Anionic Polymerization of 2-Pyrrolidone

In a recent patent, a preparation of powdered PA 12 by dispersion polymerization in hydrocarbon solvents was described where the polymerization mixture contained, in addition to the initiation system, a mineral filler and bisamide [88]. Powdered polyester-amides were prepared in a similar way, namely by the copolymerization of a lactam and a lactone [89]. 

Polyamide/layered silicate nanocomposites with improved mechanical properties can in general be prepared in three ways (i) in situ polymerization (ii) mixing in melt or (iii) exfoliation-adsorption. A successful research study initiated during the 1980s by Toyota Co. focused on a polymerization of e aprolactam by a hydrolytic mechanism in the presence of an organically modified montmoriUonite (MMT) sodium ions present in the interlayers of MMT were substituted by pro-tonated co-aminolauric acid [90, 91]. e-Caprolactam, e-aminocaproic acid and H3PO4 were then added to a dispersion of MMT in water such that, when the polymerization had been carried out, a fully exfohated morphology of MMT was produced. 

To date, no completely successful preparation of nanocomposites using an anionic polymerization of CL in the presence of organophilized MMT has been described in the specialist literature. During the anionic polymerization, alkylam-monium cations present in the interlayer of the organophilized MMT are substituted by the counteranions of the lactam anion this leads to a decrease in the interlayer distance [92], which in turn hampers the penetration of monomer molecules between the silicate platelets. 

Recently, nanocomposites were prepared by the anionic polymerization of e-caprolactam using an unmodified MMT [93]. Due to interactions between the water molecules and the polar groups of MMT in the presence of CL, a delamination of the platelets of MMT takes place, thus allowing a stable dispersion MMT-CL-H2O to be prepared. The water and part of the CL are then distilled off from the mixture. Subsequent X-ray diffractometry (DRX) analysis confirmed a full exfoliation of the Na MMT in CL in this intermediate. The next step in the process is to introduce an activator (TDI-23) and an initiator (sodium salt of e-caprolactam). The nanocomposite thus obtained had an exfoliated stracture. 

The polymerization of 2-pyrrolidone (PD) differs markedly from that of CL, mainly because P D can be transformed into a homopolymer only by anionic polymerizahon. 

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The anionic polymerization of 2-pyrrolidone has also been accomplished employing carbon dioxide as activator. The use of this gaseous activator has made possible to prepare a PA4 possessing a satisfactory thermal stability for fiber preparation and melt spinning. Nonactivated anionic polymerization, on the contrary, enables high molar masses of poly (2-pyrrolidone) to be obtained, but at the expenses of much longer polymerization times. 

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