Three substituted unsaturated polycarbosilanes were prepared from the same parent using a two-step, one-pot ADMET polycondensation-nucleophilic substitution route. Condensation metathesis of di(4-pentenyl)dichlorosilane using Schrock's [Mo] catalyst produces a polymer backbone containing two reactive silicon-chlorine bonds per unit. Replacement of these bonds with stable alkyl moieties was performed using an excess of alkyllithium reagent without undesirable main chain alkylation or crosslinking. Upon functionalization, moisture-stable polymers were synthesized, indicating quantitative substitution was achieved. All of the resulting polymers are amorphous, elastomeric materials. Variation of the two pendant groups from phenyl to methyl resulted in a T g change of over 85°C.
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.
magnified image
Aliphatic polyoxalates in the molecular weight
(M
w) range of 5000−15 000 were produced from
alkane
α,ω-dinitrites and carbon monoxide, using a homogeneous palladium(II)-based catalytic system. The
alkane
dinitrites were synthesized from the corresponding aliphatic diols by reaction with either aqueous nitrous acid
or nitrogen oxides. Nitric oxide, given off as a
byproduct
during polymerization, can be recycled to produce additional monomer.
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