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

Abstract

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. Figure 3. Figure 3(A) glass fibers surface with large amounts of the polyamide heavily attached; (3B) inner surface of the APA6 matrix, very irregular after glass fibers detachment.

Dual catalysis with an N‐heterocyclic carbene and a Lewis acid: Thermally latent precatalyst for the polymerization of ε‐caprolactam

“…In view of the most favorable results with MgCl 2 , mixtures of CLA, CLA-Ac, MgCl 2 , and 5u-Me-CO 2 (500:1:1:1) were prepared, stirred and heated to 75 C (above the melting point of CLA) until a colorless homogeneous solution had formed (1-2 h). After cooling to room temperature, the solidified material was stored inside the glove box and polymerized in portions after 1, 3, and 9 days at 200 C within 1 h ( Table 1, Entries [16][17][18]. The double-checked experiments provided exceptional yields >96% at an initiator loading of 0.2 mol%.…”

“…Activators like N-acetylazepan-2-one (N-acyl-ε-caprolactam [CLA-Ac]) or other acylated lactams, adducts of ε-CLA and (di-) isocyanates (N-substituted carbamoyl lactams) as well as initiators like sodium ε-CLA and magnesium bromideε-CLA (CLA-MgBr) have been de-scribed. [6][7][8]11,[13][14][15][16] The viscosity of CLA melts is comparable to the one of water and allows the use of thermoplastic reaction transfer molding (T-RTM) and liquid composite molding (LCM) techniques. [2][3] Particularly for LCM, a controllable latency is useful to initiate the reaction at a certain state by external stimuli.…”

“…The monomer is well‐available and synthesized via a Beckmann rearrangement from cyclohexanone. Activators like N ‐acetylazepan‐2‐one ( N ‐acyl‐ε‐caprolactam [CLA‐Ac]) or other acylated lactams, adducts of ε‐CLA and (di‐)isocyanates ( N ‐substituted carbamoyl lactams) as well as initiators like sodium ε‐CLA and magnesium bromide‐ε‐CLA (CLA‐MgBr) have been de‐scribed 6–8,11,13–16 . The viscosity of CLA melts is comparable to the one of water and allows the use of thermoplastic reaction transfer molding (T‐RTM) and liquid composite molding (LCM) techniques 2–3 .…”

Anionic copolymerization of nylon 6/12: A comprehensive review

“…By using CLNa, CL units in the copolymer structure are distributed randomly along with LL units. During the past decades, a large number of different catalysts have been used by scientists mainly in CL polymerization process [1,2,[30][31][32][33][34]47], but CLNa and CLMgBr systems are more frequently reported especially for copolymerization of CL with LL. Transacylation and side reactions result in a more random structure in the final copolymer.…”

Polymers and Related Composites via Anionic Ring-Opening Polymerization of Lactams: Recent Developments and Future Trends

“…The search for efficient activators for linear and branched polylactams is still ongoing. Russo et al [ 15 ] mixed a 3-(triethoxysilyl)propylisocyanate blocked with CL, which proved to be a fast activator. Multifunctional activators, yielding branched polyamides, were initially prepared by blocking tri- or multifunctional polyisocyanates with CL [ 16 ].…”