Copolymerization zwitterion

Schemes for classifying surfactants are based upon physical properties or upon functionality. Charge is tire most prevalent physical property used in classifying surfactants. Surfactants are charged or uncharged, ionic or nonionic. Charged surfactants are furtlier classified as to whetlier tire amphipatliic portion is anionic, cationic or zwitterionic. Anotlier physical classification scheme is based upon overall size and molecular weight. Copolymeric nonionic surfactants may reach sizes corresponding to 10 000-20 000 Daltons. Physical state is anotlier important physical property, as surfactants may be obtained as crystalline solids, amoriDhous pastes or liquids under standard conditions. The number of tailgroups in a surfactant has recently become an important parameter. Many surfactants have eitlier one or two hydrocarbon tailgroups, and recent advances in surfactant science include even more complex assemblies [7, 8 and 9].

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... 

While most polymerizations require an initiator, catalyst, or some other form of activation, zwitterionic copolymerizations do not. These copolymerizations require a specific combination... 

Ziegler-Natta (or Natta-Ziegler) catalyst (ZNC) Able to produce stereoregular pol5uners. zwitterionic polymerization Copolymerization between nucleophilic and electrophilic comonomers. 

Kobayashi, S. and T. Saegusa, Alternating Copolymerization Involving Zwitterions, Chap. 22 in Alternating Copolymers, J. M. G. Cowie, ed., Plenum Press, New York, 1985. 

Proton donors may be present or formed at the beginning of copolymerization and are necessary for the formation of primary active centres. In such a case, initiation according to Fischer s mechanism 39,40 (Eq. (37)) does not take place. Although the formation of a zwitterion (betaine-like structure) supports the possibility of the generation of charge-transfer complexes between cyclic anhydrides and amines, which may yield betaine-like structures82), simple anhydrides are much weaker ti acceptors than the often employed tetrachlorophthalic anhydride. 

Initiation involves the reaction of the tertiary amine (the most widely used Lewis base) with an epoxy group, giving rise to a zwitterion that contains a quaternary nitrogen atom and an alkoxide anion. The alkoxide reacts at a very fast rate with an anhydride group, leading to a species containing a carboxylate anion as the active center. This ammonium salt can be considered as the initiator of the chainwise copolymerization. 

Ethyleneimine has been also copolymerized in the absence of an initiator by zwitterion copolymerization with maleic anhydride [79] and methacrylic acid [80]. Both copolymers were checked following the batch method for copper(II), uranium(VI) and iron(III) and did not adsorb iron(HI), but copper(II) and uranium(VI) at pH 2. Poly (ethyleneimine-co-methacrylic acid) adsorbed more than 95% UO +. The ions were almost quantitatively eluted by contact of the loaded resin with 1 M aq. H2S04 [79, 80]. 

A zwitterionic tetramethylene initiates ionic homopolymerization, while a diradical tetramethylene initiates free radical copolymerization. As initiating species, zwitterions are likely to remain in the coiled gauche-conformation and collapse to small molecules. Diradicals, on the other hand, are easily transferred to the trans-conformation. Accordingly, diradicals are more effective initiators and more radical copolymerizations occur than ionic homopolymerizations. Addition of solvent will also influence the reaction of polar tetramethylene. A polar non-donor solvent may permit carbenium ion polymerization, while a polar donor solvent impedes it. 

The above subject has been selected as an example of the design of new polymerization reactions. It is concerned with a concept of copolymerization by spontaneous initiation and subsequent propagation via zwitterion intermediates. This copolymerization, which was invented and has been developed by the author, is called no catalyst copolymerization . It is very characteristic since usual polymerization reactions require either an initiator or a catalyst. 

The above concept is based on the fact that in organic chemistry the reaction between a nucleophile and an electrophile proceeds without any catalyst. The new copolymerization consists of the combination between a monomer (MN) having nucleophilic reactivity and a monomer (ME) having electrophilic reactivity. The interaction between these two monomers generates a zwitterion 27 called genetic zwitterion . 

A typical and illustrative example is the copolymerization of 2-oxazoline 30 with P-propiolactone 31 which yields a 1 1 alternating copolymer 32 at room temperature. A genetic zwitterion 33 is produced by ring opening of 31 upon attack of the nucleophile 30 (Eq. (23)). 

The concept of no catalyst copolymerization has demonstrated its usefulness in the exploration of phosphorus-containing polymers. For example, the cyclic phosphonite 34 was successfully copolymerized both with p-propiolactone (31) and acrylic acid 35). These copolymerizations proceed via a common zwitterion 36 and hence produce the same copolymer 37. 

The key intermediate of the above redox copolymerization is a zwitterion 41. The propagation step involves opening of the phosphonium ring of a zwitterion by... 

These copolymerizations start spontaneously without the addition of initiator. They were discovered by Saegusa et al. [306]. Originally only a few monomer pairs were known which yielded zwitterions by way of DA complexes. Representatives of MD are... 

Zwitterions formed in this way can mutually combine yielding a ternary, periodic copolymer. An example of this kind of copropagation is the copolymerization of the three units... 

Zwitterionic propagating species have been implicated in both homopolymerization and copolymerization reactions. An early example of the involvement of zwitterions in an alternating copolymerization was provided by the copolymerization of p-benzoquinone diazides with tetrahy-drofuran [Eq. (88)] [314,315]. This reaction could be thermally or photo-chemically initiated. A similar 1 1 alternating copolymer was obtained... 

Vinyl- and 4-vinylpyridines and 4-dimethylaminostyrene copolymerize with 2,4,6-trinitrostyrene without added initiator. The authors conclude that zwitterion formation is the first step. These copolymerizations seem to be analogous to those recently investigated by Saegusa and to be described later. 

Hall has introduced an empirical test to estimate the relative importance of diradical and zwitterionic forms in tetramethylene intermediates rrans-1,4-tetramethylene diradical intermediates may initiate alternating radical copolymerizations if they add to another alkene faster than they undergo conformational isomerization to the gauche form and give a cyclobutane product through carbon-carbon bond formation, while zwitterionic 1,4-tetramethylene intermediates may initiate ionic homopolymerizations. 

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 —... 

Random copolymerization of different oxazolines is described in Section 15.1,2.2. The reactivity ratios increase as expected with monomer basicity 18). Statistical copolymers of cyclic imino ethers with other groups of monomers are not known, although oxazolines and oxazines form readily alternating copolymers with a number of electrophilic monomers by spontaneous zwitterionic polymerization. The mechanism and examples of this process are discussed in Section 15.2.1. 

Later Kagiya et al. described the zwitterionic spontaneous copolymerization of P-propiolactone with different aziridines69), and since 1972 Saegusa has started extensive studies of zwitterionic alternating copolymerization 70 79). In most of these systems the molecular weights of the copolymers are low. 

Table 15.6. Examples of zwitterionic, spontaneous, alternating copolymerization... 

In the copolymerization with PPL, only route a has been considered by Saegusa, and transfer was not taken into account. Macrocyclization by end-to-end closure is another possibility, however, these macrocycles cannot easily be isolated and studied. The presence of macrocycles may be corroborated by comparison of DPn determined from end-groups with those measured by other methods e.g. GPC, osmometry, etc., i.e. when cyclic and linear molecules are counted separately. Such macrocycles were indeed observed by Schmidt in the polymerization of aryl sulfonium zwitterion 86) ... 

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