Amine-Functionalized Polybutadiene Synthesis by Tunable Postpolymerization Hydroaminoalkylation.

Early transition metal-catalyzed hydroaminoalkylation is a powerful single-step method to selectively add amines to polybutadienes, offering an efficient strategy to access amine-functionalized polyolefins. Aryl and alkyl secondary amines were used with a tantalum catalyst to functionalize both 28 wt% (PBD13) and 70 wt% (PBD50) 1,2-polybutadiene polymers. The degree of amination was controlled by modifying amine and catalyst loading in both small- and multigram-scale reactions. The vinyl groups of 1,2-polybutadiene were aminated with ease, and unexpectedly the hydroaminoalkylation of challenging internal alkenes of the 1,4-polybutadiene unit was observed. This unanticipated reactivity was proposed to be due to a directing group effect. This hypothesis was supported with small-molecule model substrates, which also showed directed internal alkene amination. Increasing degrees of amination resulted in materials with dramatically higher and tunable glass transition temperature (Tg) values, due to the dynamic cross-linking accessible to hydrogen-bonding, amine-containing materials. Primary amine-functionalized polybutadiene was also prepared, demonstrating that a broad new class of amine-containing polyolefins can be accessed by postpolymerization hydroaminoalkylation.

Commodity Polymers to Functional Aminated Materials: Single-Step and Atom-Economic Synthesis by Hydroaminoalkylation.

Hydroaminoalkylation (HAA) is demonstrated to be a promising postpolymerization route to catalytically prepare amine-functionalized atactic polypropylene. Using a recently reported tantalum catalyst supported by a N,O-chelating cyclic ureate ligand, vinyl-terminated polypropylene (VTPP) is transformed into both aryl and alkyl secondary amine-terminated polyolefins. Early transition-metal-catalyzed hydroaminoalkylation avoids protection/deprotection protocols typically required for secondary amine synthesis. This single-step reaction can be performed at multigram scale with minimal solvent and is atom economic, thereby allowing for optimized product isolation. Materials are characterized by multinuclear NMR spectroscopy, IR spectroscopy, DSC, and TGA. The utility of the reactive and unprotected amine terminus is highlighted by the installation of a fluorescent end group and the assembly of a graft copolymer by condensation of the secondary amine terminus with carboxylic acid moieties.

Mono, bis, and tris(phosphoramidate) titanium complexes: synthesis, structure, and reactivity investigations.

A series of variously substituted phosphoramidate titanium complexes bearing dimethylamido ligands are reported. Aryl-substituted ligands impart crystallinity to the systems and allow for the elucidation of the molecular structures via X-ray crystallography. Higher-substituted complexes, including a tris(phosphoramidate)mono(dimethylamido) complex, were isolated and characterized in the solid state, as well as in solution using variable temperature 1H and 31P NMR spectroscopy. The steric bulk possessed by this ligand system, relative to amidate and ureate ligands, has allowed access to a mono(phosphoramidate)tris(dimethylamido) complex. The first solid-state-molecular structure of a mono-ligated 1,3-N,O chelated complex of titanium is reported and compared to the respective bis- and tris-analogues. These complexes were screened for hydroaminoalkylation activity between secondary amines and terminal alkenes and the intramolecular hydroamination of a terminal aminoalkene. Mono(phosphoramidate)tris(dimethylamido) complexes were screened in situ and found to be more active than their respective bis(N,O)-chelated analogues. The elucidation of these complexes allows for a direct comparison to other N,O-chelates of early transition metals, particularly in their hydroaminoalkylation and hydroamination reactivity.

Titanium pyridonates for the homo- and copolymerization of rac-lactide and ε-caprolactone.

A series of titanium pyridonate complexes have been synthesized under very mild reaction conditions from a common precursor, Ti(NMe2)4. These complexes have been explored as initiators for the ring-opening polymerization of rac-lactide and ε-caprolactone and have proven to be competitive with leading titanium initiators. Furthermore, these complexes have been shown to be competent initiators for the synthesis of copolymers (CL-LA block copolymers and random copolymers). Metal complex reactivity trends in both homo- and copolymerization show that poly(lactic acid) is most susceptible to chain scission and transesterification.