Preparation and reactivity of polyepoxides and polyketones: catalytic oxidation of polybutadienes

Abstract

The epoxidation of polybutadienes containing varying proportions of pendant (1,2-polymerized) and backbone (1,4-polymerized) double bonds with Bu^tOOH catalysed by [MoO₂Cl₂(3-diethoxyphosphoryl)camphor]{systematic name: dichloro [(IR)-endo-(+)-3-(diethoxyphosphoryl)camphor] dioxomolybdenum(VI)}, gives very high selectivity to epoxidation of the backbone double bonds. In the absence of molecular sieves some diol units are produced, but addition of molecular sieves (4A) prevents the formation of diols and greatly increases the rate of the reaction. With [Pt(Ph₂PCHCHPPh₂)CF₃(CH₂Cl₂)]BF₄ as catalyst and Bu_tOOH as oxidant, polyketones are formed with pendant: trans : cis reactivities in the ratio 6 : 5 : 3. The introduction of ketonic functions on the pendant double bonds allows functionalisation on the carbon atom next to the main chain, a position that is otherwise difficult to functionalise. The polyepoxides are found to be unreactive towards ring-opening reactions with water, alcohols, amines etc., although ring-opening is observed in reactions with alcohols or carboxylic acids under forcing conditions in the presence of H₂SO₄ as a catalyst. Ring-opening is also observed with aryllithium reagents although BuⁿLi gives allyl alcohol units in the backbone of the polymer. The polyketones are more susceptible to reaction, e.g. with 6-lithio-2,2′-bipyridyl and soluble polymer-bound bipyridyl is readily synthesised. The polymers are characterised by ¹H and ¹³C NMR studies.