Copolymerization of α‐pyrrolidone and ϵ‐caprolactam

Copolymerization of α‐pyrrolidone and ϵ‐caprolactam has been carried out in the presence of sodium and acetyl compounds. A large amount of both catalysts is necessary to obtain a comparatively good yield. Infrared absorption measurement was adopted to obtain the polymer composition. The compositions of unreacting monomer were determined by equation: D958/D994 = 0.501(CclCpy), where D958 and D994 are optical densities at 958 and 994 cm.−1, which are characteristic absorptions of ϵ‐caprolactam and α‐pyrrolidone, respectively, and Ccl and Cpy, are concentrations of monomers in weight. The polymer composition was calculated from this composition of residual monomers. The polymerization was followed by this analysis and it was found that the α‐pyrrolidone polymerized a t the early stage of reaction while ϵ‐caprolactam reacts with a steady rate. Higher temperature made this phenomenon distinguishable and the degradation of α‐pyrrolidone was observed. The optimum temperature for polymerization was 90–110°C. The stability of α‐pyrrolidone anion explains these phenomena, as this anion promotes alkaline‐salt formation and degradation and reduces the chain numbers. The prepared copolymers have low melting points and good solubilities which vary according to composition. The melting point of the copolymer whose composition is 1 mole caprolactam: 1 mole pyrrolidone is as low as 140°C. and this polymer shows good solubility in ethanol. Apparent monomer reactivity ratios indicate that the copolymers formed are block copolymers.