The equilibrium acidity of cyclic and linear amides and its effect on the anionic polymerization of lactams

Abstract

The equilibrium acidity of lactams with rings of various size and of linear N-substituted amides was measured in dimethyl sulfoxide by the spectrophotometric method. The pK values of these NH-acids thus determined varied in the range 22-27. The data are used to characterize the acidobasic equilibrium between the amide groups of the monomer, polymer and their N-anions during the anionic polymerization of lactams. The effect of acidity on the anionic copolymerization of lactams is also discussed.

Poly(aminophosphazene)s and Protophosphatranes Mimic Classical Strong Anionic Base Catalysts in the Anionic Ring-Opening Polymerization of Lactams

“…It appears that to be an effective catalyst (i.e., formation of high-MW polymer in good conversion), the pK BH + must be greater than ca . 27 because the p K a of lactams from 2-pyrrolidone to laurolactam is 27 when measured in DMSO . The reported p K BH + is 28.04 (in THF) for P 4 - t -Bu, and 26.7 (in DMSO) for Verkade's protophosphatrane “Super Base”, N[CH 2 CH 2 N(CH 3 )] 3 P …”

“…27 because the pK a of lactams from 2-pyrrolidone to laurolactam is 27 when measured in DMSO. 8 The reported pK BH + is 28.04 (in THF) for P 4t-Bu, and 26.7 (in DMSO) for Verkade's protophosphatrane "Super Base", N[CH 2 CH 2 N(CH 3 )] 3 P. 5 Note that these values are substantially below those reported in setting the required base strengths for the poly(aminophosphazene)s because the pK a for the lactams and the bases have not been measured in the same solvent.) The results shown in Table 2 for the ring-opening polymerization of -caprolactam indicate that P 1 -t-Bu is not an effective catalyst whereas P 2 -Et and the P 4 -R systems give both high MW and good conversion.…”

Polymerization of lactams, 88. Copolymers poly(ϵ‐caprolactam)‐block‐polybutadiene prepared by anionic polymerization, part III. Model polymerizations initiated with potassium salt of ϵ‐caprolactam and accelerated with isocyanates and their derivatives

“…1, 5 and 8, all studied polymerizations showed a linear dependence of polymer yield on polymerization time up to at least 50% of monomer conversion; i.e., a kinetics of zero order to monomer was concerned. Hence, the initial stage of polymerization can be characterized by an overall appar- (6) where the monomer concentration [MI is replaced, not very rigorously, by the concentration of the water extractable portion, yw…”

Polymerization of lactams, 81. Anionic polymerization of lactams accelerated with N‐iminolactams, 2 ϵ‐caprolactam (6‐hexanelactam)

“…The sequence of acceleration activity of NIL strongly differs from the activity sequence in the anionic polymerization of PD, which was also evaluated from the minimum time for attaining the limit conversion3): 2 > 5 > 1 > 3 > 4. The reason can be seen particularly (a) in the considerable difference of the polymerization temperature (higher temperature favours the exchange reactions between lactam and NIL) and (b) in the different acidity of both lactams 13).…”