4-carboxymethyl caprolactam, polymerization

The polymerization of j3-carboxymethyl caprolactam has been observed to consist of initial isomerization via a second-order kinetic process followed by condensation of the isomer to polymer ... 

The thermal polymerization of /3-carboxymethyl caprolactam results in a novel polyimide which has been identified as a poly(2,6-dioxo-l, 4-piperidinediyl)trimethylene. The formation of this structure is explained by a mechanism that consists in an initial isomerization of the caprolactam derivative to 3-(3-aminopropyl)glutaranhydride or its linear dimer and subsequent polymerization by condensation involving the terminal amino group and the anhydride moiety. Suggested reaction schemes and corresponding kinetic equations are based upon the premise that the extent of polymerization is represented by the concentration of imide linkages. Results of rate studies carried out at 210°-290°C. support the proposed mechanism. 

Comparing the structure of the monomer with that of the polymer as shown in Table I, we see that the polymerization of the / -carboxy-methyl caprolactam must involve isomerization of the monomer ring system. This isomerization may be described by several possible processes, all of which are characterized by reaction between the amide and acid group of the / -carboxymethyl caprolactam. Based upon the results of our studies on the structure of this polymer (5) we may eliminate confidently those processes according to which the formation of the glutarimide moiety results either by intrachain cyclization or by trans-cyclization of certain intermediate polymer structures. The former would involve a polymer formed by a conventional ring opening polymerization ... 

Polymerizations were carried out at temperatures of 210°, 220°, 230°, 240°, 250°, 270°, and 290°C. For each series about 10 small (8-10 mm. i.d.) polymerization tubes were used. Pure / -carboxymethyl caprolactam was placed into these tubes, and air was removed by alternate application... 

The experimental data are presented in Figures 1 and 2. Figure 1 shows the conversion U as a function of time for the various temperatures of polymerization. The conversion was determined by extracting the polymer sample with water. Since it was found that the water-soluble fraction was essentially pure / -carboxymethyl caprolactam, U was calculated from the value of the water insoluble weight fraction. 

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. 

Information on possible reaction mechanisms were obtained from kinetic studies. The conversions of 3-carboxymethyl caprolactam to the polylmlde amd of 5,5-dlmethyl-4-ccu boxy-2-pyrroll-done to Isopropylldene succlnlmlde have been considered representative exasples for respectively the polymerization and rearrangement reactions. The evaluation of eicperlmental data for the polymerization was based upon the concept that the extent of reaction Is represented by the momentary concentration of Imlde linkages(I) which Is related to the respective concentrations of both unreacted monomer(M) euid polymer molecules(c) by the stoichiometric relation ... 

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