Cyclic amines polymerization

The initiator used is important for copolymerizations between monomers containing different polymerizing functional groups. Basic differences in the propagating centers (oxonium ion, amide anion, carbocation, etc.) for different types of monomer preclude some copolymerizations. Even when two different monomer types undergo polymerization with similar propagating centers, there may not be complete compatibility in the two crossover reactions. For example, oxonium ions initiate cyclic amine polymerization, but ammonium ions do not initiate cyclic ether polymerization [Kubisa, 1996]. 

For aliphatic monoamine [43], it is shown that secondary amines R2NH always possess a higher promoting effect for the polymerization of AAM and even the primary amine PA will enhance the polymerization with Rr = 1.47 and Ea = 36.4 kJ/mol, while the tertiary aliphatic amine TPA will not provide the polymerization due to some steric hindrance (Table 6). All of the data of cyclic amines listed in Table 7 are effective, i.e., NMMP with Rr = 1.81 and Ea = 29.9 kJ/mol showing the absence of steric hindrance. 

Table 7 Effects of Aliphatic Cyclic Amines on Polymerization...

Lithium hexafluoroarsenate is thermally stable [54, 55] but shows environmental risks due to possible degradation products [56-58], even though it is itself not very toxic. Its LD 50 value is similar to that of lithium perchlorate [55]. Just like lithium hexafluorophosphate, it can initiate the polymerization of cyclic ethers. Polymerization may be inhibited by tertiary amines [59], or 2-methylfuran [60], yielding highly stable electrolytes. 

An alternative method of preparing the saturated cyclic amines via cyclopolymerization of diallylamine or diallylammonium chloride was unsuccessful. Common free radical initiators such as 2,2 -azobisisobutyronitrile, ammonium persulfate, benzoyl peroxide were found to be ineffective. Several procedures reported in the literature were followed, and unfortunately all of them have resulted only a small amount of low molecular weight oligomers. Further research for polymerization conditions and types of initiation is still required. 

A wide variety of cyclic monomers have been successfully polymerized by the ring-opening process [Frisch and Reegan, 1969 Ivin and Saegusa, 1984 Saegusa and Goethals, 1977]. This includes cyclic amines, sulfides, olefins, cyclotriphosphazenes, and IV-carboxy-oc-amino acid anhydrides, in addition to those classes of monomers mentioned above. The ease of polymerization of a cyclic monomer depends on both thermodynamic and kinetic factors as previously discussed in Sec. 2-5. 

Cyclic amines (referred to as imines) are polymerized by acids and other cationic initiators [Goethals, 1984, 1989a,b Hauser, 1969 Kubisa, 1996 Tomalia and Killat, 1985]. The 3-membered imines (IUPAC aziridines) are the most studied of the cyclic amines. Polyethy-leneimine [IUPAC name poly(iminoethylene)] had been commercially available and used in the treatment of paper and textiles. It is no longer available in the United States because of the high toxicity of the monomer. 

Goethals, E. J., Cyclic Amines, Chap. 10 in Ring-Opening Polymerization, Vol. 2, K. J. Ivin and... 

A few papers have examined the range of Lewis bases that are effective for isobutene controlled/living polymerization [91,149,156]. One proposal is that effective nucleophiles (electron donors) should have relatively high donor numbers (DN > 26) [149]. Another screening shows that triethylamine is exceedingly effective for isobutene [156]. Pratap et al., also reported recently the use of cyclic amides (lactams l-methyl-2-pyr-rolidone) [158] and cyclic amines [152] for the dicumyl acetate/BCL initiating system. 

Although the pKa or H0 values for several acids are known [10,11], the definition of strong acid is somewhat arbitrary, because the position of equilibrium (13) depends on the basicity of heterocyclic monomer. Because this basicity varies from rather low (e.g., cyclic acetals) to rather high (e.g., cyclic amines) no universal rule describing the behavior of particular protonic acids in ring-opening polymerization exists. 

In the polymerization of strongly nucleophilic cyclic monomers, however (oxazolines, cyclic amines), monomer may compete successfully with Br or I counterion (cf., Section H.B.6.C.). For these monomers initiation with HBr, for example, may lead to high molecular weight polymers. 

Covalent compounds, which are strong alkylating or acylating agents may initiate the cationic polymerization of heterocycles. Again, as in the case of acids, classification of these agents is relative for example, alkyl bromide will efficiently alkylate strongly nucleophilic monomers like cyclic amines or oxazolines and thus initiate their polymerization whereas it will be uneffective in the polymerization of cyclic ethers. 

