The use of chromium/bis(diphenylphosphino)amine catalysts in tandem ethylene copolymerization processes

Du Toit, Aletta (2012-03)

Thesis (PhD)--Stellenbosch University, 2012.

Thesis

ENGLISH ABSTRACT: The possibility of utilizing the chromium/bis(diphenylphosphino)amine (PNP) type of catalysts in ethylene polymerization processes was investigated. These processes include the production of linear low density polyethylene (LLDPE), the production of polyethylene waxes and the synthesis of special comonomers for ethylene copolymerization. The chromium/Ph2PN{CH(CH3)2}PPh2 tetramerization system was used in combination with a polymerization catalyst to yield ethylene copolymers with controlled branching. Copolymers with bimodal chemical composition distributions were obtained in these tandem reactions. This chromium/PNP-type tetramerization catalyst and metallocene polymerization catalysts are not completely compatible in tandem catalytic systems due to different optimum temperatures for their effective functioning. The oligomerization to polymerization catalyst ratios, the catalyst to cocatalyst ratios and the temperature profile are all factors influencing the amount of -olefins formed and therefore the type of copolymer produced. The activity of the polymerization catalyst decreases in the presence of the oligomerization catalyst, indicating that the two catalysts interfere chemically. The main difference between copolymers produced in conventional or tandem fashion is the presence of a small amount of low molecular weight material produced by the oligomerization catalyst and also the presence of a highly crystalline component. The latter component results from the initial low concentration of a-olefins in the first conversion, but such a component is also independently produced by the oligomerization catalyst. LLDPE with butyl branches is obtained when a selective trimerization catalyst is used in combination with a polymerization catalyst. The chromium/(o-OMeC6H4)2 PN(CH3)P(o-OMeC6H4)2 trimerization system is more suitable than the chromium/Ph2PN{CH(CH3)2}PPh2 tetramerization system for use in tandem reactions with a metallocene catalyst due to its high activity and selectivity at higher temperatures. The chemical composition distribution varies with an increase in reaction time due to the increasing amount of 1-hexene produced. Comparison of CRYSTAF traces of tandem copolymers with conventional copolymers show that the tandem copolymers have a broader chemical composition distribution. Addition of 1- hexene during the course of a conventional copolymerization reaction produces copolymers with similar chemical composition distributions to that of the tandem copolymers. Later addition of the polymerization catalyst to the oligomerization reaction mixture results in copolymers with higher comonomer content, similar to conventional copolymers. Chromium/(o-EtC6H4)2PN(CH3)P(o-EtC6H4)2 is not suitable for LLDPE production in tandem reactions, since it is selective to higher oligomers or polyethylene waxes at higher temperatures. Variation of the MAO cocatalyst and hydrogen concentrations significantly influences the yield, viscosity and crystallization behaviour of the waxlike products. Low MAO concentrations resulted in multiple melting peaks, while higher concentrations display single melting peaks and lower viscosity values. Ethylene co-oligomerization reactions with styrene or p-methylstyrene using the chromium/PNP-type oligomerization technology produce various phenyl-hexene and phenyl-octene isomers either through cotrimerization or cotetramerization. The known ethylene trimerization catalysts show cotrimerization behaviour, while the catalysts with known selectivity for ethylene tetramerization also yield cotetramerization products. Chromium complexes that contain the more bulky ligands display lower selectivity towards co-oligomerization and greater preference for ethylene homotrimerization. These co-oligomerization products can be incorporated into a polyethylene chain by copolymerization in a simultaneous or sequential tandem reaction. The combined co-oligomerization-polymerization reactions yield copolymers with lower crystallinity than obtained from the conventional ethylene-styrene copolymerization reaction due to higher comonomer incorporation. The polymer yields are higher in the cooligomerization- copolymerization reactions. The ability of the different cooligomerization products to incorporate into the polyethylene chain was established: unreacted styrene and the more bulky isomers, 3-phenyl-1-hexene and 3-phenyl-1- octene, are not incorporated readily, while branches resulting from 4-phenyl-1- hexene, 4-phenyl-1-octene, 5-phenyl-1-octene and 6-phenyl-1-octene are detected in the NMR spectrum.

