Lactam isomerization polymerization

In his review, Reimschuessel described [353] isomerization polymerizations of lactams containing a carboxyl group as a substituent or part of a substituent. Whereas normal lactam ring opening leads to polyamides, isomerization polymerization produces polyimides in a complicated way, with proton transfer and through bicyclic intermediates... 

Polyimides are also produced by isomerization polymerization of those lactams where a carboxyl group can interact with the amide group ... 

Isomerization polymerization is feasible with lactams containing a carboxylic group capable of interacting with the lactam amide function it affords macromolecules whose repeating units derive from isomers of the original monomers. Tlius, the polymers obtained eu e polyimides rather than polyamides. 

Poly(P-alanine) (PA3) cannot be obtained by chemically initiated ROP of the unsubstituted azetidin-2-one (p-lactam), but only by anionic isomerization polymerization of acrylamide. The latter synthesis, however, generally leads to stmcturally irregular polyamide 3. On the contrary, the polymerization of p-lactams may be accessible by novel enzymatic routes. 

In conclusion, the results of our study indicate that the principal features of the formation of poly (2,6-dioxo-l,4-piperidinediyl) trimethylene by thermal polymerization of / -carboxymethyl caprolactam consists in an initial isomerization of the caprolactam derivative to a reactive species and subsequent polymerization of the latter by condensation. The reactive intermediate is in all probability either or both the 3-(3-aminopropyl)-glutaranhydride or its linear dimer. Both the conversion of the lactam by isomerization and the polycondensation follow second-order kinetics. 

The polymerization of lactams does not necessarily lead to polyzimides composed of the corresponding open chain units. Reimschuessel [245] introduced a new category of lactam derivatives the polymerization of which does not yield polyamides. Certain carboxyl substituted lactams prefer to polymerize in an isomerization—polycondensation process resulting in the formation of linear polyimides [245—251], viz. 

The polymerization of the carboxy-lactam (XXXIII) proceeded with a distinct induction period [247] (tj) which was taken into account in the evaluation of the conversion data. The monomer is consumed in the isomerization reaction (152) with the formation of the amino anhydride (S) the rate being... 

Anionic polymerization. For some heterocyclic monomers the unique chemical structure of the growing species follows unequivocally from the monomer structure. However, in many cases isomeric structures have to be taken into account. For instance, for symmetrical monomers, like thietane, the carbanion but not the thiolate anion was proposed (4). Unsymmetrically substituted monomers can provide active species by a- or B- ring scission. Unusual structure of activated monomer was proposed for NCA and lactams. These structures can not be distinguished by spectrophotometric methods, and application of H- or 13C-NMR looks more promising. 

Introduction of additional but non-reactive substituents into the corresponding lactams results in isomerization to other stable ring systems rather than in polymerization. 

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