Ring-Opening Polymerization of Cyclic Amides (Lactams)

Sustainable, Stereoregular, and Optically Active Polyamides via Cationic Polymerization of ε-Lactams Derived from the Terpene β-Pinene

“…Polymerization of substituted lactams can be complex and depends on enthalpy and entropy effects as well as on gauche interactions within the lactam cycle . Hydrogen crowding obviously makes 4a polymerize a bit easier than, for example, the lactams derived from similar—but no bridge‐containing—menthone .…”

“…For cationic polymerization of 4a , H 3 PO 4 (14.8 m , 85%) was used as initiator, as well as HCl aq (12.1 m ; 37%) and aminocaproic acid (ACA; pure), which were chosen due to the easy availability of these common standard reagents; for further details see the Supporting Information. In general, when using aqueous acid, a cationic and a hydrolytic ROP mechanism occur in parallel . Experiments were performed at 250 °C (usually used for cationic polymerization of ε‐caprolactam) as well as at different temperatures for comparison.…”

Sustainable Chiral Polyamides with High Melting Temperature via Enhanced Anionic Polymerization of a Menthone-Derived Lactam

“…Polymerizability of lactams depends on enthalpy and entropy effects, and—in case of assisted anionic ROP (as here)—on the nucleophilicity of the lactam anion and the electrophilicity of the N‐acyl lactam (activator). Gauche interactions in the ring and the conformation of the amide bonds play important roles for the polymerizability of substituted lactams and the equilibrium between lactam and polyamide . In this study, an enlarged scale than described before as well as the fact that the remaining monomer can be washed out and reutilized directly compensates for the initially incomplete conversion (see the Supporting Information).…”

“…These two different powdery bases make this approach much more convenient and generally applicable. Furthermore, a benzoylated lactam was used as a new coinitiator—acylated lactams are in general more electrophilic than nonacylated lactams . Therefore, the whole ROP procedure is completely revised compared to the previously described method, polyamides are synthesized in a larger scale and many further analytical details are revealed.…”

“…Another explanation might be an equilibrium between monomer and polymer that is formed and/or the fact that polymers precipitate from bulk and are thus removed from the reaction in melt medium. This is not surprising as it is very complex to define a generally applicable classification of the chemical reactivity of (substituted) lactams toward ROP . For instance, the “equilibrium monomer concentration” of methyl‐substituted caprolactams in bulk polymerizations is remarkably higher than for unsubstituted CL .…”