Resins chromium oxidants support

Second, in the early 1950s, Hogan and Bank at Phillips Petroleum Company, discovered (3,4) that ethylene could be catalyticaHy polymerized into a sohd plastic under more moderate conditions at a pressure of 3—4 MPa (435—580 psi) and temperature of 70—100°C, with a catalyst containing chromium oxide supported on siUca (Phillips catalysts). PE resins prepared with these catalysts are linear, highly crystalline polymers of a much higher density of 0.960—0.970 g/cnr (as opposed to 0.920—0.930 g/cnf for LDPE). These resins, or HDPE, are currentiy produced on a large scale, (see Olefin polymers, HIGH DENSITY POLYETHYLENE). 

Chromium Oxide-Based Catalysts. Chromium oxide-based catalysts were originally developed by Phillips Petroleum Company for the manufacture of HDPE resins subsequendy, they have been modified for ethylene—a-olefin copolymerisation reactions (10). These catalysts use a mixed sihca—titania support containing from 2 to 20 wt % of Ti. After the deposition of chromium species onto the support, the catalyst is first oxidised by an oxygen—air mixture and then reduced at increased temperatures with carbon monoxide. The catalyst systems used for ethylene copolymerisation consist of sohd catalysts and co-catalysts, ie, triaLkylboron or trialkyl aluminum compounds. Ethylene—a-olefin copolymers produced with these catalysts have very broad molecular weight distributions, characterised by M.Jin the 12—35 and MER in the 80—200 range. 

Chromium oxide-based catalysts, which were originally developed for the manufacture of HDPE resins, have been modified for cthylcnc-< -olcfin copolymerization reactions. These catalysts use. a mixed silica-titania support containing from 2 to 20 wt % of Ti. 

Supported chromium oxidants fall in to three main categories (i) adsorbed on alumina, silica or celite (Section 2.7.5.1) (ii) adsorbed on a polymer or resin (Section 2.7.5.2) and (iii) adsorbed on carbon (Section 2.7.S.3). 

If a copolymer such as VLDPE or LLDPE is the target resin, satisfactory comonomer incorporation must be achieved. This is manifested by the amount of comonomer incorporated (evidenced by density) and the distribution of comonomer in the polymer (evidenced by composition distribution). In general, supported chromium oxide catalysts incorporate comonomer more easily than Ziegler-Natta catalysts. 

Pyridinium and quaternary ammonium resins react with chromium trioxide, producing polymer-supported complex chromates that oxidize alcohols, and provide a very facile work-up.427... 

Polymer-supported /eagent. Italian chemists have prepared a supported form of this oxidant by reaction of the Cl" form of an anion exchange resin (Anibcriyst A-26, Amberlyst A-29, Amberlite IRA 400, or Ainberlite 904) in llaO with chromium trioxide to obtain a CrOaH" form of the resin. This polymeric reagent oxidizes primary and secondary alcohols in high yield (usually 85-957o). The chloride form of the resin is regenerated by wash with NaOH and HCI solutions. 

This acylation strategy was used to prepare pol5mier-supported chromium carbenes. Microwave irradiation on Wang resin shows the same regioselectivity as solution chemistry but fewer side products. The resin-bound phenol 21 is simultaneously released and oxidized to the benzoquinone 22 with ceric ammonium nitrate. Microwave irradiation has been shown to accelerate the DBR and provide high yields of benzannulated products in short reaction times (ca. 5 min). ... 

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