Thesis (PhD)--Stellenbosch University, 2012. / 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.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/20121 |
| Date | 03 1900 |
| Creators | Du Toit, Aletta |
| Contributors | Van Reenen, A. J., Stellenbosch University. Faculty of Science. Dept. of Chemistry and Polymer Science. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Detected Language | English |
| Type | Thesis |
| Rights | Stellenbosch University |
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