Recent advances in polyolefin manufacture have focused on the production of differentiated commodity polyolefins, specialty polyolefins, and polyolefins hybrids. What differentiates these new polyolefin types from commodity polyolefins is that their molecular architectures are much more complex and often contain long chain branches (LCBs), leading to unique properties that make them competitive with specialty polymers. One approach to produce these novel polyolefins is to use one or two single-site catalysts in two CSTRs in series. The first CSTR is used to make semicrystalline polymer chains, some of which must be vinyl-terminated (macromonomers). These macromonomers are then incorporated, via terminal branching, onto the chains growing in the second CSTR, becoming LCBs. If the backbone and the macromonomer have different compositions, they are called cross-products. Since it is not possible to incorporate all macromonomers, the final polymer will consist of a complex mixture of linear chains made by the two catalysts, homogeneous-branched chains (that is, chains where the backbone and all LCBs are of the same type), and cross-product macromolecules. The cross-product will add rather special properties to the polymer and, depending on its molecular architecture, the final product may act as a thermoplastic elastomer (TPE). Developing polymer reactor models for different catalyst combinations can help understand the details of these complex syntheses and to control the properties and fractions of linear chains, homogeneous-branched chains, and cross-products. Two mathematical models were developed in this thesis for the solution polymerization of olefins with two single-site catalysts to predict the microstructure of long chain branched polyolefins. The first model was developed for a semi-batch reactor and the second one for two CSTRs in series. The models can predict the fractions of different polymer populations made in CSTRs and semibatch reactors, as well as their average chain lengths and LCB densities. Simulation results show that CSTRs are more efficient than semi-batch reactors to make polymers with high LCB densities and/or cross product fraction. Simulation results also show that to increase the weight percent of cross-product using a linear-catalyst and a LCB-catalyst, the rate of macromonomer formation of the linear-catalyst should be high. The fraction of cross-product can be increased even further when both catalysts are capable of incorporating macromonomers to form LCB-chains because; in this case, both catalysts can form cross-product chains. Monomer concentration has no effect on cross-product mass fraction and polydispersity index, but increasing monomer concentration will decrease LCB density and increase the average chain lengths. Catalyst deactivation also has a great impact on polymer properties: LCB density, polydispersity index, cross-product fraction, and average chain lengths will all decrease by increasing the catalyst deactivation rate of both catalysts. Simulation results for two CSTRs in series shows that increasing residence time in the second CSTR will lead to higher cross-product formation and LCB density. This rate of increase is more significant if the residence time in the second CSTR is similar to that of the first CSTR. The catalyst feed policy also has a great impact on polymer properties. We found out that feeding the linear-catalyst and the LCB-catalyst in equal amounts to the first CSTR and just adding the LCB-catalyst to the second CSTR is the preferred catalyst injection method for making polymer with a high mass fraction of cross-product, high chain length averages, and lower polydispersity index (PDI). These simulation studies indicate that detailed polymerization kinetics for each catalyst is needed in order to synthesize these novel polyolefins. In the experimental part of this thesis, ethylene polymerization kinetics studies were performed first with two individual metallocene catalysts, then with both of them simultaneously. First, ethylene polymerization with rac-Et(Ind)2ZrCl2/MAO was carried out in a semi-batch solution reactor. Reaction temperature, monomer, MAO, and catalyst concentrations were the factors studied to establish a framework to predict catalyst decay, polymer yield and molecular weight averages. The polymerization order with respect to ethylene and catalyst concentration was found to be first order. Chain transfer to monomer was the dominating chain transfer reaction while β-hydride elimination was negligible. An increase in MAO concentration led to a decrease in molecular weight. Catalyst decay could be described with a first order mechanism. At low MAO concentration this catalyst could make polymer with about one vinyl group per chain. A similar ethylene polymerization kinetics study using dimethylsilyl(N-tert-butylamido)-(tetramethylcyclopentadienyl)-titanium dichloride (CGC-Ti)/MAO system showed that the polymerization order with respect to catalyst concentration was first order, but first order catalyst decay failed to explain catalyst deactivation. The polymerization order with respect to ethylene concentration was not unity for the whole range of ethylene concentration. The trigger mechanism, along with reversible first order activation and deactivation with MAO and first order thermal decay, could explain the effect of time, monomer and catalyst concentration on the rate of polymerization. Decrease in MAO concentration increased the amount of polymer chains with terminal vinyl groups and consequently led to polymers with LCBs. Decreasing monomer concentration at low MAO concentration also led to production of polymer chain with more long chain branching. Ethylene homopolymerization and copolymerization with 1-octene were conducted using combined catalysts system at low and high MAO concentrations. Reactivity ratios were calculated and polymer samples with bimodal MWDs were obtained but no increase in LCB frequency or cross product formation was detected using carbon-13 nuclear magnetic resonance (13C NMR) and high-temperature gel permeation chromatography (GPC) coupled with a viscosity detector. In order to promote the formation of cross-product macromolecules, 1,9-decadiene was copolymerized with ethylene using the Et(Ind)2ZrCl2/MAO to make tailored macromonomers with pendant 1-octenyl branches. The macromonomers ranged from having 1 to 6.5 vinyl groups per chain. These macromonomers were then incorporated into growing ethylene/1-butene or ethylene/1-octene copolymer chains using a titanium-based constrained geometry catalyst (CGC-Ti) to form branch block polymer chains with amorphous main backbone having short chain branch density (SCBD) up to 50 per 1 000 carbon atoms, and high crystalinity long chain branches with SCBD up to 3/1000 C atoms (cross product). Increase in polymerization time or catalyst concentration in the second stage of polymerization was observed to increase the cross-product weight fraction. We also observed that an increase in ethylene pressure during the second stage of polymerization, while 1-butene concentration was constant, favoured the formation of cross product. When 1-octene was used as comonomer in the second stage of polymerization, the presence of more pendant vinyl groups in the macromonomer led to increased long chain branching.