AFRIKAANSE OPSOMMING: Die moontlikheid om die chroom/bis-(difenielfosfino)amien (PNP) tipe katalisatore in etileen-polimerisasie reaksies te gebruik is ondersoek. Hierdie prosesse sluit die produksie van lineêre lae digtheid poliëtileen (LLDPE), die produksie van poliëtileenwasse en die sintese van spesiale komonomere vir etileenkopolimerisasie in. Die chroom/Ph2PN{CH(CH3)2}PPh2 tetramerisasie-sisteem is gebruik in kombinasie met ¢n polimerisasiekatalisator om etileenkopolimere met gekontroleerde vertakkings te vorm. Kopolimere met ‘n bimodale chemiese samestellingsverspreiding word verkry in hierdie tandemreaksies. Hierdie chroom/PNP-tipe tetramerisasiekatalisator en die metalloseenkatalisators is nie heeltemal verenigbaar in die tandemsisteem nie weens verskille in hul optimum reaksietemperature vir effektiewe funksionering. Die oligomerisasie tot polimerisasiekatalisatorverhouding, die katalisator tot kokatalisatorverhouding en die temperatuurprofiel is almal faktore wat die gevormde hoeveelheid -olefiene beinvloed, en dus die tipe kopolimeer wat gevorm word. Die aktiwiteid van die polimerisasiekatalisator verminder in die teenwoordigheid van die oligomerisasiekatalisator, wat aandui dat die twee katalisatore chemies met mekaar inmeng. Die duidelikste verskil tussen die kopolimere wat geproduseer word op die konvensionele of die tandem manier is die teenwoordigheid van ‘n klein hoeveelheid lae molekulere massa materiaal wat gevorm word deur die oligomerisasiekatalisator, asook ‘n komponent met baie hoë kristalliniteit. Die laasgenoemde komponent ontstaan weens die aanvanklike lae konsentrasie van die a-olefiene in die eerste omsetting, maar so ‘n komponent word ook onafhanklik gevorm deur die oligomerisasiekatalisator. LLDPE met butiel-vertakkings word verkry wanneer ‘n selektiewe trimerisasiekatalisator in kombinasie met ‘n polimerisasiekatalisator gebruik word. Die chroom/(o-OMeC6H4)2PN(CH3)P(o-OMeC6H4)2 trimerisasiesisteem is meer geskik as die chroom/Ph2PN{CH(CH3)2}PPh2 tetramerisasiesisteem vir gebruik in tandem met ‘n metalloseenkatalisator weens die katalisator se hoë aktiwiteit en selektiwiteid vir 1-hekseen by hoër reaksietemperature. Die chemiese samestellingsverspreiding verander soos die reaksietyd toeneem weens die toenemende hoeveelheid 1-hekseen wat gevorm word. Vergelyking van die CRYSTAF-diagram van die tandemkopolimere met konvensionele kopolimere toon dat die tandemkopolimere ‘n wyer chemiese samestellingsverspreiding het. Geleidelike byvoeging van 1-hekseen gedurende die loop van ‘n konvensionele reaksie, vorm kopolimere met ‘n soortgelyke chemiese samestelingsverspreiding as die tandemkopolimere. Latere byvoeging van die polimerisasiekatalisator lei tot die vorming van kopolimere met ‘n hoër komonomeerinhoud, soortgelyk aan die konvensionele kopolimere. Chroom/(o-EtPC6H4)2PN(CH3)P(o-EtC6H4)2 is nie geskik om LLDPE in tandemreaksies te vorm nie, aangesien dit selektief is vir hoër oligomere of poliëtileenwasse by hoër reaksietemperature. Variasie van die MAO-kokatalisator en die waterstofkonsentrasies beinvloed die hoeveelheid produk wat gevorm word, asook die viskositeit en kristallisasiegedrag daarvan. Lae MAO konsentrasies lei tot meer as een smeltpiek, terwyl hoër konsentraises ‘n enkelpiek vertoon. Die viskositeit van die produkmengsel is ook laer. Die gebruik van die chroom/PNP-tipe oligomerisasietegnologie in etileenkooligomerisasiereaksies met stireen, lei tot die vorming van verskeie feniel-hekseenen fieniel-okteenisomere deur of kotrimeriasie, of kotetramerisasie. Katilisatore met bekende etileentrimerisasieligande vertoon kotrimerisasiegedrag terwyl die ligande wat bekend is vir selektiwiteit in etileentetramerisasie, kotetramerisasieprodukte vorm. Die chroomkomplekse met die meer bonkige ligande het laer selektiwiteit vir ko-oligomerisasie en vertoon ‘n groter voorkeur vir etileenhomo-trimerisasie. Die ko-oligomerisasieprodukte kan in ‘n poliëtileenketting ingebou word deur kopolimerisasie in ‘n gelyktydige of opeenvolgende tandemreaksie. Die gekombineerde ko-oligomerisasie-polimerisasiereaksie vorm kopolimere van ‘n laer kristalliniteit as wat gevind word met die konvensionele etileen-stireen kopolimerisasie reaksie weens hoer komonomeerinkorporasie. Meer polimeer word gevorm in die ko-oligomerisasie-kopolimerisasie reaksie. Die vermoë van die verskillende ko-oligomerisasieprodukte om in die poliëtileenketting ingesluit te word is bepaal. Ongereageerde stireen en die meer bonkige isomere, 3-feniel-1-hekseen en 3-feniel-1-okteen, word nie maklik ingevoeg nie. Vertakkings as gevolg van die inkorporasie van 4-feniel-1-hekseen, 4-feniel-1-okteen, 5-feniel-1-okteen and 6- feniel-1-okteen kan waargeneem word in die KMR spektrum.

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