The factors, governing the reactivities of branched onium ions are of complex nature and will not be discussed here. It has been shown, however, that in the polymerization of cyclic sulfides and cyclic amines the formation of branched onium ions of the type ... 

Polymerization of 3-membered cyclic amines-aziridines is a good example to illustrate the influence of steric factor on the relative rates of propagation and termination. 

The results show that the presence of bulky substituent on a polymer chain may effectively inhibit the termination proceeding by this mechanism. The results presented at this point may be summarized as follows chain transfer to polymer is a general feature of cationic ring-opening polymerization although for different systems the contribution of this reaction may vary only in some systems this process results in termination (These systems involve, e.g., cyclic amines (3- and 4-membered) and cyclic sulfides (3- and 4-membered) and the contribution of the reaction is reduced for substituted chains. 

The problem of water in ionic ring-opening polymerization is much less critical than in vinyl polymerization, because, if present, water in the former system has to compete with relatively nucleophilic monomer present in large excess. Thus, certain polymerizations (e.g., polymerization of cyclic amine-conidine) can be conducted even in alcohols as solvents. 

Cationic polymerization of unsubstituted 4-membered cyclic amine proceeds in a way similar to that of aziridine, giving branched polymer containing, according to H NMR, 20% of primary, 60% of secondary, and 20% of tertiary amino groups [174]. Purely linear polymer can be obtained by polymerization of 5,6-dihydro-4H-l,3-oxazine, followed by hydrolysis [175] ... 

The other limitation stems from very different structure of heterocyclic monomers and thus very different reactivity of resulting active species. As already discussed, oxonium ions may initiate the polymerization of cyclic amines, but ammonium ions would not initiate the polymerization of cyclic ethers. Thus, the sequential polymerization is possible only when the first monomer is not a stronger nucleophile than the second monomer. 

In the random copolymerization process, both types of active species should be able to participate in the cross-propagation reactions. This imposes certain limitations on the choice of comonomers in the cationic polymerization of heterocyclic monomers. Onium ions, being the active species of these polymerizations, differ considerably in reactivity thus, as already discussed, oxonium ions initiate the polymerization of cyclic amines, whereas ammonium ions do not initiate the polymerization of cyclic ethers and the corresponding cross-propagation reaction would not proceed ... 

Thus, random copolymerization of cyclic ethers with cyclic amines is not possible. The other limitation, which will be discussed in more detail in a later part of this section, is the reversibility of homo- and/or crosspropagation steps, when one or both comonomers polymerize reversibly. 

Some cyclic amines, iminoethers, sulfides, ethers, esten, and acetals were indeed demonstrated to polymerize without appreciable transfer and/or termination. It cannot be excluded that for monomers belonging to other compound classes, e.g. lactams or cyclic esters of phosphoric acid, the conditions for the transfer- and terminationless processes will be found in the near future. 

The formation of additkm products and further ionization according to Eq. (17) w e shown directly also in the polymerization of cyclic amines. 

Thus, halonium ions (e.g. Et2Cr, A ) can initiate polymerization of acetals, ethers, sulfides, or amines. Oxonium ions also initiate more or less successfully the polymerization of these monomers while ammonium ions can only be applied in the polymerization of some cyclic amines. 

The choice of counterions (anions) in the cationic polymerization of heterocyclic monomers can be almost as wide as in anionic polymerization, but only for the most nucleophilic monomers (i. e. cyclic amines). Unfortunately, in the polymerization of cyclic ethers, this choice is much more restricted. Thus, the small anions like F or OH cannot be used because, due to their high nucleophilicity and ability to form covalent bonds, they give rise to fast termination. In order to suppress or even to eliminate termination by collapse within an ton pair (cf. Sect. 5.1.), it is necessary to use complexed anions having large ionic radii. These are shown below (rctyst)-... 

Enikolopyan studied the polymerization of cyclic amines such as conidine ... 

The data collected by Goethals on the kp/k ratio in the polymerization of cyclic amines (determined from Eq. (153) permits to show (Fig. 16) that there is a linear relationship between In (kp/kf) and the effective volume of substituents. These volumes were calculated according to Ref. 262. Thus, although the linearity itself has little importance, this dependence is in good agreement with the discussed earlier influence of substituents on the rate constants of termination and fuopagation. 

Lewis acids to give the desired 2-aminopyridines (37). The dimethyldisila-nol (159), formed on amination, polymerizes to silicon oil (1(>0) or cyclic oligomers, which can be readily removed by extraction with pentane or hexane. 

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