric perchlorate, nitrosyl hexafluorophosphate, or nitryl hexafluorophosphate (156) and by interaction of free radicals with certain metal salts (157). Reports of "new" initiating systems are often the result of such secondary reactions. Other reports suggest standard polymerization processes with perhaps novel anions. These latter include (Tf)4Al (158) heteropoly acids, eg, tungstophosphate anion (159,160) transition-metal-based systems, eg, Pt (161) or rare earths (162) and numerous systems based on tri flic acid (158,163—166). Coordination polymerization of THF may be in a different class (167). 

Styrene (see Fig. 3.4 and Example 3-35). Conversely, monomer pairs whose copolymerization behavior is well known can be used to test new initiator systems in order to draw conclusions about the polymerization mechanism. 

Recently, Crivello and coworkers have developed synthesis of a new initiating system called S,S-dialkyl-S-(3,5-dimethyl-4-hydroxyphenyl)-sulfonium salts (4HPS) [29-31] with absorption maxima in the middle UV region. More recently, the same group also reported a facile synthesis of its isomeric counterparts, 5, 5 -dialkyl-5 -(3,5-dimethyl-2-hydroxyphenyl) sulfonium salts (2HPS) (Chart 11.5). 

In ATRP, the range of polymerizable monomers have been extended to vinyl acetate, dienes and vinyl chloride.Also, new metals (Mo, Os, Ti) and new ligands were successfully introduced. ATRP was successfully carried out in miniemulsion and microemulsion as well as in CO2 or in ionic liquids. New initiating systems were developed for ATRP, such as ARGET and ICAR. They start from oxidatively stable transition metal complexes (Cu") and are activated in the presence of reducing agents. Reduced amount of catalyst and its... 

Further advances in initiators can give more degrees of fieedom for the poly(vinyl acetate) (PVAc) producer. Low residual monomer is a primary coiKem for many latex produces, and new initiator systems can aid in reducing final monomer levels. Initiato type also affects latex properties by altering molar mass. Thus a variety of initiators allows for the productitHi of differoit products. 

In the radical copolymeiization of styrene and methyl methacrylate the reactivities are about the same, but for anionic initiation of an equimolar mixture of the two monomers the incorporation of methyl methacrylate is much preferred, while for cationic initiation of the same mixture the copolymer contains mostly styrene (see Fig. 3.4 and Example 3.35). Conversely, monomer pairs whose copolymerization behavior is well known can be used to test new initiator systems in order to draw conclusions about the polymerization mechanism. 

Fayt, R. Forte, R. Jacobs, C. Jerome, R. Ouhadi, T. Teyssie, Ph. Varshney, S. K. New initiator system for the living anionic polymerization of tert-alkyl acrylates. Macromolecules 1987, 20, 1442-1444. 

Cameron, P. A. New initiating systems for the polymerizations of acrylates. Ph.D. Thesis, Imperial College London, 1998. 

Synthesis of various functionalized 2008 [30] iV-isopropylacrylamide- and vinylether-based polymers grafting onto various substrates detailed review of thermoresponsive polymers, block and graft copolymers synthesis of PiPAAm of various shapes ionic and neutral block copolymers self-assembly stimuli-responsive polymers new initiating systems and synthetic methodologies... 

Another approach to PMMA is the polymerization of MMA using iodo-malonates in combination with ( Bu)4N I (1 1) as initiators, a new initiator system which is specific for methacrylate, i.e., acrylates are not polymerized (Scheme 20) [227]. 

Subsequently, Deming identified new initiating systems based on amido-sulfonamide metallacycles prepared by deprotonation of the corresponding amine complexes. Seidel and Deming studied a ruthenium(II) amido-sulfonamide complex, which although not an amido-amidate metallacycle, was... 

While reverse initiation simplified setting up a miniemulsion ATRP, it limited the range of materials that could be prepared and the catalysts that could be employed in the reaction. In a reverse initiation procedure one cannot independently adjust catalyst level and DPo,ge since formation of both the lower oxidation state catalyst complex and the ATRP initiator depends on the amount of standard free radical initiator added to the reaction. Therefore, a new initiation system was developed, SR NI, that involved addition of both an ATRP initiator and a free radical initiator. SR NI allowed the preparation of block and star copolymers in a miniemulsion with low levels of an active catalyst and low levels of surfactant.The use of SR Nl provided stable latexes with high soUds content. As shown in the 2D chromatography plot in Figure 13(a), only 4.5% of linear homopolystyrene was present in the final polymer when a tri-arm poly(methyl acrylate) macroinitiator was chain extended by styrene in an SR NI it miniemulsion process. The homopolymer results from the... 

Several new initiating systems have been identified in the last two or three decades for the living polymerization of alkyl (meth)acrylates. There are three main approaches employed... 

All of these initiating systems enhance the livingness of the (meth)acrylate polymerization to varying degrees to suppress secondary reactions and achieve living polymerization that enables manipulations of active chain-ends such as chain extension, block copolymerization, and functionalization. In addition, they moderate the position and the dynamics of the association equilibrium. Some details of the polymerization of (meth)acrylates using these new initiating systems are outlined below. More detailed results were reviewed by Baskaran. ... 

Abstract This paper discusses the principle, initiator design, and synthetic application of living cationic polymerization of vinyl monomers. The principle is based on the nucleophilic stablization of the growing carbocation some new initiating systems have been developed with use of phosphate esters and end-functionalized and starshaped polymers have been synthesized. 

This paper discusses (i) the principles of living cationic polymerization, (ii) new initiating systems for living polymerization of vinyl ethers, which are based on phosphate esters as initiators, and (iii) some selected topics in the controlled polymer syntheses by our living cationic processes, specifically focused on end-functionalized polymers and star-shaped or multi-armed macromolecules. 

In this way, we have demonstrated that careful selection of an initiatior (A B ) and a Lewis acid activator (Y) permits living cationic polymerization, as generalized in Eq. 6. According to this approach, there may be a variety of candidates for the initiators and the activators that should lead to new initiating systems. 

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