The air tolerant precatalyst, [Rh­(L)­(NBD)]Cl ([1]­Cl) [L = κ3-( i Pr2PCH2CH2)2NH, NBD = norbornadiene], mediates the selective synthesis of N-methylpolyaminoborane, (H2BNMeH) n , by dehydropolymerization of H3B·NMeH2. Kinetic, speciation, and DFT studies show an induction period in which the active catalyst, Rh­(L)­H3 (3), forms, which sits as an outer-sphere adduct 3·H 3 BNMeH 2 as the resting state. At the end of catalysis, dormant Rh­(L)­H2Cl (2) is formed. Reaction of 2 with H3B·NMeH2 returns 3, alongside the proposed formation of boronium [H2B­(NMeH2)2]­Cl. Aided by isotopic labeling, Eyring analysis, and DFT calculations, a mechanism is proposed in which the cooperative “PNHP” ligand templates dehydrogenation, releasing H2BNMeH (ΔG ‡ calc = 19.6 kcal mol–1). H2BNMeH is proposed to undergo rapid, low barrier, head-to-tail chain propagation for which 3 is the catalyst/initiator. A high molecular weight polymer is formed that is relatively insensitive to catalyst loading (M n ∼71 000 g mol–1; Đ, of ∼ 1.6). The molecular weight can be controlled using [H2B­(NMe2H)2]Cl as a chain transfer agent, M n = 37 900–78 100 g mol–1. This polymerization is suggested to arise from an ensemble of processes (catalyst speciation, dehydrogenation, propagation, chain transfer) that are geared around the concentration of H3B·NMeH2. TGA and DSC thermal analysis of polymer produced on scale (10 g, 0.01 mol % [1]­Cl) show a processing window that allows for melt extrusion of polyaminoborane strands, as well as hot pressing, drop casting, and electrospray deposition. By variation of conditions in the latter, smooth or porous microstructured films or spherical polyaminoboranes beads (∼100 nm) result.

Tungsten disulfide nanotubes enhance flow-induced crystallization and radio-opacity of polylactide without adversely affecting in vitro toxicity, Acta Biomaterialia (2021), doi:

Multi-walled WS 2 nanotubes (NTs) with lengths ranging from 2 to 65 μm and widths from 50 to 110 nm were synthesized in a horizontal quartz-made reactor by a process yielding NTs with aspect ratios (ARs) between ∼40 and >1000. The NTs obtained were thermally stable in air up to 400 °C but were oxidized within the temperature range 400−550 °C to produce yellow WO 3 particles. Critically, 400 °C is well above the temperature used to mix additives with the majority of meltprocessable polymers. The hydrophilic WS 2 NTs were easily dispersed in poly(lactic) acid (PLA) using a twin-screw extruder, but the shear stresses applied during melt mixing resulted in chopping of the NTs such that the AR decreased by >95% and the tensile mechanical properties of the PLA were unchanged. Although the as-extruded unfilled PLA was >99% amorphous, the much-shortened WS 2 NTs had a significant effect on the crystallization behavior of PLA, inducing heterogeneous nucleation, increasing the crystallization temperature (T c ) by ∼3 °C and the crystalline content by 15%, and significantly increasing the rate of PLA crystallization, producing smaller and more densely packed spherulites. The reduction in the AR and the nucleating effect of WS 2 NTs for PLA are critical considerations in the preparation, by melt mixing, of composites of rigid 1D NTs and polymers, irrespective of the target application, including bone tissue engineering and bioresorbable vascular scaffolds.

Functionalisation of nanofillers is required for the promotion of strong interfacial interactions with polymers and is essential as a route for the preparation of (nano)composites with superior mechanical properties. Tungsten...