Thesis (Ph.D.) -- McMaster University, 2003. / Includes bibliographical references (p. 154-172). Also available via World Wide Web.

Thesis (Ph.D.) -- McMaster University, 2003. / Includes bibliographical references (p. 154-172). Also available via World Wide Web.

Thesis (M.E.)--University of Waikato, 2008. / Title from PDF cover (viewed August 26, 2008) Includes bibliographical references (p. 92-96)

Filmes de polietileno (PE) contendo aditivo pró-degradante à base de um composto de cobalto foram expostos a intemperismo natural por 12 meses, em Canoas, RS (30º S, 59º W), sob condições de umidade ambiente e saturação de umidade. Procurou-se desenvolver condições de ensaio adequado para a degradação abiótica e biótica, visando monitorar alterações na estrutura da cadeia e propriedades mecânicas. Obtiveram-se valores crescentes de índice de carbonila com o aumento do tempo de exposição ao intemperismo natural, por meio de espectroscopia de infravermelho por transformada de Fourier (FTIR). A massa molar ponderal média decresceu de 170.000 para próximo de 8.000 g mol-1 com 4 – 5 meses de exposição, com fragilização progressiva das amostras e diminuição da resistência mecânica. A degradação biótica dos resíduos de PE originados a partir da degradação abiótica foi realizada em células fechadas, a 58º C. Após 90 dias de ensaio, as amostras de PE tiveram 12 % do seu carbono convertido a CO2, contra 70% obtidos com celulose (padrão positivo). Mesmo com essa diferença elevada em relação ao padrão positivo, a biodegradabilidade desenvolvida pelo PE pode ser considerada muito boa, uma vez que a biodegradação dessa poliolefina sem aditivo promotor de degradaçao é extremamente pequena. Assim, o aditivo pródegradante teve uma eficiência significativa em acelerar a degradação abiótica dos filmes de PE expostos ao intemperismo natural, em condições de umidade ambiente ou saturação de umidade. / Plastic bags of polyethylene (PE) containing cobalt prodegradant additive were exposed to natural weathering for 12 months, in Canoas, RS (30° S, 59º W). An appropriate test methodology for monitoring abiotic and biotic degradation was chosen, with evaluation of changes in the structure of the polymeric chain, mechanical parameters and biodegradation. Increasing results of carbonyl index demonstrated accelerated oxidation of the samples. The molar mass (weight average) decreased from 170.000 to 8.000 g mol-1 after 4 – 5 months of exposure, being followed by fragilization and mechanical resistance decrease. Biotic degradation tests of PE bags residues were performed in closed vessels, at the temperature of 58 ºC. According to the tests, residues of PE films reached a mineralization of 12% after 90 days, compared to 70 % for cellulose. That degree of biodegradation may be considered high, because biodegradation of PE films not containing prodegradant additives is very slow. Thus, the additive was showed efficient to accelerate the abiotic degradation, conferring biodegradability to PE films.

