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A series of bis(phenoxyketimine)titanium dichloride complexes were synthesized and evaluated as catalysts for living, isoselective propylene polymerization upon activation with methylaluminoxane (MAO). Catalysts bearing phenoxyketimine ligands with different substituents at the ortho and para positions of the phenolate ring and substituents at the ketimine carbon were investigated. The identity of the ketimine substituent had the largest effect on the activity and isoselectivity of propylene polymerization. Complex 12/MAO promoted the living, isoselective polymerization of propylene ([m4] = 0.73, alpha = 0.94). This catalyst system was used for the synthesis of a number of block copolymers featuring isotactic polypropylene semicrystalline blocks and poly(ethylene-co-propylene) amorphous blocks. Several triblock samples with varying block lengths, a pentablock, and a heptablock copolymer were synthesized. Mechanical testing has revealed that each is elastomeric with elongations at break between approximately 790-1000%.

A new living and isoselective propylene polymerization precatalyst was generated via the intramolecular insertion of a ligand-appended vinyl group into the Hf-C bond of a neutral pyridylamidohafnium trimethyl complex.

A method for the preparation of poly(aryl ether thianthrene)s has been developed in which the aryl ether linkage is generated in the polymer‐forming reaction. The thianthrene heterocycle is sufficiently electron‐withdrawing to allow fluoro displacement with phenoxides by nucleophilic aromatic substitution. The monomer for this reaction, 2,7‐difluorothianthrene, can be synthesized in a moderate yield by a simple reaction sequence. Semiempirical calculations at the PM3 level suggest that 2,7‐difluorothianthrene is sufficiently activated, whereas NMR spectroscopy (1H and 13C) indicates that the monomer is only slightly activated or (19F) not sufficiently activated for nucleophilic aromatic substitution. Model reactions with p‐cresol have demonstrated that the fluorine atoms on 2,7‐difluorothianthrene are readily displaced by phenoxides in high yields, and the process has been deemed suitable for polymer‐forming reactions. High‐molecular‐weight polymers have been produced from bisphenol A, bisphenol AF, and 4,4′‐biphenol. The polymers have been characterized with gel permeation chromatography, NMR spectroscopy, differential scanning calorimetry, thermogravimetric analysis, and matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry. The glass‐transition temperatures for the polymers of different compositions and molecular weights range from 138 to 181 °C, and all the polymers have shown high thermooxidative stability, with 5% weight loss values in an air environment approaching 500 °C. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 6353–6363, 2004

Visible-light-absorbing tris(bipyridyl)ruthenium(II) has been used to mediate electron transfer to N-methylpicolinium carbamates that undergo C-O bond fragmentation followed by spontaneous carbon dioxide release to give free amines. Release of several aliphatic and aromatic primary amines has been demonstrated under mild conditions using visible light.

The reaction of vinyl‐appended phenoxyamine 2 with tetrabenzyltitanium provided the phenoxyaminetitanium(II) alkene complex [rac‐Lig2TiBn], arising from intramolecular vinyl‐group insertion followed by toluene elimination. Whereas [rac‐Lig2TiBn] was inactive for olefin polymerization upon benzyl abstraction, treatment with ethylene led to the formation of stable titanacyclopentane complex [rac‐Lig2(CH2)2TiBn]. Alternatively, six‐membered metallacyclic complexes [rac‐Lig1ZrBn2‐a/b] and [rac‐Lig1HfBn2‐a/b] were obtained from reaction of vinyl‐appended phenoxyamine 1 with tetrabenzylzirconium or tetrabenzylhafnium in a further rare example of intramolecular vinyl‐group insertion into neutral tribenzyl group IV precursors. Living and isoselective polymerization of 1‐hexene was promoted by [rac‐Lig1HfBn2‐a/b]/B(C6F5)3 at 0 °C, whereas [rac‐Lig1ZrBn2‐a/b]/B(C6F5)3 catalyzed the living and isoselective polymerization of propylene ([m4]=0.76) at 0 °C. This catalyst system was employed for the synthesis of a diblock copolymer featuring an isotactic polypropylene semicrystalline block and poly(ethylene‐co‐propylene) amorphous block.

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Cyclopolymerization of nonconjugated dienes produces poly(methylene-1,3-cycloalkanes) and provides a pathway to a number of stereochemically complex polymers. Activation of a diastereomeric mixture of a six-membered metallacycle complex (rac-1) in the presence of 1,5-hexadiene produced poly(methylene-1,3-cyclopentane) (PMCP) with >98% cyclization of the diene monomer. The catalyst was found to cyclopolymerize 1,5-hexadiene with relatively high activity. The microstructure of the PMCP furnished by rac-1 was found to contain a high proportion of cis-cyclopentane rings (σ = 0.70-0.74) and a relatively high isotactic content (α = 0.93-0.96). These are the first cis-enriched isotactic cyclopolymers of 1,5-hexadiene. Cyclopolymerization of 1,6-heptadiene with rac-1/B(C(6) F(5) )(3) produced poly(methylene-1,3-cyclohexane) containing 97% cis-isotactic rings. This is the first report of this highly isotactic and diastereomerically-pure microstructure.