Synthesis of an intercalated compound of montmorillonite and 6-polyamide

Abstract

Natural montmorillonite, fractionated from bentonite produced in Yamagata, Japan, was ion-exchanged for NH ⁺₃ −(CH₂)₁₁−COOH, NH ⁺₃ −(CH₂)₅−COOH, Al³⁺, Cu²⁺, Mg²⁺, Co²⁺, Li⁺, K⁺ and H⁺. The mixtures of the ion-exchanged montmorillonite and ε-caprolactam were heated at 263°C in glass ampoules for various periods. The intercalated compounds before and after the heating were examined by X-ray powder diffraction, DSC and GPC. Although ε-caprolactam was not polymerized without montmorillonite, it was polymerized at 263°C in the presence of montmorillonite. The polymerization rate varied with the interlayer cations in the order of NH ⁺₃ −(CH₂)₁₁−COOH>Al³⁺>NH ⁺₃ −(CH₂)₅−COOH>H⁺>Cu²⁺>Mg²⁺>Co²⁺>Li⁺>K⁺. After heating at 263°C for 5 h, the mean number-average molecular weight was about 1.5×10⁴. Although the interlayer distance of NH ⁺₃ −(CH₂)₁₁−COOH type montmorillonite/ε-caprolactam compound increased from 2.85 nm to 4.90 nm by heating at temperatures above the melting point of ε-caprolactam, those of other compounds were not changed. After heating at 263°C, an intercalated compound of montmorillonite and 6-polyamide, whose interlayer distance was more than 10 nm, was obtained. It is concluded that montmorillonite acts as a Brönsted acid and initiates the open ring polymerization of ε-caprolactam and that the driving force of swelling is the polymerization energy.