Filmes de polietileno (PE) contendo aditivo pró-degradante à base de um composto de cobalto foram expostos a intemperismo natural por 12 meses, em Canoas, RS (30º S, 59º W), sob condições de umidade ambiente e saturação de umidade. Procurou-se desenvolver condições de ensaio adequado para a degradação abiótica e biótica, visando monitorar alterações na estrutura da cadeia e propriedades mecânicas. Obtiveram-se valores crescentes de índice de carbonila com o aumento do tempo de exposição ao intemperismo natural, por meio de espectroscopia de infravermelho por transformada de Fourier (FTIR). A massa molar ponderal média decresceu de 170.000 para próximo de 8.000 g mol-1 com 4 – 5 meses de exposição, com fragilização progressiva das amostras e diminuição da resistência mecânica. A degradação biótica dos resíduos de PE originados a partir da degradação abiótica foi realizada em células fechadas, a 58º C. Após 90 dias de ensaio, as amostras de PE tiveram 12 % do seu carbono convertido a CO2, contra 70% obtidos com celulose (padrão positivo). Mesmo com essa diferença elevada em relação ao padrão positivo, a biodegradabilidade desenvolvida pelo PE pode ser considerada muito boa, uma vez que a biodegradação dessa poliolefina sem aditivo promotor de degradaçao é extremamente pequena. Assim, o aditivo pródegradante teve uma eficiência significativa em acelerar a degradação abiótica dos filmes de PE expostos ao intemperismo natural, em condições de umidade ambiente ou saturação de umidade. / Plastic bags of polyethylene (PE) containing cobalt prodegradant additive were exposed to natural weathering for 12 months, in Canoas, RS (30° S, 59º W). An appropriate test methodology for monitoring abiotic and biotic degradation was chosen, with evaluation of changes in the structure of the polymeric chain, mechanical parameters and biodegradation. Increasing results of carbonyl index demonstrated accelerated oxidation of the samples. The molar mass (weight average) decreased from 170.000 to 8.000 g mol-1 after 4 – 5 months of exposure, being followed by fragilization and mechanical resistance decrease. Biotic degradation tests of PE bags residues were performed in closed vessels, at the temperature of 58 ºC. According to the tests, residues of PE films reached a mineralization of 12% after 90 days, compared to 70 % for cellulose. That degree of biodegradation may be considered high, because biodegradation of PE films not containing prodegradant additives is very slow. Thus, the additive was showed efficient to accelerate the abiotic degradation, conferring biodegradability to PE films.

No description available.

