Group transfer polymerization anionic

A brief review has appeared covering the use of metal-free initiators in living anionic polymerizations of acrylates and a comparison with Du Font s group-transfer polymerization method (149). Tetrabutylammonium thiolates mn room temperature polymerizations to quantitative conversions yielding polymers of narrow molecular weight distributions in dipolar aprotic solvents. Block copolymers are accessible through sequential monomer additions (149—151) and interfacial polymerizations (152,153). 

The anionic polymerization of methacrylates using a silyl ketene acetal initiator has been termed group-transfer polymerization (GTP). First reported by Du Pont researchers in 1983 (100), group-transfer polymerization allows the control of methacrylate molecular stmcture typical of living polymers, but can be conveniendy mn at room temperature and above. The use of GTP to prepare block polymers, comb-graft polymers, loop polymers, star polymers, and functional polymers has been reported (100,101). 

Group-Transfer Polymerization. Du Pont has patented (29) a technique known as group-transfer polymerization and appHed it primarily to the polymerization of acrylates and methacrylates. It is mechanistically similar to anionic polymerization, giving living chains, except that chain transfer can occur (30). 

These TMS-carbamate-mediated NCA polymerizations resemble to some extent the group-transfer polymerization (GTP) of acrylic monomers initiated by organo-silicon compounds [40]. Unlike GTPs that typically require Lewis acid activators or nucelophilic catalysts to facilitate the polymerization [41], TMS-carbamate-mediated NCA polymerizations do not appear to require any additional catalysts or activators. However, it is still unclear whether the TMS transfer proceeds through an anionic process as in GTP [41] or through a concerted process as illustrated in Scheme 14. 

The controlled polymerization of (meth)acrylates was achieved by anionic polymerization. However, special bulky initiators and very low temperatures (- 78 °C) must be employed in order to avoid side reactions. An alternative procedure for achieving the same results by conducting the polymerization at room temperature was proposed by Webster and Sogah [84], The technique, called group transfer polymerization, involves a catalyzed silicon-mediated sequential Michael addition of a, /f-unsaluralcd esters using silyl ketene acetals as initiators. Nucleophilic (anionic) or Lewis acid catalysts are necessary for the polymerization. Nucleophilic catalysts activate the initiator and are usually employed for the polymerization of methacrylates, whereas Lewis acids activate the monomer and are more suitable for the polymerization of acrylates [85,86]. 

The anionic polymerization of methylmethacrylate at room temperature (originally called group transfer polymerization) [75-77] has provided a means for preparing star poly(methylmethacrylate) via the block polymerization with ethyleneglycoldimethacrylate ... 

Stars with high arm numbers are commonly prepared by the arm-first method. This procedure involves the synthesis of living precursor arms which are then used to initiate the polymerization of a small amount of a difunctional monomer, i.e., for linking. The difunctional monomer produces a crosslinked microgel (nodule), the core for the arms. The number of arms is a complex function of reaction variables. The arm-first method has been widely used in anionic [3-6,32-34], cationic [35-40], and group transfer polymerizations [41] to prepare star polymers having varying arm numbers and compositions. 

Atom-transfer and group-transfer polymerizations are variants of these processes, in which radical or anionic chain ends - instead of occurring freely as such - are temporarily released by breaking a suitably labile, but otherwise protective bond (e.g. to a Cu atom or to a McsSi group) which then gets reattached to the newly-formed chain end. 

Although group transfer polymerization does not involve ionic reactions, it is reviewed in this chapter because it bears many practical similarities to anionic polymerizations and is an alternative route to (mcth-)acrylic polymers and block... 

Unlike anionic polymerizations, the reaction sites are not ion pairs the catalyst is believed to facilitate transfer of the trimethylsilyl group by dipolar interaction with the Si atom. As in anionic polymerizations, however, the reactive end group is deactivated by compounds carrying labile hydrogens. Group transfer polymerizations therefore must be carried out under anhydrous conditions. 

Rh138 was almost the same (almost atactic, slightly syndiotactic) as the tacticity of those obtained with conventional radical initiators such as AIBN under similar conditions. The triad ratio of rr.mr.mm as determined by 13C NMR is usually 58 38 4 and does not change even with the use of chiral and/or bulky ligands.103116 These results may exclude a coordination mechanism and suggest a radical nature. However, the stereochemical structure alone is not strong evidence for the radical polymerization because, for example, group-transfer polymerization, basically via an anionic mechanism, results in a stereo structure of PMMA similar to those for free radical processes.263... 

Measurement of reactivity ratios under normal free-radical and CCT polymerization conditions indicates that CCT is a modified free-radical polymerization as expected.434 The reactivity ratios for MMA and butyl methacrylate were used as a mechanistic probe. Reactivity ratios were 1.04 and 0.81 for classical anionic polymerization, 1.10 and 0.72 for alkyllithium/trialkylaluminum initiated polymerization, 1.76 and 0.67 for group transfer polymerization, 0.98 and 1.26 for atom transfer radical polymerization, 0.75 and 0.98 for CCT, and 0.93 and 1.22 for classical free-radical polymerization. These ratios suggest that ATRP and CCT proceed via radical propagation. 

The anionic and group transfer polymerizations used for this study are living polymerization techniques that typically produce copolymers having very narrow molecular weight distributions, whereas copolymers produced by a... 

After synthesis, the methacryloxy-terminated PDMS macromonomers were purified, and the macromonomers were copolymerized with methyl methacrylate using free-radical, anionic, and group transfer polymerization. Detailed descriptions of the polymerization are provided by DeSimone (1990) and Hellstern (1989). In addition to well-defined graft copolymers, there is... 

Macromonomers can be prepared by all the common polymerization techniques, e.g., free radical, anionic, cationic, condensation, or group transfer polymerization. Typical examples are given below ... 

New developments in group transfer polymerization have made possible the living polymerization of acrylate and methacrylate monomers using silyl ketene acetal initiators with a nucleophilic or Lewis acid catalyst (73). By this method we may circumvent the side reactions which accompany conventional anionic polymerizations of acrylates and methacrylates and prepare almost mono-... 

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