Some new perspectives of anionic polyamide 6 (APA 6) synthesis

The anionic polymerization of ε‐caprolactam in the bulk is now enriched by a new member belonging to the family of very fast activators, represented by blocked (triethoxysilyl)propylisocyanate. The activator is able to allow polymerization completion in a few tens of seconds in quasi‐adiabatic conditions starting from ca. 150°C. The most relevant and unexpected feature of its role in ε‐caprolactam activated anionic polymerization arises from the observation that the resultant APA 6 is extensively crosslinked in situ up to ca. 80% despite the isocyanate monofunctionality of the activator. Comparison with the behavior of a commercial trifunctional activator/crosslinker is carried out and possible explanation of (triethoxysilyl)propylisocyanate role as a crosslinker is put forward. Optimization of the procedure to properly evaluate the degree of APA 6 crosslinking in comparison with a literature method is established. Other tested silane derivatives do not behave similarly in the same experimental conditions of synthesis. The strong adhesion, due to the triethoxysilyl group, to glass fibers introduced in the polymerizing medium is a relevant additional advantage of the quoted activator. Possible industrial applications can be foreseen.