Studies On The Catalyst System And Polymerization Process For Synthesis Of Polyketone

Polyketone(PK)is a class of engineering plastic with excellent mechanical properties.Its impact strength is 80%over of that of nylon 6 and nylon 66.Additionally,PK has outstanding chemical resistance and barrier properties.PK is widely used in the fields of aerospace,electronics,fiber spinning.PK is generally produced through a onestep copolymerization of olefins(ethene/propene)and carbon monoxide(CO),and its synthesis process realizes the efficient use of CO,which echoes the "carbon neutral"policy.Therefore,the research on the synthesis of PK is of great significance.Currently,palladium-based catalysts are used in the industrial production of PK.The price of catalysts accounts for the largest part of the cost of PK production due to the difficulty of recovering catalysts buried in polymers as a result of the slurry polymerization process.On the other hand,for the palladium catalyst system,methanol is particularly important for maintaining high activity.Therefore,methanol is used as the reaction medium in the industry.However,PK can not be dissolved in methanol.The precipitation of PK is likely to cause serious problems such as the reactor fouling and formation of low bulk density PK product.Limited by factors such as pipeline clogging,the slurry process can only be carried out batch-wise.In this thesis,with the aim of reducing the catalyst cost,a nickel-based nonprecious metal catalyst,which has the best potential to replace the palladium-based catalyst,has been selected for the synthesis of PK with the expectation to be further improve the activity by optimizing the reaction conditions and modifying the catalyst structures.After that,from the point of view of polymerization process methods,refer to the methoed of solving the reactor fouling problem in the conventional rubber and thermoplastic elastomer production,the homogeneous solution polymerization of PK has been achieved by using a mixture of hexafluoroisopropanol(HFIP),a good solvent for PK,and methanol as the polymerization medium,which is expected to promote the continuous production of PK while solving the problem of reactor fouling.In addition,the homogeneous polymer solution facilitates the recycling of palladium catalyst by using the adsorbent,the addition of various additives,and removal of the residual monomers.Finally,by adjusting the crystallization behavior of the PK in the reaction medium,a PK product with good particle morphology has been obtained in the heterogeneous system,which overcomes the problem of reactor fouling.The main results are listed as follows:(1)The introduction of a co-catalyst,Ni(COD)2,and the use of polar dichloromethane solvent resulted in an increase of 29.0%and 119%in the catalytic activity for the nickel-based catalyst,respectively.The highest activity can reach 5.55 kg PK·g-1 Ni·h-1.The mechanism of of the nickel-based catalyst was modified based on the results of catalyst aging experiments in the CO atmosphere.The optimum polymerization temperature was 80℃ in the toluene and 60℃ in the dichloromethane.The thermal stability of the catalyst was better in the toluene than that in the dichloromethane.(2)Five nickel-based catalysts with novel structures were synthesized and characterized.The detailed structural data such as molecular bond lengths and bond angles of all catalysts was obtained using the single-crystal XRD.For the first time,nickel-based binuclear catalyst capable of catalyzing the copolymerization of ethylene and CO was synthesized.All the novel catalysts were experimentally evaluated for the homopolymerization of ethylene and the copolymerization of ethylene and CO.(3)Due to the low activity of nickel-based catalysts and insufficient polymer generated in the polymerization,palladium-based catalyst systems were employed in the development of solution polymerization processes.Using the mixture of HFIP and methanol as the reaction solvent,the homogeneous solution polymerization for PK synthesis was achieved with an activity up to 36.1 kg PK·g-1 Pd·h-1 and molecular weight of PK up to 240.3 kDa.Both the catalytic activity and molecular weight of PK are an order of magnitude higher than the values of the reported solution polymerization process.The solution polymerization overcomes the severe problems of reactor fouling and the formation of low bulk density PK in the current industrial slurry process.(4)For the first time,HFIP was found to be able to directly activate organometallic catalysts for efficient coordination polymerization.The analysis of the mechanism shows that HFIP plays an important role in the polymerization process without strong acids.HFIP can form strong hydrogen bonding with the acetate of the catalyst,which weakens the coordination ability between the acetate and the palladium center and subsequently facilitates the reaction between the methanol and the catalyst,leading to the formation of the active centers,and allowing the initiation process to proceed without the involvement of any strong acid.(5)Unlike the traditional catalytic systems containing strong acids,the amount of benzoquinone used in the catalytic system involving HFIP had almost no effect on either the activity or the molecular weight of PK,indicating that HFIP has a strong stabilizing effect on the active centers.A comparative analysis of these two systems revealed that the absence of the divalent ion(L2Pd2+)and the equilibrium reaction between the monovalent active center[L2PdOCH3]+and the hydrogen bonded acetate reduce the exposure of the active centers and increase the stability of the active centers significantly.(6)In a heterogeneous system,the particle morphology of polyketone was improved by adjusting the volume ratio of HFIP without using any supported catalysts.The bulk density of polyketone product was increased,and the reactor fouling was avoided even with a solid content up to 36.7%.