ADMET Polymerization Research Articles

Synthesis and Crystallization of Precision ADMET Polyolefins Containing Halogens

We report the synthesis and characterization of a series of precision polyethylene (PE) structures containing either a fluorine, chlorine, or bromine on each and every 19th carbon. The use of ADMET polymerization chemistry allows unprecedented control in the synthesis of these halogen containing PE derivatives, and results in the first bromine containing polyolefin with a precisely defined primary structure. Polymerization with Grubbs' first generation catalyst followed by hydrogenation by diimide reduction or Wilkinson's catalyst leads to these precise structures, which have been characterized by 1H NMR, solution and solid state 13C NMR, solid state 19F NMR, IR, elemental analysis, TGA, DSC, AFM, and WAXD. The TGA data, coupled with elemental analysis, supply definitive proof of the structural composition through the observed thermal decomposition and release of exact masses of HX (X = F, Cl, or Br). In reference to analogous random copolymers, these precisely substituted polymers display sharper WAXD di...

Metathesis Activity and Stability of New Generation Ruthenium Polymerization Catalysts

A kinetic study of three ruthenium carbene catalysts, (H2IPr)(PCy3)(Cl)2RuCHPh, 3 (investigated extensively by Mol), (H2IMes)(Cl)2RuCH(o-iPrOC6H4), 4 (Hoveyda's catalyst), and (H2IPr)(Cl)2RuCH(o-iPrOC6H4), 5 (a new catalyst structure), was conducted under ADMET polymerization conditions. The kinetic behavior of these catalysts was compared to the classical first- and second-generation Grubbs' complexes at 30, 45, and 60 °C. Complex 3 exhibits the highest initial ADMET rate (80 DP s-1) of any phosphine complex to date and efficiently promotes metathesis even at temperatures as low as 0 °C. Complex 4 alone does not polymerize 1,9-decadiene in the bulk; however, addition of a polar solvent induces polymerization. Combining elements of catalysts 3 and 4 yielded the new complex 5. This complex results in higher polycondensation rates than previous Hoveyda-type structures and exhibits an increased stability over its parent phosphine complex. The new catalyst polymerizes 1,9-decadiene in the bulk to high polymer...

Synthesis and structural characterization of trans‐tactic vinylene–silylene(siloxylene) polymers

AbstractDivinyldimethylsilane (1), divinyldiphenylsilane (2), divinyltetramethyldisiloxane (3) and divinyltetraethoxydisiloxane (4) in the presence of [{RuCl2(CO)3}2] (I) as a catalyst undergo effective silylative coupling (SC) polycondensation giving stereoselectively trans‐tactic polymers (5–8) (Mw=3800–8500), yield 75–84%. The products isolated and characterized by 1H and 13C NMR and GPC methods cannot be synthesized via ADMET polymerization. Copyright © 2003 John Wiley & Sons, Ltd.

Synthesis of Silylene−Alkylene−Silylene−Vinylene Polymers via Catalytic Silylative Coupling (SC) Polycondensation

α,ω-Bis(vinyldimethylsilyl)alkanes (1−4) of the general formula CH2CH(CH3)2Si(CH2)n(CH3)2SiCHCH2 (where n = 1−4) undergo effective silylative coupling (SC) polycondensation, if catalyzed by [RuCl2(PPh3)3] (II) or [RuHCl(CO)(PPh3)3] (III), giving linear polymers (5−8) (Mw = 7300−8500) containing a mixture of trans-1,2- and gem-fragments, but in the presence of [{RuCl2(CO)3}2] (I) as a catalyst, highly stereoselective trans-tactic linear polymers are isolated (9−12) (Mw = 6200−9200). The products of both new processes cannot be synthesized via ADMET polymerization or ring-closing metathesis (RCM).

ADMET Polymerization as a Route to Functionalized Polycarbosilanes

It is now evident that ADMET chemistry can be employed to prepare a family of unsaturated carbosilane polymers containing a common backbone decorated with different alkoxysilane pendant groups, demonstrating the generality and potential utility of this chemistry. Four functionalized silicon containing dienes have been synthesized by nucleophilic substitution of the same parent diene monomer containing two reactive silicon-chlorine bonds. These new α,ω-diene monomers have been polymerized under ADMET conditions using the 2nd generation Grubbs's ruthenium catalyst, producing polymers with useful molecular weights. Variation of the pendant group results in differing chemical and physical properties of the resulting polymers. We believe this chemistry offers much to broaden the synthetic pathways to new organosilicon polymers.

Olefin isomerization promoted by olefin metathesis catalysts

A model study was conducted to determine the extent to which olefin isomerization occurs during olefin metathesis of simple olefins with Grubbs ruthenium catalysts and Schrock's molybdenum catalyst under conditions similar to those employed in ADMET polymerization. It was found that the N-heterocyclic carbene (NHC)-ligated ruthenium complex promotes extensive isomerization of both internal and terminal olefins at temperatures of 50–60 °C, whereas the bisphosphine ruthenium complex and Schrock's molybdenum complex do not. Isomerization occurs concurrently with metathesis for the NHC ruthenium complex to produce a mixture of linear olefins of consecutive carbon numbers.

Synthesis of Cyclolinear Phosphazene-Containing Polymers via ADMET Polymerization

We report here a new method for the synthesis of cyclolinear organic−inorganic polymers with phosphazene rings in the main chain structure by the use of ADMET polymerization. In this work, cyclic phosphazene trimers bearing two nongeminal alkene chains were prepared. Both of the alkene chains have a terminal double bond that together form the diene structure required for ADMET polymerizations. The remaining four substituents were varied to include phenoxy, benzyloxyphenoxy, methoxyethoxyethoxy, and dimethylamino groups. The resultant polymers are well-defined, low-polydispersity materials with phosphazene cyclic trimers uniformly incorporated into the backbone structure. The variation of substituents on the phosphazene ring affects both the polymerization and the properties of the resultant polymers.

Silicometallics and catalysis

Several processes of silicon substrates (such as hydrosilylation, dehydrogenative silylation and double silylation of alkenes and alkynes, silylative coupling versus cross-metathesis of vinylsilanes with alkenes, polycondensation of divinyl-substituted silicon compounds versus ADMET polymerization, dehydrocoupling of hydrosilanes and silylformylation of acetylene) by transition-metal complexes are briefly overviewed. All the reactions occur via a mechanism involving intermediates containing metal-silicon (i.e. silicometallics versus organometallics) and metal-hydrogen bonds, only occasionally accompanied (sided) by intermediates including metal-carbon bonds.