Anionic polymerization of lactams in the presence of metal dialkoxyaluminum hydrides: presentation of a new mechanism

Abstract

Metal dialkoxyaluminum hydrides (1) form a new class of catalysts for anionic polymerization of lactams. Propagation proceeds in their presence-as it does in the presence of conventional catalysts such as alkali metal hydrides-by successive additions of the anionically active species to the end-standing Nacyllactam function carried by the polymer chain. However, this is the only similarity between the two polymerization processes. The active species generated when c-caprolactam (2) is treated with sodium dialkoxyaluminum hydride is the sodium salt of 2-(dialkoxyaluminoxy)-1-azacycloheptane (6) and is therefore quite different in terms of nucleophilicity from the mere activated monomer, sodium caprolactamate. The new reactive salt (6) is obtained upon deprotonation of a lactam monomer at ita amide position followed by the reduction of its carbonyl function. During lactam polymerization, after each monomer addition, the active species is re-formed in two steps: first, proton exchange followed by instantaneous reduction of the lactamate formed by transfer of both hydrogen and the Al(OR)Z group from the previous monomer unit added. This displacement regenerates the end-standing N-acyllactam and the salt of the (dialkoxyaluminoxy)-azacycloheptane (6), allowing propagation to proceed by addition of 6 to this latter function. This new mechanism still propagates by an "activated monomer" mechanism but it also involves the transfer of the dialkoxyaluminum hydride group throughout polymerization.

Polyamide from lactams by reactive rotational molding via anionic ring-opening polymerization: Optimization of processing parameters

“…Before the rotation started, the liquid formed a pool at the bottom of the mold. During rotation the liquid was lifted up the mold wall in the direction of the rotation [2,4]. The thickness of the layer is dependent on the linear velocity of rotation, the liquid viscosity and the liquid density.…”

“…It is well known that anionic polymerization of !-CL (APCL) occurs faster (i.e., over a few minutes) than classical hydrolytic polymerization, which takes about 12-24 h [4]. A fast polymerization process in addition to good mechanical properties of PA6 results in a wide range of applications for this polymer in reaction injection molding [5,6], rotational molding [1,7] and centrifugal molding [8][9].…”

Dispersion of nano-silica in monomer casting nylon6 and its effect on the structure and properties of composites

“…Considering that the tremendous energy offered by ultrasonic is likely to break the nanoparticles aggregations into smaller ones or even mono-dispersing particles [13], in the present work, ultrasound was employed to disperse nanosilica in melted caprolactam. Therefore, the agglomerated nanoparticles would be pulled apart and coated with caprolactam, leading to the improved stability of smaller aggregations and mono-dispersing nanoparticles against re-agglomeration, and (iii) in comparison with classical hydrolytic polymerization of caprolactam which takes about 12-24 hrs [14,15], the rapid anionic polymerization of caprolactam (usually within 1 hr [12,16]) also contributed to the avoidance of re-agglomeration and deposition of nanoparticles during the polymerization process, leading to the uniform distribution of nanoparticles in polymer matrix (Figure 1). Besides, it is well known that the anionic polymerization of caprolactam proceeds well below the melting temperature of the nylon6, which could avoid the degradation in comparison with conventional melt compounding.…”

Microwave syntheses of poly(?-caprolactam-co-?-caprolactone)

“…However, the use of metallic aluminum alkylate for the anionic polymerization of lactams is well known. 16 -19 Activating agents such as sodium dihydrobis(2-methoxyethoxy) aluminate 18 and lithium dihydrobis(tert-butoxy)aluminate 19 have been investigated in the anionic polymerization of -caprolactam.…”