Thesis (MSc)--Stellenbosch University, 2004. / ENGLISH ABSTRACT: This study describes the design, building and optimization of a fully functional preparative TREF (Prep-TREF) apparatus. This apparatus allows for the fractionation of semicrystalline polyolefins according to the crystallizability of the molecules. Various factors, such as the sample cooling rate and the effect of on-support and off-support crystallization, are investigated. The preparative TREF is used to fractionate a commercial low-density polyethylene (LOPE), two commercially available plastomers (polyethylene-l-octene copolymers), as well as blends of the LOPE and the respective plastomers. It is shown that in each case the samples fractionated by crystallizability. The fractions recovered from the Prep-TREF were characterized by CRYSTAF, OSC and NMR analysis. It is shown how the results of this preparative fractionation allow for a better understanding of the molecular heterogeneity in the LOPE and plastomers. New ways of presenting the data from the preparative fractionation, in terms of 3- dimensional plots, are also investigated. These plots offer a novel way of presenting the molecular heterogeneity in the samples in terms of the molecular crystallizability. These plots highlight features that are difficult to detect in the conventional two-dimensional plots. In conclusion, the influences of various blending ratios of LOPE and plastomer on the morphological and physical properties of the blends, such as haze, clarity, and tear-and impact strength are determined. / AFRIKAANSE OPSOMMING: Die doel van hierdie studie was die ontwikkeling en optimisering van 'n ten volle funksionerende TREF. Hierdie tegniek word gebruik om polimeermengsels te fraksioneer deur gebruik te maak van die kristaliseerbaarheid van polimere. Verskeie faktore soos die afkoel spoed en die effect van met en sonder 'n ondersteuning(seesand) vir kristaliseering was ondersoek. Hierna is navorsing gedoen om 'n beter begrip ten opsigte van die meganiese, fisiese en optiese eienskappe van lae-digtheid poliëtileen (LDPE) te ontwikkel. Hierdie LDPE is met die affiniteitsreeks plastomere van die maatskappy, Dow Chemicals, gemeng om tendense in die gefraksioneerde polimere te indentifiseer. Een van Sasol se kommersiële LDPE produkte en twee van Dow Chemicals se plastomere is individueel gefraksioneer. Die mengsel van die twee ongefraksioneerde LDPE en plastomere is nog nooit voorheen op 'n molekulêre basis ondersoek nie. Dit is in hierdie studie gedoen deur van TREF gebruik te maak. Nuwe maniere is ontwikkel om data op 'n nuwe manier voor te stel deur middel van 3 Dimensionele grafieke te skep om resultate voor te stel wat andersins baie moelilik was om voor te stel in een dimensie agv die hoeveelheid data wat geinterpreteer word. Ten slotte is die invloed van die verskillende mengverhoudings van LDPE en plastomere op die morfologiese en fisiese eienskappe soos deursigtigheid, helderheid, skeur- en impaksterkte, ook ondersoek.

Thesis (DSc (Chemistry and Polymer Science))--University of Stellenbosch, 2006. / Commercial polyolefins degrade under the influence of light, heat, chemical and mechanical factors. They are therefore stabilised to ensure that they maintain performance characteristics during their service life. Degradation results in changes in the molar mass, molar mass distribution, chemical composition and chemical composition distribution. Classical analytical techniques only provide averaged values of these properties. Much information is available in the open literature on the changes in molar mass, molar mass distribution and chemical composition of polypropylene upon degradation, but no information was available on the changes in chemical composition distribution (CCD) during degradation. This study describes the use of the following analytical techniques to study this: temperature rising elution fractionation (TREF), crystallisation analysis fractionation (CRYSTAF) and coupled size exclusion chromatography-Fourier transform infrared analysis (SEC-FTIR). The CRYSTAF results complimented those obtained by classical techniques: there was a broadening of the crystallisation peak (CCD), an increase in the soluble fraction and a decrease in crystallisation temperatures. SEC-FTIR analysis showed that most of the degraded products were concentrated in the low molar mass regions. TREF analysis was used to separate a degraded sample into fractions of different degrees of degradation. It was then possible to study the spatial heterogeneity in a thick, degraded polypropylene sample using SEC, FTIR and CRYSTAF. The degradation behaviour of selected Sasol propylene-1-pentene random copolymers was investigated. CRYSTAF, SEC-FTIR and TREF analyses provided information on the thermo-oxidative degradation behaviour differences between unstabilised polypropylene homopolymers and these propylene-1-pentene copolymers. It was found that the pentene copolymers degraded significantly faster compared to the homopolymers, even at low levels of pentene (< 3%). The reduction in stability was virtually linear with an increase in pentene content (up to 8 mol% pentene), indicating that higher levels of primary stabilisers are needed to ensure similar life spans for the Sasol propylene-1-pentene copolymers. The extrusion stability of the propylene-1-pentene copolymers was, however, similar to that of the polypropylene homopolymers, indicating that similar processing stabiliser packages may be used.

