Polymerization zwitterions

As for any other functional polymer, polymeric betaines are accessible by two different synthetic routes (1) the polymerization of zwitterionic monomers or (2) the zwitterionic functionalization of reactive precursor polymers. Both routes have inherent advantages and disadvantages. The polymerization of the zwitterionic monomers leads to polymers with 100% betaine functionality, but their molecular characterization is difficult for several reasons. For instance, the conformation of the polymers in aqueous solution is very sensitive, not only to the ionic strength but also to the type of added salt, and in the case of polycarbobetaines also to the pH. Furthermore, polymeric zwitterions often exhibit strong interactions with other matter, e.g., chromatographic colmnns. Hence, reliable GPC or HPLC measurements are very difficult to perform, if at all. 

Zwitterionic Polymerizations. Zwitterionic intermediates also appear to be responsible for the spontaneous specific 1 1 copolymerizations of some acrylate-type monomers with cyclic nucleophilic species reported by Saegusa and his CO-workers.In many ways these resemble the spontaneous polymerizations of strong donor and acceptor vinyl moities mentioned earlier. s —... 

Johnsen et al. separated nucleoside triphosphates on a polymeric zwitterionic phase (ZlC-pHlLlC) that provided a better separation than the respective... 

The polymerisation does not normally have a termination step. This is in contrast to most other anionic polymerisations, which are very sensitive to trace impurities such as components of the atmosphere or moisture (only strong acids are terminating agents) [46]. Other initiators such as tertiary amines and phosphines have been postulated to polymerise via polymeric zwitterions. This mechanism has been proved by the isolation of stable zwitterions [47]. 

Figure 9.4 NEXAFS of conjugated polymeric zwitterions. The major peak intensity change reflects the preferred orientation of the conjugated backbone of the polymer. Reprinted from ref. 51 with permission from Wiley-VCH.

Oxiranones (a-lactones) 81JA686, 80AG(E)276), e.g. (6), are highly reactive, readily polymerizing (Scheme 18), possibly via a zwitterion (18). Such a species (19) would also account for the rearranged products (20) and (21) from (22 Scheme 19). 

However, as can also be seen in Fig. 11, primary and secondary amines do not perform very effectively as primers, compared to tertiary amines, even though they also contain long alkyl chains. It has been demonstrated that, instead of directly initiating ECA polymerization, primary and secondary amines first form aminocyanopropionate esters, 12, because proton transfer occurs after formation of the initial zwitterionic species, as shown in Eq. 7 [8,9]. 

Hall112,329 has proposed a unifying concept based on tetramethylen.es (resonance hybrids of 1,4-diradical and zwitterionic limiting structures - Scheme 3.67) to rationalize all donor-acceptor polymerizations. The predominant character of the tetramethylenes (zwitterionic or diradical) depends on the nature of the substituents. 12" 40 However, more evidence is required to prove the more global application of the mechanism. 

Protonation of the TMM complexes with [PhNMe2H][B(C6Fs)4] in chlorobenzene at —10 °C provided cationic methallyl complexes which are thermally robust in solution at elevated temperatures as determined by NMR spectroscopy. In contrast, addition of BfCgFsls to the neutral TMM precursors provided zwitterionic allyl complexes (Scheme 98). Surprisingly, it was found that neither the cationic nor the zwitterionic complexes are active initiators for the Ziegler-Natta polymerization of ethylene and a-olefins. °°... 

Due to the retractive forces in stretched mbber, the aldehyde and zwitterion fragments are separated at the molecular-relaxation rate. Therefore, the ozonides and peroxides form at sites remote from the initial cleavage, and underlying mbber chains are exposed to ozone. These unstable ozonides and polymeric peroxides cleave to a variety of oxygenated products, such as acids, esters, ketones, and aldehydes, and also expose new mbber chains to the effects of ozone. The net result is that when mbber chains are cleaved, they retract in the direction of the stress and expose underlying unsaturation. Continuation of this process results in the formation of the characteristic ozone cracks. It should be noted that in the case of butadiene mbbers a small amount of cross-linking occurs during ozonation. This is considered to be due to the reaction between the biradical of the carbonyl oxide and the double bonds of the butadiene mbber [47]. 

Surfactants used as lubricants are added to polymer resins to improve the flow characteristics of the plastic during processing they also stabilise the cells of polyurethane foams during the foaming process. Surfactants are either nonionic (e.g. fatty amides and alcohols), cationic, anionic (dominating class e.g. alkylbenzene sulfonates), zwitterionic, hetero-element or polymeric (e.g. EO-PO block copolymers). Fluorinated anionic surfactants or super surfactants enable a variety of surfaces normally regarded as difficult to wet. These include PE and PP any product required to wet the surface of these polymers will benefit from inclusion of fluorosurfactants. Surfactants are frequently multicomponent formulations, based on petro- or oleochemicals. 

Water soluble block copolymers consisting of N-isopropylacrylamidc, NIPA, and the zwitterionic monomer 3-[N-(3-methacrylamidopropyl)-N,N-dimethyl]ammoniopropane sulfonate, SPP, were prepared via the RAFT process [82] (Scheme 31). NIPA was polymerized first using AIBN as the initiator and benzyl dithiobenzoate as the chain transfer agent. To avoid the problem of incomplete end group functionalization the polymerization yield was kept very low (less than 30%). The block copolymerization was then performed... 

The most commonly used catalysts for cationic polymerization are the Lewis acids BFa, A1C18, SnCl4, FeCl3, etc. There are two plausible modes of action for a Lewis acid. One of these, and rather a doubtful one, is the formation of a zwitterion and the growth at the positive end of the zwitterionic chain. 

It will be shown in the following discussion that (i) and (ii) are extremely unlikely, but that (iii) and (iv) are at least possible under some conditions. Hunter-Yohe and Medvedev-Gantmakher mechanism (HY-MG). The first theory of cationic polymerization [41] was based on the supposition that metal halide and monomer form a complex which is so polar that it can be considered as a zwitterion, and that polymerization proceeds from the positive end of this complex... 

A slightly different mechanism of proteins separation results from the use of porous polymeric monoliths containing zwitterionic sulfobetaine groups [68]. 

Hydrophilic interaction chromatography (HB IC) or aqueous normal-phase chromatography (ANP) refers to the use of polar stationary phases (e.g., bare silica, silica, or polymeric phases with bonded zwitterionic ligands, diol phases) in combination with a mobile phase rich in organic solvent but containing a significant amount of water (typically at least 3%). Bell [97] summarized the advantages of this technique as follows ... 

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