Living Organotitanium(IV)-Catalyzed Polymerizations of Isocyanates

Abstract

An organotitanium(IV) compound, TiCl3OCH2CF3, 1, was found to polymerize n-hexyl isocyanate to high yields and without the formation of cyclic trimer. CpTiCl2L (L = −OCH2CF3, −N(CH3)2, −CH3), 2−4, respectively, likewise polymerized n-hexyl isocyanate but also polymerized isocyanates in the presence of donor solvents and isocyanates possessing donor functional groups, activated olefins, and strained olefins. The activity of the organotitanium(IV) catalysts decreased with increasing steric bulk about the metal center and increasing electron donation to the metal center from the ligands. The polymerization of n-hexyl isocyanate using organotitanium(IV) compounds is living. The PDIs of PHIC synthesized using catalysts 1−4 were found to range from 1.05 to 1.2. The molecular weight of the polymer formed in polymerizations of n-hexyl isocyanate using catalysts 1−4 varied linearly as a function of the monomer-to-initiator ratio and the percent conversion of the polymerization. Polymerizations using 2 can be endcapped quantitatively, and well-defined block copolymers can be synthesized using catalysts 1−4. The kinetics for polymerizations using catalysts 1 and 2 are first-order in both monomer and catalyst (k 1 = 8.5 × 10-4 mol L-1 s-1, k - 1 = 3.8 × 10-4 s-1). The active endgroup of a polymerization using 3 was observed using IR spectroscopy, and the frequency of the IR stretch (1548 cm-1) was consistent with an η2-amidate endgroup structure. Finally, the kinetic data for the polymerization of n-hexyl isocyanate and the known chemistry of CpTiCl2L compounds were found to be consistent with a propagation step that occurs via a bifunctional activation mechanism.

Characterization of Rodlike Poly(n-hexyl isocyanate) Macromonomers and Their Polymacromonomers by Light Scattering, SAXS, Intrinsic Viscosity, and Scanning Force Microscopy

“…31 The details for preparation were described in the previous papers. 27,28 To make a calibration curve in an SEC with a series of PHIC's as a standard, five PHIC samples with a broad molecular weight distribution were prepared by an anionic polymerization of HIC using a sodium naphthalenide as an initiator in THF at À78 C. They were fractionated by repeating fractional precipitation with benzene as a solvent and methanol as a precipitant.…”

Modular N,O‐Chelating Ligands: Group‐4 Amidate Complexes for Catalytic Hydroamination

“…With respect to polymerization catalysis, complexes like 12 are relevant to more recent examples using TiCl 3 OCH 2 CF 3 and CpTiCl 2 L [L = -OCH 2 CF 3 , -N-(CH 3 ) 2 , -CH 3 ] as catalysts for the living polymerization of isocyanates. [53] It was proposed, based on IR spectroscopic analysis, that the propagating endgroup during chain growth is an amidate-Ti complex, 13 ( Figure 6), with a chelating bonding motif. [53] There have only been a few reports of titanium amidate chelates that were not formed as intermediates in organometallic reactions.…”

“…[53] It was proposed, based on IR spectroscopic analysis, that the propagating endgroup during chain growth is an amidate-Ti complex, 13 ( Figure 6), with a chelating bonding motif. [53] There have only been a few reports of titanium amidate chelates that were not formed as intermediates in organometallic reactions. One example includes the use of caprolactam as a precursor to form the titanium complex 14 (Figure 7), which is postulated to be an intermediate in the ringopening polymerization of lactams to form polyamides.…”

Synthesis and characterization of chiral poly(alkyl isocyanates) by coordination polymerization using a chiral half‐titanocene complex

“…1 These complexes have been employed for the synthesis of more complex macromolecular architectures containing polyisocyanate blocks, such as diblock copolymers, triblock terpolymers, graft copolymers, and miktoarm star copolymers. 2 Poly(hexyl isocyanate) has also been grafted from carbon nanotubes by an anchored half-titanocene complex.…”