Thesis (PhD)--University of Stellenbosch, 2006. / ENGLISH ABSTRACT: Metalloxycarbene complexes [(CO)5M1=O(R)M2(Cl)L2] (M1 = Cr , W; M2 = Zr, Hf; L = Cp, Cp*) were synthesized from the reaction between anionic Fischer-type carbene complex salts [(CO)5M1=C(O)R][NEt4] and metallocene chlorides. The molecular and crystal structures of [(CO)5W=C(Me)OZr(Cp)2Cl], [(CO)5Cr=C(Me)OZr(Cp)2Cl] and [(CO)5W=C(Ph)OHf(Cl)Cp2] determined by X-ray methods, show a short Ccarbene-O and relatively long O-Zr and O-Hf separations. Metalloxycarbene complexes in the presence of MAO are active catalysts for homo- and copolymerization of -olefins and produce polymers with heterogeneous properties. 1-Pentene oligomers, homopolymers of ethylene and ethylene/1-pentene copolymers were successfully synthesized using metalloxycarbenes/MAO and the results obtained were critically compared with those synthesized with metallocene/MAO catalysts. The GC and GPC show that 1-pentene oligomers produced with both metalloxycarbenes and metallocenes catalysts range from simple dimers to more complicated high molecular weight (2 600 g/mol) products. The properties of polyethylene and ethylene/1-pentene copolymers were evaluated by, among others, GPC, SEC-FTIR, preparative molecular weight fractionation and HPer DSC. Generally the polymers obtained using metalloxycarbene/MAO catalysts have broad and bimodal molecular weight distributions. The copolymers have higher concentration of 1- pentene in the lower molecular weight fraction than those produced with metallocene/MAO as shown by SEC-FTIR. Consequently, HPer DSC shows a decrease of melting and crystallization temperature towards the low molecular weight fractions. / AFRIKAANSE OPSOMMING: Metaaloksikarbeenkomplekse [(CO)5M1=C(R)OM2(Cl)L2] (M1 = Cr , W; M2 = Zr, Hf; L = Cp, Cp*] is gesintetiseer in die reaksie tussen anioniese Fischer-tipe karbeenkomplekssoute, [(CO)5M1=C(O)R][NEt4], en metalloseen dichloriedes. Die molekulêre- en kristalstrukture van [(CO)5W=C(Me)OZr(Cp)2Cl], [(CO)5Cr=C(Me)OZr(Cp)2Cl] en [(CO)5W=C(Ph)OHf(Cl)Cp2] bepaal deur X-straalkristallografiese metodes, toon die aanwesigheid van kort Ckarbeen-O- en relatief lang O-Zr- en O-Hf-bindings. Metaaloksikarbeenkomplekse, in die aanwesigheid van MAO, is aktiewe katalisatore vir die homo- en ko-polimerisering van α-olefiene en is verantwoordelik vir die vorming van polimere met heterogene eienskappe. 1-Penteen oligomere, homopolimere van etileen en etileen/1-penteen ko-polimere is suksesvol gesintetiseer met metaaloksikarbeenkomplekse/MAO en die resultate sodoende verkry, is krities vergelyk met produkte gesintetiseer vanuit metalloseen/MAO prekatalisatore. Die GC en GPC resultate toon dat die 1-penteen oligomere, geproduseer met beide metaaloksikarbeenkomplekse en metallosene, kan wissel van eenvoudige dimere tot meer komplekse, hoë molekulêre massa (2 600g/mol) produkte. Die polietileen en etileen/1- penteen ko-polimere is gekarakteriseer deur onder andere gevorderde, GPC, SEC-FTIR, preparatiewe molekulêre massa fraksionering en HPer DSC. In die algemeen het die polimere verkry met metaaloksikarbeen/MAO katalisatore, breë en bimodale molekulêre massaverspreidings. Die ko-polimere bevat hoër konsentrasies van 1-penteen in die lae molekulêre massa fraksie in vergelyking met dié gevorm vanuit metalloseen/MAO–gekataliseerde mengsels, soos aangedui deur SEC-FTIR-analise. HperDSC wys 'n verlaging in smelt- en kristallisasietemperature in die laer molekulêre massa fraksies.